Recently, carriers of a common variant in the autism risk gene, CNTNAP2, were found to have altered functional brain connectivity using functional MRI. Here we scanned 328 young adults with high-field (4-Tesla) diffusion imaging, to test the hypothesis that carriers of this gene variant would have altered structural brain connectivity. All participants (209 females, 119 males, age: 23.4 +/−2.17 SD years) were scanned with 105-gradient high angular diffusion imaging (HARDI) at 4 Tesla. After performing a whole-brain fiber tractography using the full angular resolution of the diffusion scans, 70 cortical surface-based regions of interest were created from each individual’s co-registered anatomical data to compute graph metrics for all pairs of cortical regions. In graph theory analyses, subjects homozygous for the risk allele (CC) had lower characteristic path length, greater small-worldness and global efficiency in whole brain analyses, as well as greater eccentricity (maximum path length) in 60 of 70 nodes in regional analyses. These results were not reducible to differences in more commonly studied traits such as fiber density or fractional anisotropy. This is the first study to link graph theory metrics of brain structural connectivity to a common genetic variant linked with autism and will help us understand the neurobiology of circuits implicated in risk for autism.
structural connectivity; HARDI; autism; CNTNAP2; graph theory; twins
To refine a previously reported linkage peak for endometriosis on chromosome 10q26, and conduct follow-up analyses and a fine-mapping association study across the region to identify new candidate genes for endometriosis.
Cases = 3,223 women with surgically confirmed endometriosis; Controls = 1,190 women without endometriosis and 7,060 population samples.
Analysis of 11,984 SNPs on chromosome 10.
Main outcome measure(s)
Allele frequency differences between cases and controls.
Linkage analyses on families grouped by endometriosis symptoms (primarily subfertility) provided increased evidence for linkage (logarithm of odds (LOD) score = 3.62) near a previously reported linkage peak. Three independent association signals were found at 96.59 Mb (rs11592737, P=4.9 × 10−4), 105.63 Mb (rs1253130, P=2.5 × 10−4) and 124.25 Mb (rs2250804, P=9.7 × 10−4). Analyses including only samples from linkage families supported the association at all three regions. However, only rs11592737 in the cytochrome P450 subfamily C (CYP2C19) gene was replicated in an independent sample of 2,079 cases and 7060 population controls.
The role of the CYP2C19 gene in conferring risk for endometriosis warrants further investigation.
Endometriosis; linkage; association; subfertility; CYP2C19
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).
twins; association; lipids; apolipoproteins; interaction
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.
Structural connectivity; neuroimaging genetics; Dijkstra’s algorithm; HARDI tractography; path length
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.
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.
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.
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.
adolescent substance use; parental separation; parental substance dependence; children of twins
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.
association study; heroin dependence; OPRD1; OPRK1; OPRM1
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.
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.
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.
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.
Twin study; sexual intercourse onset; substance use onset; problem behavior theory
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.
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.
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.
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.
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.
cannabis; education; environment; genetics; school drop-out; twin research
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.
HARDI; Tractography; Fiber Clustering; Label Fusion; Genetic Heritability
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.
allergy; eQTL; expression; disease
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.
Fractional anisotropy; diffusion tensor imaging; single nucleotide polymorphism; schizophrenia; obsessive compulsive disorder; bipolar disorder
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.
tractography; high angular resolution diffusion imaging (HARDI); small-world effect; connectome; laterality
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.
impulsivity; sensation seeking; lack of planning; genetics; risky; twins; dual-systems
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/).
Diffusion Tensor Imaging (DTI); Imaging genetics; Heritability; Meta-analysis; Multi-site; Reliability
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.
genome-wide association analysis; nicotine dependence; smoking behavior; smoking quantity; schizophrenia; ADHD
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.
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
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.
HARDI; Tractography; Image Registration; White Matter Probabilistic Atlas; Fiber Alignment; Clustering; Curve Matching; Heritability
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.
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.
telomere length; heritability; paternal age effect
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).
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.
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.
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.
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.
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.
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.
Cases = 2,271 women with surgically confirmed endometriosis; Controls = 939 women with self-report of no endometriosis and 1,770 unscreened population samples.
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.
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.
Functional variants in CYP2C19 may contribute to endometriosis susceptibility in both familial and sporadic cases.
Endometriosis; association; pooled sequencing; CYP2C19; rs12248560; rs4244285
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.
genetics; cannabis; heritability; association