Multiple, independent, common variants at RET, SEMA3 and NRG1 gut enhancers specify Hirschsprung disease risk in European ancestry subjects.

PURPOSE: Hirschsprung disease (HSCR) is a developmental disorder of the enteric nervous system (ENS) characterized by congenital aganglionosis arising from coding variants in ENS genes causing partial or total loss-of-function. Low-penetrance, common, noncoding variants at RET, SEMA3 and NRG1 loci are also associated with HSCR, with small-to-moderate loss of gene expression mediated through sequence variants in cis-regulatory elements (CRE) as another causal mechanism. Since these latter variants are common, many individuals carry multiple risk variants. However, the extent and combinatorial effects of all putative CRE variants within and across these loci on HSCR is unknown. METHODS: Using 583 HSCR subjects, one of the largest samples of European ancestry studied, and genotyping 56 tag variants, we evaluated association of all common variants overlapping putative gut CREs and fine-mapped causal variants at RET, SEMA3 and NRG1. RESULTS: We demonstrate that 28 and 8 tag variants, several of which are genetically independent, overlap putative-enhancers at the RET and SEMA3 loci, respectively, as well as two fine-mapped tag variants at the NRG1 locus, are significantly associated with HSCR. Importantly, disease risk increases with increasing numbers of risk alleles from multiple variants within and across these loci, varying >25-fold across individuals. CONCLUSION: This increasing allele number-dependent risk, we hypothesize, arises from HSCR-relevant ENS cells sensing the reduced gene expression at multiple ENS genes since their developmental effects are integrated through gene regulatory networks.

αKlotho Regulates Age-Associated Vascular Calcification and Lifespan in Zebrafish.

The hormone αKlotho regulates lifespan in mice, as knockouts die early of what appears to be accelerated aging due to hyperphosphatemia and soft tissue calcification. In contrast, the overexpression of αKlotho increases lifespan. Given the severe mouse phenotype, we generated zebrafish mutants for αklotho as well as its binding partner fibroblast growth factor-23 (fgf23). Both mutations cause shortened lifespan in zebrafish, with abrupt onset of behavioral and degenerative physical changes at around 5 months of age. There is a calcification of vessels throughout the body, most dramatically in the outflow tract of the heart, the bulbus arteriosus (BA). This calcification is associated with an ectopic activation of osteoclast differentiation pathways. These findings suggest that the gradual loss of αKlotho found in normal aging might give rise to ectopic calcification.

Abnormal Behavior of Zebrafish Mutant in Dopamine Transporter Is Rescued by Clozapine.

Dopamine transporter (SLC6A3) deficiency causes infantile Parkinson disease, for which there is no effective therapy. We have explored the effects of genetically deleting SLC6A3 in zebrafish. Unlike the wild-type, slc6a3-/- fish hover near the tank bottom, with a repetitive digging-like behavior. slc6a3-/- fish manifest pruning and cellular loss of particular tyrosine hydroxylase-immunoreactive neurons in the midbrain. Clozapine, an effective therapeutic for treatment-resistant schizophrenia, rescues the abnormal behavior of slc6a3-/- fish. Clozapine also reverses the abnormalities in the A8 region of the mutant midbrain. By RNA sequencing analysis, clozapine increases the expression of erythropoietin pathway genes. Transgenic over-expression of erythropoietin in neurons of slc6a3-/- fish partially rescues the mutant behavior, suggesting a potential mechanistic basis for clozapine's efficacy.

Molecular Genetic Anatomy and Risk Profile of Hirschsprung's Disease.

BACKGROUND: Hirschsprung's disease, or congenital aganglionosis, is a developmental disorder of the enteric nervous system and is the most common cause of intestinal obstruction in neonates and infants. The disease has more than 80% heritability, including significant associations with rare and common sequence variants in genes related to the enteric nervous system, as well as with monogenic and chromosomal syndromes. METHODS: We genotyped and exome-sequenced samples from 190 patients with Hirschsprung's disease to quantify the genetic burden in patients with this condition. DNA sequence variants, large copy-number variants, and karyotype variants in probands were considered to be pathogenic when they were significantly associated with Hirschsprung's disease or another neurodevelopmental disorder. Novel genes were confirmed by functional studies in the mouse and human embryonic gut and in zebrafish embryos. RESULTS: The presence of five or more variants in four noncoding elements defined a widespread risk of Hirschsprung's disease (48.4% of patients and 17.1% of controls; odds ratio, 4.54; 95% confidence interval [CI], 3.19 to 6.46). Rare coding variants in 24 genes that play roles in enteric neural-crest cell fate, 7 of which were novel, were also common (34.7% of patients and 5.0% of controls) and conferred a much greater risk than noncoding variants (odds ratio, 10.02; 95% CI, 6.45 to 15.58). Large copy-number variants, which were present in fewer patients (11.4%, as compared with 0.2% of controls), conferred the highest risk (odds ratio, 63.07; 95% CI, 36.75 to 108.25). At least one identifiable genetic risk factor was found in 72.1% of the patients, and at least 48.4% of patients had a structural or regulatory deficiency in the gene encoding receptor tyrosine kinase (RET). For individual patients, the estimated risk of Hirschsprung's disease ranged from 5.33 cases per 100,000 live births (approximately 1 per 18,800) to 8.38 per 1000 live births (approximately 1 per 120). CONCLUSIONS: Among the patients in our study, Hirschsprung's disease arose from common noncoding variants, rare coding variants, and copy-number variants affecting genes involved in enteric neural-crest cell fate that exacerbate the widespread genetic susceptibility associated with RET. For individual patients, the genotype-specific odds ratios varied by a factor of approximately 67, which provides a basis for risk stratification and genetic counseling. (Funded by the National Institutes of Health.).

Functional loss of semaphorin 3C and/or semaphorin 3D and their epistatic interaction with ret are critical to Hirschsprung disease liability.

Innervation of the gut is segmentally lost in Hirschsprung disease (HSCR), a consequence of cell-autonomous and non-autonomous defects in enteric neuronal cell differentiation, proliferation, migration, or survival. Rare, high-penetrance coding variants and common, low-penetrance non-coding variants in 13 genes are known to underlie HSCR risk, with the most frequent variants in the ret proto-oncogene (RET). We used a genome-wide association (220 trios) and replication (429 trios) study to reveal a second non-coding variant distal to RET and a non-coding allele on chromosome 7 within the class 3 Semaphorin gene cluster. Analysis in Ret wild-type and Ret-null mice demonstrates specific expression of Sema3a, Sema3c, and Sema3d in the enteric nervous system (ENS). In zebrafish embryos, sema3 knockdowns show reduction of migratory ENS precursors with complete ablation under conjoint ret loss of function. Seven candidate receptors of Sema3 proteins are also expressed within the mouse ENS and their expression is also lost in the ENS of Ret-null embryos. Sequencing of SEMA3A, SEMA3C, and SEMA3D in 254 HSCR-affected subjects followed by in silico protein structure modeling and functional analyses identified five disease-associated alleles with loss-of-function defects in semaphorin dimerization and binding to their cognate neuropilin and plexin receptors. Thus, semaphorin 3C/3D signaling is an evolutionarily conserved regulator of ENS development whose dys-regulation is a cause of enteric aganglionosis.

Loss of δ-catenin function in severe autism.

Autism is a multifactorial neurodevelopmental disorder affecting more males than females; consequently, under a multifactorial genetic hypothesis, females are affected only when they cross a higher biological threshold. We hypothesize that deleterious variants at conserved residues are enriched in severely affected patients arising from female-enriched multiplex families with severe disease, enhancing the detection of key autism genes in modest numbers of cases. Here we show the use of this strategy by identifying missense and dosage sequence variants in the gene encoding the adhesive junction-associated δ-catenin protein (CTNND2) in female-enriched multiplex families and demonstrating their loss-of-function effect by functional analyses in zebrafish embryos and cultured hippocampal neurons from wild-type and Ctnnd2 null mouse embryos. Finally, through gene expression and network analyses, we highlight a critical role for CTNND2 in neuronal development and an intimate connection to chromatin biology. Our data contribute to the understanding of the genetic architecture of autism and suggest that genetic analyses of phenotypic extremes, such as female-enriched multiplex families, are of innate value in multifactorial disorders.

Population variation in total genetic risk of Hirschsprung disease from common RET, SEMA3 and NRG1 susceptibility polymorphisms.

The risk of Hirschsprung disease (HSCR) is ∼15/100 000 live births per newborn but has been reported to show significant inter-individual variation from the effects of seven common susceptibility alleles at the RET, SEMA3 and NRG1 loci. We show, by analyses of these variants in 997 samples from 376 HSCR families of European ancestry, that significant genetic risk can only be detected at RET (rs2435357 and rs2506030) and at SEMA3 (rs11766001), but not at NRG1. RET rs2435357 also showed significant frequency differences by gender, segment length of aganglionosis and familiality. Further, in combination, disease risk varied >30-fold between individuals with none and up to 6 susceptibility alleles. Thus, these polymorphisms can be used to stratify the newborn population into distinct phenotypic classes with defined risks to understand HSCR etiology.

Effects of RET and NRG1 polymorphisms in Indonesian patients with Hirschsprung disease.

BACKGROUND: Hirschsprung disease (HSCR) is a neurocristopathy characterized by absence of intramural ganglion cells along variable lengths of the gastrointestinal tract in neonates. Three polymorphisms, rs2435357, within a conserved transcriptional enhancer of RET, and, rs7835688 and rs16879552, within intron 1 of NRG1, have been shown to be associated with isolated forms of HSCR. We wished to replicate these findings, and study the interactions between these variants, in Indonesian HSCR patients. METHODS: Sixty isolated HSCR patients and 124 controls were ascertained for this study. The three genetic markers were examined using TaqMan Genotyping Assays in genomic DNA for association studies. RESULTS: RET rs2435357 showed the strongest association with HSCR both by case-control analysis (p=2.5 × 10(-8)) and transmission disequilibrium test (p=4.2 × 10(-6)). NRG1 rs7835688 was modestly associated with HSCR only by case-control analysis (p=4.3 × 10(-3)), whereas rs16879552 demonstrated no association (p>0.097). Two locus analyses of variants showed significant interactions with increased and decreased disease risks of HSCR at NRG1 but conditional on rs2435357 genotype. CONCLUSIONS: RET and NRG1 variants are common susceptibility factors for HSCR in Indonesia. These common variants demonstrate that development of HSCR requires joint effects of RET and NRG1 early in gut development.

Rapid and efficient human mutation detection using a bench-top next-generation DNA sequencer.

Next-generation sequencing (NGS) technologies can be a boon to human mutation detection given their high throughput: consequently, many genes and samples may be simultaneously studied with high coverage for accurate detection of heterozygotes. In circumstances requiring the intensive study of a few genes, particularly in clinical applications, a rapid turn around is another desirable goal. To this end, we assessed the performance of the bench-top 454 GS Junior platform as an optimized solution for mutation detection by amplicon sequencing of three type 3 semaphorin genes SEMA3A, SEMA3C, and SEMA3D implicated in Hirschsprung disease (HSCR). We performed mutation detection on 39 PCR amplicons totaling 14,014 bp in 47 samples studied in pools of 12 samples. Each 10-hr run was able to generate ∼75,000 reads and ∼28 million high-quality bases at an average read length of 371 bp. The overall sequencing error was 0.26 changes per kb at a coverage depth of ≥20 reads. Altogether, 37 sequence variants were found in this study of which 10 were unique to HSCR patients. We identified five missense mutations in these three genes that may potentially be involved in the pathogenesis of HSCR and need to be studied in larger patient samples.