A novel common variant in DCST2 is associated with length in early life and height in adulthood.

Common genetic variants have been identified for adult height, but not much is known about the genetics of skeletal growth in early life. To identify common genetic variants that influence fetal skeletal growth, we meta-analyzed 22 genome-wide association studies (Stage 1; N = 28 459). We identified seven independent top single nucleotide polymorphisms (SNPs) (P < 1 × 10(-6)) for birth length, of which three were novel and four were in or near loci known to be associated with adult height (LCORL, PTCH1, GPR126 and HMGA2). The three novel SNPs were followed-up in nine replication studies (Stage 2; N = 11 995), with rs905938 in DC-STAMP domain containing 2 (DCST2) genome-wide significantly associated with birth length in a joint analysis (Stages 1 + 2; ß = 0.046, SE = 0.008, P = 2.46 × 10(-8), explained variance = 0.05%). Rs905938 was also associated with infant length (N = 28 228; P = 5.54 × 10(-4)) and adult height (N = 127 513; P = 1.45 × 10(-5)). DCST2 is a DC-STAMP-like protein family member and DC-STAMP is an osteoclast cell-fusion regulator. Polygenic scores based on 180 SNPs previously associated with human adult stature explained 0.13% of variance in birth length. The same SNPs explained 2.95% of the variance of infant length. Of the 180 known adult height loci, 11 were genome-wide significantly associated with infant length (SF3B4, LCORL, SPAG17, C6orf173, PTCH1, GDF5, ZNFX1, HHIP, ACAN, HLA locus and HMGA2). This study highlights that common variation in DCST2 influences variation in early growth and adult height.

Neurocognitive abilities in the general population and composite genetic risk scores for attention-deficit hyperactivity disorder.

BACKGROUND: The genetic architecture of ADHD is complex, with rare and common variants involved. Common genetic variants (as indexed by a composite risk score) associated with clinical ADHD significantly predict ADHD and autistic-like behavioural traits in children from the general population, suggesting that ADHD lies at the extreme of normal trait variation. ADHD and other neurodevelopmental disorders share neurocognitive difficulties in several domains (e.g. impaired cognitive ability and executive functions). We hypothesised that ADHD composite genetic risk scores derived from clinical ADHD cases would also contribute to variation in neurocognitive abilities in the general population. METHODS: Children (N = 6,832) from a UK population cohort, the Avon Longitudinal Study of Parents and Children (ALSPAC), underwent neurocognitive testing. Parent-reported measures of their children's ADHD and autistic-like traits were used to construct a behavioural latent variable of 'neurodevelopmental traits'. Composite genetic risk scores for ADHD were calculated for ALSPAC children based on findings from an independent ADHD case-control genome-wide association study. Structural equation modelling was used to assess associations between ADHD composite genetic risk scores and IQ, working memory, inhibitory control and facial emotion recognition, as well as the latent 'neurodevelopmental trait' measure. RESULTS: The results confirmed that neurocognitive and neurodevelopmental traits are correlated in children in the general population. Composite genetic risk scores for ADHD were independently associated with lower IQ (ß = -.05, p < .001) and working memory performance (ß = -.034, p = .013), even after accounting for the relationship with latent neurodevelopmental behavioural trait scores. No associations were found between composite genetic risk scores and inhibitory control or emotion recognition (p > .05). CONCLUSIONS: These findings suggest that common genetic variants relevant to clinically diagnosed ADHD have pleiotropic effects on neurocognitive traits as well as behavioural dimensions in the general population. This further suggests that the well-recognised association between cognition and neurodevelopmental behavioural traits is underpinned at a biological level.

Genome-wide association study of height-adjusted BMI in childhood identifies functional variant in ADCY3.

OBJECTIVE: Genome-wide association studies (GWAS) of BMI are mostly undertaken under the assumption that "kg/m(2) " is an index of weight fully adjusted for height, but in general this is not true. The aim here was to assess the contribution of common genetic variation to a adjusted version of that phenotype which appropriately accounts for covariation in height in children. METHODS: A GWAS of height-adjusted BMI (BMI[x] = weight/height(x) ), calculated to be uncorrelated with height, in 5809 participants (mean age 9.9 years) from the Avon Longitudinal Study of Parents and Children (ALSPAC) was performed. RESULTS: GWAS based on BMI[x] yielded marked differences in genomewide results profile. SNPs in ADCY3 (adenylate cyclase 3) were associated at genome-wide significance level (rs11676272 (0.28 kg/m(3.1) change per allele G (0.19, 0.38), P = 6 × 10(-9) ). In contrast, they showed marginal evidence of association with conventional BMI [rs11676272 (0.25 kg/m(2) (0.15, 0.35), P = 6 × 10(-7) )]. Results were replicated in an independent sample, the Generation R study. CONCLUSIONS: Analysis of BMI[x] showed differences to that of conventional BMI. The association signal at ADCY3 appeared to be driven by a missense variant and it was strongly correlated with expression of this gene. Our work highlights the importance of well understood phenotype use (and the danger of convention) in characterising genetic contributions to complex traits.

Genome-wide association study of sexual maturation in males and females highlights a role for body mass and menarche loci in male puberty.

Little is known about genes regulating male puberty. Further, while many identified pubertal timing variants associate with age at menarche, a late manifestation of puberty, and body mass, little is known about these variants' relationship to pubertal initiation or tempo. To address these questions, we performed genome-wide association meta-analysis in over 11 000 European samples with data on early pubertal traits, male genital and female breast development, measured by the Tanner scale. We report the first genome-wide significant locus for male sexual development upstream of myocardin-like 2 (MKL2) (P = 8.9 × 10(-9)), a menarche locus tagging a developmental pathway linking earlier puberty with reduced pubertal growth (P = 4.6 × 10(-5)) and short adult stature (p = 7.5 × 10(-6)) in both males and females. Furthermore, our results indicate that a proportion of menarche loci are important for pubertal initiation in both sexes. Consistent with epidemiological correlations between increased prepubertal body mass and earlier pubertal timing in girls, body mass index (BMI)-increasing alleles correlated with earlier breast development. In boys, some BMI-increasing alleles associated with earlier, and others with delayed, sexual development; these genetic results mimic the controversy in epidemiological studies, some of which show opposing correlations between prepubertal BMI and male puberty. Our results contribute to our understanding of the pubertal initiation program in both sexes and indicate that although mechanisms regulating pubertal onset in males and females may largely be shared, the relationship between body mass and pubertal timing in boys may be complex and requires further genetic studies.

Genetic risk for attention-deficit/hyperactivity disorder contributes to neurodevelopmental traits in the general population.

BACKGROUND: Attention-deficit/hyperactivity disorder (ADHD) can be viewed as the extreme end of traits in the general population. Epidemiological and twin studies suggest that ADHD frequently co-occurs with and shares genetic susceptibility with autism spectrum disorder (ASD) and ASD-related traits. The aims of this study were to determine whether a composite of common molecular genetic variants, previously found to be associated with clinically diagnosed ADHD, predicts ADHD and ASD-related traits in the general population. METHODS: Polygenic risk scores were calculated in the Avon Longitudinal Study of Parents and Children (ALSPAC) population sample (N = 8229) based on a discovery case-control genome-wide association study of childhood ADHD. Regression analyses were used to assess whether polygenic scores predicted ADHD traits and ASD-related measures (pragmatic language abilities and social cognition) in the ALSPAC sample. Polygenic scores were also compared in boys and girls endorsing any (rating ≥ 1) ADHD item (n = 3623). RESULTS: Polygenic risk for ADHD showed a positive association with ADHD traits (hyperactive-impulsive, p = .0039; inattentive, p = .037). Polygenic risk for ADHD was also negatively associated with pragmatic language abilities (p = .037) but not with social cognition (p = .43). In children with a rating ≥ 1 for ADHD traits, girls had a higher polygenic score than boys (p = .003). CONCLUSIONS: These findings provide molecular genetic evidence that risk alleles for the categorical disorder of ADHD influence hyperactive-impulsive and attentional traits in the general population. The results further suggest that common genetic variation that contributes to ADHD diagnosis may also influence ASD-related traits, which at their extreme are a characteristic feature of ASD.

Shared polygenic contribution between childhood attention-deficit hyperactivity disorder and adult schizophrenia.

BACKGROUND: There is recent evidence of some degree of shared genetic susceptibility between adult schizophrenia and childhood attention-deficit hyperactivity disorder (ADHD) for rare chromosomal variants. AIMS: To determine whether there is overlap between common alleles conferring risk of schizophrenia in adults with those that do so for ADHD in children. METHOD: We used recently published Psychiatric Genome-wide Association Study (GWAS) Consortium (PGC) adult schizophrenia data to define alleles over-represented in people with schizophrenia and tested whether those alleles were more common in 727 children with ADHD than in 2067 controls. RESULTS: Schizophrenia risk alleles discriminated ADHD cases from controls (P = 1.04 × 10(-4), R(2) = 0.45%); stronger discrimination was given by alleles that were risk alleles for both adult schizophrenia and adult bipolar disorder (also derived from a PGC data-set) (P = 9.98 × 10(-6), R(2) = 0.59%). CONCLUSIONS: This increasing evidence for a small, but significant, shared genetic susceptibility between adult schizophrenia and childhood ADHD highlights the importance of research work across traditional diagnostic boundaries.

High loading of polygenic risk for ADHD in children with comorbid aggression.

OBJECTIVE Although attention deficit hyperactivity disorder (ADHD) is highly heritable, genome-wide association studies (GWAS) have not yet identified any common genetic variants that contribute to risk. There is evidence that aggression or conduct disorder in children with ADHD indexes higher genetic loading and clinical severity. The authors examine whether common genetic variants considered en masse as polygenic scores for ADHD are especially enriched in children with comorbid conduct disorder. METHOD Polygenic scores derived from an ADHD GWAS meta-analysis were calculated in an independent ADHD sample (452 case subjects, 5,081 comparison subjects). Multivariate logistic regression analyses were employed to compare polygenic scores in the ADHD and comparison groups and test for higher scores in ADHD case subjects with comorbid conduct disorder relative to comparison subjects and relative to those without comorbid conduct disorder. Association with symptom scores was tested using linear regression. RESULTS Polygenic risk for ADHD, derived from the meta-analysis, was higher in the independent ADHD group than in the comparison group. Polygenic score was significantly higher in ADHD case subjects with conduct disorder relative to ADHD case subjects without conduct disorder. ADHD polygenic score showed significant association with comorbid conduct disorder symptoms. This relationship was explained by the aggression items. CONCLUSIONS Common genetic variation is relevant to ADHD, especially in individuals with comorbid aggression. The findings suggest that the previously published ADHD GWAS meta-analysis contains weak but true associations with common variants, support for which falls below genome-wide significance levels. The findings also highlight the fact that aggression in ADHD indexes genetic as well as clinical severity.

Investigating the contribution of common genetic variants to the risk and pathogenesis of ADHD.

OBJECTIVE: A major motivation for seeking disease-associated genetic variation is to identify novel risk processes. Although rare copy number variants (CNVs) appear to contribute to attention deficit hyperactivity disorder (ADHD), common risk variants (single-nucleotide polymorphisms [SNPs]) have not yet been detected using genome-wide association studies (GWAS). This raises the concern as to whether future larger-scale, adequately powered GWAS will be worthwhile. The authors undertook a GWAS of ADHD and examined whether associated SNPs, including those below conventional levels of significance, influenced the same biological pathways affected by CNVs. METHOD: The authors analyzed genome-wide SNP frequencies in 727 children with ADHD and 5,081 comparison subjects. The gene sets that were enriched in a pathway analysis of the GWAS data (the top 5% of SNPs) were tested for an excess of genes spanned by large, rare CNVs in the children with ADHD. RESULTS: No SNP achieved genome-wide significance levels. As previously reported in a subsample of the present study, large, rare CNVs were significantly more common in case subjects than comparison subjects. Thirteen biological pathways enriched for SNP association significantly overlapped with those enriched for rare CNVs. These included cholesterol-related and CNS development pathways. At the level of individual genes, CHRNA7, which encodes a nicotinic receptor subunit previously implicated in neuropsychiatric disorders, was affected by six large duplications in case subjects (none in comparison subjects), and SNPs in the gene had a gene-wide p value of 0.0002 for association in the GWAS. CONCLUSIONS: Both common and rare genetic variants appear to be relevant to ADHD and index-shared biological pathways.

What causes attention deficit hyperactivity disorder?

Attention deficit hyperactivity disorder (ADHD) affects around 1-3% of children. There is a high level of comorbidity with developmental and learning problems as well as with a variety of psychiatric disorders. ADHD is highly heritable, although there is no single causal risk factor and non-inherited factors also contribute to its aetiology. The genetic and environmental risk factors that have been implicated appear to be associated with a range of neurodevelopmental and neuropsychiatric outcomes, not just ADHD. The evidence to date suggests that both rare and multiple common genetic variants likely contribute to ADHD and modify its phenotype. ADHD or a similar phenotype also appears to be more common in extreme low birth weight and premature children and those exposed to exceptional early adversity. In this review, the authors consider recent developments in the understanding of risk factors that influence ADHD.

Clinical and cognitive characteristics of children with attention-deficit hyperactivity disorder, with and without copy number variants.

BACKGROUND: Submicroscopic, rare chromosomal copy number variants (CNVs) contribute to neurodevelopmental disorders but it is not known whether they define atypical clinical cases. AIMS: To identify whether large, rare CNVs in attention-deficit hyperactivity disorder (ADHD) are confined to a distinct clinical subgroup. METHOD: A total of 567 children with ADHD aged 5-17 years were recruited from community clinics. Psychopathology was assessed using the Child and Adolescent Psychiatric Assessment. Large, rare CNVs (>500 kb, <1% frequency) were defined from single nucleotide polymorphism data. RESULTS: Copy number variant carriers (13.6%) showed no differences from non-carriers in ADHD symptom severity, symptom type, comorbidity, developmental features, family history or pre-/perinatal markers. The only significant difference was a higher rate of intellectual disability (24% v. 9%, χ(2) = 15.5, P = 0.001). Most CNV carriers did not have intellectual disability. CONCLUSIONS: Large, rare CNVs are not restricted to an atypical form of ADHD but may be more highly enriched in children with cognitive problems.

Fitting the pieces together: current research on the genetic basis of attention-deficit/hyperactivity disorder (ADHD).

Attention-deficit/hyperactivity disorder (ADHD) is a highly disruptive childhood-onset disorder that often persists into adolescence and adulthood. Comorbidity with other problems, such as autism, dyslexia and conduct disorder (CD) is very common. Although little is known about the pathophysiology of ADHD, family, twin and adoption studies have shown that it is highly heritable. Whole genome linkage studies suggest there are no common susceptibility genes of moderate effect size. Most published research has been based on functional candidate gene studies. The most consistent evidence for association with ADHD relates to a dopamine D4 receptor (DRD4) gene variable number tandem repeat (VNTR), a dopamine D5 receptor (DRD5) gene microsatellite and a dopamine transporter (DAT1) gene VNTR. In addition, the catechol-O-methyltransferase (COMT) val158/108 met variant has been shown to increase risk for associated antisocial behavior. The first genome-wide association studies (GWAS) of ADHD have been completed and although larger studies are still required to detect common risk variants, novel risk pathways are being suggested for ADHD. Further research on the contribution of rare variants, larger genome-wide association and sequencing studies and ADHD phenotype refinement is now needed.

The Role of the Y Chromosome in Brain Function.

In mammals, sex differences are evident in many aspects of brain development, brain function and behaviour. Ultimately, such differences must arise from the differential sex chromosome complements in males and females: males inherit a single X chromosome and a Y chromosome, whilst females inherit two X chromosomes. One possible mechanism for sexual differentiation of the brain is via male-limited expression of genes on the small Y chromosome. Many Y-linked genes have been implicated in the development of the testes, and therefore could theoretically contribute to sexual differentiation of the brain indirectly, through influencing gonadal hormone production. Alternatively, Y-linked genes that are expressed in the brain could directly influence neural masculinisation. The present paper reviews evidence from human genetic studies and animal models for Y-linked effects (both direct and indirect) on neurodevelopment, brain function and behaviour. Besides enhancing our knowledge of the mechanisms underlying mammalian neural sexual differentiation, studies geared towards understanding the role of the Y chromosome in brain function will help to elucidate the molecular basis of sex-biased neuropsychiatric disorders, allowing for more selective sex-specific therapies.

An Overview on the Genetics of ADHD.

Attention Deficit Hyperactivity is a childhood-onset disorder that can persist into adult life. Traditional family, twin and adoption studies have shown that ADHD defined both categorically and dimensionally is familial and heritable. Twin studies are now being used to examine ways of defining the ADHD phenotype, to investigate gender differences, the effects on genes on continuity and comorbidity and to consider gene-environment interplay. Molecular genetic findings on ADHD have mainly arisen from functional candidate gene association studies and a number of pooled and meta-analyses have now been conducted. There is consistent evidence of association between ADHD and a dopamine D4 receptor gene VNTR and a dopamine D5 receptor gene microsatellite marker. More recent evidence from different studies and a pooled analysis suggests that conduct problems in those with ADHD is influenced by the COMT val158/108 met variant. Linkage studies suggest that there are no genes of moderate effect size and findings from large scale whole genome association studies are currently awaited. Overall the evidence to date, suggests that examining gene-phenotype links and testing whether gene variants have modifying effects on the ADHD phenotype are important. The contribution of gene-environment interplay (G x E) to psychopathology is becoming increasingly recognised, although for ADHD little is known on causal environmental risk factors.

Genetic influences on the development of childhood psychiatric disorders.

This review covers the key types of genetic research design, the methodology involved and emerging, and established findings in relation to child and adolescent psychiatry. Traditional family, twin, and adoption studies show that child and adolescent psychiatric disorders are familial and genetically influenced. Genes and environment contribute to all disorders. Genetic factors seem especially important for autism and attention deficit hyperactivity disorder. Twin and adoption study designs are now being used to examine gene-environment interplay, the effects of environmental risk factors, co-morbidity, phenotype definition, and developmental change. Molecular genetic strategies are increasingly being adopted to identify gene variants that increase risk of specific disorders. The ways in which specific gene variants exert risk effects at cellular and biological system levels are proving to be highly complex. There is also interest in examining the brain mechanisms that may be involved in risk pathways that link gene variant to psychopathology. Finally, molecular genetic studies also highlight the importance of gene-environment interplay, which seems to be especially important in depression and antisocial behaviour.