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1.  A Genome-Wide Association Study of Monozygotic Twin-Pairs Suggests a Locus Related to Variability of Serum High-Density Lipoprotein Cholesterol 
Genome-wide association analysis on monozygotic twin pairs offers a route to discovery of gene–environment interactions through testing for variability loci associated with sensitivity to individual environment/lifestyle. We present a genome-wide scan of loci associated with intra-pair differences in serum lipid and apolipoprotein levels. We report data for 1,720 monozygotic female twin pairs from GenomEUtwin project with 2.5 million SNPs, imputed or genotyped, and measured serum lipid fractions for both twins. We found one locus associated with intra-pair differences in high density lipoprotein (HDL) cholesterol, rs2483058 in an intron of SRGAP2, where twins carrying the C allele are more sensitive to environmental factors (p = 3.98 × 10−8). We followed up the association in further genotyped monozygotic twins (N = 1 261) which showed a moderate association for the variant (p = .002, same direction of an effect). In addition, we report a new association on the level of apolipoprotein A-II (p = 4.03 × 10−8).
doi:10.1017/thg.2012.63
PMCID: PMC4333218  PMID: 23031429
twins; association; lipids; apolipoproteins; interaction
2.  Genetics of Path Lengths in Brain Connectivity Networks: HARDI-Based Maps in 457 Adults 
Brain connectivity analyses are increasingly popular for investigating organization. Many connectivity measures including path lengths are generally defined as the number of nodes traversed to connect a node in a graph to the others. Despite its name, path length is purely topological, and does not take into account the physical length of the connections. The distance of the trajectory may also be highly relevant, but is typically overlooked in connectivity analyses. Here we combined genotyping, anatomical MRI and HARDI to understand how our genes influence the cortical connections, using whole-brain tractography. We defined a new measure, based on Dijkstra’s algorithm, to compute path lengths for tracts connecting pairs of cortical regions. We compiled these measures into matrices where elements represent the physical distance traveled along tracts. We then analyzed a large cohort of healthy twins and show that our path length measure is reliable, heritable, and influenced even in young adults by the Alzheimer’s risk gene, CLU.
doi:10.1007/978-3-642-33530-3_3
PMCID: PMC4288784  PMID: 25584366
Structural connectivity; neuroimaging genetics; Dijkstra’s algorithm; HARDI tractography; path length
3.  Parental Separation and Early Substance Involvement: Results from Children of Alcoholic and Cannabis Dependent Twins 
Drug and alcohol dependence  2013;134:78-84.
Background
Risks associated with parental separation have received limited attention in research on children of parents with substance use disorders. We examined early substance involvement as a function of parental separation during childhood and parental alcohol and cannabis dependence.
Method
Data were drawn from 1,318 adolescent offspring of monozygotic (MZ) or dizygotic (DZ) Australian twin parents. Cox proportional hazards regression analyses were conducted predicting age at first use of alcohol, first alcohol intoxication, first use and first regular use of cigarettes, and first use of cannabis, from parental separation and both parent and cotwin substance dependence. Parent and cotwin alcohol and cannabis dependence were initially modeled separately, with post-hoc tests for equality of effects.
Results
With few exceptions, risks associated with parental alcohol versus cannabis dependence could be equated, with results largely suggestive of genetic transmission of risk from parental substance (alcohol or cannabis) dependence broadly defined. Controlling for parental substance dependence, parental separation was a strong predictor for all substance use variables, especially through age 13.
Conclusion
Together, findings underscore the importance of parental separation as a risk-factor for early substance involvement over and above both genetic and environmental influences specific to parental alcohol and cannabis dependence.
doi:10.1016/j.drugalcdep.2013.09.010
PMCID: PMC3908916  PMID: 24120074
adolescent substance use; parental separation; parental substance dependence; children of twins
4.  Association of OPRD1 Polymorphisms with Heroin Dependence in a Large Case-control Series 
Addiction biology  2012;19(1):10.1111/j.1369-1600.2012.00445.x.
Genes encoding the opioid receptors (OPRM1, OPRD1, and OPRK1) are obvious candidates for involvement in risk for heroin dependence. Prior association studies commonly had samples of modest size, included limited single nucleotide polymorphism (SNP) coverage of these genes, and yielded inconsistent results. Participants for the current investigation included 1459 heroin dependent cases ascertained from maintenance clinics in New South Wales, Australia, 1495 unrelated individuals selected from an Australian sample of twins and siblings as not meeting DSM-IV criteria for lifetime alcohol or illicit drug dependence (non-dependent controls), and 531 controls ascertained from economically-disadvantaged neighborhoods in proximity to the maintenance clinics. A total of 136 OPRM1, OPRD1, and OPRK1 SNPs were genotyped in this sample. After controlling for admixture with principal components analysis, our comparison of cases to non-dependent controls found 4 OPRD1 SNPs in fairly high linkage disequilibrium for which adjusted p values remained significant (e.g., rs2236857; OR 1.25; p=2.95 × 10−4) replicating a previously reported association. A post-hoc analysis revealed that the two-SNP (rs2236857 and rs581111) GA haplotype in OPRD1 is associated with greater risk (OR 1.68; p=1.41 × 10−5). No OPRM1 or OPRK1 SNPs reached more than nominal significance. Comparisons of cases to neighborhood controls reached only nominal significance. Our results replicate a prior report providing strong evidence implicating OPRD1 SNPs and, in particular, the two SNP (rs2236857 and rs581111) GA haplotype in liability for heroin dependence. Support was not found for similar association involving either OPRM1 or OPRK1 SNPs.
doi:10.1111/j.1369-1600.2012.00445.x
PMCID: PMC3867542  PMID: 22500942
association study; heroin dependence; OPRD1; OPRK1; OPRM1
5.  Substance Use and Sexual Intercourse Onsets in Adolescence: A Genetically Informative Discordant Twin Design 
Purpose
The objective of this study was to examine if earlier onset of drinking and smoking behaviors predicted early sexual intercourse onset using a genetically informed, discordant twin analysis.
Methods
3424 adult same-sex twins from the Australian Twin Registry completed a structured interview which included retrospective reports on onsets of smoking, drinking, intoxication and sexual intercourse and conduct disorder symptoms. A two-level frailty model estimated within-twin-pair and between-twin-pair comparisons. Onsets of smoking, drinking, drunkenness and conduct disorder symptoms were estimated as sexual intercourse onset predictors.
Results
After controlling for conduct disorder, smoking and drinking onset did not predict sexual intercourse onset for either within-twin-pair or between-twin-pair comparisons. Drunkenness onset had a significant effect on sexual intercourse onset, such that twins who first experienced alcohol intoxication at a younger age than their co-twins were also more likely to have sex earlier than their co-twins.
Conclusions
Relationships between substance use and sexual intercourse onsets may be due mostly to shared underlying factors; there was only a small relation between intoxication onset and sexual intercourse onset, and no direct relation between smoking and drinking onset and sexual intercourse onset.
doi:10.1016/j.jadohealth.2013.07.013
PMCID: PMC3872214  PMID: 23992762
Twin study; sexual intercourse onset; substance use onset; problem behavior theory
6.  POT1 loss-of-function variants predispose to familial melanoma 
Nature genetics  2014;46(5):478-481.
Deleterious germline variants in CDKN2A account for around 40% of familial melanoma cases1, while rare variants in CDK4, BRCA2, BAP1, and the promoter of TERT, have also been linked to the disease2-5. Here we set out to identify novel high-penetrance susceptibility genes in unexplained cases by sequencing 184 melanoma patients from 105 pedigrees recruited in the United Kingdom, the Netherlands, and Australia that were negative for variants in known predisposition genes. We identify families where melanoma co-segregates with loss-of-function variants in the protection of telomeres 1 (POT1) gene, a proportion of members presenting with an early age of onset and multiple primaries. We show that these variants either affect POT1 mRNA splicing or alter key residues in the highly conserved oligonucleotide-/oligosaccharide-binding (OB) domains of POT1, disrupting protein-telomere binding, leading to increased telomere length. Thus, POT1 variants predispose to melanoma formation via a direct effect on telomeres.
doi:10.1038/ng.2947
PMCID: PMC4266105  PMID: 24686849
7.  Is the relationship between early-onset cannabis use and educational attainment causal or due to common liability? 
Drug and alcohol dependence  2013;133(2):10.1016/j.drugalcdep.2013.07.034.
Background
Several studies have shown that early cannabis use is correlated with poor educational performance including high school drop-out. The predominant explanation for this relationship is that cannabis use causes disengagement from education. Another explanation is that the association between early cannabis use and educational attainment is not causal, but the result of overlapping risk factors that increase the likelihood of both early cannabis use and disengagement from education. These confounding factors could be of genetic and/or environmental origin.
Methods
Here we use data from a large community-based sample of adult twins (N=3337) who completed a comprehensive semi-structured telephone interview. We first apply the classical twin-design to determine whether genetic and/or environmental influences underlie the relationship between early-onset cannabis use (prior to age 18) and early school leaving. Next, with a co-twin control design we investigate whether the relationship between the two variables is more likely due to direct causality or overlapping risk factors.
Results
We find a significant phenotypic correlation between early-onset cannabis use and early school leaving (r=0.26), which could be explained by familial influences (of genetic and/or shared environmental origin). The pattern of odds ratios found in the co-twin control design is not consistent with direct causation, but rather suggests that the association is due to shared environmental factors influencing both variables.
Conclusion
Our findings suggest that the relationship between early-onset cannabis use and school leaving is due to shared environmental risk factors influencing both the risk of early-onset cannabis use and early school leaving.
doi:10.1016/j.drugalcdep.2013.07.034
PMCID: PMC3818343  PMID: 23972999
cannabis; education; environment; genetics; school drop-out; twin research
8.  LABELING WHITE MATTER TRACTS IN HARDI BY FUSING MULTIPLE TRACT ATLASES WITH APPLICATIONS TO GENETICS 
Accurate identification of white matter structures and segmentation of fibers into tracts is important in neuroimaging and has many potential applications. Even so, it is not trivial because whole brain tractography generates hundreds of thousands of streamlines that include many false positive fibers. We developed and tested an automatic tract labeling algorithm to segment anatomically meaningful tracts from diffusion weighted images. Our multi-atlas method incorporates information from multiple hand-labeled fiber tract atlases. In validations, we showed that the method outperformed the standard ROI-based labeling using a deformable, parcellated atlas. Finally, we show a high-throughput application of the method to genetic population studies. We use the sub-voxel diffusion information from fibers in the clustered tracts based on 105-gradient HARDI scans of 86 young normal twins. The whole workflow shows promise for larger population studies in the future.
doi:10.1109/ISBI.2013.6556524
PMCID: PMC4236723  PMID: 25419442
HARDI; Tractography; Fiber Clustering; Label Fusion; Genetic Heritability
9.  A new regulatory variant in the interleukin-6 receptor gene associates with asthma risk 
Genes and immunity  2013;14(7):441-446.
The main genetic determinant of soluble IL-6R levels is the missense variant rs2228145, which maps to the cleavage site of IL-6R. For each Ala allele, sIL-6R serum levels increase by ~20 ng/ml and asthma risk by 1.09-fold. However, this variant does not explain the total heritability for sIL-6R levels. Additional independent variants in IL6R may therefore contribute to variation in sIL-6R levels and influence asthma risk. We imputed 471 variants in IL6R and tested these for association with sIL-6R serum levels in 360 individuals. An intronic variant (rs12083537) was associated with sIL-6R levels independently of rs4129267 (P = 0.0005), a proxy SNP for rs2228145. A significant and consistent association for rs12083537 was observed in a replication panel of 354 individuals (P = 0.033). Each rs12083537:A allele increased sIL-6R serum levels by 2.4 ng/ml Analysis of mRNA levels in two cohorts did not identify significant associations between rs12083537 and IL6R transcription levels. On the other hand, results from 16 705 asthmatics and 30 809 controls showed that the rs12083537:A allele increased asthma risk by 1.04-fold (P = 0.0419). Genetic risk scores based on IL6R regulatory variants may prove useful in explaining variation in clinical response to tocilizumab, an anti-IL-6R monoclonal antibody.
doi:10.1038/gene.2013.38
PMCID: PMC4233139  PMID: 23945879
allergy; eQTL; expression; disease
10.  Relation between variants in the neurotrophin receptor gene, NTRK3, and white matter integrity in healthy young adults 
NeuroImage  2013;82:146-153.
The NTRK3 gene (also known as TRKC) encodes a high affinity receptor for the neurotrophin 3′-nucleotidase (NT3), which is implicated in oligodendrocyte and myelin development. We previously found that white matter integrity in young adults related to genetic variants in genes encoding neurotrophins and their receptors. This underscores the importance of neurotrophins for white matter development. NTRK3 variants are putative risk factors for schizophrenia, bipolar disorder, and obsessive-compulsive disorder hoarding, suggesting that some NTRK3 variants may affect the brain.
To test this, we scanned 392 healthy adult twins and their siblings (mean age, 23.6 ± 2.2 years; range: 20-29 years) with 105-gradient 4-Tesla diffusion tensor imaging (DTI). We identified 18 single nucleotide polymorphisms (SNPs) in the NTRK3 gene that have been associated with neuropsychiatric disorders. We used a multi-SNP model, adjusting for family relatedness, age, and sex, to relate these variants to voxelwise fractional anisotropy (FA) – a DTI measure of white matter integrity.
FA was optimally predicted (based on the highest false discovery rate critical p), by five SNPs (rs1017412, rs2114252, rs16941261, rs3784406, and rs7176429; overall FDR critical p = 0.028). Gene effects were widespread and included the corpus callosum genu and inferior longitudinal fasciculus - regions implicated in several neuropsychiatric disorders and previously associated with other neurotrophin-related genetic variants in an overlapping sample of subjects. NTRK3 genetic variants, and neurotrophins more generally, may influence white matter integrity in brain regions implicated in neuropsychiatric disorders.
doi:10.1016/j.neuroimage.2013.05.095
PMCID: PMC3948328  PMID: 23727532
Fractional anisotropy; diffusion tensor imaging; single nucleotide polymorphism; schizophrenia; obsessive compulsive disorder; bipolar disorder
11.  LEFT VERSUS RIGHT HEMISPHERE DIFFERENCES IN BRAIN CONNECTIVITY: 4-TESLA HARDI TRACTOGRAPHY IN 569 TWINS 
Diffusion imaging can map anatomical connectivity in the living brain, offering new insights into fundamental questions such as how the left and right brain hemispheres differ. Anatomical brain asymmetries are related to speech and language abilities, but less is known about left/right hemisphere differences in brain wiring. To assess this, we scanned 457 young adults (age 23.4±2.0 SD years) and 112 adolescents (age 12-16) with 4-Tesla 105-gradient high-angular resolution diffusion imaging. We extracted fiber tracts throughout the brain with a Hough transform method. A 70×70 connectivity matrix was created, for each subject, based on the proportion of fibers intersecting 70 cortical regions. We identified significant differences in the proportions of fibers intersecting left and right hemisphere cortical regions. The degree of asymmetry in the connectivity matrices varied with age, as did the asymmetry in network topology measures such as the small-world effect.
doi:10.1109/ISBI.2012.6235601
PMCID: PMC4232939  PMID: 25404993
tractography; high angular resolution diffusion imaging (HARDI); small-world effect; connectome; laterality
12.  Are bottom-up and top-down traits in dual-systems models of risky behavior genetically distinct? 
Behavior genetics  2013;43(6):480-490.
Numerous dual-systems models of personality have been posited, which propose that behavior is influenced by two complementary systems. A bottom-up system is characterized by emotion-based drive (e.g., urge for rewarding experience), and a top-down system is characterized by the ability to control those urges. Although evidence suggests that these two systems are distinct and may be important in explaining some behaviors, these constructs are also moderately correlated. Notably, there has been little molecular or behavior genetic research on the genetic distinctness of the two systems central to the dual-systems model. The current study used a national twin sample to investigate the degree to which bottom-up and top-down systems, measured here as personality traits of sensation seeking and lack of planning, respectively, covary through genetic and environmental influences. Whereas the overlap between these systems was primarily comprised of unshared environmental influences (e.g., measurement error and unshared systematic variation) in females, a statistically significant proportion of the overlap was accounted for by genetic factors in men. Further, the genetic factors for these systems were moderately to highly correlated in men (rG=.62–.79). These results provide clear support for a dual-systems model in women; however, these systems appear to share some common genetic influences in men.
doi:10.1007/s10519-013-9615-9
PMCID: PMC3929393  PMID: 24065563
impulsivity; sensation seeking; lack of planning; genetics; risky; twins; dual-systems
13.  Multi-site genetic analysis of diffusion images and voxelwise heritability analysis: A pilot project of the ENIGMA–DTI working group 
NeuroImage  2013;81:455-469.
The ENIGMA (Enhancing NeuroImaging Genetics through Meta-Analysis) Consortium was set up to analyze brain measures and genotypes from multiple sites across the world to improve the power to detect genetic variants that influence the brain. Diffusion tensor imaging (DTI) yields quantitative measures sensitive to brain development and degeneration, and some common genetic variants may be associated with white matter integrity or connectivity. DTI measures, such as the fractional anisotropy (FA) of water diffusion, may be useful for identifying genetic variants that influence brain microstructure. However, genome-wide association studies (GWAS) require large populations to obtain sufficient power to detect and replicate significant effects, motivating a multi-site consortium effort. As part of an ENIGMA–DTI working group, we analyzed high-resolution FA images from multiple imaging sites across North America, Australia, and Europe, to address the challenge of harmonizing imaging data collected at multiple sites. Four hundred images of healthy adults aged 18–85 from four sites were used to create a template and corresponding skeletonized FA image as a common reference space. Using twin and pedigree samples of different ethnicities, we used our common template to evaluate the heritability of tract-derived FA measures. We show that our template is reliable for integrating multiple datasets by combining results through meta-analysis and unifying the data through exploratory mega-analyses. Our results may help prioritize regions of the FA map that are consistently influenced by additive genetic factors for future genetic discovery studies. Protocols and templates are publicly available at (http://enigma.loni.ucla.edu/ongoing/dti-working-group/).
doi:10.1016/j.neuroimage.2013.04.061
PMCID: PMC3729717  PMID: 23629049
Diffusion Tensor Imaging (DTI); Imaging genetics; Heritability; Meta-analysis; Multi-site; Reliability
14.  Genome-wide association study on detailed profiles of smoking behavior and nicotine dependence in a twin sample 
Molecular psychiatry  2013;19(5):615-624.
Smoking is a major risk factor for several somatic diseases, and is also emerging as a causal factor for neuropsychiatric disorders. Genome-wide association (GWA) and candidate gene studies for smoking behavior and nicotine dependence (ND) have disclosed too few predisposing variants to account for the high estimated heritability. Prior large-scale GWA studies have had very limited phenotypic definitions of relevance to smoking-related behavior, which has likely impeded the discovery of genetic effects. We performed genome-wide association analyses on 1114 adult twins ascertained for ever smoking from the population-based Finnish Twin Cohort study. The availability of 17 smoking-related phenotypes allowed us to comprehensively portray the dimensions of smoking behavior, clustered into the domains of smoking initiation, amount smoked, and ND. Our results highlight a locus on 16p12.3, with several SNPs in the vicinity of CLEC19A showing association (P<1×10−6) with smoking quantity. Interestingly, CLEC19A is located close to a previously reported attention deficit hyperactivity disorder (ADHD) linkage locus and an evident link between ADHD and smoking has been established. Intriguing preliminary association (P<1×10−5) was detected between DSM-IV ND diagnosis and several SNPs in ERBB4, coding for a Neuregulin receptor, on 2q33. The association between ERBB4 and DSM-IV ND diagnosis was replicated in an independent Australian sample. Interestingly, in the paper by Turner et al., significant increase in ErbB4 and Neuregulin 3 (Nrg3) expression was revealed following chronic nicotine exposure and withdrawal in mice. Turner et al. also detected an association between NRG3 SNPs and smoking cessation success in a clinical trial. ERBB4 has previously been associated with schizophrenia; further, it is located within an established schizophrenia linkage locus and within a linkage locus for a smoker phenotype identified in this sample. As a conclusion, we disclose novel tentative evidence for the involvement of ERBB4 in ND, suggesting the involvement of the Neuregulin/ErbB signalling pathway in addictions and providing a plausible link between the high co-morbidity of schizophrenia and ND.
doi:10.1038/mp.2013.72
PMCID: PMC3883996  PMID: 23752247
genome-wide association analysis; nicotine dependence; smoking behavior; smoking quantity; schizophrenia; ADHD
15.  Genetic Factors That Increase Male Facial Masculinity Decrease Facial Attractiveness of Female Relatives 
Psychological science  2013;25(2):476-484.
For women, choosing a facially masculine man as a mate is thought to confer genetic benefits to offspring. Crucial assumptions of this hypothesis have not been adequately tested. It has been assumed that variation in facial masculinity is due to genetic variation and that genetic factors that increase male facial masculinity do not increase facial masculinity in female relatives. We objectively quantified the facial masculinity in photos of identical (n = 411) and nonidentical (n = 782) twins and their siblings (n = 106). Using biometrical modeling, we found that much of the variation in male and female facial masculinity is genetic. However, we also found that masculinity of male faces is unrelated to their attractiveness and that facially masculine men tend to have facially masculine, less-attractive sisters. These findings challenge the idea that facially masculine men provide net genetic benefits to offspring and call into question this popular theoretical framework.
doi:10.1177/0956797613510724
PMCID: PMC4205959  PMID: 24379153
mate preference; sexual dimorphism; intralocus sexual conflict; evolution; immunocompetence-handicap principle; good genes; pathogen; health; sexually antagonistic selection; behavior genetics; evolutionary psychology; face perception; human mate selection
16.  Heritability of White Matter Fiber Tract Shapes: A HARDI Study of 198 Twins* 
Genetic analysis of diffusion tensor images (DTI) shows great promise in revealing specific genetic variants that affect brain integrity and connectivity. Most genetic studies of DTI analyze voxel-based diffusivity indices in the image space (such as 3D maps of fractional anisotropy) and overlook tract geometry. Here we propose an automated workflow to cluster fibers using a white matter probabilistic atlas and perform genetic analysis on the shape characteristics of fiber tracts. We apply our approach to large study of 4-Tesla high angular resolution diffusion imaging (HARDI) data from 198 healthy, young adult twins (age: 20–30). Illustrative results show heritability for the shapes of several major tracts, as color-coded maps.
PMCID: PMC4205954  PMID: 25346947
HARDI; Tractography; Image Registration; White Matter Probabilistic Atlas; Fiber Alignment; Clustering; Curve Matching; Heritability
17.  Detection and replication of epistasis influencing transcription in humans 
Nature  2014;508(7495):249-253.
Epistasis is the phenomenon whereby one polymorphism’s effect on a trait depends on other polymorphisms present in the genome. The extent to which epistasis influences complex traits1 and contributes to their variation2,3 is a fundamental question in evolution and human genetics. Though often demonstrated in artificial gene manipulation studies in model organisms4,5, and some examples have been reported in other species6, few examples exist for epistasis amongst natural polymorphisms in human traits7,8. Its absence from empirical findings may simply be due to low incidence in the genetic control of complex traits2,3, but an alternative view is that it has previously been too technically challenging to detect due to statistical and computational issues9. Here we show that, using advanced computation10 and a gene expression study design, many instances of epistasis are found between common single nucleotide polymorphisms (SNPs). In a cohort of 846 individuals with 7339 gene expression levels measured in peripheral blood, we found 501 significant pairwise interactions between common SNPs influencing the expression of 238 genes (p < 2.91 × 10−16). Replication of these interactions in two independent data sets11,12 showed both concordance of direction of epistatic effects (p = 5.56 ×10−31) and enrichment of interaction p-values, with 30 being significant at a conservative threshold of p < 0.05/501. Forty-four of the genetic interactions are located within 2Mb of regions of known physical chromosome interactions13 (p = 1.8 × 10−10). Epistatic networks of three SNPs or more influence the expression levels of 129 genes, whereby one cis-acting SNP is modulated by several trans-acting SNPs. For example MBNL1 is influenced by an additive effect at rs13069559 which itself is masked by trans-SNPs on 14 different chromosomes, with nearly identical genotype-phenotype (GP) maps for each cis-trans interaction. This study presents the first evidence for multiple instances of segregating common polymorphisms interacting to influence human traits.
doi:10.1038/nature13005
PMCID: PMC3984375  PMID: 24572353
18.  Meta-analysis of telomere length in 19 713 subjects reveals high heritability, stronger maternal inheritance and a paternal age effect 
European Journal of Human Genetics  2013;21(10):1163-1168.
Telomere length (TL) has been associated with aging and mortality, but individual differences are also influenced by genetic factors, with previous studies reporting heritability estimates ranging from 34 to 82%. Here we investigate the heritability, mode of inheritance and the influence of parental age at birth on TL in six large, independent cohort studies with a total of 19 713 participants. The meta-analysis estimate of TL heritability was 0.70 (95% CI 0.64–0.76) and is based on a pattern of results that is highly similar for twins and other family members. We observed a stronger mother–offspring (r=0.42; P-value=3.60 × 10−61) than father–offspring correlation (r=0.33; P-value=7.01 × 10−5), and a significant positive association with paternal age at offspring birth (β=0.005; P-value=7.01 × 10−5). Interestingly, a significant and quite substantial correlation in TL between spouses (r=0.25; P-value=2.82 × 10−30) was seen, which appeared stronger in older spouse pairs (mean age ≥55 years; r=0.31; P-value=4.27 × 10−23) than in younger pairs (mean age<55 years; r=0.20; P-value=3.24 × 10−10). In summary, we find a high and very consistent heritability estimate for TL, evidence for a maternal inheritance component and a positive association with paternal age.
doi:10.1038/ejhg.2012.303
PMCID: PMC3778341  PMID: 23321625
telomere length; heritability; paternal age effect
19.  Genome-wide association study identifies loci affecting blood copper, selenium and zinc 
Human Molecular Genetics  2013;22(19):3998-4006.
Genetic variation affecting absorption, distribution or excretion of essential trace elements may lead to health effects related to sub-clinical deficiency. We have tested for allelic effects of single-nucleotide polymorphisms (SNPs) on blood copper, selenium and zinc in a genome-wide association study using two adult cohorts from Australia and the UK. Participants were recruited in Australia from twins and their families and in the UK from pregnant women. We measured erythrocyte Cu, Se and Zn (Australian samples) or whole blood Se (UK samples) using inductively coupled plasma mass spectrometry. Genotyping was performed with Illumina chips and >2.5 m SNPs were imputed from HapMap data. Genome-wide significant associations were found for each element. For Cu, there were two loci on chromosome 1 (most significant SNPs rs1175550, P = 5.03 × 10−10, and rs2769264, P = 2.63 × 10−20); for Se, a locus on chromosome 5 was significant in both cohorts (combined P = 9.40 × 10−28 at rs921943); and for Zn three loci on chromosomes 8, 15 and X showed significant results (rs1532423, P = 6.40 × 10−12; rs2120019, P = 1.55 × 10−18; and rs4826508, P = 1.40 × 10−12, respectively). The Se locus covers three genes involved in metabolism of sulphur-containing amino acids and potentially of the analogous Se compounds; the chromosome 8 locus for Zn contains multiple genes for the Zn-containing enzyme carbonic anhydrase. Where potentially relevant genes were identified, they relate to metabolism of the element (Se) or to the presence at high concentration of a metal-containing protein (Cu).
doi:10.1093/hmg/ddt239
PMCID: PMC3766178  PMID: 23720494
20.  The Effect on Melanoma Risk of Genes Previously Associated With Telomere Length 
Telomere length has been associated with risk of many cancers, but results are inconsistent. Seven single nucleotide polymorphisms (SNPs) previously associated with mean leukocyte telomere length were either genotyped or well-imputed in 11108 case patients and 13933 control patients from Europe, Israel, the United States and Australia, four of the seven SNPs reached a P value under .05 (two-sided). A genetic score that predicts telomere length, derived from these seven SNPs, is strongly associated (P = 8.92x10-9, two-sided) with melanoma risk. This demonstrates that the previously observed association between longer telomere length and increased melanoma risk is not attributable to confounding via shared environmental effects (such as ultraviolet exposure) or reverse causality. We provide the first proof that multiple germline genetic determinants of telomere length influence cancer risk.
doi:10.1093/jnci/dju267
PMCID: PMC4196080  PMID: 25231748
21.  Genetic variants associated with disordered eating 
Objective
While the genetic contribution to the development of anorexia nervosa (AN) has long been recognized, there has been little progress relative to other psychiatric disorders in identifying specific susceptibility genes. Here we have carried out a GWAS on an unselected community sample of female twins surveyed for eating disorders.
Method
We conducted genome wide association analyses in 2564 female twins for four different phenotypes derived from self-report data relating to lifetime presence of 15 types of disordered eating: anorexia nervosa spectrum, bulimia nervosa spectrum, purging via substances, and a binary measure of no disordered eating behaviors versus 3 or more. To complement the variant level results we also conducted gene-based association tests using VEGAS.
Results
While no variants reached genome-wide significance at the level of p<10−8, six regions were suggestive (p<5×10−7). The current results implicate the following genes: CLEC5A; LOC136242, TSHZ1 and SYTL5 for the anorexia nervosa spectrum phenotype, NT5C1B for the bulimia nervosa spectrum phenotype, and ATP8A2 for the disordered eating behaviors phenotype.
Discussion
As with other medical and psychiatric phenotypes, much larger samples and meta-analyses will ultimately be needed to identify genes and pathways contributing to predisposition to eating disorders.
doi:10.1002/eat.22133
PMCID: PMC3775874  PMID: 23568457
22.  Common variants in the CYP2C19 gene are associated with susceptibility to endometriosis 
Fertility and sterility  2014;102(2):496-502.e5.
Objective
To follow-up previous studies highlighting a possible role for cytochrome P450, family 2, subfamily C, 19 (CYP2C19) in susceptibility to endometriosis by searching for additional variants in the CYP2C19 gene that may be associated with the disease.
Design
Case-control study.
Setting
Academic research.
Subject(s)
Cases = 2,271 women with surgically confirmed endometriosis; Controls = 939 women with self-report of no endometriosis and 1,770 unscreened population samples.
Intervention(s)
Sequencing of the CYP2C19 region and follow-up of 80 SNPs in two case-control samples.
Main outcome measure(s)
Allele frequency differences between cases and controls.
Results
Sequencing of the CYP2C19 gene region resulted in the detection of a large number of known and novel SNPs. Genotyping of 80 polymorphic SNPs in 901 endometriosis cases and 939 controls resulted in study-wide significant association signals for SNPs in moderate or complete LD with rs4244285, a functional SNP in exon 5 that abrogates CYP2C19 function through the creation of an alternative splice site. Evidence of association was also detected for another functional SNP in the CYP2C19 promoter, rs12248560, highlighted in our previous study.
Conclusion(s)
Functional variants in CYP2C19 may contribute to endometriosis susceptibility in both familial and sporadic cases.
doi:10.1016/j.fertnstert.2014.04.015
PMCID: PMC4150687  PMID: 24796765
Endometriosis; association; pooled sequencing; CYP2C19; rs12248560; rs4244285
23.  The genetic etiology of cannabis use initiation: a meta-analysis of genome-wide association studies and a SNP-based heritability estimation 
Addiction biology  2012;18(5):846-850.
While initiation of cannabis use is around 40% heritable, not much is known about the underlying genetic etiology. Here, we meta-analysed two genome-wide association studies of initiation of cannabis use with (>10,000 individuals). None of the genetic variants reached genome-wide significance. We also performed a gene-based association test, which also revealed no significant effects of individual genes. Finally, we estimated that only approximately 6.0% of the variation in cannabis initiation is due to common genetic variants. Future genetic studies using larger sample sizes and different methodologies (including sequencing) might provide more insight in the complex genetic etiology of cannabis use.
doi:10.1111/j.1369-1600.2012.00478.x
PMCID: PMC3548058  PMID: 22823124
genetics; cannabis; heritability; association
24.  Refining genome-wide linkage intervals using a meta-analysis of genome-wide association studies identifies loci influencing personality dimensions 
Personality traits are complex phenotypes related to psychosomatic health. Individually, various gene finding methods have not achieved much success in finding genetic variants associated with personality traits. We performed a meta-analysis of four genome-wide linkage scans (N=6149 subjects) of five basic personality traits assessed with the NEO Five-Factor Inventory. We compared the significant regions from the meta-analysis of linkage scans with the results of a meta-analysis of genome-wide association studies (GWAS) (N∼17 000). We found significant evidence of linkage of neuroticism to chromosome 3p14 (rs1490265, LOD=4.67) and to chromosome 19q13 (rs628604, LOD=3.55); of extraversion to 14q32 (ATGG002, LOD=3.3); and of agreeableness to 3p25 (rs709160, LOD=3.67) and to two adjacent regions on chromosome 15, including 15q13 (rs970408, LOD=4.07) and 15q14 (rs1055356, LOD=3.52) in the individual scans. In the meta-analysis, we found strong evidence of linkage of extraversion to 4q34, 9q34, 10q24 and 11q22, openness to 2p25, 3q26, 9p21, 11q24, 15q26 and 19q13 and agreeableness to 4q34 and 19p13. Significant evidence of association in the GWAS was detected between openness and rs677035 at 11q24 (P-value=2.6 × 10−06, KCNJ1). The findings of our linkage meta-analysis and those of the GWAS suggest that 11q24 is a susceptible locus for openness, with KCNJ1 as the possible candidate gene.
doi:10.1038/ejhg.2012.263
PMCID: PMC3722675  PMID: 23211697
personality; KCNJ1; NEO; linkage; GSMA
25.  Association of Adiposity Genetic Variants With Menarche Timing in 92,105 Women of European Descent 
Fernández-Rhodes, Lindsay | Demerath, Ellen W. | Cousminer, Diana L. | Tao, Ran | Dreyfus, Jill G. | Esko, Tõnu | Smith, Albert V. | Gudnason, Vilmundur | Harris, Tamara B. | Launer, Lenore | McArdle, Patrick F. | Yerges-Armstrong, Laura M. | Elks, Cathy E. | Strachan, David P. | Kutalik, Zoltán | Vollenweider, Peter | Feenstra, Bjarke | Boyd, Heather A. | Metspalu, Andres | Mihailov, Evelin | Broer, Linda | Zillikens, M. Carola | Oostra, Ben | van Duijn, Cornelia M. | Lunetta, Kathryn L. | Perry, John R. B. | Murray, Anna | Koller, Daniel L. | Lai, Dongbing | Corre, Tanguy | Toniolo, Daniela | Albrecht, Eva | Stöckl, Doris | Grallert, Harald | Gieger, Christian | Hayward, Caroline | Polasek, Ozren | Rudan, Igor | Wilson, James F. | He, Chunyan | Kraft, Peter | Hu, Frank B. | Hunter, David J. | Hottenga, Jouke-Jan | Willemsen, Gonneke | Boomsma, Dorret I. | Byrne, Enda M. | Martin, Nicholas G. | Montgomery, Grant W. | Warrington, Nicole M. | Pennell, Craig E. | Stolk, Lisette | Visser, Jenny A. | Hofman, Albert | Uitterlinden, André G. | Rivadeneira, Fernando | Lin, Peng | Fisher, Sherri L. | Bierut, Laura J. | Crisponi, Laura | Porcu, Eleonora | Mangino, Massimo | Zhai, Guangju | Spector, Tim D. | Buring, Julie E. | Rose, Lynda M. | Ridker, Paul M. | Poole, Charles | Hirschhorn, Joel N. | Murabito, Joanne M. | Chasman, Daniel I. | Widen, Elisabeth | North, Kari E. | Ong, Ken K. | Franceschini, Nora
American Journal of Epidemiology  2013;178(3):451-460.
Obesity is of global health concern. There are well-described inverse relationships between female pubertal timing and obesity. Recent genome-wide association studies of age at menarche identified several obesity-related variants. Using data from the ReproGen Consortium, we employed meta-analytical techniques to estimate the associations of 95 a priori and recently identified obesity-related (body mass index (weight (kg)/height (m)2), waist circumference, and waist:hip ratio) single-nucleotide polymorphisms (SNPs) with age at menarche in 92,116 women of European descent from 38 studies (1970–2010), in order to estimate associations between genetic variants associated with central or overall adiposity and pubertal timing in girls. Investigators in each study performed a separate analysis of associations between the selected SNPs and age at menarche (ages 9–17 years) using linear regression models and adjusting for birth year, site (as appropriate), and population stratification. Heterogeneity of effect-measure estimates was investigated using meta-regression. Six novel associations of body mass index loci with age at menarche were identified, and 11 adiposity loci previously reported to be associated with age at menarche were confirmed, but none of the central adiposity variants individually showed significant associations. These findings suggest complex genetic relationships between menarche and overall obesity, and to a lesser extent central obesity, in normal processes of growth and development.
doi:10.1093/aje/kws473
PMCID: PMC3816344  PMID: 23558354
adiposity; body mass index; genetic association studies; menarche; obesity; waist circumference; waist:hip ratio; women's health

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