Frequency of RET mutations in long- and short-segment Hirschsprung disease

A Single RET Mutation in Hirschsprung Disease Induces Intestinal Aganglionosis Via a Dominant-Negative Mechanism

BACKGROUND & AIMS

Hirschsprung disease (HSCR) is a congenital disorder characterized by the absence of the enteric nervous system (ENS). HSCR potentially involves multiple gene aberrations and displays complex patterns of inheritance. Mutations of the RET gene, encoding the RET receptor tyrosine kinase, play a central role in the pathogenesis of HSCR. Although a wide variety of coding RET mutations have been identified, their pathogenetic significance in vivo has remained largely unclear.

METHODS

We introduced a HSCR-associated RET missense mutation, RET(S811F), into the corresponding region (S812) of the mouse Ret gene. Pathogenetic impact of Ret(S812F) was assessed by histologic and functional analyses of the ENS and by biochemical analyses. Interactions of the Ret(S812F) allele with HSCR susceptibility genes, the RET9 allele and the Ednrb gene, were examined by genetic crossing in mice.

RESULTS

Ret^S812F/+ mice displayed intestinal aganglionosis (incidence, 50%) or hypoganglionosis (50%), impaired differentiation of enteric neurons, defecation deficits, and increased lethality. Biochemical analyses revealed that Ret(S811F) protein was not only kinase-deficient but also abrogated function of wild-type RET in trans. Moreover, the Ret(S812F) allele interacted with other HSCR susceptibility genes and caused intestinal aganglionosis with full penetrance.

CONCLUSIONS

This study demonstrates that a single RET missense mutation alone induces intestinal aganglionosis via a dominant-negative mechanism. The Ret^S812F/+ mice model HSCR displays dominant inheritance with incomplete penetrance and serves as a valuable platform for better understanding of the pathogenetic mechanism of HSCR caused by coding RET mutations.

Distribution of RET proto-oncogene variants in children with appendicitis

Background

In addition to patient‐related systemic factors directing the immune response, the pathomechanisms of appendicitis (AP) might also include insufficient drainage leading to inflammation caused by decreased peristalsis. Genetic predisposition accounts for 30%–50% of AP. M. Hirschsprung (HSCR), also characterized by disturbed peristalsis, is associated with variants in the RET proto‐oncogene. We thus hypothesized that RET variants contribute to the etiology of AP.

Methods

DNA from paraffin‐embedded appendices and clinical data of 264 children were analyzed for the RET c.135A>G variant (rs1800858, NC_000010.11:g.43100520A>G). In 46 patients with gangrenous or perforated AP (GAP), peripheral blood DNA was used for RET sequencing.

Results

Germline mutations were found in 13% of GAP, whereas no RET mutations were found in controls besides the benign variant p.Tyr791Phe (NC_000010.11:g.43118460A>T). In GAP, the polymorphic G‐allele in rs2435352 (NC_000010.11:g.43105241A>G) in intron 4 was underrepresented (p = 0.0317).

Conclusion

Our results suggest an impact of the RET proto‐oncogene in the etiology of AP. Mutations were similar to patients with HSCR but no clinical features of HSCR were observed. The pathological phenotypes in both populations might thus represent a multigenic etiology including RET germline mutations with phenotypic heterogeneity and incomplete penetrance.

Association of rs2435357 and rs2506030 polymorphisms in RET with susceptibility to hirschsprung disease: A systematic review and meta-analysis

BACKGROUND

There are numerous published studies on the association between RET polymorphisms and susceptibility to Hirschsprung disease (HSCR). However, some of the results are inconsistent and the studies were conducted with small sample sizes. Therefore, we performed a meta-analysis to clarify the relationship.

METHODS

Relevant data were retrieved from PubMed, Web of Science, Cochrane Library, EMBASE, CNKI, and Google Scholar according to PRISMA guidelines. Odds ratios (OR) were calculated to assess susceptibility to HSCR. Meanwhile, heterogeneity and publication bias were also calculated by R software package (version 4.2.1). The protocol was published in PROSPERO (CRD42022348940).

RESULTS

A total of 12 studies were included in the meta-analysis and comprised 12 studies on the RET polymorphism rs2435357 (1,939 subjects and 3,613 controls) and 7 studies on the RET polymorphism rs2506030 (1,849 patients with HSCR and 3,054 controls). The analysis revealed that rs2435357 [A vs. G: odds ratio (OR) = 3.842, 95% confidence interval (CI) 2.829-5.220; AA vs. GG: OR = 2.597, 95% CI 1.499-4.501; AA + AG vs. GG: OR = 6.789, 95% CI 3.0711-14.9973; AA vs. AG + GG: OR = 8.156, 95%CI 5.429-12.253] and rs2506030 (A vs. G: OR = 0.519, 95% CI 0.469-0.573; AA vs. GG: OR = 0.543, 95% CI 0.474-0.623; AA + AG vs. GG: OR = 0.410, 95% CI 0.360-0.468; AA vs. AG + GG: OR = 0.361, 95%CI 0.292-0.447) were significantly associated with susceptibility to HSCR.

CONCLUSIONS

The polymorphisms rs2435357 and rs2506030 in the RET may be related to susceptibility to HSCR, of which rs2435357 (T > C) is the causal locus and rs2506030 (A > G) is the protective locus.

SYSTEMATIC REVIEW REGISTRATION

https://www.crd.york.ac.uk/prospero/, identifier:CRD42022348940.

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.

Results and Clinical Interpretation of Germline RET Analysis in a Series of Patients with Medullary Thyroid Carcinoma: The Challenge of the Variants of Uncertain Significance

Germline RET variants are responsible for approximately 25% of medullary thyroid carcinoma (MTC) cases. Identification of RET variant carriers allows for the adoption of preventative measures which are dependent on the risk associated with the specific alteration. From 2002 to 2020, at our cancer genetics clinic, RET genetic testing was performed in 163 subjects (102 complete gene analyses and 61 targeted analyses), 72 of whom presented with MTC. A germline RET variant was identified in 31.9% of patients affected by MTC (93.8% of those having positive family history and 14.3% of clinically sporadic cases). Subsequent target testing in relatives allowed us to identify 22 asymptomatic carriers, who could undertake appropriate screening. Overall, patients with germline RET variants differed significantly from those who tested negative by family history (p < 0.001) and mean age at MTC diagnosis (44.45 vs. 56.42 years; p = 0.010), but the difference was not significant when only carriers of moderate risk variants were considered (51.78 vs. 56.42 years; p = 0.281). Out of 12 different variants detected in 49 patients, five (41.7%) were of uncertain significance (VUS). For two of these, p.Ser904Phe and p.Asp631_Leu633delinsGlu, co-segregation and genotype/phenotype analysis, matched with data from the literature, provided evidence supporting their classification in the moderate and the highest/high risk class (with a MEN2B phenotype), respectively.

A study on genetic polymorphism of RET proto-oncogene in Hirschsprung's disease in children

BACKGROUND

Hirschsprung's disease (HD) is a genetic disorder with a complex pattern of inheritance. Some single-nucleotide polymorphisms (SNPs) are identified to be associated with the risk of Hirschsprung's Disease (HSCR).

AIMS AND OBJECTIVES

The aim of this study is to know the association between the rearranged during transfection (RET) proto-oncogene polymorphism and HD and to characterize the SNPs of RET proto-oncogene affecting HD.

MATERIALS AND METHODS

The study was conducted in the Department of Pathology in association with the Department of Pediatric Surgery. Blood samples were collected from the patients diagnosed with confirmed HD and from age- and sex-matched controls. This case-control study consisted of 53 HSCR cases and 50 controls. Genotypes of rs1800860 and rs1800861 were analysed in by polymerase chain reaction amplification and sanger sequencing. Associations with the risk of HSCR were estimated by odds ratio (OR) and their 95% confidence intervals (95% CI) using.

RESULTS

We observed that in the case of rs1800860A > G genotype AG was not associated with the increasing risk of disease (OR with 95% CI = 0.568 [0.238-1.356]) while genotype GG was associated with increasing the risk of the disease (OR with 95% CI = 2.278 [0.967-5.366]). In the case of rs1800861G > T genotype GT was associated with lowering the risk of the disease (OR with 95% CI = 0.230 [0.0981-0.539]) while genotype TT was associated with increasing the risk of the disease (OR with 95% CI = 9.647 [3.830-24.302]). The difference in the genotypic distribution of GT and TT at rs1800861G > T between Short segment disease (SSD) cases and Long Segment Disease (LSD) and total colonic aganglionosis was made by Fisher's exact test and it was statistically significant (P = 0.0476 and 0.0054).

CONCLUSION

The results of this study support the hypothesis that variations in RET pathway might play an important role in the development of HSCR.

Clinical features of children with Haddad syndrome: A single-center experience

BACKGROUND/PURPOSE

Haddad syndrome (HS) is a very rare disease considered a form of neurocristopathy. It is characterized by a combination of congenital central hypoventilation syndrome (CCHS) and Hirschsprung's disease (HD). We report the clinical features and disease progression of HS to provide better care for HS patients by achieving an earlier diagnosis and optimal treatment.

METHODS

Medical records of patients diagnosed with HS from 2005 to 2016 were retrospectively reviewed. Demographic data including gestational age, birth weight and height, and paired-like homeobox 2b (PHOX2B) gene mutation were collected.

RESULTS

Seven males and three females were identified (mean gestational age 39.76 ± 1.49 weeks, mean birth weight 3117.5 ± 288.9 g). PHOX2B gene mutation was identified in all patients. Immediate ventilation care after birth was required in five patients due to poor respiration. The current median age of the children is 5.4 years (range, 1.8-10.1). Tracheostomy was performed in nine patients. Eight patients required sleep ventilation and two patients, 24-h continuous ventilation support. Six patients showed rectosigmoid aganglionosis and four patients exhibited total colonic aganglionosis, of these one had aganglionosis extended to the distal small bowel. Soiling was observed in seven patients (5 with laparoscopy-assisted transanal endorectal pull-through and 2 with Duhamel procedure) and one patient showed grade 2 constipation with Duhamel procedure. Six patients had developmental delay. All patients are alive.

CONCLUSIONS

HS may require lifelong medical care. This study could be helpful to understand the clinical features of HS including associated abnormalities and disease progression. By assisting to understand the clinical features, we could provide better care for HS patients by achieving an earlier diagnosis and appropriate treatment.

TYPE OF STUDY

Prognosis study.

LEVEL OF EVIDENCE

Level IV.

Long-term follow-up of RET Y791F carriers in Denmark 1994-2017: A National Cohort Study

BACKGROUND AND OBJECTIVES

Recently, a comprehensive study presented evidence that a long-disputed REarranged during Transfection (RET) variant, RET Y791F, should be classified as nonpathogenic. In spite of this, several subsequently published papers, including the revised American Thyroid Association guidelines for medullary thyroid carcinoma, refer to the variant as pathogenic. This study presents data from a unique national Danish cohort of RET Y791F carriers who have been followed by watchful waiting instead of being subjected to early thyroidectomy, to determine if any carrier shows evidence of multiple endocrine neoplasia 2A (MEN2A) at long-term follow-up.

METHODS

A national cohort of all patients tested for RET mutations in Denmark from September 1994 to October 2017 was searched for carriers of RET Y791F. Medical records and laboratory reports of carriers were reviewed for signs of MEN2A at latest follow-up (medullary thyroid carcinoma, primary hyperparathyroidism, pheochromocytoma, cutaneous lichen amyloidosis, or Hirschsprung's disease).

RESULTS

In total, twenty RET Y791F-carriers were identified, none of whom showed any evidence of MEN2A, despite an age range from 7 to 87 years.

CONCLUSIONS

Our national cohort study of all Danish RET Y791F carriers substantiates the claim that the RET Y791F variant is nonpathogenic.

Significance of neurexin and neuroligin polymorphisms in regulating risk of Hirschsprung's disease

By performing a basic case-control study among a Chinese population, the aims of this study were to explore if single nucleotide polymorphisms (SNPs) within neurexin and neuroligin were associated with susceptibility to Hirschsprung's disease (HD). Eleven SNPs within neurexin and neuroligin were selected in this basic case-control study, and this study recruited 210 children with HD and 187 healthy children. The t-test and Χ² test were used to find the difference between case and control in their clinical variables. OR and 95% CI were used to assess the association between HD susceptibility and neurexin/neuroligin polymorphisms/haplotypes. Several SNPs were significantly associated with altered risk of HD in the Chinese Han population, including rs1421589 within NRXN1, rs11795613 and rs4844285 within NLGN3, as well as rs5961397, rs7157669 and rs724373 within NLGX4X (all P<0.05). Further studies presented that the effects of rs1421589 within NRXN1, rs4844285 and rs11795613 within NLGN3, as well as rs5961397 within NLGX4X on HD phenotypes were also statistically significant (all P<0.05). Conclusively, the polymorphisms and haplotypes situated within neurexin and neuroligin were markedly associated with the onset of HD, implying that mutations of neurexin and neuroligin might serve as the treatment target for HD for the Chinese children.

Hirschsprung disease - integrating basic science and clinical medicine to improve outcomes

Hirschsprung disease is defined by the absence of enteric neurons at the end of the bowel. The enteric nervous system (ENS) is the intrinsic nervous system of the bowel and regulates most aspects of bowel function. When the ENS is missing, there are no neurally mediated propulsive motility patterns, and the bowel remains contracted, causing functional obstruction. Symptoms of Hirschsprung disease include constipation, vomiting, abdominal distension and growth failure. Untreated disease usually causes death in childhood because bloodstream bacterial infections occur in the context of bowel inflammation (enterocolitis) or bowel perforation. Current treatment is surgical resection of the bowel to remove or bypass regions where the ENS is missing, but many children have problems after surgery. Although the anatomy of Hirschsprung disease is simple, many clinical features remain enigmatic, and diagnosis and management remain challenging. For example, the age of presentation and the type of symptoms that occur vary dramatically among patients, even though every affected child has missing neurons in the distal bowel at birth. In this Review, basic science discoveries are linked to clinical manifestations of Hirschsprung disease, including partial penetrance, enterocolitis and genetics. Insights into disease mechanisms that might lead to new prevention, diagnostic and treatment strategies are described.

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.

Genetic variation in the GDNF promoter affects its expression and modifies the severity of Hirschsprung's disease (HSCR) in rats carrying Ednrb(sl) mutations

Glial cell line-derived neurotrophic factor (GDNF) is necessary for the migration of neural crest stem cells in the gut. However, mutations in GDNF per se are deemed neither necessary nor sufficient to cause Hirschsprung's disease (HSCR). In a previous study, a modifier locus on chromosome 2 in rats carrying Ednrb(sl) mutations was identified, and several mutations in the putative regulatory region of the Gdnf gene in AGH-Ednrb(sl) rats were detected. Specifically, the mutation -232C>T has been shown to be strongly associated with the severity of HSCR. In the present study, the influence of genetic variations on the transcription of the Gdnf gene was tested using dual-luciferase assay. Results showed that the mutation -613C>T, located near the mutation -232C>T in AGH-Ednrb(sl) rats, decreased Gdnf transcription in an in vitro dual-luciferase expression assay. These data suggested an important role of -613C in Gdnf transcription. Expression levels of the Gdnf gene may modify the severity of HSCR in rats carrying Ednrb(sl) mutations.

RET gene is a major risk factor for Hirschsprung's disease: a meta-analysis

PURPOSE

During the past two decades several genes have been identified that control morphogenesis and differentiation of the enteric neuron system (ENS). These genes, when mutated or deleted, interfere with ENS development. RET gene is the major gene causing Hirschsprung's disease (HD). Mutations in RET gene are responsible for 50% of familial HD cases and 15-20% of sporadic cases. The aim of this meta-analysis was to determine the incidence of RET gene mutations in patients with HD and to correlate RET mutations with the extent of aganglionosis.

METHODS

A systematic literature-based search for relevant cohorts was performed using the terms "Hirschsprung's disease AND RET Proto-oncogene", "Hirschsprung's disease AND genetic polymorphism" and "RET Gene". The relevant cohorts of HD were systematically searched for reported mutations in the RET gene (RET+). Data on mutation site, phenotype, and familial or sporadic cases were extracted. Combined odds ratio (OR) with 95% CI was calculated to estimate the strength of the different associations.

RESULTS

In total, 23 studies concerning RET with 1270 individuals affected with HD were included in this study. 228 (18%) of these HDs were RET+. Of these 228, 96 (42%) presented as rectosigmoid, 81 (36%) long segment, 18 (8%) as TCA, 16 (7%) as total intestinal aganglionosis and 17 (7%) individuals were RET+ but no extent of aganglionosis was not reported. In the rectosigmoid group, no significant association between phenotype and RET mutation could be shown (P = 0.006), whereas a clear association could be shown between long-segment disease, total colonic- and total intestinal aganglionosis and RET mutations (P = 0.0002). Mutations most often occurred in Exon 13 (24) and showed significant association with rectosigmoid disease (P = 0.004). No significance could be shown between RET+ and sporadic cases (P = 0.53), albeit a trend towards RET+ and Familial cases could be observed (P = 0.38).

CONCLUSIONS

The association with the RET gene and HD is well recognized. This study showed a clear association between RET+ mutations and the long-segment, total colonic- and total intestinal aganglionosis. Exon 13 appears to be a mutational "hot spot" in rectosigmoid disease.

Clinical and genetic correlations of familial Hirschsprung's disease

BACKGROUND

The risk of familial transmission in Hirschsprung's disease (HSCR) currently lacks correlation between the clinical phenotype and the underlying genetic factors. The aim of this study was to clinically evaluate familial HSCR transmission and to correlate with the genetic background.

METHODS

Clinical and gene analysis of familial HSCR patients were explored. DNA from 45 patients (35 kindreds) was screened for genetic variations of the RET, and EDNRB genes were screened for genetic variation by semi-automated bi-directional sequencing analysis and matched to controls.

MAIN RESULTS

Male:female ratio (3:1) had a female proband in 4 families. Aganglionosis was significantly more frequent with total colonic aganglionosis (TCA) in 40% familial cases (viz: 17/43 (43%) vs. 19/342 non-familial patients (5.6%) (p<0.01)). Transmission of S-HSCR was observed in 13 (31%), which was associated with EDNRB variation. RET gene promoter variation correlated with extended aganglionosis in 6/35 kindreds (17%). In 3 kindreds, both significant EDNRB and RET mutations were identified and where present were associated with increased penetrance in succeeding generations. An increased penetrance with succeeding generations occurred in 6 (14%). In a further 3 generation family, extensive variations in exon 6, 13, and 18 affected 3 males with progressive penetration and aganglionic length, including total intestinal aganglionosis in the further offspring. RET and MEN association was noted in 5 kindreds (14.3%) related to RET variations at Cysteine sites.

CONCLUSIONS

Cumulative effects of the RET and EDNRB genes contribute to long-segment and total colonic aganglionosis.

Comprehensive assessment of the disputed RET Y791F variant shows no association with medullary thyroid carcinoma susceptibility

Accurate interpretation of germline mutations of the rearranged during transfection (RET) proto-oncogene is vital for the proper recommendation of preventive thyroidectomy in medullary thyroid carcinoma (MTC)-prone carriers. To gain information regarding the most disputed variant of RET, ATA-A Y791F, we sequenced blood DNA samples from a cohort of 2904 cancer-free elderly individuals (1261 via Sanger sequencing and 1643 via whole-exome/genome sequencing). We also accessed the exome sequences of an additional 8069 individuals from non-cancer-related laboratories and public databanks as well as genetic results from the Catalogue of Somatic Mutations in Cancer (COSMIC) project. The mean allelic frequency observed in the controls was 0.0031, with higher occurrences in Central European populations (0.006/0.008). The prevalence of RET Y791F in the control databases was extremely high compared with the 40 known RET pathogenic mutations (P=0.00003), while no somatic occurrence has been reported in tumours. In this study, we report new, unrelated Brazilian individuals with germline RET Y791F-only: two tumour-free elderly controls; two individuals with sporadic MTC whose Y791F-carrying relatives did not show any evidence of tumours; and a 74-year-old phaeochromocytoma patient without MTC. Furthermore, we showed that the co-occurrence of Y791F with the strong RET C634Y mutation explains the aggressive MTC phenotypes observed in a large affected family that was initially reported as Y791F-only. Our literature review revealed that limited analyses have led to the misclassification of RET Y791F as a probable pathogenic variant and, consequently, to the occurrence of unnecessary thyroidectomies. The current study will have a substantial clinical influence, as it reveals, in a comprehensive manner, that RET Y791F only shows no association with MTC susceptibility.

RET revisited: expanding the oncogenic portfolio

The RET receptor tyrosine kinase is crucial for normal development but also contributes to pathologies that reflect both the loss and the gain of RET function. Activation of RET occurs via oncogenic mutations in familial and sporadic cancers - most notably, those of the thyroid and the lung. RET has also recently been implicated in the progression of breast and pancreatic tumours, among others, which makes it an attractive target for small-molecule kinase inhibitors as therapeutics. However, the complex roles of RET in homeostasis and survival of neural lineages and in tumour-associated inflammation might also suggest potential long-term pitfalls of broadly targeting RET.

Tissue specific somatic mutations and aganglionosis in Hirschsprung's disease

BACKGROUND

RET proto-oncogene intron 1 variations [e.g. SNP1 (rs2506004) and SNP2 (rs 2435357)] have been shown to be etiologically important in the pathogenesis of Hirschsprung's disease (HSCR). Although activating somatic RET rearrangements have been identified in certain tumours, this is the first study to confirm somatic gene variation in HSCR.

METHODS

DNA was extracted from 53 paraffin embedded tissue samples (HSCR patients n=33, multiple levels n=17), and controls (n=3). Patients were grouped into aganglionic (Group 1), ganglionated (group 2), and transitional (group 3). PCR products of RET intron 1 were screened for genetic variation by semi-automated bi-directional sequencing analysis and matched to unaffected controls from the general population. Comparison was by Fishers exact test. P <0.05 was regarded as significant.

RESULTS

HSCR patients included short segment (n=26), long segment colonic [(n=4 (24%)], and total colonic aganglionosis (n=3). RET intronic variations [SNP1 (rs2506004) or SNP2 (rs 2435357)] showed somatic homozygous in affected tissue in 9/12 (75%) Group 1 (aganglionic tissue) compared with 2/5 (40%) and 1/10 (10%) of groups 2 and 3 (P<0.001). Homozygous SNP2 variation was observed in all long segment versus 4/10 short segment. 50% of the short segment cases showing homozygous SNP 1 variation.

CONCLUSION

We report somatic mutations in the RET intron 1 region of affected HSCR tissue, confirming for the first time that somatic mutations are present in aganglionic tissue and may promote local aganglionosis through deregulated receptor activity. Detailed understanding of the somatic genetic events that drive congenital aganglionosis may have bearing on diagnosis and therapy.

Screening of the RET gene of Vietnamese Hirschsprung patients identifies 2 novel missense mutations

BACKGROUND/PURPOSE

Hirschsprung disease (HSCR; megacolon, congenital aganglionosis) is a congenital disorder characterized by the absence of ganglion cells along variable segments of the gut. Both rare (RV) and common variants of the RET gene are associated with HSCR. The aim of this study is to assess, for the first time, the variation in the RET gene of Vietnamese HSCR patients.

METHODS

We used Sanger sequencing to screen the coding sequence of the RET gene of 97 Vietnamese HSCR patients of Southern Chinese ancestry. The healthy population consisted of 250 Southern Chinese individuals with no diagnosis of HSCR.

RESULTS

We detected 8 heterozygous RVs distributed among 13 patients (13.40%) and that were not present in healthy individuals. Among those variants, there were 2 novel and deleterious (R133C [c.397 C>T]; R144C [c.430 C>T]) missense amino acid substitutions, 2 novel silent variants (P667P [c.2001 A>T]; Y809Y [c.2427 C>T]), and 4 previously described missense substitutions (R114H [c.341 G>A]; V292M [c.874 G>A]; G533S [c.1597 G>A]; R982C [c.2944 C>T]). As expected, the common RET coding sequence variants rs1800858 (A45A [c.135 G>A]) and rs1800861 (L769L [c.2307 T>G]) were highly associated with the disease.

CONCLUSIONS

The identification of novel deleterious variants together with the fact RET RVs are virtually unique to HSCR patients indicates that the RET gene is a target for mutations among Hirschsprung patients of any population.

RET 3'UTR polymorphisms and its protective role in Hirschsprung disease in southeastern Chinese

BACKGROUND

Hirschsprung disease (HSCR) is a complex congenital disorder characterized by intestinal obstructions owing to the absence of the intestinal ganglion cells of the nerve plexuses in variable lengths of the digestive tract. Several RET polymorphisms and haplotypes have been described as underrepresented in HSCR patients with respect to controls. We thus sought to investigate whether polymorphisms in RET 3'UTR are associated with isolated HSCR in the Chinese population.

METHODS

Polymerase chain reaction amplification and direct sequencing were used to screen polymorphisms in RET 3'UTR in patients with sporadic HSCR and ethnically matched controls in Han Chinese populations. Association tests of RET 3'UTR variants and haplotypes with HSCR were performed.

RESULTS

We examined a total of 107 Chinese sporadic HSCR patients and 89 ethnically matched controls by sequencing the 3'UTR of the RET gene. Five single nucleotide polymorphisms (SNPs) and 2 monomorphic SNPs were identified. The genotype distributions and the allele frequencies of the 5 SNPs were significantly different between HSCR cases and controls and occurred more frequently in the control population. Haplotype analysis has shown a higher frequency of haplotypes comprising variant alleles in controls as compared with cases.

CONCLUSIONS

The significant deviations of the genotype distributions and the allele frequencies of these SNPs in the HSCR population compared with the control population demonstrate that these SNPs have a strong negative association with HSCR and could act as protective alleles.

Multiple functional effects of RET kinase domain sequence variants in Hirschsprung disease

The REarranged during Transfection (RET) gene encodes a receptor tyrosine kinase required for maturation of the enteric nervous system. RET sequence variants occur in the congenital abnormality Hirschsprung disease (HSCR), characterized by absence of ganglia in the intestinal tract. Although HSCR-RET variants are predicted to inactivate RET, the molecular mechanisms of these events are not well characterized. Using structure-based models of RET, we predicted the molecular consequences of 23 HSCR-associated missense variants and how they lead to receptor dysfunction. We validated our predictions in biochemical and cell-based assays to explore mutational effects on RET protein functions. We found a minority of HSCR-RET variants abrogated RET kinase function, while the remaining mutants were phosphorylated and transduced intracellular signals. HSCR-RET sequence variants also impacted on maturation, stability, and degradation of RET proteins. We showed that each variant conferred a unique combination of effects that together impaired RET protein activity. However, all tested variants impaired RET-mediated cellular functions, including cell transformation and migration. Our data indicate that the molecular mechanisms of impaired RET function in HSCR are highly variable. Although a subset of variants cause loss of RET kinase activity and downstream signaling, enzymatic inactivation is not the sole mechanism at play in HSCR.

Hirschsprung's disease and variants in genes that regulate enteric neural crest cell proliferation, migration and differentiation

Hirschsprung's disease (HSCR) results from failed colonization of the embryonic gut by enteric neural crest cells (ENCCs); colonization requires RET proto-oncogene (RET) signaling. We sequenced RET to identify coding and splice-site variants in a population-based case group and we tested for associations between HSCR and common variants in RET and candidate genes (ASCL1, homeobox B5 (HOXB5), L1 cell adhesion molecule (L1CAM), paired-like homeobox 2b (PHOX2B), PROK1 and PROKR1) chosen because they are involved in ENCC proliferation, migration and differentiation in animal models. We conducted a nested case-control study of 304 HSCR cases and 1215 controls. Among 38 (12.5%) cases with 34 RET coding and splice-site variants, 18 variants were previously unreported. We confirmed associations with common variants in HOXB5 and PHOX2B but the associations with variants in ASCL1, L1CAM and PROK1 were not significant after multiple comparisons adjustment. RET variants were strongly associated with HSCR (P-values between 10(-3) and 10(-31)) but this differed by race/ethnicity: associations were absent in African-Americans. Our population-based study not only identified novel RET variants in HSCR cases, it showed that common RET variants may not contribute to HSCR in all race/ethnic groups. The findings for HOXB5 and PHOX2B provide supportive evidence that genes regulating ENCC proliferation, migration and differentiation could be risk factors for HSCR.

Multiple endocrine neoplasias type 2B and RET proto-oncogene

Multiple Endocrine Neoplasia type 2B (MEN 2B) is an autosomal dominant complex oncologic neurocristopathy including medullary thyroid carcinoma, pheochromocytoma, gastrointestinal disorders, marphanoid face, and mucosal multiple ganglioneuromas. Medullary thyroid carcinoma is the major cause of mortality in MEN 2B syndrome, and it often appears during the first years of life. RET proto-oncogene germline activating mutations are causative for MEN 2B. The 95% of MEN 2B patients are associated with a point mutation in exon 16 (M918/T). A second point mutation at codon 883 has been found in 2%-3% of MEN 2B cases. RET proto-oncogene is also involved in different neoplastic and not neoplastic neurocristopathies. Other RET mutations cause MEN 2A syndrome, familial medullary thyroid carcinoma, or Hirschsprung's disease. RET gene expression is also involved in Neuroblastoma. The main diagnosis standards are the acetylcholinesterase study of rectal mucosa and the molecular analysis of RET. In our protocol the rectal biopsy is, therefore, the first approach. RET mutation detection offers the possibility to diagnose MEN 2B predisposition at a pre-clinical stage in familial cases, and to perform an early total prophylactic thyroidectomy. The surgical treatment of MEN 2B is total thyroidectomy with cervical limphadenectomy of the central compartment of the neck. When possible, this intervention should be performed with prophylactic aim before 1 year of age in patients with molecular genetic diagnosis. Recent advances into the mechanisms of RET proto-oncogene signaling and pathways of RET signal transduction in the development of MEN 2 and MTC will allow new treatment possibilities.

Cell death and the developing enteric nervous system

This review discusses current knowledge about cell death in the developing enteric nervous system (ENS). It also includes findings about the molecular mechanisms by which such death is mediated. Additional consideration is given to trophic factors that contribute to survival of the precursors and neurons and glia of the ENS, as well to genes that, when mutated or deleted, trigger their death. Although further confirmation is needed, present observations support the view that enteric neural crest-derived precursor cells en route to the gut undergo substantial levels of apoptotic death, but that once these cells colonize the gut, there is relatively little death of precursor cells or of neurons and glia during the fetal period. There are also indications that normal neuron loss occurs in the ENS, but at times beyond the perinatal stage. Taken together, these findings suggest that ENS development is similar is some ways, but different in others from extra-enteric areas of the vertebrate central and peripheral nervous systems, in which large-scale apoptotic death of precursor neurons and glia occurs during the fetal and perinatal periods. Potential reasons for these differences are discussed such as a fetal enteric microenvironment that is especially rich in trophic support. In addition to the cell death that occurs during normal ENS development, this review discusses mechanisms of experimentally-induced ENS cell death, such as those that are associated with defective glial cell-line derived neurotrophic factor/Ret signaling, which are an animal model of human congenital megacolon (aganglionosis; Hirschsprung's disease). Such considerations underscore the importance of understanding cell death in the developing ENS, not just from a curiosity-driven point of view, but also because the pathophysiology behind many disorders of human gastrointestinal function may originate in abnormalities of the mechanisms that govern cell survival and death during ENS development.

Hirschsprung's disease and medullary thyroid carcinoma: 15-year experience with molecular genetic screening of the RET proto-oncogene

PURPOSE

Inactivating germline mutations in the RET proto-oncogene are the major genetic cause of Hirschsprung's disease (HD). In some cases, HD can be associated with medullary thyroid carcinoma (MTC) that is commonly caused by activating RET mutations.

METHODS

The retrospective and prospective genetic analyses of 157 patients with HD operated on between December 1979 and June 2011 were carried out. DNA was isolated from peripheral leukocytes. HD patients and family members were tested for RET mutations by direct sequencing and single-strand conformation polymorphism methods.

RESULTS

RET mutations were detected in 16 patients (10%). Association with MTC was found in two families, other eight families had a mutation with potentially high risk of MTC development and four novel mutations were detected. Total colonic aganglionosis was noted to have a high mutation detection rate (40%). Three patients underwent total thyroidectomy (two had clinical manifestation of MTC, one C-cell hyperplasia).

CONCLUSION

Results show the benefit of systematic RET mutation screening in HD patients in order to identify the risk of MTC in the preclinical stage of the disease. All patients should be tested for RET mutations at least in exon 10, and now additionally in exon 11 and 13, as well.

Intronic RET gene variants in Down syndrome-associated Hirschsprung disease in an African population

BACKGROUND

Clinical association between Hirschsprung disease (HD) and Down syndrome (DS) is well established. RET promoter and intron 1 variations have been shown to interfere with RET function, increasing the risk of HD pathogenesis. The intronic single-nucleotide polymorphism 2 (SNP2 [rs2435357]) has been associated with DS-associated HD (DS-HD). This study focuses on variations of specific RET intron, 1 SNPs (viz, SNP1 [rs2506004] and SNP2 [rs2435357]) in DS-HD.

PATIENTS AND METHODS

DNA was extracted from paraffin-embedded tissue samples and whole blood in 14 patients with DS with histologically proven HD. Polymerase chain reaction products of RET intron 1 were screened for genetic variation and matched to DS and controls from the general population.

RESULTS

Thirty-seven blood and/or tissue from 14 patients with DS-HD were investigated. RET intronic variations (SNP1 [rs2506004] or SNP2 [rs2435357]) were detected in all patients. SNP1 was detected in all patients, was heterozygous in 9, and homozygous in 5 samples (all aganglionic and 1 total colonic aganglionosis). SNP2 was absent in 6 patients, heterozygous in 6, and homozygous in 3. Three DS controls had a heterozygous SNP1. Homozygous intronic SNP RET variations were related to aganglionic tissue but not normally ganglionated or transitional zone from the same individual.

CONCLUSIONS

Potential disease-related RET mutations were identified in the intron region in 80% of patients with DS-HD investigated, suggesting a causal relationship. The presence of a homozygous form in the aganglionic tissue probably represents a somatic mutation, which suggests local microenvironmental factors in HD pathogenesis.

Molecular mechanisms of RET receptor-mediated oncogenesis in multiple endocrine neoplasia 2

Multiple endocrine neoplasia type 2 is an inherited cancer syndrome characterized by tumors of thyroid and adrenal tissues. Germline mutations of the REarranged during Transfection (RET) proto-oncogene, leading to its unregulated activation, are the underlying cause of this disease. Multiple endocrine neoplasia type 2 has been a model in clinical cancer genetics, demonstrating how knowledge of the genetic basis can shape the diagnosis and treatment of the disease. Here, we discuss the nature and effects of the most common recurrent mutations of RET found in multiple endocrine neoplasia type 2. Current understanding of the molecular mechanisms of RET mutations and how they alter the structure and function of the RET protein leading to its aberrant activation, and the effects on RET localization and signaling are described.

RET mutational spectrum in Hirschsprung disease: evaluation of 601 Chinese patients

Rare (RVs) and common variants of the RET gene contribute to Hirschsprung disease (HSCR; congenital aganglionosis). While RET common variants are strongly associated with the commonest manifestation of the disease (males; short-segment aganglionosis; sporadic), rare coding sequence (CDS) variants are more frequently found in the lesser common and more severe forms of the disease (females; long/total colonic aganglionosis; familial).

Here we present the screening for RVs in the RET CDS and intron/exon boundaries of 601 Chinese HSCR patients, the largest number of patients ever reported. We identified 61 different heterozygous RVs (50 novel) distributed among 100 patients (16.64%). Those include 14 silent, 29 missense, 5 nonsense, 4 frame-shifts, and one in-frame amino-acid deletion in the CDS, two splice-site deletions, 4 nucleotide substitutions and a 22-bp deletion in the intron/exon boundaries and 1 single-nucleotide substitution in the 5′ untranslated region. Exonic variants were mainly clustered in RET the extracellular domain. RET RVs were more frequent among patients with the most severe phenotype (24% vs. 15% in short-HSCR). Phasing RVs with the RET HSCR-associated haplotype suggests that RVs do not underlie the undisputable association of RET common variants with HSCR. None of the variants were found in 250 Chinese controls.

Neural precursor death is central to the pathogenesis of intestinal aganglionosis in Ret hypomorphic mice

The RET tyrosine kinase is required for the migration, proliferation, and survival of the enteric neural crest-derived cells (ENCCs) that form the enteric nervous system (ENS). Hypomorphic RET alleles cause intestinal aganglionosis [Hirschsprung disease (HSCR)], in which delayed migration and successive nonapoptotic ENCC death are considered to be major contributory factors. The significance of ENCC death in intestinal aganglionosis, however, has remained unclear. We show that elevated expression of Bcl-xL inhibits ENCC death in both Ret-null and hypomorphic states. However, the rescued Ret-null mice showed ENS malfunction with reduced nitric oxide synthase expression in colonic neurons, revealing the requirement of RET for neuronal differentiation. In contrast, the inhibition of cell death allows morphologically and functionally normal ENS formation in Ret hypomorphic mice. These results indicate that ENCC death is a principal cause of intestinal aganglionosis in a Ret hypomorphic state, and suggest that the inhibition of cell death is a route to the prevention of HSCR.

Polymorphisms of the RET gene in hirschsprung disease, anorectal malformation and intestinal pseudo-obstruction in Taiwan

BACKGROUND/PURPOSE

Mutations in the receptor tyrosine kinase RET gene are associated with Hirschsprung disease (HD), which is also known as congenital intestinal aganglionosis. We found an association with specific alleles in five single nucleotide polymorphism (SNP) sites of the RET gene in our HD patients.

METHODS

We compared the association of specific RET SNP alleles in patients with severe GI disorders such as anorectal malformation (ARM) or pediatric intestinal pseudo-obstruction (IPO) to that in HD patients. Sixty-four HD, 23 ARM and 35 IPO patients were included. Genomic DNA extracted from blood samples was analyzed by polymerase chain reaction and DNA sequencing analysis.

RESULTS

The allele distributions of all five RET SNPs in the HD patients deviated from those in the normal population (p < 0.05), whereas those of the ARM patients did not. The allele distributions of these RET SNPs in the IPO patients were all significantly different from those in the HD patients. Allele distributions of exon 2 and 13 in the IPO patients were also significantly different from those of the normal population. The frequencies of all the HD-predominant alleles were lower in the HD patients than the normal population, and were even lower in the IPO patients.

CONCLUSION

This study strengthens the association of specific RET SNP alleles with typical HD in Taiwan.

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.

Pathogenicity of DNA variants and double mutations in multiple endocrine neoplasia type 2 and von Hippel-Lindau syndrome

CONTEXT

Cancer genetics is fundamental for preventive medicine, in particular in pheochromocytoma-associated syndromes. Variants in two susceptibility genes, SDHC and RET, were found in a kindred with head and neck paraganglioma. This observation of coincident DNA variants, both reported as pathogenic, in two known susceptibility genes prompted the question of their pathogenic relevance.

OBJECTIVE

Our objective was to elucidate the pathogenic role of the detected variants and study the prevalence of such variants.

PATIENTS

Patients were registrants from the European-American Pheochromocytoma-Paraganglioma and German von Hippel-Lindau Disease Registries.

DESIGN

Analysis of germline mutation screening results for all pheochromocytoma-paraganglioma susceptibility genes, including RET [multiple endocrine neoplasia type 2 (MEN 2)] and VHL [von Hippel-Lindau disease (VHL)]. Cases in which more than one DNA variant was found were clinically reevaluated, and cosegregation of the disease with the variant was analyzed within the registrants' families. A total of 1000 controls were screened for the presence of detected variants, and in silico analyses were performed.

RESULTS

Three variants were identified, RET p.Tyr791Phe and p.Ser649Leu and VHL p.Pro81Ser. The frequencies of RET p.Ser649Leu (0.07%) and p.Tyr791Phe (0.9%) compared with controls excluded the two variants' role in the etiology of MEN 2 and VHL. None of the carriers of the RET variants who underwent prophylactic thyroidectomy showed medullary thyroid carcinoma. Clinical reinvestigation of 18 variant carriers excluded MEN 2. VHL variant p.Pro81Ser, also previously described as a mutation, did not segregate with the VHL in one family. In silico analyses for these variants predicted unmodified protein function.

CONCLUSIONS

RET p.Tyr791Phe and p.Ser649Leu and VHL p.Pro81Ser are definitely not pathogenic mutations for VHL and MEN 2. Misinterpretation results in irreversible clinical consequences.

RET mutation Tyr791Phe: the genetic cause of different diseases derived from neural crest

Activating germline RET mutations are presented in patients with familial medullary thyroid carcinoma (FMTC) and multiple endocrine neoplasia (MEN) types 2A and 2B, whereas inactivating germline mutations in patients with Hirschsprung's disease (HSCR). The aim of this study was to evaluate genotype-phenotype correlations of the frequently discussed Tyr791Phe mutation in exon 13 of the RET proto-oncogene. Screening of three groups of patients was performed (276 families with medullary thyroid carcinoma (MTC), 122 families with HSCR, and 29 patients with pheochromocytoma). We found this mutation in 3 families with apparently sporadic MTC, 3 families with FMTC/MEN2, 1 patient with pheochromocytoma, and 3 families with HSCR. All gene mutation carriers have a silent polymorphism Leu769Leu in exon 13. In three families second germline mutations were detected: Cys620Phe (exon 10) in MEN2A family, Met918Thr (exon 16) in MEN2B family, and Ser649Leu (exon 11) in HSCR patient. Detection of the Tyr791Phe mutation in MEN2/MTC and also in HSCR families leads to the question whether this mutation has a dual character (gain-of-function as well as loss-of-function). A rare case of malignant pheochromocytoma in a patient with the Tyr791Phe mutation is presented. This study shows various clinical characteristics of the frequently discussed Tyr791Phe mutation.

Multiple endocrine neoplasia type 2 RET protooncogene database: repository of MEN2-associated RET sequence variation and reference for genotype/phenotype correlations

Multiple endocrine neoplasia type 2 (MEN2) is an inherited, autosomal-dominant disorder caused by deleterious mutations within the RET protooncogene. MEN2 RET mutations are mainly heterozygous, missense sequence changes found in RET exons 10, 11, and 13-16. Our group has developed the publicly available, searchable MEN2 RET database to aid in genotype/phenotype correlations, using Human Genome Variation Society recommendations for sequence variation nomenclature and database content. The MEN2 RET database catalogs all RET sequence variation relevant to the MEN2 syndromes, with associated clinical information. Each database entry lists a RET sequence variation's location within the RET gene, genotype, pathogenicity classification, MEN2 phenotype, first literature reference, and comments (which may contain information on other clinical features, complex genotypes, and additional literature references). The MEN2 phenotype definitions were derived from the International RET Mutation Consortium guidelines for classification of MEN2 disease phenotypes. Although nearly all of the 132 RET sequence variation entries initially cataloged in the database were from literature reports, novel sequence variation and updated phenotypic information for any existing database entry can be submitted electronically on the database website. The database website also contains links to selected MEN2 literature reviews, gene and protein information, and RET reference sequences. The MEN2 RET database (www.arup.utah.edu/database/MEN2/MEN2_welcome.php) will serve as a repository for MEN2-associated RET sequence variation and reference for RET genotype/MEN2 phenotype correlations.

Genetic basis of Hirschsprung's disease

Hirschsprung's disease (HSCR) is a developmental disorder characterized by the absence of ganglion cells in the lower digestive tract. Aganglionosis is attributed to a disorder of the enteric nervous system (ENS) whereby ganglion cells fail to innervate the lower gastrointestinal tract during embryonic development. HSCR is a complex disease that results from the interaction of several genes and manifests with low, sex-dependent penetrance and variability in the length of the aganglionic segment. The genetic complexity observed in HSCR can be conceptually understood in light of the molecular and cellular events that take place during the ENS development. DNA alterations in any of the genes involved in the ENS development may interfere with the colonization process, and represent a primary etiology for HSCR. This review will focus on the genes known to be involved in HSCR pathology, how they interact, and on how technology advances are being employed to uncover the pathological processes underlying this disease.

Genetic testing in other GI diseases

Gastrointestinal development is a complex process comprising folding of the endodermal layer to form the primitive gut tube, cell differentiation along its anteroposterior axis, the budding of the various organ primordia and development of derivative organs like the liver and pancreas and the colonisation of the gut with neuronal precursors. Genetic factors are increasingly recognised as playing a significant role in the disturbance of this developmental process which underlies congenital malformations and gastrointestinal disorders. Furthermore, genetic variation and its interaction with environmental influences play an important role in the pathogenesis of functional gastrointestinal disorders. In this review, we discuss the contribution of genetic variants, ranging from highly penetrant mutations and chromosomal abnormalities to genetic polymorphisms, to the pathogenesis of a number of structural and functional gastrointestinal disorders.

The nervous system and gastrointestinal function

The enteric nervous system is an integrative brain with collection of neurons in the gastrointestinal tract which is capable of functioning independently of the central nervous system (CNS). The enteric nervous system modulates motility, secretions, microcirculation, immune and inflammatory responses of the gastrointestinal tract. Dysphagia, feeding intolerance, gastroesophageal reflux, abdominal pain, and constipation are few of the medical problems frequently encountered in children with developmental disabilities. Alteration in bowel motility have been described in most of these disorders and can results from a primary defect in the enteric neurons or central modulation. The development and physiology of the enteric nervous system is discussed along with the basic mechanisms involved in controlling various functions of the gastrointestinal tract. The intestinal motility, neurogastric reflexes, and brain perception of visceral hyperalgesia are also discussed. This will help better understand the pathophysiology of these disorders in children with developmental disabilities.

TNF signaling inhibition in the CNS: implications for normal brain function and neurodegenerative disease

The role of tumor necrosis factor (TNF) as an immune mediator has long been appreciated but its function in the brain is still unclear. TNF receptor 1 (TNFR1) is expressed in most cell types, and can be activated by binding of either soluble TNF (solTNF) or transmembrane TNF (tmTNF), with a preference for solTNF; whereas TNFR2 is expressed primarily by microglia and endothelial cells and is preferentially activated by tmTNF. Elevation of solTNF is a hallmark of acute and chronic neuroinflammation as well as a number of neurodegenerative conditions including ischemic stroke, Alzheimer's (AD), Parkinson's (PD), amyotrophic lateral sclerosis (ALS), and multiple sclerosis (MS). The presence of this potent inflammatory factor at sites of injury implicates it as a mediator of neuronal damage and disease pathogenesis, making TNF an attractive target for therapeutic development to treat acute and chronic neurodegenerative conditions. However, new and old observations from animal models and clinical trials reviewed here suggest solTNF and tmTNF exert different functions under normal and pathological conditions in the CNS. A potential role for TNF in synaptic scaling and hippocampal neurogenesis demonstrated by recent studies suggest additional in-depth mechanistic studies are warranted to delineate the distinct functions of the two TNF ligands in different parts of the brain prior to large-scale development of anti-TNF therapies in the CNS. If inactivation of TNF-dependent inflammation in the brain is warranted by additional pre-clinical studies, selective targeting of TNFR1-mediated signaling while sparing TNFR2 activation may lessen adverse effects of anti-TNF therapies in the CNS.

The proliferating field of neural crest stem cells

Neural crest stem cells were first isolated from early embryonic neural crest in the early 1990s, but in the past 5 years, there has been a burst of discoveries of neural crest-derived stem cells from diverse locations. Here, we summarize these data, highlighting the characteristics of each stem cell type. These cells vary widely in the markers they express and the variety of cell types they appear to generate. They occupy diverse locations, but in some cases multiple stem cell types apparently occupy physically proximate niches. To date, few molecular similarities can be identified between these stem cells, although a systematic comparison is required. We note other issues worthy of attention, including aspects of the in vivo behavior of these stem cells, their niches, and their lineage relationships. Together, analysis of these issues will clarify this expanding, but still young, field and contribute to exploration of the important therapeutic potential of these cells.

Mutation analysis of endothelin-B receptor gene in patients with Hirschsprung disease in Taiwan

BACKGROUND

Endothelin-B receptor (EDNRB) signaling pathway is associated for Hirschsprung disease (HSCR). The aim of this study was to investigate the EDNRB gene mutation in patients with HSCR in Taiwan and correlate the genotype and phenotype.

PATIENTS AND METHODS

Using polymerase chain reaction amplification and direct sequencing, we screened for mutations in the coding regions and intron/exon boundaries of the EDNRB gene in 39 isolated HSCR cases and compared them with those in 400 control chromosomes.

RESULTS

In 3 cases, heterozygous variations in exon 1 and 2 of the EDNRB gene predicted missense mutations of the first cytosolic (M132I), second transmembrane (I157V), second exoplasmic (M173T), and third transmembrane (V185M) domains of the EDNRB protein. Three of the 4 mutations in our study have not been reported previously. For total 39 unrelated cases, the mutation rates were estimated to be 10% (3 of 30) for short-segment HSCR and 7.7% (3 of 39) for all HSCR cases.

CONCLUSIONS

We did not detect a significant genotype-phenotype correlation. In conclusion, this study identified 4 mutations within the EDNRB gene associated with HSCR. Because HSCR is a multifactorial and multigene disorder, the higher mutation rate of 10% for short-segment HSCR suggests the important role that the EDNRB gene plays in the pathogenesis of short-segment HSCR in Taiwan.

Gastrointestinal motility disorders in adolescent patients: transitioning to adult care

A wide spectrum of gastrointestinal motility disorders present in childhood. Some are unique to children, especially congenital disorders including certain pseudo-obstruction disorders or those associated with anatomic developmental defects, whereas others are common adult disorders, such as achalasia, that rarely manifest in children. This article reviews the pediatric presentations and sequelae of childhood gastrointestinal motility disorders and then discusses long-term management issues for these children as they progress into adulthood. The goal is to optimize medical care and ensure the adequate nutritional status essential for neurocognitive and psychosocial development of the child. Multidisciplinary care from specialists, including gastroenterologists, psychologists, and pain specialists, is often required to optimize the lives of these patients.

Molekularbiologie, Grundlagenforschung und Diagnose des Morbus Hirschsprung

The proto-oncogene RET is the major gene responsible for Hirschsprung's disease (HSCR), with RET mutations also implied in different pathologies. A variety of mutations of the RET proto-oncogene have been detected in HSCR patients. Special attention should be paid to rare patients who carry mutations of one of the critical cysteine residues of these exons, known to predispose to MEN2A. In these cases, HSCR can be associated with the development of neuroendocrine tumors such as medullary thyroid carcinoma (MTC) or MEN2A, for which a prophylactic thyroidectomy is advisable in the presence of a tumor causing RET mutation. In combined MEN2A/HSCR families, RET gene testing, tumor screening and prophylactic thyroidectomy are indicated as in MEN2A. The multigenic origin of HSCR and the absence of a "standard" RET mutation associated with HSCR currently make a routine molecular diagnosis impossible.

Concomitant existence of total bowel aganglionosis and congenital central hypoventilation syndrome in a neonate with PHOX2B gene mutation

Hirschsprung's disease (HSCR) is characterized by the absence of intramural ganglion cells in the distal gut, resulting in bowel obstruction shortly after birth. Congenital central hypoventilation syndrome (CCHS) results in hypoventilation, most pronounced during sleep, with relative insensitivity to hypercarbia and reduced insensitivity to hypoxia. Congenital central hypoventilation syndrome with HSCR is a rare condition with variable severity. Both CCHS and HSCR are uncommon and their co-occurrence may suggest a common etiology, probably involving a fault of neural crest development. Recent reports have identified the paired-like homeobox 2B (PHOX2B) gene as the major gene for CCHS and HSCR. We report here an identified PHOX2B gene in a newborn baby who had concurrence of CCHS and total colonic aganglionosis with proximal small bowel involvement. Management of this rare disorder is challenging not only because it presents in newborn stage but also because it has extensive HSCR. Considering the issue of medical futility, the therapeutic and ethical dilemma of this infant was discussed.

Single nucleotide polymorphisms in the RET gene and their correlations with Hirschsprung disease phenotype

Hirschsprung disease (HSCR) is a congenital, heterogeneous disorder, characterized by the absence of intestinal ganglion cells. Recent advances show that the RET gene is a major locus involved in the pathogenesis of HSCR. The aim of this study was to analyse if the HSCR phenotype in the Polish population is associated with the presence of polymorphisms in exons 2, 3, 7, 11, 13, 14 and 15 of the RET gene. Molecular results were compared with clinical and long-term follow-up data in 70 Polish patients with HSCR (84.3% with a short segment and 15.7% with a long segment of aganglionic gut). Single-nucleotide polymorphisms were analysed by using the minisequencing SNaPshot multiplex method. The 135G>A polymorphism in RET exon 2 was overrepresented in HSCR patients, compared with a healthy control group. Moreover, the 135G>A variant was shown to be associated with the severe HSCR phenotype. Two other polymorphisms, 2071G>A in exon 11 and 2712C>G in exon 15, were underrepresented in the patients. The results confirm that these RET polymorphisms play a role in the aetiology of HSCR.

Allele dosage-dependent penetrance of RET proto-oncogene in an Israeli-Arab inbred family segregating Hirschsprung disease

Hirschsprung disease (HSCR) is characterised by intestinal obstruction resulting from an absence of ganglion cells in the intestinal tract. The mutations in the major gene, RET, associated with isolated HSCR, are dominant loss-of-function mutations with incomplete penetrance and variable expressivity. We have ascertained a large inbred Israeli-Arab family segregating HSCR. Sequencing of the RET gene showed a splicing mutation, IVS6+5G- >A, in the homozygous state in all the females with severe forms of HSCR and in the heterozygous state in the male patient with short-segment HSCR. The recently described hypomorphic-RET predisposing allele, rs2435357, was transmitted in the heterozygous state to the male patient, but was not transmitted to the three affected females. Although the heterozygous IVS6+5G- >A is of low-penetrance for short-segment HSCR disease, the homozygous state is fully penetrant for total aganglionosis or long-segment HSCR. As in other inbred populations segregating a weakly penetrant RET allele (Mennonite), our findings support the hypothesis that the penetrance of RET gene mutations for the HSCR phenotype depends on: (i) the nature of the mutation, (ii) the allele dosage and (iii) modifier-loci.

A complex additive model of inheritance for Hirschsprung disease is supported by both RET mutations and predisposing RET haplotypes

PURPOSE

The RET proto-oncogene is considered to be the major susceptibility gene involved in Hirschsprung disease. Traditional RET germline mutations account for a small subset of Hirschsprung disease patients, but several studies have shown that there is a specific haplotype of RET associated with the sporadic forms of Hirschsprung disease. We have investigated for RET germline mutations and analyzed the RET haplotypic distribution in carriers versus noncarriers of RET germline mutations.

METHODS

We have screened the coding region of RET in 106 Spanish Hirschsprung disease patients using dHPLC technology. Statistical comparisons of the distribution of RET haplotypes between sporadic patients with and without a RET germline mutation were performed.

RESULTS

Nine novel germline mutations and one previously described were identified. A significant over-transmission of the "Hirschsprung disease haplotype" was detected when comparing transmitted versus nontransmitted alleles in the group of Hirschsprung disease triads without mutation. However, no distortion of the transmission of alleles was found in the group of mutated families.

CONCLUSIONS

These results would be concordant with a complex additive model of inheritance. The whole findings seem to suggest that low-penetrance mutations would be necessary but not sufficient and the additional presence of the "Hirschsprung disease haplotype" could contribute to the manifestation of the disease.

A novel susceptibility locus for Hirschsprung's disease maps to 4q31.3-q32.3

We report on a multigenerational family with isolated Hirschsprung's disease (HSCR). Five patients were affected by either short segment or long segment HSCR. The family consists of two main branches: one with four patients (three siblings and one maternal uncle) and one with one patient. Analysis of the RET gene, the major gene involved in HSCR susceptibility, revealed neither linkage nor mutations. A genome wide linkage analysis was performed, revealing suggestive linkage to a region on 4q31-q32 with a maximum parametric multipoint LOD score of 2.7. Furthermore, non-parametric linkage (NPL) analysis of the genome wide scan data revealed a NPL score of 2.54 (p = 0.003) for the same region on chromosome 4q (D4S413-D4S3351). The minimum linkage interval spans a region of 11.7 cM (12.2 Mb). No genes within this chromosomal interval have previously been implicated in HSCR. Considering the low penetrance of disease in this family, the 4q locus may be necessary but not sufficient to cause HSCR in the absence of modifying loci elsewhere in the genome. Our results suggest the existence of a new susceptibility locus for HSCR at 4q31.3-q32.3.

Pseudo-obstruction intestinale chronique

Chronic intestinal pseudo-obstruction (CIPO) is a disease characterized by episodes resembling mechanical obstruction in the absence of organic, systemic, or metabolic disorders. Pseudo-obstruction is an uncommon condition and can result from primary (40%) or secondary (60%) causes. The most common symptoms are nausea, vomiting, abdominal distension, abdominal pain and constipation or diarrhea. These symptoms are usually present many years before CIPO diagnosis. They can lead to severe electrolyte disorders and malnutrition. Principles for management of patients with CIPO are: to establish a correct clinical diagnosis in excluding mechanical obstruction; to perform a symptomatic and physiologic assessment of the gastrointestinal tract involved; to look for extra-intestinal manifestations, especially for myopathy and neuropathy; to discuss in some cases a surgery for full-thickness intestinal biopsies, and/or a neuromuscular biopsy in case of mitochondrial cytopathy suspicion. The management is primarily focused on symptom control and nutritional support to prevent weight loss and malnutrition. Treatment of CIPO includes prokinetic agents which may help to reduce gastrointestinal symptoms Courses of antibiotics may be needed in patients with symptoms suggestive of bacterial overgrowth. When necessary, enteral nutrition is preferred. In carefully selected patients, feeding jejunostomy with or without decompression gastrostomy may be tried. Long term parenteral nutrition should be reserved for patients who can not tolerate enteral nutrition. Intestinal transplantation can be discussed in selected patients.