Identification of Genes Associated With Hirschsprung Disease, Based on Whole-Genome Sequence Analysis, and Potential Effects on Enteric Nervous System Development.

BACKGROUND & AIMS: Hirschsprung disease, or congenital aganglionosis, is believed to be oligogenic-that is, caused by multiple genetic factors. We performed whole-genome sequence analyses of patients with Hirschsprung disease to identify genetic factors that contribute to disease development and analyzed the functional effects of these variants. METHODS: We performed whole-genome sequence analyses of 443 patients with short-segment disease, recruited from hospitals in China and Vietnam, and 493 ethnically matched individuals without Hirschsprung disease (controls). We performed genome-wide association analyses and gene-based rare-variant burden tests to identify rare and common disease-associated variants and study their interactions. We obtained induced pluripotent stem cell (iPSC) lines from 4 patients with Hirschsprung disease and 2 control individuals, and we used these to generate enteric neural crest cells for transcriptomic analyses. We assessed the neuronal lineage differentiation capability of iPSC-derived enteric neural crest cells using an in vitro differentiation assay. RESULTS: We identified 4 susceptibility loci, including 1 in the phospholipase D1 gene (PLD1) (P = 7.4 × 10-7). The patients had a significant excess of rare protein-altering variants in genes previously associated with Hirschsprung disease and in the ß-secretase 2 gene (BACE2) (P = 2.9 × 10-6). The epistatic effects of common and rare variants across these loci provided a sensitized background that increased risk for the disease. In studies of the iPSCs, we observed common and distinct pathways associated with variants in RET that affect risk. In functional assays, we found variants in BACE2 to protect enteric neurons from apoptosis. We propose that alterations in BACE1 signaling via amyloid ß precursor protein and BACE2 contribute to pathogenesis of Hirschsprung disease. CONCLUSIONS: In whole-genome sequence analyses of patients with Hirschsprung disease, we identified rare and common variants associated with disease risk. Using iPSC cells, we discovered some functional effects of these variants.

Trans-ethnic meta-analysis of genome-wide association studies for Hirschsprung disease.

Hirschsprung disease (HSCR) is the most common cause of neonatal intestinal obstruction. It is characterized by the absence of ganglia in the nerve plexuses of the lower gastrointestinal tract. So far, three common disease-susceptibility variants at the RET, SEMA3 and NRG1 loci have been detected through genome-wide association studies (GWAS) in Europeans and Asians to understand its genetic etiologies. Here we present a trans-ethnic meta-analysis of 507 HSCR cases and 1191 controls, combining all published GWAS results on HSCR to fine-map these loci and narrow down the putatively causal variants to 99% credible sets. We also demonstrate that the effects of RET and NRG1 are universal across European and Asian ancestries. In contrast, we detected a European-specific association of a low-frequency variant, rs80227144, in SEMA3 [odds ratio (OR) = 5.2, P = 4.7 × 10-10]. Conditional analyses on the lead SNPs revealed a secondary association signal, corresponding to an Asian-specific, low-frequency missense variant encoding RET p.Asp489Asn (rs9282834, conditional OR = 20.3, conditional P = 4.1 × 10-14). When in trans with the RET intron 1 enhancer risk allele, rs9282834 increases the risk of HSCR from 1.1 to 26.7. Overall, our study provides further insights into the genetic architecture of HSCR and has profound implications for future study designs.

Actionable secondary findings from whole-genome sequencing of 954 East Asians.

Recently, the American College of Medical Genetics (ACMG) recommended the return of actionable secondary findings detected from clinical sequencing. The reported frequency of secondary findings in Asian populations were highly variable and it is unclear whether the uniformity in coverage offered by whole-genome sequencing (WGS) may impact the estimate. In this analysis, we aimed to refine the rate of secondary findings on East Asians through a large-scale WGS study. We classified 1256 protein-altering or splicing variants of the 59 actionable genes detected from WGS of 954 East Asians in strict accordance with the ACMG and the Association for Molecular Pathology guidelines. A total of 21 pathogenic or likely pathogenic variants were detected in 24 of the 954 East Asian genomes with an estimate of 2.5% of East Asians carrying actionable variants. Although the overall estimate of secondary findings was consistent with those reported for non-East Asian ethnicities, genetic and allelic heterogeneity was observed. WGS offers a wider breadth of coverage over WES, which highlights the need to further investigate the variable sensitivity of WES and WGS in the detection of secondary findings. Identifying secondary findings in populations underrepresented in previous genetic literature might improve variant interpretation and has a profound impact on local decision-making with regard to the cost-effectiveness of returning the secondary findings from clinical sequencing.

Genome-wide copy number variation study in anorectal malformations.

Anorectal malformations (ARMs, congenital obstruction of the anal opening) are among the most common birth defects requiring surgical treatment (2-5/10 000 live-births) and carry significant chronic morbidity. ARMs present either as isolated or as part of the phenotypic spectrum of some chromosomal abnormalities or monogenic syndromes. The etiology is unknown. To assess the genetic contribution to ARMs, we investigated single-nucleotide polymorphisms and copy number variations (CNVs) at genome-wide scale. A total of 363 Han Chinese sporadic ARM patients and 4006 Han Chinese controls were included. Overall, we detected a 1.3-fold significant excess of rare CNVs in patients. Stratification of patients by presence/absence of other congenital anomalies showed that while syndromic ARM patients carried significantly longer rare duplications than controls (P = 0.049), non-syndromic patients were enriched with both rare deletions and duplications when compared with controls (P = 0.00031). Twelve chromosomal aberrations and 114 rare CNVs were observed in patients but not in 868 controls nor 11 943 healthy individuals from the Database of Genomic Variants. Importantly, these aberrations were observed in isolated ARM patients. Gene-based analysis revealed 79 genes interfered by CNVs in patients only. In particular, we identified a de novo DKK4 duplication. DKK4 is a member of the WNT signaling pathway which is involved in the development of the anorectal region. In mice, Wnt disruption results in ARMs. Our data suggest a role for rare CNVs not only in syndromic but also in isolated ARM patients and provide a list of plausible candidate genes for the disorder.

Chinese family with diffuse oesophageal leiomyomatosis: a new COL4A5/COL4A6 deletion and a case of gonosomal mosaicism.

BACKGROUND: Diffuse oesophageal leiomyomatosis (DOL) is a rare disorder characterized by tumorous overgrowth of the muscular wall of the oesophagus. DOL is present in 5 % of Alport syndrome (AS) patients. AS is a rare hereditary disease that involves varying degrees of hearing impairment, ocular changes and progressive glomerulonephritis leading to renal failure. In DOL-AS patients, the genetic defect consists of a deletion involving the COL4A5 and COL4A6 genes on the X chromosome. CASE PRESENTATION: We report a two-generation family (4 individuals; parents and two children, one male and one female) with two members (mother and son) affected with oesophageal leiomyomatosis. Signs of potential renal failure, which characterizes AS, were only apparent in the index patient (son) 2 years and three months after the initial diagnosis of DOL. Blood DNA from the four family members were submitted to exome sequencing and array genotyping to perform a genome wide screening for disease causal single nucleotide (SN) and copy number (CN) variations. Analyses revealed a new 40kb deletion encompassing from intron 2 of COL4A5 to intron 1 of COL4A6 at Xq22.3. The breakpoints were also identified. Possible confounding pathogenic exonic variants in genes known to be involved in other extracellular matrices disorders were also shared by the two affected individuals. Meticulous analysis of the maternal DNA revealed a case of gonosomal mosaicism. CONCLUSIONS: This is the first report of gonadosomal mosaicism associated to DOL-AS.

Genome-wide copy number analysis uncovers a new HSCR gene: NRG3.

Hirschsprung disease (HSCR) is a congenital disorder characterized by aganglionosis of the distal intestine. To assess the contribution of copy number variants (CNVs) to HSCR, we analysed the data generated from our previous genome-wide association study on HSCR patients, whereby we identified NRG1 as a new HSCR susceptibility locus. Analysis of 129 Chinese patients and 331 ethnically matched controls showed that HSCR patients have a greater burden of rare CNVs (p = 1.50 × 10(-5)), particularly for those encompassing genes (p = 5.00 × 10(-6)). Our study identified 246 rare-genic CNVs exclusive to patients. Among those, we detected a NRG3 deletion (p = 1.64 × 10(-3)). Subsequent follow-up (96 additional patients and 220 controls) on NRG3 revealed 9 deletions (combined p = 3.36 × 10(-5)) and 2 de novo duplications among patients and two deletions among controls. Importantly, NRG3 is a paralog of NRG1. Stratification of patients by presence/absence of HSCR-associated syndromes showed that while syndromic-HSCR patients carried significantly longer CNVs than the non-syndromic or controls (p = 1.50 × 10(-5)), non-syndromic patients were enriched in CNV number when compared to controls (p = 4.00 × 10(-6)) or the syndromic counterpart. Our results suggest a role for NRG3 in HSCR etiology and provide insights into the relative contribution of structural variants in both syndromic and non-syndromic HSCR. This would be the first genome-wide catalog of copy number variants identified in HSCR.

Targeted next-generation sequencing on Hirschsprung disease: a pilot study exploits DNA pooling.

To adopt an efficient approach of identifying rare variants possibly related to Hirschsprung disease (HSCR), a pilot study was set up to evaluate the performance of a newly designed protocol for next generation targeted resquencing. In total, 20 Chinese HSCR patients and 20 Chinese sex-matched individuals with no HSCR were included, for which coding sequences (CDS) of 62 genes known to be in signaling pathways relevant to enteric nervous system development were selected for capture and sequencing. Blood DNAs from eight pools of five cases or controls were enriched by PCR-based RainDance technology (RDT) and then sequenced on a 454 FLX platform. As technical validation, five patients from case Pool-3 were also independently enriched by RDT, indexed with barcode and sequenced with sufficient coverage. Assessment for CDS single nucleotide variants showed DNA pooling performed well (specificity/sensitivity at 98.4%/83.7%) at the common variant level; but relatively worse (specificity/sensitivity at 65.5%/61.3%) at the rare variant level. Further Sanger sequencing only validated five out of 12 rare damaging variants likely involved in HSCR. Hence more improvement at variant detection and sequencing technology is needed to realize the potential of DNA pooling for large-scale resequencing projects.

Allele-specific expression at the RET locus in blood and gut tissue of individuals carrying risk alleles for Hirschsprung disease.

RET common variants are associated with Hirschsprung disease (HSCR; colon aganglionosis), a congenital defect of the enteric nervous system. We analyzed a well-known HSCR-associated RET haplotype that encompasses linked alleles in coding and noncoding/regulatory sequences. This risk haplotype correlates with reduced level of RET expression when compared with the wild-type counterpart. As allele-specific expression (ASE) contributes to phenotypic variability in health and disease, we investigated whether RET ASE could contribute to the overall reduction of RET mRNA detected in carriers. We tested heterozygous neuroblastoma cell lines, ganglionic gut tissues (18 HSCR and 14 non-HSCR individuals) and peripheral blood mononuclear cells (PBMCs; 16 HSCR and 14 non-HSCR individuals). Analysis of the data generated by SNaPshot and Pyrosequencing revealed that the RET risk haplotype is significantly more expressed in gut than in PBMCs (P = 0.0045). No ASE difference was detected between patients and controls, irrespective of the sample type. Comparison of total RET expression levels between gut samples with and without ASE, correlated reduced RET expression with preferential transcription from the RET risk haplotype. Nonrandom RET ASE occurs in ganglionic gut regardless of the disease status. RET ASE should not be excluded as a disease mechanism acting during development.

Common genetic variants regulating ADD3 gene expression alter biliary atresia risk.

BACKGROUND & AIMS: Biliary atresia (BA) is a rare and most severe cholestatic disease in neonates, but the pathogenic mechanisms are unknown. Through a previous genome wide association study (GWAS) on Han Chinese, we discovered association of the 10q24.2 region encompassing ADD3 and XPNPEP1 genes, which was replicated in Chinese and Thai populations. This study aims to fully characterize the genetic architecture at 10q24.2 and to reveal the link between the genetic variants and BA. METHODS: We genotyped 107 single nucleotide polymorphisms (SNPs) in 10q24.2 in 339 Han Chinese patients and 401 matched controls using Sequenom. Exhaustive follow-up studies of the association signals were performed. RESULTS: The combined BA-association p-value of the GWAS SNP (rs17095355) achieved 6.06×10(-10). Further, we revealed the common risk haplotype encompassing 5 tagging-SNPs, capturing the risk-predisposing alleles in 10q24.2 [p=5.32×10(-11); odds ratio, OR: 2.38; confidence interval, CI: (2.14-2.62)]. Through Sanger sequencing, no deleterious rare variants (RVs) residing in the risk haplotype were found, dismissing the theory of "synthetic" association. Moreover, in bioinformatics and in vivo genotype-expression investigations, the BA-associated potentially regulatory SNPs correlated with ADD3 gene expression (n=36; p=0.0030). Remarkably, the risk haplotype frequency coincides with BA incidences in the population, and, positive selection (favoring the derived alleles that arose from mutations) was evident at the ADD3 locus, suggesting a possible role for the BA-associated common variants in shaping the general population diversity. CONCLUSIONS: Common genetic variants in 10q24.2 can alter BA risk by regulating ADD3 expression levels in the liver, and may exert an effect on disease epidemiology and on the general population.

RET and NRG1 interplay in Hirschsprung disease.

Hirschsprung disease (HSCR, aganglionic megacolon) is a complex genetic disorder of the enteric nervous system (ENS) characterized by the absence of enteric neurons along a variable length of the intestine. While rare variants (RVs) in the coding sequence (CDS) of several genes involved in ENS development lead to disease, the association of common variants (CVs) with HSCR has only been reported for RET (the major HSCR gene) and NRG1. Importantly, RVs in the CDS of these two genes are also associated with the disorder. To assess independent and joint effects between the different types of RET and NRG1 variants identified in HSCR patients, we used 254 Chinese sporadic HSCR patients and 143 ethnically matched controls for whom the RET and/or NRG1 variants genotypes (rare and common) were available. Four genetic risk factors were defined and interaction effects were modeled using conditional logistic regression analyses and pair-wise Kendall correlations. Our analysis revealed a joint effect of RET CVs with RET RVs, NRG1 CVs or NRG1 RVs. To assess whether the genetic interaction translated into functional interaction, mouse neural crest cells (NCCs; enteric neuron precursors) isolated from embryonic guts were treated with NRG1 (ErbB2 ligand) or/and GDNF (Ret ligand) and monitored during the subsequent neural differentiation process. Nrg1 inhibited the Gdnf-induced neuronal differentiation and Gdnf negatively regulated Nrg1-signaling by down-regulating the expression of its receptor, ErbB2. This preliminary data suggest that the balance neurogenesis/gliogenesis is critical for ENS development.

Reduced RET expression in gut tissue of individuals carrying risk alleles of Hirschsprung's disease.

Receptor tyrosine kinase (RET) single nucleotide polymorphisms (SNPs) are associated with the Hirschsprung's disease (HSCR). We investigated whether the amount of RET expressed in the ganglionic gut of human was dependent on the genotype of three regulatory SNPs (-5G>A rs10900296 and -1A>C rs10900297 in the promoter, and C>T rs2435357 in intron 1). We examined the effects of three regulatory SNPs on the RET gene expression in 67 human ganglionic gut tissues using quantitative real-time PCR. Also, 315 Chinese HSCR patients and 325 ethnically matched controls were genotyped for the three SNPs by polymerase chain reaction (PCR) and direct sequencing. The expression of RET mRNA in human gut tissue did indeed correlate with the genotypes of the individuals. The lowest RET expression was found for those individuals homozygous for the three risk alleles (A-C-T/A-C-T), and the highest for those homozygous for the 'wild-type' counterpart (G-A-C/G-A-C), with expression values ranging from 218.32 +/- 125.69 (mean +/- SE) in tissues from individuals carrying G-A-C/G-A-C to 31.42 +/- 8.42 for individuals carrying A-C-T/A-C-T (P = 0.018). As expected, alleles -5A, -1C and intron 1 T were associated with HSCR (P = 5.94 x 10(-31), 3.12 x 10(-24) and 5.94 x 10(-37), respectively) as was the haplotype encompassing the three associated alleles (A-C-T) when compared with the wild-type counterpart G-A-C (chi2 = 155.29, P << 0.0001). To our knowledge, this is the first RET expression genotype-phenotype correlation study conducted on human subjects to indicate common genetic variants in the regulatory region of RET may play a role in mediating susceptibility to HSCR, by conferring a significant reduction of the RET expression.

Genome-wide association study identifies a susceptibility locus for biliary atresia on 10q24.2.

Biliary atresia (BA) is characterized by the progressive fibrosclerosing obliteration of the extrahepatic biliary system during the first few weeks of life. Despite early diagnosis and prompt surgical intervention, the disease progresses to cirrhosis in many patients. The current theory for the pathogenesis of BA proposes that during the perinatal period, a still unknown exogenous factor meets the innate immune system of a genetically predisposed individual and induces an uncontrollable and potentially self-limiting immune response, which becomes manifest in liver fibrosis and atresia of the extrahepatic bile ducts. Genetic factors that could account for the disease, let alone for its high incidence in Chinese, are to be investigated. To identify BA susceptibility loci, we carried out a genome-wide association study (GWAS) using the Affymetrix 5.0 and 500 K marker sets. We genotyped nearly 500 000 single-nucleotide polymorphisms (SNPs) in 200 Chinese BA patients and 481 ethnically matched control subjects. The 10 most BA-associated SNPs from the GWAS were genotyped in an independent set of 124 BA and 90 control subjects. The strongest overall association was found for rs17095355 on 10q24, downstream XPNPEP1, a gene involved in the metabolism of inflammatory mediators. Allelic chi-square test P-value for the meta-analysis of the GWAS and replication results was 6.94 x 10(-9). The identification of putative BA susceptibility loci not only opens new fields of investigation into the mechanisms underlying BA but may also provide new clues for the development of preventive and curative strategies.

Mutations in the NRG1 gene are associated with Hirschsprung disease.

Hirschsprung disease (HSCR, congenital colon aganglionosis) is a relatively common complex genetic condition caused by abnormal development of the enteric nervous system (ENS). Through a recent genome-wide association study conducted on Chinese HSCR patients, we identified a new HSCR contributing locus, neuregulin 1 (NRG1; 8p12), a gene known to be involved in the development of the ENS. As genes in which disease-associated common variants are found are to be considered as candidates for the search of deleterious rare variants (RVs) in the coding sequences, we sequenced the NRG1 exons of 358 sporadic HSCR patients and 333 controls. We identified a total of 13 different heterozygous RVs including 8 non-synonymous (A28G, E134K, V266L, H347Y, P356L, V486M, A511T, P608A) and 3 synonymous amino acid substitutions (P24P, T169T, L483L), a frameshift (E239fsX10), and a c.503-4insT insertion. Functional analysis of the most conserved non-synonymous substitutions, H347Y and P356L, showed uneven intracellular distribution and aberrant expression of the mutant proteins. Except for T169T and V486M, all variants were exclusive to HSCR patients. Overall, there was a statistically significant over-representation of NRG1 RVs in HSCR patients (p = 0.008). We show here that not only common, but also rare variants of the NRG1 gene contribute to HSCR. This strengthens the role of NRG1.

Functional analyses of RET mutations in Chinese Hirschsprung disease patients.

BACKGROUND: Hirschsprung disease (HSCR) is a congenital disease characterized by the absence of ganglion cells in various length of distal digestive tract. The rearranged during transfection gene (RET) is considered the major gene in HSCR. Although an increasing number of HSCR-associated RET coding sequence (CDS) mutations have been identified in recent years, not many have been investigated for functional consequence on the RET protein. METHODS AND RESULTS: We examined the functional implications of the de novo RET-CDS mutations V145G, Y483X, V636fsX1, and F961L that we first identified in sporadic Chinese patients with HSCR. The V145G disrupted RET glycosylation and F961L RET phosphorylation. Presumably, the truncation mutations would affect the translocation or the anchoring of the RET protein onto the cellular membrane. CONCLUSION: The study of RET-CDS mutations that appear de novo is essential not only for understanding the mechanistic of the disease but also for penetrance and recurrence risk estimations, being the ultimate goal for the improvement in disease management and counseling.

Genome-wide association study identifies NRG1 as a susceptibility locus for Hirschsprung's disease.

Hirschsprung's disease (HSCR), or aganglionic megacolon, is a congenital disorder characterized by the absence of enteric ganglia in variable portions of the distal intestine. RET is a well-established susceptibility locus, although existing evidence strongly suggests additional loci contributing to sporadic HSCR. To identify these additional genetic loci, we carried out a genome-wide association study using the Affymetrix 500K marker set. We successfully genotyped 293,836 SNPs in 181 Chinese subjects with sporadic HSCR and 346 ethnically matched control subjects. The SNPs most associated with HSCR were genotyped in an independent set of 190 HSCR and 510 control subjects. Aside from SNPs in RET, the strongest overall associations in plausible candidate genes were found for 2 SNPs located in intron 1 of the neuregulin1 gene (NRG1) on 8p12, with rs16879552 and rs7835688 yielding odds ratios of 1.68 [CI(95%):(1.40, 2.00), P = 1.80 x 10(-8)] and 1.98 [CI(95%):(1.59, 2.47), P = 1.12 x 10(-9)], respectively, for the heterozygous risk genotypes under an additive model. There was also a significant interaction between RET and NRG1 (P = 0.0095), increasing the odds ratio 2.3-fold to 19.53 for the RET rs2435357 risk genotype (TT) in the presence of the NRG1 rs7835688 heterozygote, indicating that NRG1 is a modifier of HSRC penetrance. Our highly significant association findings are backed-up by the important role of NRG1 as regulator of the development of the enteric ganglia precursors. The identification of NRG1 as an additional HSCR susceptibility locus not only opens unique fields of investigation into the mechanisms underlying the HSCR pathology, but also the mechanisms by which a discrete number of loci interact with each other to cause disease.

Identification of a wide spectrum of ciliary gene mutations in nonsyndromic biliary atresia patients implicates ciliary dysfunction as a novel disease mechanism.

BACKGROUND: Biliary atresia (BA) is the most common obstructive cholangiopathy in neonates, often progressing to end-stage cirrhosis. BA pathogenesis is believed to be multifactorial, but the genetic contribution, especially for nonsyndromic BA (common form: > 85%) remains poorly defined. METHODS: We conducted whole exome sequencing on 89 nonsyndromic BA trios to identify rare variants contributing to BA etiology. Functional evaluation using patients' liver biopsies, human cell and zebrafish models were performed. Clinical impact on respiratory system was assessed with clinical evaluation, nasal nitric oxide (nNO), high speed video analysis and transmission electron microscopy. FINDINGS: We detected rare, deleterious de novo or biallelic variants in liver-expressed ciliary genes in 31.5% (28/89) of the BA patients. Burden test revealed 2.6-fold (odds ratio (OR) [95% confidence intervals (CI)]= 2.58 [1.15-6.07], adjusted p = 0.034) over-representation of rare, deleterious mutations in liver-expressed ciliary gene set in patients compared to controls. Functional analyses further demonstrated absence of cilia in the BA livers with KIF3B and TTC17 mutations, and knockdown of PCNT, KIF3B and TTC17 in human control fibroblasts and cholangiocytes resulted in reduced number of cilia. Additionally, CRISPR/Cas9-engineered zebrafish knockouts of KIF3B, PCNT and TTC17 displayed reduced biliary flow. Abnormally low level of nNO was detected in 80% (8/10) of BA patients carrying deleterious ciliary mutations, implicating the intrinsic ciliary defects. INTERPRETATION: Our findings support strong genetic susceptibility for nonsyndromic BA. Ciliary gene mutations leading to cholangiocyte cilia malformation and dysfunction could be a key biological mechanism in BA pathogenesis. FUNDING: The study is supported by General Research Fund, HMRF Commissioned Paediatric Research at HKCH and Li Ka Shing Faculty of Medicine Enhanced New Staff Start-up Fund.

A random forest-based framework for genotyping and accuracy assessment of copy number variations.

Detection of copy number variations (CNVs) is essential for uncovering genetic factors underlying human diseases. However, CNV detection by current methods is prone to error, and precisely identifying CNVs from paired-end whole genome sequencing (WGS) data is still challenging. Here, we present a framework, CNV-JACG, for Judging the Accuracy of CNVs and Genotyping using paired-end WGS data. CNV-JACG is based on a random forest model trained on 21 distinctive features characterizing the CNV region and its breakpoints. Using the data from the 1000 Genomes Project, Genome in a Bottle Consortium, the Human Genome Structural Variation Consortium and in-house technical replicates, we show that CNV-JACG has superior sensitivity over the latest genotyping method, SV2, particularly for the small CNVs (≤1 kb). We also demonstrate that CNV-JACG outperforms SV2 in terms of Mendelian inconsistency in trios and concordance between technical replicates. Our study suggests that CNV-JACG would be a useful tool in assessing the accuracy of CNVs to meet the ever-growing needs for uncovering the missing heritability linked to CNVs.

Cancer gene mutations in congenital pulmonary airway malformation patients.

BACKGROUND: Newborns affected with congenital pulmonary airway malformations (CPAMs) may present with severe respiratory distress or remain asymptomatic. While surgical resection is the definitive treatment for symptomatic CPAMs, prophylactic elective surgery may be recommended for asymptomatic CPAMs owing to the risk of tumour development. However, the implementation of prophylactic surgery is quite controversial on the grounds that more evidence linking CPAMs and cancer is needed. The large gap in knowledge of CPAM pathogenesis results in uncertainties and controversies in disease management. As developmental genes control postnatal cell growth and contribute to cancer development, we hypothesised that CPAMs may be underlain by germline mutations in genes governing airways development. METHODS: Sequencing of the exome of 19 patients and their unaffected parents. RESULTS: A more than expected number of mutations in cancer genes (false discovery rate q-value <5.01×10-5) was observed. The co-occurrence, in the same patient, of damaging variants in genes encoding interacting proteins is intriguing, the most striking being thyroglobulin (TG) and its receptor, megalin (LRP2). Both genes are highly relevant in lung development and cancer. CONCLUSIONS: The overall excess of mutations in cancer genes may account for the reported association of CPAMs with carcinomas and provide some evidence to argue for prophylactic surgery by some surgeons.

Mapping of a Hirschsprung's disease locus in 3p21.

Hirschsprung's disease (HSCR) is a congenital disorder in which ganglion cells are absent in variable portions of the lower digestive tract according to which patients are classified. The RET gene is the major HSCR gene, although reduced penetrance of RET mutations and variable expression of HSCR phenotype indicates that more than one gene is required. An unidentified RET-dependent modifier on 3p21 appears to be necessary for transmission of the short HSCR (S-HSCR) phenotype. We investigated 6 Mb of the 3p21 region on a quest for the HSCR-susceptibility locus. Fifty-eight S-HSCR case-parent trios were genotyped using Sequenom technology for 214 tag single nucleotide polymorphisms (SNPs) distributed along 6 Mb of the 3p21 region. A five-marker haplotype, spanning a 118 kb gene-rich region, was found to be overtransmitted to affected offspring. The associated haplotype encompasses three genes involved in neurological phenotypes. Importantly, this association was replicated in an independent sample of 172 S-HSCR cases and 153 unrelated controls. Ranking markers by proximity to candidate genes or by expected functional consequences could be used in follow-up studies to finally pinpoint this HSCR locus.

Identification of a HOXD13 mutation in a VACTERL patient.

VACTERL acronym is assigned to a non-random association of malformations in humans with poorly known etiology. It is comprised of vertebral defects (V), anal atresia (A), cardiac anomaly (C), tracheoesophageal fistula with esophageal atresia (TE), renal dysplasia (R) and limb lesions (L). Here, we report on, for the first time, a female patient with VACTERL association with a 21 base-pair deletion in the exon 1 triplet repeats of HOXD13, a sonic hedgehog (SHH) downstream target. Our data provide the first piece of clinical evidence of the implication of the SHH pathway in VACTERL. Moreover, HOXD13 may not only be implicated in limb malformations but also in the development of gut and genitourinary structures, as predicted from the mouse models.