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Certain human traits such as neurodevelopmental disorders (NDs) and congenital anomalies (CAs) are believed to be primarily genetic in origin. However, even after whole-genome sequencing (WGS), a substantial fraction of such disorders remain unexplained. We hypothesize that some cases of ND–CA are caused by aberrant DNA methylation leading to dysregulated genome function. Comparing DNA methylation profiles from 489 individuals with ND–CAs against 1534 controls, we identify epivariations as a frequent occurrence in the human genome. De novo epivariations are significantly enriched in cases, while RNAseq analysis shows that epivariations often have an impact on gene expression comparable to loss-of-function mutations. Additionally, we detect and replicate an enrichment of rare sequence mutations overlapping CTCF binding sites close to epivariations, providing a rationale for interpreting non-coding variation. We propose that epivariations contribute to the pathogenesis of some patients with unexplained ND–CAs, and as such likely have diagnostic relevance. A proportion of neurodevelopmental disorder and congenital anomaly cases remain without a genetic diagnosis. Here, the authors study aberrations of DNA methylation in such cases and find that epivariations might provide an explanation for some of these undiagnosed patients.

Autism spectrum disorder (ASD) is a highly heritable and heterogeneous group of neurodevelopmental phenotypes diagnosed in more than 1% of children. Common genetic variants contribute substantially to ASD susceptibility, but to date no individual variants have been robustly associated with ASD. With a marked sample-size increase from a unique Danish population resource, we report a genome-wide association meta-analysis of 18,381 individuals with ASD and 27,969 controls that identified five genome-wide-significant loci. Leveraging GWAS results from three phenotypes with significantly overlapping genetic architectures (schizophrenia, major depression, and educational attainment), we identified seven additional loci shared with other traits at equally strict significance levels. Dissecting the polygenic architecture, we found both quantitative and qualitative polygenic heterogeneity across ASD subtypes. These results highlight biological insights, particularly relating to neuronal function and corticogenesis, and establish that GWAS performed at scale will be much more productive in the near term in ASD. A genome-wide-association meta-analysis of 18,381 austim spectrum disorder (ASD) cases and 27,969 controls identifies five risk loci. The authors find quantitative and qualitative polygenic heterogeneity across ASD subtypes.

Joseph Buxbaum and colleagues use an epidemiological sample from Sweden to investigate the genetic architecture of autism spectrum disorders. They conclude that most inherited risk for autism is determined by common variation and that rare variation explains a smaller fraction of total heritability. A key component of genetic architecture is the allelic spectrum influencing trait variability. For autism spectrum disorder (herein termed autism), the nature of the allelic spectrum is uncertain. Individual risk-associated genes have been identified from rare variation, especially de novo mutations 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 . From this evidence, one might conclude that rare variation dominates the allelic spectrum in autism, yet recent studies show that common variation, individually of small effect, has substantial impact en masse 9 , 10 . At issue is how much of an impact relative to rare variation this common variation has. Using a unique epidemiological sample from Sweden, new methods that distinguish total narrow-sense heritability from that due to common variation and synthesis of results from other studies, we reach several conclusions about autism's genetic architecture: its narrow-sense heritability is ∼52.4%, with most due to common variation, and rare de novo mutations contribute substantially to individual liability, yet their contribution to variance in liability, 2.6%, is modest compared to that for heritable variation.

Elise Robinson and colleagues present the polygenic transmission disequilibrium test (pTDT) for evaluating transmission of polygenic risk in family-based study designs. The authors apply pTDT to a cohort of autism spectrum disorder (ASD) families and find that common polygenic variation acts additively with de novo variants to contribute to ASD risk. Autism spectrum disorder (ASD) risk is influenced by common polygenic and de novo variation. We aimed to clarify the influence of polygenic risk for ASD and to identify subgroups of ASD cases, including those with strongly acting de novo variants, in which polygenic risk is relevant. Using a novel approach called the polygenic transmission disequilibrium test and data from 6,454 families with a child with ASD, we show that polygenic risk for ASD, schizophrenia, and greater educational attainment is over-transmitted to children with ASD. These findings hold independent of proband IQ. We find that polygenic variation contributes additively to risk in ASD cases who carry a strongly acting de novo variant. Lastly, we show that elements of polygenic risk are independent and differ in their relationship with phenotype. These results confirm that the genetic influences on ASD are additive and suggest that they create risk through at least partially distinct etiologic pathways.

Background Over the past decade genome-wide association studies (GWAS) have been applied to aid in the understanding of the biology of traits. The success of this approach is governed by the underlying effect sizes carried by the true risk variants and the corresponding statistical power to observe such effects given the study design and sample size under investigation. Previous ASD GWAS have identified genome-wide significant (GWS) risk loci; however, these studies were of only of low statistical power to identify GWS loci at the lower effect sizes (odds ratio (OR) <1.15). Methods We conducted a large-scale coordinated international collaboration to combine independent genotyping data to improve the statistical power and aid in robust discovery of GWS loci. This study uses genome-wide genotyping data from a discovery sample (7387 ASD cases and 8567 controls) followed by meta-analysis of summary statistics from two replication sets (7783 ASD cases and 11359 controls; and 1369 ASD cases and 137308 controls). Results We observe a GWS locus at 10q24.32 that overlaps several genes including PITX3 , which encodes a transcription factor identified as playing a role in neuronal differentiation and CUEDC2 previously reported to be associated with social skills in an independent population cohort. We also observe overlap with regions previously implicated in schizophrenia which was further supported by a strong genetic correlation between these disorders (Rg = 0.23; P  = 9 × 10 −6 ). We further combined these Psychiatric Genomics Consortium (PGC) ASD GWAS data with the recent PGC schizophrenia GWAS to identify additional regions which may be important in a common neurodevelopmental phenotype and identified 12 novel GWS loci. These include loci previously implicated in ASD such as FOXP1 at 3p13, ATP2B2 at 3p25.3, and a ‘neurodevelopmental hub’ on chromosome 8p11.23. Conclusions This study is an important step in the ongoing endeavour to identify the loci which underpin the common variant signal in ASD. In addition to novel GWS loci, we have identified a significant genetic correlation with schizophrenia and association of ASD with several neurodevelopmental-related genes such as EXT1 , ASTN2 , MACROD2 , and HDAC4.

Susceptibility to autism Several lines of evidence point to genetic involvement in autism spectrum disorders (ASDs), neurodevelopmental and neuropsychiatric disorders characterized by impaired verbal communication and social interaction. The clinical and genetic complexities of the condition make it difficult to identify susceptibility factors, but two related studies now present robust evidence for a genetic involvement. The first, a genome-wide association study, identifies six single-nucleotide polymorphisms strongly associated with autism. These variants lie between two genes encoding neuronal cell-adhesion molecules (cadherins 9 and 10), suggesting possible involvement in ASD pathogenesis. The second study used copy number variation screens to identify genetic variants in two major gene pathways in children with ASDs. The changes are in the ubiquitin pathway, which has previously been associated with neurological disease, and in genes for neuronal cell-adhesion molecules. Autism spectrum disorders (ASDs) are neurodevelopmental disorders characterized by impairments in social and communication skills. Accumulating evidence suggests a genetic component to ASDs, and here a two-stage, genome-wide approach is used to identify candidate genomic loci enriched in ASD cases. The majority of these loci are found to be involved in neuronal adhesion and ubiquitin degradation, suggesting novel susceptibility mechanisms. Autism spectrum disorders (ASDs) are childhood neurodevelopmental disorders with complex genetic origins 1 , 2 , 3 , 4 . Previous studies focusing on candidate genes or genomic regions have identified several copy number variations (CNVs) that are associated with an increased risk of ASDs 5 , 6 , 7 , 8 , 9 . Here we present the results from a whole-genome CNV study on a cohort of 859 ASD cases and 1,409 healthy children of European ancestry who were genotyped with ∼550,000 single nucleotide polymorphism markers, in an attempt to comprehensively identify CNVs conferring susceptibility to ASDs. Positive findings were evaluated in an independent cohort of 1,336 ASD cases and 1,110 controls of European ancestry. Besides previously reported ASD candidate genes, such as NRXN1 (ref. 10 ) and CNTN4 (refs 11 , 12 ), several new susceptibility genes encoding neuronal cell-adhesion molecules, including NLGN1 and ASTN2 , were enriched with CNVs in ASD cases compared to controls ( P = 9.5 × 10 -3 ). Furthermore, CNVs within or surrounding genes involved in the ubiquitin pathways, including UBE3A , PARK2 , RFWD2 and FBXO40 , were affected by CNVs not observed in controls ( P = 3.3 × 10 -3 ). We also identified duplications 55 kilobases upstream of complementary DNA AK123120 ( P = 3.6 × 10 -6 ). Although these variants may be individually rare, they target genes involved in neuronal cell-adhesion or ubiquitin degradation, indicating that these two important gene networks expressed within the central nervous system may contribute to the genetic susceptibility of ASD.

Identification of the genetic basis of common disease may require comprehensive sequence analysis of coding regions and regulatory elements in patients and controls to find genetic effects caused by rare or heterogeneous mutations. In this study, we demonstrate how mismatch repair detection on tag arrays can be applied in a case-control study. Mismatch repair detection allows > 1,000 amplicons to be screened for variations in a single laboratory reaction. Variation scanning in 939 amplicons, mostly in coding regions within a linkage peak, was done for 372 patients and 404 controls. In total, >180 Mb of DNA was scanned. Several variants more prevalent in patients than in controls were identified. This study demonstrates an approach to the discovery of susceptibility genes for common disease: large-scale direct sequence comparison between patients and controls. We believe this approach can be scaled up to allow sequence comparison in the whole-genome coding regions among large sets of cases and controls at a reasonable cost in the near future.

Tourette Syndrome (TS) is a complex neurodevelopmental disorder characterized by vocal and motor tics lasting more than a year. It is highly polygenic in nature with both rare and common previously associated variants. Epidemiological studies have shown TS to be correlated with other phenotypes, but large-scale phenome wide analyses in biobank level data have not been performed to date. In this study, we used the summary statistics from the latest meta-analysis of TS to calculate the polygenic risk score (PRS) of individuals in the UK Biobank data and applied a Phenome Wide Association Study (PheWAS) approach to determine the association of disease risk with a wide range of phenotypes. A total of 57 traits were found to be significantly associated with TS polygenic risk, including multiple psychosocial factors and mental health conditions such as anxiety disorder and depression. Additional associations were observed with complex non-psychiatric disorders such as Type 2 diabetes, heart palpitations, and respiratory conditions. Cross-disorder comparisons of phenotypic associations with genetic risk for other childhood-onset disorders (e.g.: attention deficit hyperactivity disorder [ADHD], autism spectrum disorder [ASD], and obsessive-compulsive disorder [OCD]) indicated an overlap in associations between TS and these disorders. ADHD and ASD had a similar direction of effect with TS while OCD had an opposite direction of effect for all traits except mental health factors. Sex-specific PheWAS analysis identified differences in the associations with TS genetic risk between males and females. Type 2 diabetes and heart palpitations were significantly associated with TS risk in males but not in females, whereas diseases of the respiratory system were associated with TS risk in females but not in males. This analysis provides further evidence of shared genetic and phenotypic architecture of different complex disorders.

Scanning for links to autism Autism is a highly heritable neurodevelopmental disorder, and yet very few specific susceptibility genes have been identified to date. A genome-wide scan using half a million genome-wide SNPs (single nucleotide polymorphisms) in a common set of 1,031 multiplex autism families has now revealed significant linkage and association to autism. The linkage regions identified provide targets for rare variation screening while the discovery of a single novel association, between SEMA5A and TAS2R1 on chromosome 5p15. The expression of SEMA5A was found to be reduced in brains from autistic patients, further confirmation that it is an autism susceptibility gene. Autism is a highly heritable neurodevelopmental disorder, and yet few specific susceptibility genes have been identified to date. A linkage and association mapping study using half a million genome-wide single nucleotide polymorphisms is now described in a common set of 1,031 multiplex autism families. The linkage regions identified provide targets for rare variation screening whereas the discovery of a single novel association, SEMA5A , demonstrates the action of common variants. Although autism is a highly heritable neurodevelopmental disorder, attempts to identify specific susceptibility genes have thus far met with limited success 1 . Genome-wide association studies using half a million or more markers, particularly those with very large sample sizes achieved through meta-analysis, have shown great success in mapping genes for other complex genetic traits. Consequently, we initiated a linkage and association mapping study using half a million genome-wide single nucleotide polymorphisms (SNPs) in a common set of 1,031 multiplex autism families (1,553 affected offspring). We identified regions of suggestive and significant linkage on chromosomes 6q27 and 20p13, respectively. Initial analysis did not yield genome-wide significant associations; however, genotyping of top hits in additional families revealed an SNP on chromosome 5p15 (between SEMA5A and TAS2R1 ) that was significantly associated with autism ( P = 2 × 10 -7 ). We also demonstrated that expression of SEMA5A is reduced in brains from autistic patients, further implicating SEMA5A as an autism susceptibility gene. The linkage regions reported here provide targets for rare variation screening whereas the discovery of a single novel association demonstrates the action of common variants.

Hemiergis is a distinctive limb-reduced clade of skinks of the Australian Sphenomorphus group that occur throughout much of southern Australia. Mitochondrial 12S and 16S rRNA gene-sequence data and Bayesian inference (relaxed clock and time-free models) are used to infer the phylogenetic relationships within Hemiergis, as well as test the monophyly of this clade with respect to Glaphyromorphus gracilipes, a southwestern Australia species of the polyphyletic “Glaphyromorphus” assemblage. Hemiergis monophyly is not supported by the mtDNA data, with G. gracilipes being placed as the sister lineage to H. decresiensis sensu lato. Using the Bayes factor, comparison of an alternative hypothesis of Hemiergis monophyly to the preferred hypothesis (i.e., the mtDNA inferred hypothesis with the highest posterior probability) indicates positive support (BF = 3.9–4.1) for the preferred hypothesis demonstrating Hemiergis paraphyly; thus, G. gracilipes is transferred to Hemiergis. Whereas these data strongly support the placement of the two-toed H. quadrilineatum as being closely related to the three- and four-toed populations of H. peronii, the interrelationships among these three limb-reduced phenotypes is unresolved. All other interspecific relationships within Hemiergis are weakly supported by the mtDNA. Within H. decresiensis sensu lato, there is strong support for two divergent lineages that are allopatric. The eastern lineage occurring in Victoria, New South Wales, and extreme southern Queensland is elevated to full species (=H. talbingoensis), with H. decresiensis sensu stricto restricted to the western lineage of South Australia. While many of the interspecific relationships within Hemiergis are weakly supported, these mtDNA data do very strongly favor our preferred hypothesis over an alternative phylogenetic hypothesis implied by a previously proposed parsimonious transformation series of limb reduction; this result implies more independent limb reduction events during the evolution of Hemiergis.