Genomic architecture of autism from comprehensive whole-genome sequence annotation.

Fully understanding autism spectrum disorder (ASD) genetics requires whole-genome sequencing (WGS). We present the latest release of the Autism Speaks MSSNG resource, which includes WGS data from 5,100 individuals with ASD and 6,212 non-ASD parents and siblings (total n = 11,312). Examining a wide variety of genetic variants in MSSNG and the Simons Simplex Collection (SSC; n = 9,205), we identified ASD-associated rare variants in 718/5,100 individuals with ASD from MSSNG (14.1%) and 350/2,419 from SSC (14.5%). Considering genomic architecture, 52% were nuclear sequence-level variants, 46% were nuclear structural variants (including copy-number variants, inversions, large insertions, uniparental isodisomies, and tandem repeat expansions), and 2% were mitochondrial variants. Our study provides a guidebook for exploring genotype-phenotype correlations in families who carry ASD-associated rare variants and serves as an entry point to the expanded studies required to dissect the etiology in the ∼85% of the ASD population that remain idiopathic.

Mild Idiopathic Infantile Hypercalcemia-Part 1: Biochemical and Genetic Findings.

CONTEXT: Idiopathic infantile hypercalcemia (IIH), an uncommon disorder characterized by elevated serum concentrations of 1,25 dihydroxyvitamin D (1,25(OH)2D) and low parathyroid hormone (PTH) levels, may present with mild to severe hypercalcemia during the first months of life. Biallelic variants in the CYP24A1 or SLC34A1 genes are associated with severe IIH. Little is known about milder forms. OBJECTIVE: This work aims to characterize the genetic associations and biochemical profile of mild IIH. METHODS: This is a cross-sectional study including children between age 6 months and 17 years with IIH who were followed in the Calcium Clinic at the Hospital for Sick Children (SickKids), Toronto, Canada. Twenty children with mild IIH on calcium-restricted diets were evaluated. We performed a dietary assessment and analyzed biochemical measures including vitamin D metabolites and performed a stepwise molecular genetic analysis. Complementary biochemical assessments and renal ultrasounds were offered to first-degree family members of positive probands. RESULTS: The median age was 16 months. Median serum levels of calcium (2.69 mmol/L), urinary calcium:creatinine ratio (0.72 mmol/mmol), and 1,25(OH)2D (209 pmol/L) were elevated, whereas intact PTH was low normal (22.5 ng/L). Mean 1,25(OH)2D/PTH and 1,25(OH)2D/25(OH)D ratios were increased by comparison to healthy controls. Eleven individuals (55%) had renal calcification. Genetic variants were common (65%), with the majority being heterozygous variants in SLC34A1 and SLC34A3, while a minority showed variants of CYP24A1 and other genes related to hypercalciuria. CONCLUSION: The milder form of IIH has a distinctive vitamin D metabolite profile and is primarily associated with heterozygous SLC34A1 and SLC34A3 variants.

A large data resource of genomic copy number variation across neurodevelopmental disorders.

Copy number variations (CNVs) are implicated across many neurodevelopmental disorders (NDDs) and contribute to their shared genetic etiology. Multiple studies have attempted to identify shared etiology among NDDs, but this is the first genome-wide CNV analysis across autism spectrum disorder (ASD), attention deficit hyperactivity disorder (ADHD), schizophrenia (SCZ), and obsessive-compulsive disorder (OCD) at once. Using microarray (Affymetrix CytoScan HD), we genotyped 2,691 subjects diagnosed with an NDD (204 SCZ, 1,838 ASD, 427 ADHD and 222 OCD) and 1,769 family members, mainly parents. We identified rare CNVs, defined as those found in <0.1% of 10,851 population control samples. We found clinically relevant CNVs (broadly defined) in 284 (10.5%) of total subjects, including 22 (10.8%) among subjects with SCZ, 209 (11.4%) with ASD, 40 (9.4%) with ADHD, and 13 (5.6%) with OCD. Among all NDD subjects, we identified 17 (0.63%) with aneuploidies and 115 (4.3%) with known genomic disorder variants. We searched further for genes impacted by different CNVs in multiple disorders. Examples of NDD-associated genes linked across more than one disorder (listed in order of occurrence frequency) are NRXN1, SEH1L, LDLRAD4, GNAL, GNG13, MKRN1, DCTN2, KNDC1, PCMTD2, KIF5A, SYNM, and long non-coding RNAs: AK127244 and PTCHD1-AS. We demonstrated that CNVs impacting the same genes could potentially contribute to the etiology of multiple NDDs. The CNVs identified will serve as a useful resource for both research and diagnostic laboratories for prioritization of variants.

A microcosting and cost-consequence analysis of clinical genomic testing strategies in autism spectrum disorder.

PurposeWhole-exome (WES) and whole-genome sequencing (WGS) increase the diagnostic yield in autism spectrum disorder (ASD) compared to chromosomal microarray (CMA), but there have been no comprehensive cost analyses. The objective was to perform such an assessment of CMA, WES, and WGS and compare the incremental cost per additional positive finding in hypothetical testing scenarios.MethodsFive-year patient and program costs were estimated from an institutional perspective. WES and WGS estimates were based on HiSeq 2500 with an additional WGS estimate for HiSeq X platforms. Parameter uncertainty was assessed with probabilistic and deterministic sensitivity analysis.ResultsThe cost per ASD sample was CAD$1,655 (95% CI: 1,611; 1,699) for WES, CAD$2,851 (95% CI: 2,750; 2,956) for WGS on HiSeq X, and CAD$5,519 (95% CI: 5,244; 5,785) on HiSeq 2500, compared to CAD$744 (95% CI 714, 773) for CMA. The incremental cost was over CAD$25,000 per additional positive finding if CMA was replaced by newer technology.ConclusionWhile costs for WES and WGS remain high, future reductions in material and equipment costs, and increased understanding of newly discovered variants and variants of unknown significance will lead to improved value.

Topoisomerase II beta interacts with cohesin and CTCF at topological domain borders.

BACKGROUND: Type II DNA topoisomerases (TOP2) regulate DNA topology by generating transient double stranded breaks during replication and transcription. Topoisomerase II beta (TOP2B) facilitates rapid gene expression and functions at the later stages of development and differentiation. To gain new insight into the genome biology of TOP2B, we used proteomics (BioID), chromatin immunoprecipitation, and high-throughput chromosome conformation capture (Hi-C) to identify novel proximal TOP2B protein interactions and characterize the genomic landscape of TOP2B binding at base pair resolution. RESULTS: Our human TOP2B proximal protein interaction network included members of the cohesin complex and nucleolar proteins associated with rDNA biology. TOP2B associates with DNase I hypersensitivity sites, allele-specific transcription factor (TF) binding, and evolutionarily conserved TF binding sites on the mouse genome. Approximately half of all CTCF/cohesion-bound regions coincided with TOP2B binding. Base pair resolution ChIP-exo mapping of TOP2B, CTCF, and cohesin sites revealed a striking structural ordering of these proteins along the genome relative to the CTCF motif. These ordered TOP2B-CTCF-cohesin sites flank the boundaries of topologically associating domains (TADs) with TOP2B positioned externally and cohesin internally to the domain loop. CONCLUSIONS: TOP2B is positioned to solve topological problems at diverse cis-regulatory elements and its occupancy is a highly ordered and prevalent feature of CTCF/cohesin binding sites that flank TADs.

BRAF mutation and CDKN2A deletion define a clinically distinct subgroup of childhood secondary high-grade glioma.

PURPOSE: To uncover the genetic events leading to transformation of pediatric low-grade glioma (PLGG) to secondary high-grade glioma (sHGG). PATIENTS AND METHODS: We retrospectively identified patients with sHGG from a population-based cohort of 886 patients with PLGG with long clinical follow-up. Exome sequencing and array CGH were performed on available samples followed by detailed genetic analysis of the entire sHGG cohort. Clinical and outcome data of genetically distinct subgroups were obtained. RESULTS: sHGG was observed in 2.9% of PLGGs (26 of 886 patients). Patients with sHGG had a high frequency of nonsilent somatic mutations compared with patients with primary pediatric high-grade glioma (HGG; median, 25 mutations per exome; P = .0042). Alterations in chromatin-modifying genes and telomere-maintenance pathways were commonly observed, whereas no sHGG harbored the BRAF-KIAA1549 fusion. The most recurrent alterations were BRAF V600E and CDKN2A deletion in 39% and 57% of sHGGs, respectively. Importantly, all BRAF V600E and 80% of CDKN2A alterations could be traced back to their PLGG counterparts. BRAF V600E distinguished sHGG from primary HGG (P = .0023), whereas BRAF and CDKN2A alterations were less commonly observed in PLGG that did not transform (P < .001 and P < .001 respectively). PLGGs with BRAF mutations had longer latency to transformation than wild-type PLGG (median, 6.65 years [range, 3.5 to 20.3 years] v 1.59 years [range, 0.32 to 15.9 years], respectively; P = .0389). Furthermore, 5-year overall survival was 75% ± 15% and 29% ± 12% for children with BRAF mutant and wild-type tumors, respectively (P = .024). CONCLUSION: BRAF V600E mutations and CDKN2A deletions constitute a clinically distinct subtype of sHGG. The prolonged course to transformation for BRAF V600E PLGGs provides an opportunity for surgical interventions, surveillance, and targeted therapies to mitigate the outcome of sHGG.

MACE: model based analysis of ChIP-exo.

Understanding the role of a given transcription factor (TF) in regulating gene expression requires precise mapping of its binding sites in the genome. Chromatin immunoprecipitation-exo, an emerging technique using λ exonuclease to digest TF unbound DNA after ChIP, is designed to reveal transcription factor binding site (TFBS) boundaries with near-single nucleotide resolution. Although ChIP-exo promises deeper insights into transcription regulation, no dedicated bioinformatics tool exists to leverage its advantages. Most ChIP-seq and ChIP-chip analytic methods are not tailored for ChIP-exo, and thus cannot take full advantage of high-resolution ChIP-exo data. Here we describe a novel analysis framework, termed MACE (model-based analysis of ChIP-exo) dedicated to ChIP-exo data analysis. The MACE workflow consists of four steps: (i) sequencing data normalization and bias correction; (ii) signal consolidation and noise reduction; (iii) single-nucleotide resolution border peak detection using the Chebyshev Inequality and (iv) border matching using the Gale-Shapley stable matching algorithm. When applied to published human CTCF, yeast Reb1 and our own mouse ONECUT1/HNF6 ChIP-exo data, MACE is able to define TFBSs with high sensitivity, specificity and spatial resolution, as evidenced by multiple criteria including motif enrichment, sequence conservation, direct sequence pileup, nucleosome positioning and open chromatin states. In addition, we show that the fundamental advance of MACE is the identification of two boundaries of a TFBS with high resolution, whereas other methods only report a single location of the same event. The two boundaries help elucidate the in vivo binding structure of a given TF, e.g. whether the TF may bind as dimers or in a complex with other co-factors.

Duplication of GTF2I results in separation anxiety in mice and humans.

Duplication (dup7q11.23) and deletion (Williams syndrome) of chromosomal region 7q11.23 cause neurodevelopmental disorders with contrasting anxiety phenotypes. We found that 30% of 4- to 12-year-olds with dup7q11.23 but fewer than 5% of children with WS or in the general population met diagnostic criteria for a separation-anxiety disorder. To address the role of one commonly duplicated or deleted gene in separation anxiety, we compared mice that had varying numbers of Gtf2i copies. Relative to mouse pups with one or two Gtf2i copies, pups with additional Gtf2i copies showed significantly increased maternal separation-induced anxiety as measured by ultrasonic vocalizations. This study links the copy number of a single gene from 7q11.23 to separation anxiety in both mice and humans, highlighting the utility of mouse models in dissecting specific gene functions for genomic disorders that span many genes. This study also offers insight into molecular separation-anxiety pathways that might enable the development of targeted therapeutics.

Enhanced prefrontal serotonin 5-HT(1A) currents in a mouse model of Williams-Beuren syndrome with low innate anxiety.

Williams-Beuren syndrome (WBS) is a neurodevelopmental disorder caused by the hemizygous deletion of 28 genes on chromosome 7, including the general transcription factor GTF2IRD1. Mice either hemizygously (Gtf2ird1(+/-)) or homozygously (Gtf2ird1(-/-)) deleted for this transcription factor exhibit low innate anxiety, low aggression and increased social interaction, a phenotype that shares similarities to the high sociability and disinhibition seen in individuals with WBS. Here, we investigated the inhibitory effects of serotonin (5-HT) on the major output neurons of the prefrontal cortex in Gtf2ird1(-/-) mice and their wildtype (WT) siblings. Prefrontal 5-HT receptors are known to modulate anxiety-like behaviors, and the Gtf2ird1(-/-) mice have altered 5-HT metabolism in prefrontal cortex. Using whole cell recording from layer V neurons in acute brain slices of prefrontal cortex, we found that 5-HT elicited significantly larger inhibitory, outward currents in Gtf2ird1(-/-) mice than in WT controls. In both genotypes, these currents were resistant to action potential blockade with TTX and were suppressed by the selective 5-HT(1A) receptor antagonist WAY-100635, suggesting that they are mediated directly by 5-HT(1A) receptors on the recorded neurons. Control experiments suggest a degree of layer and receptor specificity in this enhancement since 5-HT(1A) receptor-mediated responses in layer II/III pyramidal neurons were unchanged as were responses mediated by two other inhibitory receptors in layer V pyramidal neurons. Furthermore, we demonstrate GTF2IRD1 protein expression by neurons in layer V of the prefrontal cortex. Our finding that 5-HT(1A)-mediated responses are selectively enhanced in layer V pyramidal neurons of Gtf2ird1(-/-) mice gives insight into the cellular mechanisms that underlie reduced innate anxiety and increased sociability in these mice, and may be relevant to the low social anxiety and disinhibition in patients with WBS and their sensitivity to serotonergic medicines. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s11689-010-9044-5) contains supplementary material, which is available to authorized users.

The common inversion of the Williams-Beuren syndrome region at 7q11.23 does not cause clinical symptoms.

Williams-Beuren syndrome (WBS) is caused by a approximately 1.5 million base pair deletion at 7q11.23. A common inversion of the region, WBSinv-1, exists as a polymorphism but was also found in individuals with WBS-like features but no deletion, suggesting it could cause clinical symptoms. We performed a full clinical, developmental and genetic assessment of two previously reported individuals with clinical symptoms and WBSinv-1 but no 7q11.23 deletion. We also examined expression of genes at 7q11.23 in individuals in the general population who have WBSinv-1. We show that individuals with clinical symptoms and WBSinv-1 do not show significant clinical or psychological overlap with individuals with WBS. In addition, a 1.3 Mb duplication of part of the velocardiofacial syndrome region on chromosome 22q11.2 was found in one participant with WBSinv-1 and clinical symptoms. We also demonstrate that individuals with WBSinv-1 show normal expression of genes from the WBS region. These results suggest that WBSinv-1 does not cause clinical symptoms and we advise caution when diagnosing individuals with atypical presentation of rare syndromes. Whole genome analysis may reveal previously unidentified copy number variants that could contribute to syndromic features.

Infantile spasms is associated with deletion of the MAGI2 gene on chromosome 7q11.23-q21.11.

Infantile spasms (IS) is the most severe and common form of epilepsy occurring in the first year of life. At least half of IS cases are idiopathic in origin, with others presumed to arise because of brain insult or malformation. Here, we identify a locus for IS by high-resolution mapping of 7q11.23-q21.1 interstitial deletions in patients. The breakpoints delineate a 500 kb interval within the MAGI2 gene (1.4 Mb in size) that is hemizygously disrupted in 15 of 16 participants with IS or childhood epilepsy, but remains intact in 11 of 12 participants with no seizure history. MAGI2 encodes the synaptic scaffolding protein membrane-associated guanylate kinase inverted-2 that interacts with Stargazin, a protein also associated with epilepsy in the stargazer mouse.

Severe expressive-language delay related to duplication of the Williams-Beuren locus.

The Williams-Beuren syndrome (WBS) locus, at 7q11.23, is prone to recurrent chromosomal rearrangements, including the microdeletion that causes WBS, a multisystem condition with characteristic cardiovascular, cognitive, and behavioral features. It is hypothesized that reciprocal duplications of the WBS interval should also occur, and here we present such a case description. The most striking phenotype was a severe delay in expressive speech, in contrast to the normal articulation and fluent expressive language observed in persons with WBS. Our results suggest that specific genes at 7q11.23 are exquisitely sensitive to dosage alterations that can influence human language and visuospatial capabilities.

Expanded repeat in canine epilepsy.

Epilepsy afflicts 1% of humans and 5% of dogs. We report a canine epilepsy mutation and evidence for the existence of repeat-expansion disease outside humans. A canid-specific unstable dodecamer repeat in the Epm2b (Nhlrc1) gene recurrently expands, causing a fatal epilepsy and contributing to the high incidence of canine epilepsy. Tracing the repeat origins revealed two successive events, starting 50 million years ago, unique to canid evolution. A genetic test, presented here, will allow carrier and presymptomatic diagnosis and disease eradication. Clinicopathologic characterization establishes affected animals as a model for Lafora disease, the most severe teenage-onset human epilepsy.

Loss of function of the cytoplasmic isoform of the protein laforin (EPM2A) causes Lafora progressive myoclonus epilepsy.

Lafora disease is the most severe teenage-onset progressive epilepsy, a unique form of glycogenosis with perikaryal accumulation of an abnormal form of glycogen, and a neurodegenerative disorder exhibiting an unusual generalized organellar disintegration. The disease is caused by mutations of the EPM2A gene, which encodes two isoforms of the laforin protein tyrosine phosphatase, having alternate carboxyl termini, one localized in the cytoplasm (endoplasmic reticulum) and the other in the nucleus. To date, all documented disease mutations, including the knockout mouse model deletion, have been in the segment of the protein common to both isoforms. It is therefore not known whether dysfunction of the cytoplasmic, nuclear, or both isoforms leads to the disease. In the present work, we identify six novel mutations, one of which, c.950insT (Q319fs), is the first mutation specific to the cytoplasmic laforin isoform, implicating this isoform in disease pathogenesis. To confirm this mutation's deleterious effect on laforin, we studied the resultant protein's subcellular localization and function and show a drastic reduction in its phosphatase activity, despite maintenance of its location at the endoplasmic reticulum.

Mutations in NHLRC1 cause progressive myoclonus epilepsy.

Lafora progressive myoclonus epilepsy is characterized by pathognomonic endoplasmic reticulum (ER)-associated polyglucosan accumulations. We previously discovered that mutations in EPM2A cause Lafora disease. Here, we identify a second gene associated with this disease, NHLRC1 (also called EPM2B), which encodes malin, a putative E3 ubiquitin ligase with a RING finger domain and six NHL motifs. Laforin and malin colocalize to the ER, suggesting they operate in a related pathway protecting against polyglucosan accumulation and epilepsy.