RET and NRG1 interplay in Hirschsprung disease

The interplay of common genetic variants NRG1 rs2439302 and RET rs2435357 increases the risk of developing Hirschsprung's disease

Introduction: As a congenital and genetically related disease, many single nucleotide polymorphisms (SNPs) have been reported to be associated with the risk of HSCR. Our previous research showed that SNP rs2439302 (NRG1) interacted with rs2435357 (RET) to increase the risk of HSCR development. However, the underlying molecular mechanism is still not well understood. Methods: SNP rs2439302 (NRG1) and rs2435357 (RET) were genotyped in 470 HSCR cases. The expression of NRG1 and RET was investigated in the colon of HSCR patients. Knockdown of the NRG1 and RET homologs was performed in zebrafish to investigate their synergistic effect on ENS development. The effect of SNP rs2439302 and rs2435357 polymorphism on neuron proliferation, migration, and differentiation were investigated in SHSY-5Y cells and IPSCs. Results: Significant downregulation of NRG1 and RET expression was noticed in the aganglionic segment of HSCR patients and SHSY-5Y cells with rs2439302 GG/rs2435357 TT genotype. NRG1 and RET double mutants caused the most severe reduction in enteric neuron numbers than NRG1 single mutant or RET single mutant in the hindgut of zebrafish. SHSY-5Y cells and IPSCs with rs2439302 GG/rs2435357 TT genotype exhibited a decreased proliferative, migration, and differentiative capacity. CTCF showed a considerably higher binding ability to SNP rs2439302 CC than GG. NRG1 reduction caused a further decrease in SOX10 expression via the PI3K/Akt pathway, which regulates RET expression by directly binding to rs2435357. Discussion: SNP rs2439302 (NRG1) GG increases the risk of developing HSCR by affecting the binding of transcription factor CTCF and interacting with rs2435357 (RET) to regulate RET expression via the PI3K/Akt/SOX10 pathway.

Whole genome sequencing reveals epistasis effects within RET for Hirschsprung disease

Common variants in RET and NRG1 have been associated with Hirschsprung disease (HSCR), a congenital disorder characterised by incomplete innervation of distal gut, in East Asian (EA) populations. However, the allelic effects so far identified do not fully explain its heritability, suggesting the presence of epistasis, where effect of one genetic variant differs depending on other (modifier) variants. Few instances of epistasis have been documented in complex diseases due to modelling complexity and data challenges. We proposed four epistasis models to comprehensively capture epistasis for HSCR between and within RET and NRG1 loci using whole genome sequencing (WGS) data in EA samples. 65 variants within the Topologically Associating Domain (TAD) of RET demonstrated significant epistasis with the lead enhancer variant (RET+3; rs2435357). These epistatic variants formed two linkage disequilibrium (LD) clusters represented by rs2506026 and rs2506028 that differed in minor allele frequency and the best-supported epistatic model. Intriguingly, rs2506028 is in high LD with one cis-regulatory variant (rs2506030) highlighted previously, suggesting that detected epistasis might be mediated through synergistic effects on transcription regulation of RET. Our findings demonstrated the advantages of WGS data for detecting epistasis, and support the presence of interactive effects of regulatory variants in RET for HSCR.

miR-938 rs2505901 T>C polymorphism increases Hirschsprung disease risk: a case-control study of Chinese children

Aim: To explore the association between miR-938 rs2505901 T>C polymorphism and Hirschsprung disease (HSCR) risk in Chinese children. Materials & Methods: We conducted a case-control study in a Chinese population with 1381 cases and 1457 controls. The associated correlation strengths were assessed by adjusted odds ratios (AORs) and 95% CIs. Results: The results revealed that the rs2505901 TC and rs2505901 TC/CC genotype were related to an increased HSCR risk compared to the risk contributed by the rs2505901 TT genotype. A stratification analysis showed that the rs2505901 TC/CC genotype promoted the progression of HSCR more significantly in patients with the short-segment HSCR subtype. Conclusion: Our study indicated that miR-938 rs2505901 T>C polymorphism is significantly associated with HSCR risk in Chinese children. This result needs to be confirmed with well-designed studies.

Roles of Enteric Neural Stem Cell Niche and Enteric Nervous System Development in Hirschsprung Disease

The development of the enteric nervous system (ENS) is highly modulated by the synchronized interaction between the enteric neural crest cells (ENCCs) and the neural stem cell niche comprising the gut microenvironment. Genetic defects dysregulating the cellular behaviour(s) of the ENCCs result in incomplete innervation and hence ENS dysfunction. Hirschsprung disease (HSCR) is a rare complex neurocristopathy in which the enteric neural crest-derived cells fail to colonize the distal colon. In addition to ENS defects, increasing evidence suggests that HSCR patients may have intrinsic defects in the niche impairing the extracellular matrix (ECM)-cell interaction and/or dysregulating the cellular niche factors necessary for controlling stem cell behaviour. The niche defects in patients may compromise the regenerative capacity of the stem cell-based therapy and advocate for drug- and niche-based therapies as complementary therapeutic strategies to alleviate/enhance niche-cell interaction. Here, we provide a summary of the current understandings of the role of the enteric neural stem cell niche in modulating the development of the ENS and in the pathogenesis of HSCR. Deciphering the contribution of the niche to HSCR may provide important implications to the development of regenerative medicine for HSCR.

Size matters: Large copy number losses in Hirschsprung disease patients reveal genes involved in enteric nervous system development

Hirschsprung disease (HSCR) is a complex genetic disease characterized by absence of ganglia in the intestine. HSCR etiology can be explained by a unique combination of genetic alterations: rare coding variants, predisposing haplotypes and Copy Number Variation (CNV). Approximately 18% of patients have additional anatomical malformations or neurological symptoms (HSCR-AAM). Pinpointing the responsible culprits within a CNV is challenging as often many genes are affected. Therefore, we selected candidate genes based on gene enrichment strategies using mouse enteric nervous system transcriptomes and constraint metrics. Next, we used a zebrafish model to investigate whether loss of these genes affects enteric neuron development in vivo.

This study included three groups of patients, two groups without coding variants in disease associated genes: HSCR-AAM and HSCR patients without associated anomalies (HSCR-isolated). The third group consisted of all HSCR patients in which a confirmed pathogenic rare coding variant was identified. We compared these patient groups to unaffected controls. Predisposing haplotypes were determined, confirming that every HSCR subgroup had increased contributions of predisposing haplotypes, but their contribution was highest in isolated HSCR patients without RET coding variants. CNV profiling proved that specifically HSCR-AAM patients had larger Copy Number (CN) losses. Gene enrichment strategies using mouse enteric nervous system transcriptomes and constraint metrics were used to determine plausible candidate genes located within CN losses. Validation in zebrafish using CRISPR/Cas9 targeting confirmed the contribution of UFD1L, TBX2, SLC8A1, and MAPK8 to ENS development. In addition, we revealed epistasis between reduced Ret and Gnl1 expression and between reduced Ret and Tubb5 expression in vivo. Rare large CN losses—often de novo—contribute to HSCR in HSCR-AAM patients. We proved the involvement of six genes in enteric nervous system development and Hirschsprung disease.

Hirschsprung disease is a congenital disorder characterized by the absence of intestinal neurons in the distal part of the intestine. It is a complex genetic disorder in which multiple variations in our genome combined, result in disease. One of these variations are Copy Number Variations (CNVs): large segments of our genome that are duplicated or deleted. Patients often have Hirschsprung disease without other symptoms. However, a proportion of patients has additional associated anatomical malformations and neurological symptoms. We found that CNVs, present in patients with associated anomalies, are more often larger compared to unaffected controls or Hirschsprung patients without other symptoms. Furthermore, Copy Number (CN) losses are enriched for constrained coding regions (CCR; genes usually not impacted by genomic alterations in unaffected controls) of which the expression is higher in the developing intestinal neurons compared to the intestine. We modelled loss of these candidate genes in zebrafish by disrupting the zebrafish orthologues by genome editing. For several genes this resulted in changes in intestinal neuron development, reminiscent of HSCR observed in patients. The results presented here highlight the importance of Copy Number profiling, zebrafish validation and evaluating all CCR expressed in developing intestinal neurons during diagnostic evaluation.

The Emerging Genetic Landscape of Hirschsprung Disease and Its Potential Clinical Applications

Hirschsprung disease (HSCR) is the leading cause of neonatal functional intestinal obstruction. It is a rare congenital disease with an incidence of one in 3,500-5,000 live births. HSCR is characterized by the absence of enteric ganglia in the distal colon, plausibly due to genetic defects perturbing the normal migration, proliferation, differentiation, and/or survival of the enteric neural crest cells as well as impaired interaction with the enteric progenitor cell niche. Early linkage analyses in Mendelian and syndromic forms of HSCR uncovered variants with large effects in major HSCR genes including RET, EDNRB, and their interacting partners in the same biological pathways. With the advances in genome-wide genotyping and next-generation sequencing technologies, there has been a remarkable progress in understanding of the genetic basis of HSCR in the past few years, with common and rare variants with small to moderate effects being uncovered. The discovery of new HSCR genes such as neuregulin and BACE2 as well as the deeper understanding of the roles and mechanisms of known HSCR genes provided solid evidence that many HSCR cases are in the form of complex polygenic/oligogenic disorder where rare variants act in the sensitized background of HSCR-associated common variants. This review summarizes the roadmap of genetic discoveries of HSCR from the earlier family-based linkage analyses to the recent population-based genome-wide analyses coupled with functional genomics, and how these discoveries facilitated our understanding of the genetic architecture of this complex disease and provide the foundation of clinical translation for precision and stratified medicine.

Literature review: enteric nervous system development, genetic and epigenetic regulation in the etiology of Hirschsprung's disease

Hirschsprung's disease (HSCR) is a developmental disorder of the enteric nervous system (ENS) derived from neural crest cells (NCCs), which affects their migration, proliferation, differentiation, or preservation in the digestive tract, resulting in aganglionosis in the distal intestine. The regulation of both NCCs and the surrounding environment involves various genes, signaling pathways, transcription factors, and morphogens. Therefore, changes in gene expression during the development of the ENS may contribute to the pathogenesis of HSCR.

This review discusses several mechanisms involved in the development of ENS, confirming that deviant genetic and epigenetic patterns, such as DNA methylation, histone modification, and microRNA (miRNA) regulation, can contribute to the development of neurocristopathy. Specifically, the epigenetic regulation of miRNA expression and its relationship to cellular interactions and gene activation through various major pathways in Hirschsprung's disease will be discussed.

Dysregulation of the NRG1/ERBB pathway causes a developmental disorder with gastrointestinal dysmotility in humans

Hirschsprung disease (HSCR) is the most frequent developmental anomaly of the enteric nervous system, with an incidence of 1 in 5000 live births. Chronic intestinal pseudo-obstruction (CIPO) is less frequent and classified as neurogenic or myogenic. Isolated HSCR has an oligogenic inheritance with RET as the major disease-causing gene, while CIPO is genetically heterogeneous, caused by mutations in smooth muscle-specific genes. Here, we describe a series of patients with developmental disorders including gastrointestinal dysmotility, and investigate the underlying molecular bases. Trio-exome sequencing led to the identification of biallelic variants in ERBB3 and ERBB2 in 8 individuals variably associating HSCR, CIPO, peripheral neuropathy, and arthrogryposis. Thorough gut histology revealed aganglionosis, hypoganglionosis, and intestinal smooth muscle abnormalities. The cell type-specific ErbB3 and ErbB2 function was further analyzed in mouse single-cell RNA sequencing data and in a conditional ErbB3-deficient mouse model, revealing a primary role for ERBB3 in enteric progenitors. The consequences of the identified variants were evaluated using quantitative real-time PCR (RT-qPCR) on patient-derived fibroblasts or immunoblot assays on Neuro-2a cells overexpressing WT or mutant proteins, revealing either decreased expression or altered phosphorylation of the mutant receptors. Our results demonstrate that dysregulation of ERBB3 or ERBB2 leads to a broad spectrum of developmental anomalies, including intestinal dysmotility.

Correlation analysis of IL-11 polymorphisms and Hirschsprung disease subtype susceptibility in Southern Chinese Children

BACKGROUND

Hirschsprung disease (HSCR) is a hereditary defect, which is characterized by the absence of enteric ganglia and is frequently concurrent with Hirschsprung-associated enterocolitis (HAEC). However, the pathogenesis for HSCR is complicated and remains unclear. Recent studies have shown that pro-inflammatory cytokines such as interleukin-11 (IL-11) are involved in the enteric nervous system's progress. It was found that IL-11 SNPs (rs8104023 and rs4252546) are associated with HSCR in the Korean population waiting for replication in an independent cohort. This study evaluated the relationship between IL-11 and the susceptibility of patients to HSCR by performing subphenotype interaction examination, HAEC pre-/post-surgical patient-only association analysis, and independence testing.

METHODS

In this study, a cohort consisting of children from Southern China, comprising 1470 cases and 1473 controls, was chosen to examine the relationship between two polymorphisms (rs8104023 and rs4252546 in IL-11) and susceptibility to HSCR by replication research, subphenotype association analysis, and independence testing.

RESULTS

The results showed that IL-11 gene polymorphisms (rs8104023 and rs4252546) are not associated with the risk of HSCR in the Chinese population. The results of both short-segment and long-segment (S-HSCR and L-HSCR) surgery (3.34 ≤ OR ≤ 4.05, 0.02 ≤ P ≤ 0.04) showed that single nucleotide polymorphisms (SNP) rs8104023 is associated with susceptibility to HAEC.

CONCLUSIONS

This study explored the relationship between genetic polymorphisms and susceptibility to HAEC in HSCR subtypes for the first time. These findings should be replicated in a larger and multicentre study.

Common variants of NRG1 and ITGB4 confer risk of Hirschsprung disease in Han Chinese population

BACKGROUND

Hirschsprung disease (HSCR) is a neurodevelopmental disorder with a strong genetic component. Common variants of NRG1 contributed to HSCR risk in Asians, and rare variants of ERBB2 and ITGB4 were found to be associated with HSCR. ERBB2 and ITGB4 are partners of Nrg1/ErbB pathway, which is important in HSCR pathogenesis. We aimed to investigate whether common variants in NRG1, ERBB2 and ITGB4 were associated with HSCR in Chinese Han population.

METHODS

We genotype 17 single nucleotide polymorphisms (SNPs) of NRG1, ERBB2 and ITGB4 in 420 HSCR patients and 1665 controls, and performed association analysis.

RESULTS

We validated associations of two NRG1 SNPs rs7835688 (P_Allelic = 2.2 × 10^-20, OR = 2.21, 95%CI = 1.86-2.62) and rs16879552 (P_Allelic = 5.6 × 10^-9, OR = 1.57, 95%CI = 1.35-1.83) with risk to HSCR. SNP rs3744000 located 5' upstream of ITGB4 showed association with HSCR (P_Allelic = 2.4 × 10^-3, OR = 1.27, 95%CI = 1.09-1.49). Four SNPs of ERBB2 exhibited no association.

CONCLUSIONS

Our results suggested that common variation of ITGB4 and NRG1 conferred risk to HSCR in Chinese Han population, which further highlighted Nrg-1/ErbB pathway involving in the pathogenesis of HSCR.

The Endocrine Disruptor Bisphenol A (BPA) Affects the Enteric Neurons Immunoreactive to Neuregulin 1 (NRG1) in the Enteric Nervous System of the Porcine Large Intestine

The enteric nervous system (ENS), located in the wall of the gastrointestinal (GI) tract, is characterized by complex organization and a high degree of neurochemical diversity of neurons. One of the less known active neuronal substances found in the enteric neurons is neuregulin 1 (NRG1), a factor known to be involved in the assurance of normal development of the nervous system. During the study, made up using the double immunofluorescence technique, the presence of NRG1 in the ENS of the selected segment of porcine large intestine (caecum, ascending and descending colon) was observed in physiological conditions, as well as under the impact of low and high doses of bisphenol A (BPA) which is commonly used in the production of plastics. In control animals in all types of the enteric plexuses, the percentage of NRG1-positive neurons oscillated around 20% of all neurons. The administration of BPA caused an increase in the number of NRG1-positive neurons in all types of the enteric plexuses and in all segments of the large intestine studied. The most visible changes were noted in the inner submucous plexus of the ascending colon, where in animals treated with high doses of BPA, the percentage of NRG1-positive neurons amounted to above 45% of all neuronal cells. The mechanisms of observed changes are not entirely clear, but probably result from neurotoxic, neurodegenerative and/or proinflammatory activity of BPA and are protective and adaptive in nature.

Significant Association of rs2147555 Genetic Polymorphism in the EDNRB Gene with Hirschsprung Disease in Southern Chinese Children

Hirschsprung disease (HSCR) is a human birth defect at the clinical setting, usually characterized by an absent enteric nervous system (ENS) from the distal bowel. The majority of HSCR cases represent a complex disorder resulting from the interaction of multiple genetic and environmental factors. Genetic events have been described to be involved in the abnormal development of the enteric nervous system. Although variants in several genes like RET and EDNRB have been suggested to contribute major risks to HSCR, very little is known about their involvement in the onset of HSCR. Here, we studied a large Chinese Han cohort consisting of 1,470 HSCR patients and 1,473 non-HSCR controls to further test whether there are more variants in EDNRB associated with HSCR. Our results provided the first evidence that rs2147555 in EDNRB confers a significant risk of HSCR in a Chinese Han population for both allelic frequencies (P = 4.16 × 10⁻³; OR = 1.29) and genotypic frequencies assuming either a dominant or recessive model (P = 0.011 and P = 0.027, respectively). When different subtypes of HSCR cases were analyzed, the association remained significant (OR = 1.33, P = 0.003 for short-segment HSCR; OR = 1.34, P = 0.044 for long segment HSCR).

Negative Association Between lncRNA HOTTIP rs3807598 C>G and Hirschsprung Disease

Background

Hirschsprung disease (HSCR) is a congenital disease that arises from defective intestinal neural system. LncRNA HOTTIP is a critical gene in various diseases, including HSCR. No epidemiological studies have explored the correlation between lncRNA HOTTIP single nucleotide polymorphisms (SNPs) and HSCR risk. We here lead as a pioneer to explore whether SNPs in lncRNA HOTTIP impact the risk of HSCR and HSCR subtypes in an unrelated Chinese population.

Methods

We used the TaqMan method to genotype rs3807598 C>G of the lncRNA HOTTIP gene using 1470 HSCR cases and 1473 healthy controls. Of them, 1441 cases and 1434 controls were successfully genotyped. We adopted odds ratios (ORs) and 95% confidence intervals (CIs) to quantify the relationship.

Results

We got an unexpected outcome that lncRNA HOTTIP SNP rs3807598 C>G could not modify the risk of HSCR (CG vs. CC: adjusted OR=0.89, 95% CI=0.74–1.07; GG vs. CC: adjusted OR=1.10, 95% CI=0.89–1.37; GG/CG vs CC: adjusted OR=0.95, 95% CI=0.80–1.13; and GG vs. CC/CG: adjusted OR=1.19, 95% CI=0.99–1.43). What’s more, risk effect of lncRNA HOTTIP rs3807598 C>G is still not obvious in stratification analysis by HSCR subtype.

Conclusion

Our studies did not provide statistical evidence of a correlation between lncRNA HOTTIP SNP rs3807598 C>G and susceptibility of HSCR in the Chinese population that is being studied. Further validation study with a larger sample size covering multi-ethnic groups is warranted.

Impaired Expression of Neuregulin 1 and Nicotinic Acetylcholine Receptor β4 Subunit in Diverticular Disease

Neuregulin 1 (NRG1) regulates the expression of the nicotinic acetylcholine receptor (nAChR) and is suggested to promote the survival and maintenance of the enteric nervous system (ENS), since deficiency of its corresponding receptor complex ErbB2/ErbB3 leads to postnatal colonic aganglionosis. As diverticular disease (DD) is associated with intestinal hypoganglionosis, the NRG1-ErbB2/ErbB3 system and the nAChR were studied in patients with DD and controls. Samples of tunica muscularis of the sigmoid colon from patients with DD (n = 8) and controls (n = 11) were assessed for mRNA expression of NRG1, ErbB2, and ErbB3 and the nAChR subunits α3, α5, α7, β2, and β4. Site-specific gene expression levels of the NRG1-ErbB2/3 system were determined in myenteric ganglia harvested by laser microdissection (LMD). Localization studies were performed by immunohistochemistry for the NRG1-ErbB2/3 system and nAChR subunit β4. Rat enteric nerve cell cultures were stimulated with NRG1 or glial-cell line derived neurotrophic factor (GDNF) for 6 days and mRNA expression of the aforementioned nAchR was measured. NRG1, ErbB3, and nAChR subunit β4 expression was significantly down-regulated in both the tunica muscularis and myenteric ganglia of patients with DD compared to controls, whereas mRNA expression of ErbB3 and nAChR subunits β2, α3, α5, and α7 remained unaltered. NRG1, ErbB3, and nAChR subunit β4 immunoreactive signals were reduced in neuronal somata and the neuropil of myenteric ganglia from patients with DD compared to control. nAChR subunit β4 exhibited also weaker immunoreactive signals in the tunica muscularis of patients with DD. NRG1 treatment but not GDNF treatment of enteric nerve cell cultures significantly enhanced mRNA expression of nAchR β4. The down-regulation of NRG1 and ErbB3 in myenteric ganglia of patients with DD supports the hypothesis that intestinal hypoganglionosis observed in DD may be attributed to a lack of neurotrophic factors. Regulation of nAChR subunit β4 by NRG1 and decreased nAChR β4 in patients with DD provide evidence that a lack of NRG1 may affect the composition of enteric neurotransmitter receptor subunits thus contributing to the intestinal motility disorders previously reported in DD.

Aberrant expressions of miRNA-206 target, FN1, in multifactorial Hirschsprung disease

Background

MicroRNAs (miRNAs) have been associated with the Hirschsprung disease (HSCR) pathogenesis, however, the findings are still inconclusive. We aimed to investigate the effect of miRNA-206 and its targets, fibronectin 1 (FN1), serum deprivation response (SDPR), and paired box 3 (PAX3) expressions on multifactorial HSCR in Indonesia, a genetically distinct group within Asia.

Methods

We determined the miRNA-206, FN1, SDPR and PAX3 expressions in both the ganglionic and aganglionic colon of HSCR patients and control colon by quantitative real-time polymerase chain reaction (qRT-PCR).

Results

Twenty-one sporadic HSCR patients and thirteen controls were ascertained in this study. The miRNA-206 expression was up-regulated (2-fold) in the ganglionic colon and down-regulated (0.5-fold) in the aganglionic colon compared to the control group (ΔC_T 12.4 ± 3.0 vs. 14.1 ± 3.9 vs. 13.1 ± 2.7), but these differences did not reach significant levels (p = 0.48 and p = 0.46, respectively). Interestingly, the FN1 expression was significantly increased in both the ganglionic (38-fold) and aganglionic colon (18-fold) groups compared to the control group ΔC_T 5.7 ± 3.0 vs. 6.8 ± 2.3 vs. 11.0 ± 5.0; p = 0.001 and p = 0.038, respectively). Furthermore, the expressions of SDPR were similar in the ganglionic, aganglionic and control colon groups (ΔC_T 2.4 ± 0.6 vs. 2.2 ± 0.4 vs. 2.1 ± 0.6; p = 0.16 and p = 0.39, respectively), while no change was observed in the PAX3 expression between the ganglionic, aganglionic, and control colon groups (ΔC_T 3.8 ± 0.8 vs. 4.1 ± 0.8 vs. 3.7 ± 1.1; p = 0.83 and p = 0.44, respectively).

Conclusion

Our study is the first report of aberrant FN1 expressions in the colon of patients with HSCR and supplies further insights into the contribution of aberrant FN1 expression in the HSCR pathogenesis.

The Influence of Bisphenol A (BPA) on Neuregulin 1-Like Immunoreactive Nerve Fibers in the Wall of Porcine Uterus

Bisphenol A (BPA), a substance commonly used in the manufacture of plastics, shows multidirectional negative effects on humans and animals. Due to similarities to estrogens, BPA initially leads to disorders in the reproductive system. On the other hand, it is known that neuregulin 1 (NRG-1) is an active substance which enhances the survivability of cells, inhibits apoptosis, and protects tissues against damaging factors. Because the influence of BPA on the nervous system has also been described, the aim of the present study was to investigate for the first time the influence of various doses of BPA on neuregulin 1-like immunoreactive (NRG-1-LI) nerves located in the porcine uterus using the routine single- and double-immunofluorescence technique. The obtained results have shown that BPA increases the number and affects the neurochemical characterization of NRG-1-LI in the uterus, and changes are visible even under the impact of small doses of this toxin. The character of observed changes depended on the dose of BPA and the part of the uterus studied. These observations suggest that NRG-1 in nerves supplying the uterus may play roles in adaptive and protective mechanisms under the impact of BPA.

NRG1 variant effects in patients with Hirschsprung disease

Background

Hirschsprung disease (HSCR) is a heterogeneous genetic disorder characterized by absence of ganglion cells along the intestines resulting in functional bowel obstruction. Mutations in neuregulin 1 (NRG1) gene have been implicated in some cases of intestinal aganglionosis. This study aims to investigate the contribution of the NRG1 gene to HSCR development in an Indonesian population.

Methods

We analyzed the entire coding region of the NRG1 gene in 54 histopathologically diagnosed HSCR patients.

Results

All patients were sporadic non-syndromic HSCR with 53/54 (98%) short-segment and 1/54 (2%) long-segment patients. NRG1 gene analysis identified one rare variant, c.397G > C (p.V133 L), and three common variants, rs7834206, rs3735774, and rs75155858. The p.V133 L variant was predicted to reside within a region of high mammalian conservation, overlapping with the promoter and enhancer histone marks of relevant tissues such as digestive and smooth muscle tissues and potentially altering the AP-4_2, BDP1_disc3, Egr-1_known1, Egr-1_known4, HEN1_2 transcription factor binding motifs. This p.V133 L variant was absent in 92 non-HSCR controls. Furthermore, the rs7834206 polymorphism was associated with HSCR by case–control analysis (p = 0.037).

Conclusions

This study is the first report of a NRG1 rare variant associated with HSCR patients of South-East Asian ancestry and provides further insights into the contribution of NRG1 in the molecular genetic pathogenesis of HSCR.

Electronic supplementary material

The online version of this article (10.1186/s12887-018-1265-x) contains supplementary material, which is available to authorized users.

Combined Genetic Effects of RET and NRG1 Susceptibility Variants on Multifactorial Hirschsprung Disease in Indonesia

BACKGROUND

Specific genetic variants at RET (rs2435357) and NRG1 (rs7835688, rs16879552) are associated with Hirschsprung disease (HSCR) in Indonesia. This study aimed to investigate the additional effect of RET rs2506030 on these variants to determine its potential interactions in HSCR patients of Indonesian ancestry.

METHODS

Sixty HSCR patients and 122 non-HSCR controls were ascertained for this study and genotyped for RET rs2506030 using the TaqMan assay.

RESULTS

RET rs2506030 was associated with HSCR both by case-control analysis (odds ratio = 1.68; P = 0.043) and the transmission disequilibrium test (P = 0.034). Furthermore, individuals with five or six risk alleles at RET rs2506030, rs2435357 and NRG1 rs7835688 showed ∼45-fold higher HSCR risk than those with 0 or 1 or 2 risk alleles.

CONCLUSIONS

Disease risk of HSCR is increased by the combination of specific RET and NRG1 susceptibility variants.

Migration and diversification of the vagal neural crest

Arising within the neural tube between the cranial and trunk regions of the body axis, the vagal neural crest shares interesting similarities in its migratory routes and derivatives with other neural crest populations. However, the vagal neural crest is also unique in its ability to contribute to diverse organs including the heart and enteric nervous system. This review highlights the migratory routes of the vagal neural crest and compares them across multiple vertebrates. We also summarize recent advances in understanding vagal neural crest ontogeny and discuss the contribution of this important neural crest population to the cardiovascular system and endoderm-derived organs, including the thymus, lungs and pancreas.

Association of NRG1 and AUTS2 genetic polymorphisms with Hirschsprung disease in a South Chinese population

Hirschsprung disease (HSCR) is a genetic disorder characterized by the absence of enteric ganglia. There are more than 15 genes identified as contributed to HSCR by family-based or population-based approaches. However, these findings were not fulfilled to explain the heritability of most sporadic cases. In this study, using 1470 HSCR and 1473 control subjects in South Chinese population, we replicated two variants in NRG1 (rs16879552, P = 1.05E-04 and rs7835688, P = 1.19E-07), and further clarified the two replicated SNPs were more essential for patients with short-segment aganglionosis (SHSCR) (P = 2.37E-05). We also tried to replicate the most prominent signal (rs7785360) in AUTS2, which was a potential susceptibility gene with HSCR. In our results, in terms of individual association, marginal effect was observed to affect the HSCR patients following recessive model (P = 0.089). Noteworthy, significant intergenic synergistic effect between rs16879552 (NRG1) and rs7785360 (AUTS2) was identified through cross-validation by logistic regression (P = 2.45E-03, OR = 1.53) and multifactor dimensionality reduction (MDR, P < 0.0001, OR = 1.77). Significant correlation was observed between expression of these two genes in the normal segments of the colons (P = 0.018), together with differential expression of these genes between aganglionic colonic segments and normal colonic segments of the HSCR patients (P value for AUTS2 <0.0001, P value for NRG1 = 0.0243). Although functional evaluation is required, we supply new evidence for the NRG1 to HSCR and raised up a new susceptibility gene AUTS2 to a specific symptom for the disease.

Testing the Ret and Sema3d genetic interaction in mouse enteric nervous system development

For most multigenic disorders, clinical manifestation (penetrance) and presentation (expressivity) are likely to be an outcome of genetic interaction between multiple susceptibility genes. Here, using gene knockouts in mice, we evaluated genetic interaction between loss of Ret and loss of Sema3d, two Hirschsprung disease susceptibility genes. We intercrossed Ret and Sema3d double null heterozygotes to generate mice with the nine possible genotypes and assessed survival by counting various genotypes, myenteric plexus presence by acetylcholinesterase staining and embryonic day 12.5 (E12.5) intestine transcriptome by RNA-sequencing. Survival rates of Ret wild-type, null heterozygote and null homozygote mice at E12.5, birth and weaning were not influenced by the genotypes at Sema3d locus and vice versa. Loss of myenteric plexus was observed only in all Ret null homozygotes, irrespective of the genotypes at Sema3d locus, and Sema3d null heterozygote and homozygote mice had normal intestinal innervation. As compared with wild-type mice intestinal gene expression, loss of Ret in null homozygotes led to differential expression of ∼300 genes, whereas loss of Sema3d in null homozygotes had no major consequence and there was no evidence supporting major interaction between the two genes influencing intestine transcriptome. Overall, given the null alleles and phenotypic assays used, we did not find evidence for genetic interaction between Ret and Sema3d affecting survival, presence of myenteric plexus or intestine transcriptome.

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.

Neuregulin 1 is involved in enteric nervous system development in zebrafish

BACKGROUND

Hirschsprung's disease (HD, also known as congenital colon aganglionosis) is a congenital disorder characterized by the absence of intramural ganglion cells in the distal gastrointestinal tract, which results in tonic contraction of the aganglionic gut segment and functional intestinal obstruction. Recent studies have indicated neuregulin 1 (NRG1) as a new candidate gene involved in the development of the enteric nervous system (ENS) in humans.

METHODS

In our study, we investigated the role of NRG1 in zebrafish ENS development by assessing NRG1 expression patterns during ENS development. Knockdown, overexpression and rescue zebrafish models of NRG1 were created to evaluate differences in phenotype, numbers of enteric neurons, ENS-related factors and nerve fiber arrangements.

RESULTS

NRG1 was expressed in zebrafish intestine at both the larval and adult stage. We also found that decreased expression of NRG1 resulted in reductions in enteric neuron number and decreased expression of ENS development markers. Moreover, NRG1-knockdown zebrafish exhibited a disordered arrangement of nerve fibers.

CONCLUSIONS

Collectively, these results demonstrated that NRG1 expression might play a role in zebrafish ENS development. In addition, by modulating NRG1 expression, we created a model that may be useful for investigating the mechanism underlying HD pathogenesis.

Genetic Background of Hirschsprung Disease: A Bridge Between Basic Science and Clinical Application

Hirschsprung's disease (HSCR) is a congenital disorder, defined by partial or complete loss of the neuronal ganglion cells in the intestinal tract, which is caused by the failure of neural crest cells to migrate completely during intestinal development during fetal life. HSCR has a multifactorial etiology, and genetic factors play a key role in its pathogenesis; these include mutations within several gene loci. These have been identified by screening candidate genes, or by conducting genome wide association (GWAS) studies. However, only a small portion of them have been proposed as major genetic risk factors for the HSCR. In this review, we focus on those genes that have been identified as either low penetrant or high penetrant variants that determine the risk of Hirschsprung's disease. J. Cell. Biochem. 119: 28-33, 2018. © 2017 Wiley Periodicals, Inc.

Effects of RET, NRG1 and NRG3 Polymorphisms in a Chinese Population with Hirschsprung Disease

The RET proto-oncogene was identified as a major locus involved in Hirschsprung disease (HSCR). A genome-wide association study (GWAS) and whole exome sequencing identified NRG1 and NRG3 as additional HSCR susceptibility loci. We investigated the effects of RET (rs2506030 and rs2435357), NRG1 (rs2439302, rs16879552 and rs7835688) and NRG3 (rs10748842, rs10883866 and rs6584400) polymorphisms in a Chinese population with HSCR. We assessed single nucleotide polymorphisms (SNPs) in the RET, NRG1 and NRG3 genes in a cohort of 362 sporadic HSCR patients and 1,448 normal controls using a TaqMan genotyping assay. Significant associations were found between HSCR risk and rs2506030, rs2435357, rs2439302 and rs7835688 (odds ratio [OR] 1.64, P = 1.72E-06; 2.97, P = 5.15E-33; 1.84, P = 9.36E-11; and 1.93, P = 1.88E-12, respectively). Two locus analyses of SNPs indicated increased disease risks of HSCR between NRG1 rs2439302 and RET rs2435357 or rs2506030. RET rs2506030 (GG genotype) and rs2435357 (TT genotype), in combination with NRG1 rs2439302 (GG genotype), were strongly associated with the highest risk of HSCR (OR = 56.53, P = 4.50E-07) compared with the two loci or a single SNP of either RET or NRG1. Our results support the association between genetic variation of RET and NRG1 and susceptibility to HSCR in the Chinese population.

Hirschsprung's disease: clinical dysmorphology, genes, micro-RNAs, and future perspectives

On the occasion of the 100th anniversary of Dr. Harald Hirschsprung's death, there is a worldwide significant research effort toward identifying and understanding the role of genes and biochemical pathways involved in the pathogenesis as well as the use of new therapies for the disease harboring his name (Hirschsprung disease, HSCR). HSCR (aganglionic megacolon) is a frequent diagnostic and clinical challenge in perinatology and pediatric surgery, and a major cause of neonatal intestinal obstruction. HSCR is characterized by the absence of ganglia of the enteric nervous system, mostly in the distal gastrointestinal tract. This review focuses on current understanding of genes and pathways associated with HSCR and summarizes recent knowledge related to micro RNAs (miRNAs) and HSCR pathogenesis. While commonly sporadic, Mendelian patterns of inheritance have been described in syndromic cases with HSCR. Although only half of the patients with HSCR have mutations in specific genes related to early embryonic development, recent pathway-based analysis suggests that gene modules with common functions may be associated with HSCR in different populations. This comprehensive profile of functional gene modules may serve as a useful resource for future developmental, biochemical, and genetic studies providing insights into the complex nature of HSCR.

Medullary Thyroid Carcinoma Associated with Germline RETK666N Mutation

BACKGROUND

Multiple endocrine neoplasia type 2 is an autosomal dominant inherited syndrome caused by activating mutations in the RET proto-oncogene. The RET^K666N DNA variant was previously reported in two isolated medullary thyroid carcinoma (MTC) cases, but no family studies are available, and its oncogenic significance remains unknown.

METHODS

The clinical features, genetic data, and family information of eight index MTC patients with a germline RET^K666N variant were assessed.

RESULTS

Four probands presented with MTC and extensive nodal metastasis, one with biopsy-confirmed distant metastasis. Two additional probands presented with localized disease. However, nodal status was not available. Of the final two probands, one had an incidental 1.5 mm MTC and C-cell hyperplasia uncovered after surgery for papillary thyroid carcinoma, and one had two foci of MTC (largest dimension 2.3 cm) detected after surgery for dysphagia. Genetic screening identified 16 additional family members carrying the K666N variant (aged 5-90 years), 11 of whom have documented evaluation for MTC. Of these, only two were found to have elevated basal serum calcitonin upon screening, and the remaining patients had calcitonin levels within the reference range. One patient who elected to have a thyroidectomy at 70 years of age was confirmed to have MTC. The other subject, 57 years old, elected surveillance. Four prophylactic thyroidectomies were performed, with one case of C-cell hyperplasia at 20 years and three cases that revealed normal pathology at ages 21, 30, and 30 years. None of the K666N DNA variant carriers had evidence of primary hyperparathyroidism or pheochromocytoma.

CONCLUSIONS

From this case series, the largest such experience to date, it is concluded that the RET^K666N variant is likely pathogenic and associated with low penetrance of MTC. However, the findings are insufficient to define its pathogenicity clearly and make firm recommendations for screening and treatment. Given the potential benefit associated with early detection of aberrant C-cell growth, and the noninvasive nature of genetic testing, "at risk" individuals should be screened, and if the K666N variant is identified, they should be managed using a personalized screening approach for detection of MTC.

Repair Injured Heart by Regulating Cardiac Regenerative Signals

Cardiac regeneration is a homeostatic cardiogenic process by which the sections of malfunctioning adult cardiovascular tissues are repaired and renewed employing a combination of both cardiomyogenesis and angiogenesis. Unfortunately, while high-quality regeneration can be performed in amphibians and zebrafish hearts, mammalian hearts do not respond in kind. Indeed, a long-term loss of proliferative capacity in mammalian adult cardiomyocytes in combination with dysregulated induction of tissue fibrosis impairs mammalian endogenous heart regenerative capacity, leading to deleterious cardiac remodeling at the end stage of heart failure. Interestingly, several studies have demonstrated that cardiomyocyte proliferation capacity is retained in mammals very soon after birth, and cardiac regeneration potential is correspondingly preserved in some preadolescent vertebrates after myocardial infarction. There is therefore great interest in uncovering the molecular mechanisms that may allow heart regeneration during adult stages. This review will summarize recent findings on cardiac regenerative regulatory mechanisms, especially with respect to extracellular signals and intracellular pathways that may provide novel therapeutics for heart diseases. Particularly, both in vitro and in vivo experimental evidences will be presented to highlight the functional role of these signaling cascades in regulating cardiomyocyte proliferation, cardiomyocyte growth, and maturation, with special emphasis on their responses to heart tissue injury.

Heterozygous p.S811F RET gene mutation associated with renal agenesis, oligomeganephronia and total colonic aganglionosis: a case report

Background

Several shared common gene networks participate in development of interstinal ganglia and also nephron formation; the glial cell line-derived neurotrophic factor/Ret/glial cell line-derived neurotrophic factor receptor gene network is particularly important.

Case presentation

We encountered a patient with total colonic aganglionosis as well as right renal agenesis and oligomeganephronia. Gene analysis in this patient disclosed a heterozygous p.S811F mutation was in Ret gene exon 14, resulting in a substitution of phenylalanine for serine. The large side chain of phenylalanine obstructed the opening of the hydrophobic pocket of the Ret molecule causing interference with its interaction with adenosine triphosphate and consequent marked reduction in its enzyme activity. This could account for our patient's severe intestinal disease and renal dysplasia. We know of no previous reports of concomitant Hirschsprung’s disease and oligomeganephronia.

Conclusions

The patient's overall illness could be considered a novel Ret gene mutation syndrome.

Development of the intrinsic and extrinsic innervation of the gut

The gastrointestinal (GI) tract is innervated by intrinsic enteric neurons and by extrinsic efferent and afferent nerves. The enteric (intrinsic) nervous system (ENS) in most regions of the gut consists of two main ganglionated layers; myenteric and submucosal ganglia, containing numerous types of enteric neurons and glial cells. Axons arising from the ENS and from extrinsic neurons innervate most layers of the gut wall and regulate many gut functions. The majority of ENS cells are derived from vagal neural crest cells (NCCs), which proliferate, colonize the entire gut, and first populate the myenteric region. After gut colonization by vagal NCCs, the extrinsic nerve fibers reach the GI tract, and Schwann cell precursors (SCPs) enter the gut along the extrinsic nerves. Furthermore, a subpopulation of cells in myenteric ganglia undergoes a radial (inward) migration to form the submucosal plexus, and the intrinsic and extrinsic innervation to the mucosal region develops. Here, we focus on recent progress in understanding the developmental processes that occur after the gut is colonized by vagal ENS precursors, and provide an up-to-date overview of molecular mechanisms regulating the development of the intrinsic and extrinsic innervation of the GI tract.

Exome-Wide Association Study Identified New Risk Loci for Hirschsprung's Disease

Hirschsprung disease (HSCR) is a rare congenital disease caused by impaired proliferation and migration of neural crest cells. In this study, we aimed to investigate the genetic loci involved in the pathogenesis of HSCR. The exome-wide scan was performed to screen the genetic variants with minor allele frequency (MAF) < 0.05 in exonic regions. Candidate mutation type and the wild type were overexpressed to investigate the affection on cell proliferation and migration. We found that ten variants were associated with HSCR at P < 10^-4 in the single-variant analysis while ten genes were also associated with HSCR at P < 10^-4 in the optimized sequence kernel association test (SKAT-O) test analysis. Among these SNPs, the missense variants catechol-O-methyltransferase (COMT) (rs6267) and armadillo repeat gene deleted in velocardiofacial syndrome (ARVCF) (rs80068543) indicated an ectopic expression in colon tissues of HSCR patients. The Ala72Ser variant in COMT induced proliferation suppression through NOTCH signal pathway, while the ARVCF affected cell migration via the downregulating of RHOA and ROC. In conclusion, this exome array study identified the COMT and ARVCF missense coding variants as candidate loci for HSCR. The finding implies the abnormal variant of COMT and ARVCF may account for the pathogenesis of HSCR.

Exome sequencing reveals a high genetic heterogeneity on familial Hirschsprung disease

Hirschsprung disease (HSCR; OMIM 142623) is a developmental disorder characterized by aganglionosis along variable lengths of the distal gastrointestinal tract, which results in intestinal obstruction. Interactions among known HSCR genes and/or unknown disease susceptibility loci lead to variable severity of phenotype. Neither linkage nor genome-wide association studies have efficiently contributed to completely dissect the genetic pathways underlying this complex genetic disorder. We have performed whole exome sequencing of 16 HSCR patients from 8 unrelated families with SOLID platform. Variants shared by affected relatives were validated by Sanger sequencing. We searched for genes recurrently mutated across families. Only variations in the FAT3 gene were significantly enriched in five families. Within-family analysis identified compound heterozygotes for AHNAK and several genes (N = 23) with heterozygous variants that co-segregated with the phenotype. Network and pathway analyses facilitated the discovery of polygenic inheritance involving FAT3, HSCR known genes and their gene partners. Altogether, our approach has facilitated the detection of more than one damaging variant in biologically plausible genes that could jointly contribute to the phenotype. Our data may contribute to the understanding of the complex interactions that occur during enteric nervous system development and the etiopathology of familial HSCR.

Expression and function of Neuregulin 1 and its signaling system ERBB2/3 in the enteric nervous system

Neuregulin 1 (NRG1) is suggested to promote the survival and maintenance of the enteric nervous system (ENS). As deficiency in its corresponding receptor signaling complex ERBB2/ERBB3 leads to postnatal colonic hypo/aganglionosis we assessed the distributional and expressional pattern of the NRG1-ERBB2/ERBB3 system in the human colon and explored the neurotrophic capacity of NRG1 on cultured enteric neurons. Site-specific mRNA expression of the NRG1-ERBB2/3 system was determined in microdissected samples harvested from enteric musculature and ganglia. Localization of NRG1, ERBB2 and ERBB3 was determined by dual-label-immunohistochemistry using pan-neuronal and pan-glial markers. Morphometric analysis was performed on NRG1-stimulated rat enteric nerve cultures to evaluate neurotrophic effects. mRNA expression of the NRG1-ERBB2/3 system was determined by qPCR. Co-localization of NRG1 with neuronal or synaptic markers was analyzed in enteric nerve cultures stimulated with glial cell line-derived neurotrophic factor (GDNF). The NRG1 system was expressed in both neurons and glial cells of enteric ganglia and in nerve fibers. NRG1 significantly enhanced growth parameters in enteric nerve cell cultures and ErB3 mRNA expression was down-regulated upon NRG1 stimulation. GDNF negatively regulates ErbB2 and ErbB3 mRNA expression. The NRG1-ERBB2/3 system is physiologically present in the human ENS and NRG1 acts as a neurotrophic factor for the ENS. The down-regulation of ErbB3/ErbB2 in GDNF stimulated nerve cell cultures points to an interaction of both neurotrophic factors. Thus, the data may provide a basis to assess disturbed signaling components of the NRG1 system in enteric neuropathies.

Identification of genetic loci affecting the severity of symptoms of Hirschsprung disease in rats carrying Ednrbsl mutations by quantitative trait locus analysis

Hirschsprung’s disease (HSCR) is a congenital disease in neonates characterized by the absence of the enteric ganglia in a variable length of the distal colon. This disease results from multiple genetic interactions that modulate the ability of enteric neural crest cells to populate developing gut. We previously reported that three rat strains with different backgrounds (susceptible AGH-Ednrb^sl/sl, resistant F344-Ednrb^sl/sl, and LEH-Ednrb^sl/sl) but the same null mutation of Ednrb show varying severity degrees of aganglionosis. This finding suggests that strain-specific genetic factors affect the severity of HSCR. Consistent with this finding, a quantitative trait locus (QTL) for the severity of HSCR on chromosome (Chr) 2 was identified using an F₂ intercross between AGH and F344 strains. In the present study, we performed QTL analysis using an F₂ intercross between the susceptible AGH and resistant LEH strains to identify the modifier/resistant loci for HSCR in Ednrb-deficient rats. A significant locus affecting the severity of HSCR was also detected within the Chr 2 region. These findings strongly suggest that a modifier gene of aganglionosis exists on Chr 2. In addition, two potentially causative SNPs (or mutations) were detected upstream of a known HSCR susceptibility gene, Gdnf. These SNPs were possibly responsible for the varied length of gut affected by aganglionosis.

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.

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.

Contribution of rare and common variants determine complex diseases-Hirschsprung disease as a model

Finding genes for complex diseases has been the goal of many genetic studies. Most of these studies have been successful by searching for genes and mutations in rare familial cases, by screening candidate genes and by performing genome wide association studies. However, only a small fraction of the total genetic risk for these complex genetic diseases can be explained by the identified mutations and associated genetic loci. In this review we focus on Hirschsprung disease (HSCR) as an example of a complex genetic disorder. We describe the genes identified in this congenital malformation and postulate that both common 'low penetrant' variants in combination with rare or private 'high penetrant' variants determine the risk on HSCR, and likely, on other complex diseases. We also discuss how new technological advances can be used to gain further insights in the genetic background of complex diseases. Finally, we outline a few steps to develop functional assays in order to determine the involvement of these variants in disease development.