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1.  Linkage analysis of anorexia and bulimia nervosa cohorts using selected behavioral phenotypes as quantitative traits or covariates 
To increase the likelihood of finding genetic variation conferring liability to eating disorders, we measured over 100 attributes thought to be related to liability to eating disorders on affected individuals from multiplex families and two cohorts: one recruited through a proband with anorexia nervosa (AN; AN cohort); the other recruited through a proband with bulimia nervosa (BN; BN cohort). By a multilayer decision process based on expert evaluation and statistical analysis, six traits were selected for linkage analysis (1): obsessionality (OBS), age at menarche (MENAR) and anxiety (ANX) for quantitative trait locus (QTL) linkage analysis; and lifetime minimum Body Mass Index (BMI), concern over mistakes (CM) and food-related obsessions (OBF) for covariate-based linkage analysis. The BN cohort produced the largest linkage signals: for QTL linkage analysis, four suggestive signals: (for MENAR, at 10p13; for ANX, at 1q31.1, 4q35.2, and 8q13.1); for covariate-based linkage analyses, both significant and suggestive linkages (for BMI, one significant [4q21.1] and three suggestive [3p23, 10p13, 5p15.3]; for CM, two significant [16p13.3, 14q21.1] and three suggestive [4p15.33, 8q11.23, 10p11.21]; and for OBF, one significant [14q21.1] and five suggestive [4p16.1, 10p13.1, 8q11.23, 16p13.3, 18p11.31]). Results from the AN cohort were far less compelling: for QTL linkage analysis, two suggestive signals (for OBS at 6q21 and for ANX at 9p21.3); for covariate-based linkage analysis, five suggestive signals (for BMI at 4q13.1, for CM at 11p11.2 and 17q25.1, and for OBF at 17q25.1 and 15q26.2). Overlap between the two cohorts was minimal for substantial linkage signals.
doi:10.1002/ajmg.b.30226
PMCID: PMC2590774  PMID: 16152574
Complex disease; endophenotype; liability; mixture model; regression
2.  Genetics and Epigenetics of Eating Disorders 
Eating disorders (EDs) are serious psychiatric conditions influenced by biological, psychological, and sociocultural factors. A better understanding of the genetics of these complex traits and the development of more sophisticated molecular biology tools have advanced our understanding of the etiology of EDs. The aim of this review is to critically evaluate the literature on the genetic research conducted on three major EDs: anorexia nervosa (AN), bulimia nervosa (BN), and binge eating disorder (BED). We will first review the diagnostic criteria, clinical features, prevalence, and prognosis of AN, BN, and BED, followed by a review of family, twin, and adoption studies. We then review the history of genetic studies of EDs covering linkage analysis, candidate gene association studies, genome-wide association studies, and the study of rare variants in EDs. Our review also incorporates a translational perspective by covering animal models of ED-related phenotypes. Finally, we review the nascent field of epigenetics of EDs and a look forward to future directions for ED genetic research.
doi:10.2147/AGG.S55776
PMCID: PMC4803116  PMID: 27013903
eating disorders; anorexia nervosa; bulimia nervosa; binge eating disorder; genetics; epigenetics
3.  Novel quantitative trait locus is mapped to chromosome 12p11 for left ventricular mass in Dominican families: the Family Study of Stroke Risk and Carotid Atherosclerosis 
BMC Medical Genetics  2009;10:74.
Background
Left ventricular mass (LVM) is an important risk factor for stroke and vascular disease. The genetic basis of LVM is unclear although a high heritability has been suggested. We sought to map quantitative trait loci (QTL) for LVM using large Dominican families.
Methods
Probands were selected from Dominican subjects of the population-based Northern Manhattan Study (NOMAS). LVM was measured by transthoracic echocardiography. A set of 405 microsatellite markers was used to screen the whole genome among 1360 subjects from 100 Dominican families who had complete phenotype data and DNA available. A polygenic covariate screening was run to identify the significant covariates. Variance components analysis was used to estimate heritability and to detect evidence for linkage, after adjusting for significant risk factors. Ordered-subset Analysis (OSA) was conducted to identify a more homogeneous subset for stratification analysis.
Results
LVM had a heritability of 0.58 in the studied population (p < 0.0001). The most significant evidence for linkage was found at chromosome 12p11 (MLOD = 3.11, empirical p = 0.0003) with peak marker at D12S1042. This linkage was significantly increased in a subset of families with the high average waist circumference (MLOD = 4.45, p = 0.0045 for increase in evidence for linkage).
Conclusion
We mapped a novel QTL near D12S1042 for LVM in Dominicans. Enhanced linkage evidence in families with larger waist circumference suggests that gene(s) residing within the QTL interact(s) with abdominal obesity to contribute to phenotypic variation of LVM. Suggestive evidence for linkage (LOD = 1.99) has been reported at the same peak marker for left ventricular geometry in a White population from the HyperGEN study, underscoring the importance of this QTL for left ventricular phenotype. Further fine mapping and validation studies are warranted to identify the underpinning genes.
doi:10.1186/1471-2350-10-74
PMCID: PMC2724377  PMID: 19627612
4.  Anorexia nervosa trios: behavioral profiles of individuals with anorexianervosa and their parents 
Psychological medicine  2008;39(3):451-461.
Background
Anorexia nervosa (AN) is associated with behavioral traits that predate the onset of AN and persist after recovery. We identified patterns of behavioral traits in AN trios (proband plus two biological parents).
Method
A total of 433 complete trios were collected in the Price Foundation Genetic Study of AN using standardized instruments for eating disorder (ED) symptoms, anxiety, perfectionism, and temperament. We used latent profile analysis and ANOVA to identify and validate patterns of behavioral traits.
Results
We distinguished three classes with medium to large effect sizes by mothers’ and probands’ drive for thinness, body dissatisfaction, perfectionism, neuroticism, trait anxiety, and harm avoidance. Fathers did not differ significantly across classes. Classes were distinguished by degree of symptomatology rather than qualitative differences. Class 1 (~33 %) comprised low symptom probands and mothers with scores in the healthy range. Class 2 (~43 %) included probands with marked elevations in drive for thinness, body dissatisfaction, neuroticism, trait anxiety, and harm avoidance and mothers with mild anxious/perfectionistic traits. Class 3 (~24 %) included probands and mothers with elevations on ED and anxious/perfectionistic traits. Mother–daughter symptom severity was related in classes 1 and 3 only. Trio profiles did not differ significantly by proband clinical status or subtype.
Conclusions
A key finding is the importance of mother and daughter traits in the identification of temperament and personality patterns in families affected by AN. Mother–daughter pairs with severe ED and anxious/perfectionistic traits may represent a more homogeneous and familial variant of AN that could be of value in genetic studies.
doi:10.1017/S0033291708003826
PMCID: PMC3714180  PMID: 18578898
Anorexia nervosa; eating disorder; genetics; temperament
5.  Novel genomic approaches unravel genetic architecture of complex traits in apple 
BMC Genomics  2013;14:393.
Background
Understanding the genetic architecture of quantitative traits is important for developing genome-based crop improvement methods. Genome-wide association study (GWAS) is a powerful technique for mining novel functional variants. Using a family-based design involving 1,200 apple (Malus × domestica Borkh.) seedlings genotyped for an 8K SNP array, we report the first systematic evaluation of the relative contributions of different genomic regions to various traits related to eating quality and susceptibility to some physiological disorders. Single-SNP analyses models that accounted for population structure, or not, were compared with models fitting all markers simultaneously. The patterns of linkage disequilibrium (LD) were also investigated.
Results
A high degree of LD even at longer distances between markers was observed, and the patterns of LD decay were similar across successive generations. Genomic regions were identified, some of which coincided with known candidate genes, with significant effects on various traits. Phenotypic variation explained by the loci identified through a whole-genome scan ranged from 3% to 25% across different traits, while fitting all markers simultaneously generally provided heritability estimates close to those from pedigree-based analysis. Results from ‘Q+K’ and ‘K’ models were very similar, suggesting that the SNP-based kinship matrix captures most of the underlying population structure. Correlations between allele substitution effects obtained from single-marker and all-marker analyses were about 0.90 for all traits. Use of SNP-derived realized relationships in linear mixed models provided a better goodness-of-fit than pedigree-based expected relationships. Genomic regions with probable pleiotropic effects were supported by the corresponding higher linkage group (LG) level estimated genetic correlations.
Conclusions
The accuracy of artificial selection in plants species can be increased by using more precise marker-derived estimates of realized coefficients of relationships. All-marker analyses that indirectly account for population- and pedigree structure will be a credible alternative to single-SNP analyses in GWAS. This study revealed large differences in the genetic architecture of apple fruit traits, and the marker-trait associations identified here will help develop genome-based breeding methods for apple cultivar development.
doi:10.1186/1471-2164-14-393
PMCID: PMC3686700  PMID: 23758946
GWAS; Linkage disequilibrium; Genetic architecture; Allele substitution effect; Pleiotropy; Malus × domestica
6.  Replication of linkage at chromosome 20p13 and identification of suggestive sex-differential risk loci for autism spectrum disorder 
Molecular Autism  2014;5:13.
Background
Autism spectrum disorders (ASDs) are male-biased and genetically heterogeneous. While sequencing of sporadic cases has identified de novo risk variants, the heritable genetic contribution and mechanisms driving the male bias are less understood. Here, we aimed to identify familial and sex-differential risk loci in the largest available, uniformly ascertained, densely genotyped sample of multiplex ASD families from the Autism Genetics Resource Exchange (AGRE), and to compare results with earlier findings from AGRE.
Methods
From a total sample of 1,008 multiplex families, we performed genome-wide, non-parametric linkage analysis in a discovery sample of 847 families, and separately on subsets of families with only male, affected children (male-only, MO) or with at least one female, affected child (female-containing, FC). Loci showing evidence for suggestive linkage (logarithm of odds ≥2.2) in this discovery sample, or in previous AGRE samples, were re-evaluated in an extension study utilizing all 1,008 available families. For regions with genome-wide significant linkage signal in the discovery stage, those families not included in the corresponding discovery sample were then evaluated for independent replication of linkage. Association testing of common single nucleotide polymorphisms (SNPs) was also performed within suggestive linkage regions.
Results
We observed an independent replication of previously observed linkage at chromosome 20p13 (P < 0.01), while loci at 6q27 and 8q13.2 showed suggestive linkage in our extended sample. Suggestive sex-differential linkage was observed at 1p31.3 (MO), 8p21.2 (FC), and 8p12 (FC) in our discovery sample, and the MO signal at 1p31.3 was supported in our expanded sample. No sex-differential signals met replication criteria, and no common SNPs were significantly associated with ASD within any identified linkage regions.
Conclusions
With few exceptions, analyses of subsets of families from the AGRE cohort identify different risk loci, consistent with extreme locus heterogeneity in ASD. Large samples appear to yield more consistent results, and sex-stratified analyses facilitate the identification of sex-differential risk loci, suggesting that linkage analyses in large cohorts are useful for identifying heritable risk loci. Additional work, such as targeted re-sequencing, is needed to identify the specific variants within these loci that are responsible for increasing ASD risk.
doi:10.1186/2040-2392-5-13
PMCID: PMC3942516  PMID: 24533643
Male brain; Sex differences; Intermediate phenotype; Linkage analysis; Association; AGRE
7.  Genome-Wide Association Analysis of Eating Disorder-Related Symptoms, Behaviors, and Personality Traits 
American Journal of Medical Genetics  2012;159B(7):803-811.
Eating disorders (EDs) are common, complex psychiatric disorders thought to be caused by both genetic and environmental factors. They share many symptoms, behaviors, and personality traits, which may have overlapping heritability. The aim of the present study is to perform a genome-wide association scan (GWAS) of six ED phenotypes comprising three symptom traits from the Eating Disorders Inventory 2 [Drive for Thinness (DT), Body Dissatisfaction (BD), and Bulimia], Weight Fluctuation symptom, Breakfast Skipping behavior and Childhood Obsessive-Compulsive Personality Disorder trait (CHIRP). Investigated traits were derived from standardized self-report questionnaires completed by the TwinsUK population-based cohort. We tested 283,744 directly typed SNPs across six phenotypes of interest in the TwinsUK discovery dataset and followed-up signals from various strata using a two-stage replication strategy in two independent cohorts of European ancestry. We meta-analyzed a total of 2,698 individuals for DT, 2,680 for BD, 2,789 (821 cases/1,968 controls) for Bulimia, 1,360 (633 cases/727 controls) for Childhood Obsessive-Compulsive Personality Disorder trait, 2,773 (761 cases/2,012 controls) for Breakfast Skipping, and 2,967 (798 cases/2,169 controls) for Weight Fluctuation symptom. In this GWAS analysis of six ED-related phenotypes, we detected association of eight genetic variants with P < 10−5. Genetic variants that showed suggestive evidence of association were previously associated with several psychiatric disorders and ED-related phenotypes. Our study indicates that larger-scale collaborative studies will be needed to achieve the necessary power to detect loci underlying ED-related traits. © 2012 Wiley Periodicals, Inc.
doi:10.1002/ajmg.b.32087
PMCID: PMC3494378  PMID: 22911880
Drive for Thinness; Body Dissatisfaction; Childhood Obsessive Compulsive Personality Disorder; Weight Fluctuation; Breakfast Skipping
8.  The Heritability of Eating Disorders: Methods and Current Findings 
Family, twin, and adoption studies of anorexia nervosa (AN), bulimia nervosa (BN), binge-eating disorder (BED), and the proposed purging disorder presentation (PD) have consistently demonstrated that genetic factors contribute to the variance in liability to eating disorders. In addition, endophenotypes and component phenotypes of eating disorders have been evaluated and provide further insight regarding genetic factors influencing eating disorders and eating disorder diagnostic criteria. Many of these phenotypes have demonstrated substantial heritability. This chapter reviews biometrical genetic methods and current findings from family and twin studies that investigate the role of genes and environment in the etiology of eating disorders. We review the methodology used to estimate heritability, the results of these studies, and discuss the implications of this research for the basic conceptualization of eating disorders and the future value of twin modeling in the molecular genetic era.
doi:10.1007/7854_2010_91
PMCID: PMC3599773  PMID: 21243474
9.  Multi-system Component Phenotypes of Bipolar Disorder for Genetic Investigations of Extended Pedigrees 
JAMA psychiatry  2014;71(4):375-387.
IMPORTANCE
Genetic factors contribute to risk for bipolar disorder (BP), yet its pathogenesis remains poorly understood. A focus on measuring multi-system quantitative traits that may be components of BP psychopathology may enable genetic dissection of this complex disorder, and investigation of extended pedigrees from genetically isolated populations may facilitate the detection of specific genetic variants that impact on BP as well as its component phenotypes.
OBJECTIVE
To identify quantitative neurocognitive, temperament-related, and neuroanatomic phenotypes that appear heritable and associated with severe bipolar disorder (BP-I), and therefore suitable for genetic linkage and association studies aimed at identifying variants contributing to BP-I risk.
DESIGN
Multi-generational pedigree study in two closely related, genetically isolated populations: the Central Valley of Costa Rica (CVCR) and Antioquia, Colombia (ANT).
PARTICIPANTS
738 individuals, all from CVCR and ANT pedigrees, of whom 181 are affected with BP-I.
MAIN OUTCOME MEASURE
Familial aggregation (heritability) and association with BP-I of 169 quantitative neurocognitive, temperament, magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI) phenotypes.
RESULTS
Seventy-five percent (126) of the phenotypes investigated were significantly heritable, and 31% (53) were associated with BP-I. About 1/4 of the phenotypes, including measures from each phenotype domain, were both heritable and associated with BP-I. Neuroimaging phenotypes, particularly cortical thickness in prefrontal and temporal regions, and volume and microstructural integrity of the corpus callosum, represented the most promising candidate traits for genetic mapping related to BP based on strong heritability and association with disease. Analyses of phenotypic and genetic covariation identified substantial correlations among the traits, at least some of which share a common underlying genetic architecture.
CONCLUSIONS AND RELEVANCE
This is the most extensive investigation of BP-relevant component phenotypes to date. Our results identify brain and behavioral quantitative traits that appear to be genetically influenced and show a pattern of BP-I-association within families that is consistent with expectations from case-control studies. Together these phenotypes provide a basis for identifying loci contributing to BP-I risk and for genetic dissection of the disorder.
doi:10.1001/jamapsychiatry.2013.4100
PMCID: PMC4045237  PMID: 24522887
10.  A genome-wide association study for blood lipid phenotypes in the Framingham Heart Study 
BMC Medical Genetics  2007;8(Suppl 1):S17.
Background
Blood lipid levels including low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), and triglycerides (TG) are highly heritable. Genome-wide association is a promising approach to map genetic loci related to these heritable phenotypes.
Methods
In 1087 Framingham Heart Study Offspring cohort participants (mean age 47 years, 52% women), we conducted genome-wide analyses (Affymetrix 100K GeneChip) for fasting blood lipid traits. Total cholesterol, HDL-C, and TG were measured by standard enzymatic methods and LDL-C was calculated using the Friedewald formula. The long-term averages of up to seven measurements of LDL-C, HDL-C, and TG over a ~30 year span were the primary phenotypes. We used generalized estimating equations (GEE), family-based association tests (FBAT) and variance components linkage to investigate the relationships between SNPs (on autosomes, with minor allele frequency ≥10%, genotypic call rate ≥80%, and Hardy-Weinberg equilibrium p ≥ 0.001) and multivariable-adjusted residuals. We pursued a three-stage replication strategy of the GEE association results with 287 SNPs (P < 0.001 in Stage I) tested in Stage II (n ~1450 individuals) and 40 SNPs (P < 0.001 in joint analysis of Stages I and II) tested in Stage III (n~6650 individuals).
Results
Long-term averages of LDL-C, HDL-C, and TG were highly heritable (h2 = 0.66, 0.69, 0.58, respectively; each P < 0.0001). Of 70,987 tests for each of the phenotypes, two SNPs had p < 10-5 in GEE results for LDL-C, four for HDL-C, and one for TG. For each multivariable-adjusted phenotype, the number of SNPs with association p < 10-4 ranged from 13 to 18 and with p < 10-3, from 94 to 149. Some results confirmed previously reported associations with candidate genes including variation in the lipoprotein lipase gene (LPL) and HDL-C and TG (rs7007797; P = 0.0005 for HDL-C and 0.002 for TG). The full set of GEE, FBAT and linkage results are posted at the database of Genotype and Phenotype (dbGaP). After three stages of replication, there was no convincing statistical evidence for association (i.e., combined P < 10-5 across all three stages) between any of the tested SNPs and lipid phenotypes.
Conclusion
Using a 100K genome-wide scan, we have generated a set of putative associations for common sequence variants and lipid phenotypes. Validation of selected hypotheses in additional samples did not identify any new loci underlying variability in blood lipids. Lack of replication may be due to inadequate statistical power to detect modest quantitative trait locus effects (i.e., <1% of trait variance explained) or reduced genomic coverage of the 100K array. GWAS in FHS using a denser genome-wide genotyping platform and a better-powered replication strategy may identify novel loci underlying blood lipids.
doi:10.1186/1471-2350-8-S1-S17
PMCID: PMC1995614  PMID: 17903299
11.  Anorexia nervosa 
BMJ Clinical Evidence  2011;2011:1011.
Introduction
Anorexia nervosa is characterised by a low body mass index (BMI), fear of gaining weight, denial of current low weight and its impact on health, and amenorrhoea. Estimated prevalence is highest in teenage girls, and up to 0.7% of this age group may be affected. While most people with anorexia nervosa recover completely or partially, about 5% die of the condition, and 20% develop a chronic eating disorder. Young women with anorexia nervosa are at increased risk of bone fractures later in life.
Methods and outcomes
We conducted a systematic review, and aimed to answer the following clinical questions: What are the effects of treatments in anorexia nervosa? What are the effects of interventions to prevent or treat complications of anorexia nervosa? We searched: Medline, Embase, The Cochrane Library, and other important databases up to April 2010 (Clinical Evidence reviews are updated periodically; please check our website for the most up-to-date version of this review). We included harms alerts from relevant organisations such as the US Food and Drug Administration (FDA) and the UK Medicines and Healthcare products Regulatory Agency (MHRA).
Results
We found 40 systematic reviews, RCTs, or observational studies that met our inclusion criteria. We performed a GRADE evaluation of the quality of evidence for interventions.
Conclusions
In this systematic review we present information relating to the effectiveness and safety of the following interventions: atypical antipsychotic drugs, benzodiazepines, cyproheptadine, inpatient/outpatient treatment setting, oestrogen treatment (HRT or oral contraceptives), older-generation antipsychotic drugs, psychotherapy, refeeding, selective serotonin reuptake inhibitors (SSRIs), and tricyclic antidepressants.
Key Points
Anorexia nervosa is characterised by a low body mass index (BMI), fear of gaining weight, denial of current low weight and its impact on health, and amenorrhoea. Estimated prevalence is highest in teenage girls, and the condition may affect up to 0.7% of this group.Anorexia nervosa is related to family, sociocultural, genetic, and other biological factors. Psychiatric and personality disorders such as depression, anxiety disorders, obsessive compulsive disorder, and perfectionism are commonly found in people who have anorexia nervosa.Most people with anorexia nervosa recover completely or partially, but about 5% die from the condition and 20% develop a chronic eating disorder.Young women with anorexia nervosa are at increased risk of fractures later in life.Population assessment indicates that risks to fertility may be overstated in those who reach a healthy BMI, but children born to mothers who have recovered from anorexia nervosa seem to have lower birth weights.
There is no strong RCT evidence that any treatments work well for anorexia nervosa. However, there is a gradual accumulation of evidence suggesting that early intervention is effective. Increasing evidence suggests that working with the family may also interrupt the development of a persistent form of the illness, when this work begins early in the disease.
Evidence on the benefits of psychotherapy is unclear.
Refeeding is a necessary and effective component of treatment, but is not sufficient alone. Very limited evidence from a quasi-experimental study suggests that a lenient approach to refeeding is as effective and more acceptable compared with a more strict approach.Refeeding may be as effective in an outpatient setting as during hospital admission.Nasogastric refeeding has been used to speed up weight gain in inpatient observational studies, although it is rarely studied in RCTs. Very limited RCT evidence suggests that adding nasogastric feeding to oral nutrition can increase weight gain and reduce relapse in the short term more than oral nutrition alone, but these gains are not maintained at 1 year post-discharge. Given ethical and medical concerns with tube feeding, this approach is encouraged with caution.Nutritional supplements, including zinc, have only limited evidence for their effectiveness, and additional evaluations of these measures are warranted.
We don't know whether inpatient or outpatient treatment is more effective in people with anorexia nervosa.
Limited evidence from small RCTs has not shown significant weight gain from SSRIs or tricyclic antidepressants, some of which may cause serious adverse effects. Tricyclic antidepressants may cause drowsiness, dry mouth, blurred vision, and a prolonged QT interval in people who have anorexia nervosa. SSRIs have not been shown to be beneficial, but the evidence remains very limited; in the 4 RCTs we found, conclusions were limited because of small trial size and high rates of withdrawal.
Older-generation antipsychotic drugs may prolong the QT interval, increasing the risk of ventricular tachycardia, torsades de pointes, and sudden death. Atypical antipsychotics have been evaluated for their potential role in reducing agitation and anxiety related to refeeding, as well as for potentially increasing appetite. Increasing observational data (case series) have suggested that they may decrease obsessiveness and agitation. However, further evidence from large, well-conducted RCTs is necessary to draw reliable conclusions. Newer atypical antipsychotics, in particular olanzapine, do not seem to be associated with the same cardiac risks as older-generation antipsychotic drugs, but the known association between olanzapine and weight gain may impact compliance in people with anorexia nervosa. However, further research needs to be done.
We found insufficient RCT evidence assessing benzodiazepines or cyproheptadine for treating anorexia nervosa.
Oestrogen treatment has been hypothesised to reduce the negative effects on bone mineral density associated with anorexia nervosa. However, three small RCTs have failed to demonstrate clinically relevant changes in bone mineral density after treatment with oestrogen either HRT or oral contraceptives), and these results are supported by 2-year longitudinal data, which found similar lack of improvement.
PMCID: PMC3275304  PMID: 21481284
12.  Exploring pleiotropy using principal components 
BMC Genetics  2003;4(Suppl 1):S53.
A standard multivariate principal components (PCs) method was utilized to identify clusters of variables that may be controlled by a common gene or genes (pleiotropy). Heritability estimates were obtained and linkage analyses performed on six individual traits (total cholesterol (Chol), high and low density lipoproteins, triglycerides (TG), body mass index (BMI), and systolic blood pressure (SBP)) and on each PC to compare our ability to identify major gene effects. Using the simulated data from Genetic Analysis Workshop 13 (Cohort 1 and 2 data for year 11), the quantitative traits were first adjusted for age, sex, and smoking (cigarettes per day). Adjusted variables were standardized and PCs calculated followed by orthogonal transformation (varimax rotation). Rotated PCs were then subjected to heritability and quantitative multipoint linkage analysis. The first three PCs explained 73% of the total phenotypic variance. Heritability estimates were above 0.60 for all three PCs. We performed linkage analyses on the PCs as well as the individual traits. The majority of pleiotropic and trait-specific genes were not identified. Standard PCs analysis methods did not facilitate the identification of pleiotropic genes affecting the six traits examined in the simulated data set. In addition, genes contributing 20% of the variance in traits with over 0.60 heritability estimates could not be identified in this simulated data set using traditional quantitative trait linkage analyses. Lack of identification of pleiotropic and trait-specific genes in some cases may reflect their low contribution to the traits/PCs examined or more importantly, characteristics of the sample group analyzed, and not simply a failure of the PC approach itself.
doi:10.1186/1471-2156-4-S1-S53
PMCID: PMC1866490  PMID: 14975121
multivariate analysis; principle components; quantitative traits; heritability estimates; linkage
13.  An Association Study of the A218C Polymorphism of the Tryptophan Hydroxylase 1 Gene with Eating Disorders in a Korean Population: A Pilot Study 
Psychiatry Investigation  2009;6(1):44-49.
Objective
We examined the association between the tryptophan hydroxylase 1 (TPH1) gene and eating disorders focusing on obsessionality.
Methods
The sample included 62 women with a lifetime diagnosis of anorexia nervosa (AN) as well as 50 women with a lifetime diagnosis of bulimia nervosa (BN) recruited from specialist clinics for eating disorders and 131 healthy women in Korea. Blood samples were collected from all participants for the TPH1 genotyping. The patients were ad ministered the Korean version of the Eating Disorders Examination and obsessionality was conceptualized using measures of persistence, harm avoidance, and obsessive-compulsive symptoms.
Results
In the case-control comparisons, the frequency of the A/A genotype was increased in the patients with BN, but this difference was not significant after correcting for multiple testing. We found no effect of the TPH A218C polymorphism on obsessionality in the patients with AN or BN.
Conclusion
Although the present findings should be regarded as preliminary because of the small size of our sample, they suggest that the TPH1 gene may contribute to the genetic susceptibility to BN and be associated with the other unexplored traits of bulimic case status.
doi:10.4306/pi.2009.6.1.44
PMCID: PMC2796036  PMID: 20046373
Tryptophan hydroxylase; Eating disorders; Bulimia nervosa; Obsessionality
14.  Genome-Wide Linkage Analysis of Malaria Infection Intensity and Mild Disease 
PLoS Genetics  2007;3(3):e48.
Although balancing selection with the sickle-cell trait and other red blood cell disorders has emphasized the interaction between malaria and human genetics, no systematic approach has so far been undertaken towards a comprehensive search for human genome variants influencing malaria. By screening 2,551 families in rural Ghana, West Africa, 108 nuclear families were identified who were exposed to hyperendemic malaria transmission and were homozygous wild-type for the established malaria resistance factors of hemoglobin (Hb)S, HbC, alpha+ thalassemia, and glucose-6-phosphate-dehydrogenase deficiency. Of these families, 392 siblings aged 0.5–11 y were characterized for malaria susceptibility by closely monitoring parasite counts, malaria fever episodes, and anemia over 8 mo. An autosome-wide linkage analysis based on 10,000 single-nucleotide polymorphisms was conducted in 68 selected families including 241 siblings forming 330 sib pairs. Several regions were identified which showed evidence for linkage to the parasitological and clinical phenotypes studied, among them a prominent signal on Chromosome 10p15 obtained with malaria fever episodes (asymptotic z score = 4.37, empirical p-value = 4.0 × 10−5, locus-specific heritability of 37.7%; 95% confidence interval, 15.7%–59.7%). The identification of genetic variants underlying the linkage signals may reveal as yet unrecognized pathways influencing human resistance to malaria.
Author Summary
In tropical Africa, virtually all children become infected with malaria parasites. Most of them experience several malaria attacks per year, and over a million die from disease complications. Sickle-cell anemia, thalassemias, and other inherited red blood cell disorders indicate that malaria has selected for human genetic variants, but no attempts have so far been reported to systematically screen the human genome for malaria-resistance factors. We describe a genome-wide linkage analysis performed in children living in rural Ghana, West Africa, including approaches to select an informative study cohort and to assess, over a period of 8 mo, individual disposition to malaria parasitemia, fever episodes, and anemia. Families carrying the known malaria-protective red blood cell disorders were excluded, infection intensities were adjusted to the use of mosquito-protection devices, and parasitological and clinical findings were corrected according to the state of partial malaria immunity, which, under constant exposure, gradually develops over the first 10 y of life. The study revealed several genomic regions showing evidence for linkage to the various malaria phenotypes recorded, among them a prominent signal on Chromosome 10 correlated to the frequency of fever episodes. Future identification of genes involved is expected to reveal previously unrecognized pathways that may protect children against malaria.
doi:10.1371/journal.pgen.0030048
PMCID: PMC1829404  PMID: 17381244
15.  The Genetics of Anorexia Nervosa Collaborative Study: Methods and Sample Description 
Objective
Supported by National Institute of Mental Health (NIMH), this 12-site international collaboration seeks to identify genetic variants that affect risk for anorexia nervosa (AN).
Method
Four hundred families will be ascertained with two or more individuals affected with AN. The assessment battery produces a rich set of phenotypes comprising eating disorder diagnoses and psychological and personality features known to be associated with vulnerability to eating disorders.
Results
We report attributes of the first 200 families, comprising 200 probands and 232 affected relatives.
Conclusion
These results provide context for the genotyping of the first 200 families by the Center for Inherited Disease Research. We will analyze our first 200 families for linkage, complete recruitment of roughly 400 families, and then perform final linkage analyses on the complete cohort. DNA, genotypes, and phenotypes will form a national eating disorder repository maintained by NIMH and available to qualified investigators.
doi:10.1002/eat.20509
PMCID: PMC3755506  PMID: 18236451
anorexia nervosa; eating disorders; bulimia nervosa; psychiatric disorders; genetics; linkage analysis; genomics
16.  Linkage Analysis of a Model Quantitative Trait in Humans: Finger Ridge Count Shows Significant Multivariate Linkage to 5q14.1 
PLoS Genetics  2007;3(9):e165.
The finger ridge count (a measure of pattern size) is one of the most heritable complex traits studied in humans and has been considered a model human polygenic trait in quantitative genetic analysis. Here, we report the results of the first genome-wide linkage scan for finger ridge count in a sample of 2,114 offspring from 922 nuclear families. Both univariate linkage to the absolute ridge count (a sum of all the ridge counts on all ten fingers), and multivariate linkage analyses of the counts on individual fingers, were conducted. The multivariate analyses yielded significant linkage to 5q14.1 (Logarithm of odds [LOD] = 3.34, pointwise-empirical p-value = 0.00025) that was predominantly driven by linkage to the ring, index, and middle fingers. The strongest univariate linkage was to 1q42.2 (LOD = 2.04, point-wise p-value = 0.002, genome-wide p-value = 0.29). In summary, the combination of univariate and multivariate results was more informative than simple univariate analyses alone. Patterns of quantitative trait loci factor loadings consistent with developmental fields were observed, and the simple pleiotropic model underlying the absolute ridge count was not sufficient to characterize the interrelationships between the ridge counts of individual fingers.
Author Summary
Finger ridge count (an index of the size of the fingerprint pattern) has been used as a model trait for the study of human quantitative genetics for over 80 years. Here, we present the first genome-wide linkage scan for finger ridge count in a large sample of 2,114 offspring from 922 nuclear families. Our results illustrate the increase in power and information that can be gained from a multivariate linkage analysis of ridge counts of individual fingers as compared to a univariate analysis of a summary measure (absolute ridge count). The strongest evidence for linkage was seen at 5q14.1, and the pattern of loadings was consistent with a developmental field factor whose influence is greatest on the ring finger, falling off to either side, which is consistent with previous findings that heritability for ridge count is higher for the middle three fingers. We feel that the paper will be of specific methodological interest to those conducting linkage and association analyses with summary measures. In addition, given the frequency with which this phenotype is used as a didactic example in genetics courses we feel that this paper will be of interest to the general scientific community.
doi:10.1371/journal.pgen.0030165
PMCID: PMC1994711  PMID: 17907812
17.  Anorexia nervosa 
BMJ Clinical Evidence  2009;2009:1011.
Introduction
Anorexia nervosa is characterised by a low body mass index (BMI), fear of gaining weight, denial of current low weight and its impact on health, and amenorrhoea. Estimated prevalence is highest in teenage girls, and up to 0.7% of this age group may be affected. While most people with anorexia nervosa recover completely or partially, about 5% die of the condition, and 20% develop a chronic eating disorder. Young women with anorexia nervosa are at increased risk of bone fractures later in life.
Methods and outcomes
We conducted a systematic review which aimed to answer the following clinical questions: What are the effects of treatments for anorexia nervosa? What are the effects of interventions to prevent or treat complications of anorexia nervosa? We searched: Medline, Embase, The Cochrane Library, and other important databases up to August 2007 (Clinical Evidence reviews are updated periodically, please check our website for the most up-to-date version of this review). We included harms alerts from relevant organisations such as the US Food and Drug Administration (FDA) and the UK Medicines and Healthcare products Regulatory Agency (MHRA).
Results
We found 40 systematic reviews, RCTs, or observational studies that met our inclusion criteria. We performed a GRADE evaluation of the quality of evidence for interventions.
Conclusions
In this systematic review we present information relating to the effectiveness and safety of the following interventions: anxiolytic drugs, cyproheptadine, inpatient/outpatient treatment setting, oestrogen treatment, psychotherapy, refeeding, selective serotonin reuptake inhibitors (SSRIs), and tricyclic antidepressants.
Key Points
Anorexia nervosa is characterised by a low BMI, fear of gaining weight, denial of current low weight and its impact on health, and amenorrhoea. Estimated prevalence is highest in teenage girls, and may affect up to 0.7% of this group.Anorexia nervosa is related to family, sociocultural, genetic, and other biological factors. Psychiatric and personality disorders such as depression, anxiety disorders, obsessive compulsive disorder, and perfectionism, are commonly found in people who have anorexia nervosa.Most people with anorexia nervosa recover completely or partially, but about 5% die from the condition and 20% develop a chronic eating disorder.Young women with anorexia nervosa are at increased risk of fractures later in life.
There is no strong research evidence that any treatments work well for anorexia nervosa. However, there is a gradual accumulation of evidence which suggests that early intervention is effective. Working with the family may also interrupt the development of a persistent form of the illness.
Evidence on the benefits of psychotherapy is unclear.
Refeeding is a necessary and effective component of treatment, but is not sufficient alone. Very limited evidence from a quasi-experimental study suggests that a lenient approach to refeeding is as effective and more acceptable compared with a more strict approach.Refeeding may be as effective in an outpatient setting as during hospital admission.Nasogastric feeding is rarely required and can lead to problems due to hypophosphataemia.Nutritional supplements, including zinc, have only limited evidence for their effectiveness, and additional evaluation of these measures are warranted.
Limited evidence from small RCTs has not shown significant weight gain from SSRIs or tricyclic antidepressants, some of which may cause serious adverse effects. Tricyclic antidepressants may cause drowsiness, dry mouth, blurred vision, and a prolonged QT interval in people who have anorexia nervosa. SSRIs have not been shown to be beneficial, but the evidence remains very limited; in the four RCTs we found, conclusions were limited due to small trial size and high withdrawal rates.
Anxiolytic drugs (mainly older generation antipsychotic drugs) may prolong the QT interval, increasing the risk of ventricular tachycardia, torsades de pointes, and sudden death. Atypical antipsychotics have been evaluated for their potential role in reducing agitation and anxiety related to refeeding, as well as for potentially increasing appetite. Weak observational evidence has suggested that they may decrease obsessiveness and agitation. However, we found no RCTs of sufficient quality on the effects of atypical antipsychotics, and further evidence from large, well-conducted RCTs is necessary to draw reliable conclusions. Some atypical antipsychotics do not appear to be associated with the same cardiac risks as older-generation antipsychotic drugs. However, further research needs to be done.
We found insufficient evidence assessing cyproheptadine for treating anorexia nervosa.
Oestrogen treatment has been hypothesized to reduce the negative effects on bone mineral density associated with anorexia nervosa. However, three small RCTs have failed to demonstrate significant changes in bone mineral density after treatment with oestrogen.
PMCID: PMC2907776  PMID: 19445758
18.  Perplexities of treatment resistence in eating disorders 
BMC Psychiatry  2013;13:292.
Background
Treatment resistance is an omnipresent frustration in eating disorders. Attempts to identify the features of this resistance and subsequently develop novel treatments have had modest effects. This selective review examines treatment resistant features expressed in core eating disorder psychopathology, comorbidities and biological features. Novel treatments addressing resistance are discussed.
Description
The core eating disorder psychopathology of anorexia nervosa becomes a coping mechanism likely via vulnerable neurobiological features and conditioned learning to deal with life events. Thus it is reinforcing and ego syntonic resulting in resistance to treatment. The severity of core features such as preoccupations with body image, weight, eating and exercising predicts greater resistance to treatment. Bulimia nervosa patients are less resistant to treatment with treatment failure related to greater body image concerns, impulsivity, depression, severe diet restriction and poor social adjustment. For those with binge eating disorder overweight in childhood and high emotional eating predicts treatment resistance. There is suggestive data that a diagnosis of an anxiety disorder and severe perfectionism may confer treatment resistance in anorexia nervosa and substance use disorders or personality disorders with impulse control problems may produce resistance to treatment in bulimia nervosa. Traits such as perfectionism, cognitive inflexibility and negative affect with likely genetic influences may also affect treatment resistance. Pharmacotherapy and novel therapies have been developed to address treatment resistance. Atypical antipsychotic drugs have shown some effect in treatment resistant anorexia nervosa and topiramate and high doses of SSRIs are helpful for treatment of resistant binge eating disorder patients. There are insufficient randomized controlled trials to evaluate the novel psychotherapies which are primarily based on the core psychopathological features of the eating disorders.
Conclusion
Treatment resistance in eating disorders is usually predicted by the severity of the core eating disorder psychopathology which develops from an interaction between environmental risk factors with genetic traits and a vulnerable neurobiology. Future investigations of the biological features and neurocircuitry of the core eating disorders psychopathology and behaviors may provide information for more successful treatment interventions.
doi:10.1186/1471-244X-13-292
PMCID: PMC3829659  PMID: 24199597
Treatment resistance; Anorexia nervosa; Bulimia nervosa; Binge eating disorder
19.  Genome-wide and Ordered-Subset linkage analyses provide support for autism loci on 17q and 19p with evidence of phenotypic and interlocus genetic correlates 
Background
Autism is a neurobehavioral spectrum of phenotypes characterized by deficits in the development of language and social relationships and patterns of repetitive, rigid and compulsive behaviors. Twin and family studies point to a significant genetic etiology, and several groups have performed genomic linkage screens to identify susceptibility loci.
Methods
We performed a genome-wide linkage screen in 158 combined Tufts, Vanderbilt and AGRE (Autism Genetics Research Exchange) multiplex autism families using parametric and nonparametric methods with a categorical autism diagnosis to identify loci of main effect. Hypothesizing interdependence of genetic risk factors prompted us to perform exploratory studies applying the Ordered-Subset Analysis (OSA) approach using LOD scores as the trait covariate for ranking families. We employed OSA to test for interlocus correlations between loci with LOD scores ≥1.5, and empirically determined significance of linkage in optimal OSA subsets using permutation testing. Exploring phenotypic correlates as the basis for linkage increases involved comparison of mean scores for quantitative trait-based subsets of autism between optimal subsets and the remaining families.
Results
A genome-wide screen for autism loci identified the best evidence for linkage to 17q11.2 and 19p13, with maximum multipoint heterogeneity LOD scores of 2.9 and 2.6, respectively. Suggestive linkage (LOD scores ≥1.5) at other loci included 3p, 6q, 7q, 12p, and 16p. OSA revealed positive correlations of linkage between the 19p locus and 17q, between 19p and 6q, and between 7q and 5p. While potential phenotypic correlates for these findings were not identified for the chromosome 7/5 combination, differences indicating more rapid achievement of "developmental milestones" was apparent in the chromosome 19 OSA-defined subsets for 17q and 6q. OSA was used to test the hypothesis that 19p linkage involved more rapid achievement of these milestones and it revealed significantly increased LOD* scores at 19p13.
Conclusions
Our results further support 19p13 as harboring an autism susceptibility locus, confirm other linkage findings at 17q11.2, and demonstrate the need to analyze more discreet trait-based subsets of complex phenotypes to improve ability to detect genetic effects.
doi:10.1186/1471-2350-6-1
PMCID: PMC546213  PMID: 15647115
20.  The Genetics of Reading Disability in an Often Excluded Sample: Novel Loci Suggested for Reading Disability in Rolandic Epilepsy 
PLoS ONE  2012;7(7):e40696.
Background
Reading disability (RD) is a common neurodevelopmental disorder with genetic basis established in families segregating “pure” dyslexia. RD commonly occurs in neurodevelopmental disorders including Rolandic Epilepsy (RE), a complex genetic disorder. We performed genomewide linkage analysis of RD in RE families, testing the hypotheses that RD in RE families is genetically heterogenenous to pure dyslexia, and shares genetic influences with other sub-phenotypes of RE.
Methods
We initially performed genome-wide linkage analysis using 1000 STR markers in 38 US families ascertained through a RE proband; most of these families were multiplex for RD. We analyzed the data by two-point and multipoint parametric LOD score methods. We then confirmed the linkage evidence in a second US dataset of 20 RE families. We also resequenced the SEMA3C gene at the 7q21 linkage locus in members of one multiplex RE/RD pedigree and the DISC1 gene in affected pedigrees at the 1q42 locus.
Results
In the discovery dataset there was suggestive evidence of linkage for RD to chromosome 7q21 (two-point LOD score 3.05, multipoint LOD 3.08) and at 1q42 (two-point LOD 2.87, multipoint LOD 3.03). Much of the linkage evidence at 7q21 derived from families of French-Canadian origin, whereas the linkage evidence at 1q42 was well distributed across all the families. There was little evidence for linkage at known dyslexia loci. Combining the discovery and confirmation datasets increased the evidence at 1q42 (two-point LOD = 3.49, multipoint HLOD = 4.70), but decreased evidence at 7q21 (two-point LOD = 2.28, multipoint HLOD  = 1.81), possibly because the replication sample did not have French Canadian representation.
Discussion
Reading disability in rolandic epilepsy has a genetic basis and may be influenced by loci at 1q42 and, in some populations, at 7q21; there is little evidence of a role for known DYX loci discovered in “pure” dyslexia pedigrees. 1q42 and 7q21 are candidate novel dyslexia loci.
doi:10.1371/journal.pone.0040696
PMCID: PMC3399896  PMID: 22815793
21.  The role of heritability in mapping expression quantitative trait loci 
BMC Proceedings  2007;1(Suppl 1):S86.
Gene expression, as a heritable complex trait, has recently been used in many genome-wide linkage studies. The estimated overall heritability of each trait may be considered as evidence of a genetic contribution to the total phenotypic variation, which implies the possibility of mapping genome regions responsible for the gene expression variation via linkage analysis. However, heritability has been found to be an inconsistent predictor of significant linkage signals. To investigate this issue in human studies, we performed genome-wide linkage analysis on the 3554 gene expression traits of 194 Centre d'Etude du Polymorphisme Humain individuals provided by Genetic Analysis Workshop 15. Out of the 422 expression traits with significant linkage signals identified (LOD > 5.3), 89 traits have low estimated heritability (h2 < 10%), among which 23 traits have an estimated heritability equal to 0. The linkage analysis on individual pedigree shows that the overall LOD scores may result from a few pedigrees with strong linkage signals. Screening gene expressions before linkage analysis using a relatively low heritability (h2 < 20%) may result in a loss of significant linkage signals, especially for trans-acting expression quantitative trait loci (49%).
PMCID: PMC2367577  PMID: 18466589
22.  Sex-specific genetic architecture of human fatness in Chinese: the SAPPHIRe Study 
Human genetics  2010;128(5):501-513.
To dissect the genetic architecture of sexual dimorphism in obesity-related traits, we evaluated the sex–genotype interaction, sex-specific heritability and genome-wide linkages for seven measurements related to obesity. A total of 1,365 non-diabetic Chinese subjects from the family study of the Stanford Asia–Pacific Program of Hypertension and Insulin Resistance were used to search for quantitative trait loci (QTLs) responsible for the obesity-related traits. Pleiotropy and co-incidence effects from the QTLs were also examined using the bivariate linkage approach. We found that sex-specific differences in heritability and the genotype–sex interaction effects were substantially significant for most of these traits. Several QTLs with strong linkage evidence were identified after incorporating genotype by sex (G × S) interactions into the linkage mapping, including one QTL for hip circumference [maximum LOD score (MLS) = 4.22, empirical p = 0.000033] and two QTLs: for BMI on chromosome 12q with MLS 3.37 (empirical p = 0.0043) and 3.10 (empirical p = 0.0054). Sex-specific analyses demonstrated that these linkage signals all resulted from females rather than males. Most of these QTLs for obesity-related traits replicated the findings in other ethnic groups. Bivariate linkage analyses showed several obesity traits were influenced by a common set of QTLs. All regions with linkage signals were observed in one gender, but not in the whole sample, suggesting the genetic architecture of obesity-related traits does differ by gender. These findings are useful for further identification of the liability genes for these phenotypes through candidate genes or genome-wide association analysis.
doi:10.1007/s00439-010-0877-5
PMCID: PMC4446122  PMID: 20725740
23.  Heritability and Linkage Analysis of Personality in Bipolar Disorder 
Journal of affective disorders  2013;151(2):748-755.
Background
The many attempts that have been made to identify genes for bipolar disorder (BD) have met with limited success, which may reflect an inadequacy of diagnosis as an informative and biologically relevant phenotype for genetic studies. Here we have explored aspects of personality as quantitative phenotypes for bipolar disorder through the use of the Temperament and Character Inventory (TCI), which assesses personality in seven dimensions. Four temperament dimensions are assessed: novelty seeking (NS), harm avoidance (HA), reward dependence (RD), and persistence (PS). Three character dimensions are also included: self-directedness (SD), cooperativeness (CO), and self-transcendence (ST).
Methods
We compared personality scores between diagnostic groups and assessed heritability in a sample of 101 families collected for genetic studies of BD. A genome-wide SNP linkage analysis was then performed in the subset of 51 families for which genetic data was available.
Results
Significant group differences were observed between BD subjects, their first-degree relatives, and independent controls for all but RD and PS, and all but HA and RD were found to be significantly heritable in this sample. Linkage analysis of the heritable dimensions produced several suggestive linkage peaks for NS (chromosomes 7q21 and 10p15), PS (chromosomes 6q16, 12p13, and 19p13), and SD (chromosomes 4q35, 8q24, and 18q12).
Limitations
The relatively small size of our linkage sample likely limited our ability to reach genome-wide significance in this study.
Conclusions
While not genome-wide significant, these results suggest that aspects of personality may prove useful in the identification of genes underlying BD susceptibility.
doi:10.1016/j.jad.2013.06.015
PMCID: PMC3797235  PMID: 23972719
bipolar disorder; personality; TCI; heritability; genetic linkage
24.  Multiple genome-wide analyses of smoking behavior in the Framingham Heart Study 
BMC Genetics  2003;4(Suppl 1):S102.
Background
Cigarette smoking behavior may have a genetic basis. We assessed evidence for quantitative trait loci (QTLs) affecting the maximum number of cigarettes smoked per day, a trait meant to quantify this behavior, using data collected over 40 years as part of the Framingham Heart Study's original and offspring cohorts.
Results
Heritability was estimated to be approximately 21% using variance components (VC) methods (SOLAR), while oligogenic linkage and segregation analysis based on Bayesian Markov chain Monte Carlo (MCMC) methods (LOKI) estimated a mean of two large QTLs contributing approximately 28% and 20%, respectively, to the trait's variance. Genome-wide parametric (FASTLINK) and VC linkage analyses (SOLAR) revealed several LOD scores greater than 1.0, with peak LOD scores using both methods on chromosomes 2, 17, and 20; multi-point MCMC methods followed up on these chromosomes. The most robust linkage results were for a QTL between 65 and 84 cM on chromosome 20 with signals from multiple sex- and age-adjusted analyses including two-point LOD scores of 1.30 (parametric) and 1.07 (heritability = 0.17, VC) at 70.51 cM, a multi-point LOD score of 1.50 (heritability = 0.20, VC) at 84 cM, and an intensity ratio of 12.0 (MCMC) at 65 cM.
Conclusion
Familial aggregation of the maximum number of cigarettes smoked per day was consistent with a genetic component to this behavior, and oligogenic segregation analyses using MCMC suggested two important QTLs. Linkage signals on chromosome 20 between 65 and 84 cM were seen using multiple analytical methods. No linkage result, however, met genome-wide statistical significance criteria, and the true relationship between these regions and smoking behavior remains unclear.
doi:10.1186/1471-2156-4-S1-S102
PMCID: PMC1866440  PMID: 14975170
25.  Genome-wide linkage using the Social Responsiveness Scale in Utah autism pedigrees 
Molecular Autism  2010;1:8.
Background
Autism Spectrum Disorders (ASD) are phenotypically heterogeneous, characterized by impairments in the development of communication and social behaviour and the presence of repetitive behaviour and restricted interests. Dissecting the genetic complexity of ASD may require phenotypic data reflecting more detail than is offered by a categorical clinical diagnosis. Such data are available from the Social Responsiveness Scale (SRS) which is a continuous, quantitative measure of social ability giving scores that range from significant impairment to above average ability.
Methods
We present genome-wide results for 64 multiplex and extended families ranging from two to nine generations. SRS scores were available from 518 genotyped pedigree subjects, including affected and unaffected relatives. Genotypes from the Illumina 6 k single nucleotide polymorphism panel were provided by the Center for Inherited Disease Research. Quantitative and qualitative analyses were done using MCLINK, a software package that uses Markov chain Monte Carlo (MCMC) methods to perform multilocus linkage analysis on large extended pedigrees.
Results
When analysed as a qualitative trait, linkage occurred in the same locations as in our previous affected-only genome scan of these families, with findings on chromosomes 7q31.1-q32.3 [heterogeneity logarithm of the odds (HLOD) = 2.91], 15q13.3 (HLOD = 3.64), and 13q12.3 (HLOD = 2.23). Additional positive qualitative results were seen on chromosomes 6 and 10 in regions that may be of interest for other neuropsychiatric disorders. When analysed as a quantitative trait, results replicated a peak found in an independent sample using quantitative SRS scores on chromosome 11p15.1-p15.4 (HLOD = 2.77). Additional positive quantitative results were seen on chromosomes 7, 9, and 19.
Conclusions
The SRS linkage peaks reported here substantially overlap with peaks found in our previous affected-only genome scan of clinical diagnosis. In addition, we replicated a previous SRS peak in an independent sample. These results suggest the SRS is a robust and useful phenotype measure for genetic linkage studies of ASD. Finally, analyses of SRS scores revealed linkage peaks overlapping with evidence from other studies of neuropsychiatric diseases. The information available from the SRS itself may, therefore, reveal locations for autism susceptibility genes that would not otherwise be detected.
doi:10.1186/2040-2392-1-8
PMCID: PMC2913945  PMID: 20678250

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