Hirschsprung's disease

Benzophenone-3 induced abnormal development of enteric nervous system in zebrafish through MAPK/ERK signaling pathway

Hirschsprung disease (HSCR) is a congenital disease characterized by the absence of enteric neurons, which is derived from the failure of the proliferation, differentiation or migration of the enteric neural crest cells (ENCCs). HSCR is associated with multiple risk factors, including polygenic inheritance factors and environmental factors. Genetic studies have been extensively performed, whereas studies related to environmental factors remain insufficient. Benzophenone-3 (BP-3), one important component of the ultraviolet (UV) filters, has been proved to have cytotoxicity and neurotoxicity which might be associated with HSCR. In this study, we used zebrafish as a model to investigate the relationship between BP-3 exposure and the development of the enteric nervous system (ENS) in vivo. Embryos exposed to BP-3 showed an average of 46% reduction of the number of the enteric neurons number. Besides, the ENCCs specific markers (ret and hand2) were downregulated upon BP-3 exposure. Moreover, we identified potential targets of BP-3 through Network Pharmacology Analysis and Autodock and demonstrated that the attenuation of the MAPK/ERK signaling might be the potential mechanism underlying the inhibition of the ENS development by BP-3. Importantly, MAPK/ERK signaling agonist could be used to rescue the ENS defects of zebrafish induced by BP-3. Overall, we characterized the influence of BP-3 on ENS development in vivo and explored possible molecular mechanisms.

Brain size reductions associated with endothelin B receptor mutation, a cause of Hirschsprung's disease

Background

ET_B has been reported to regulate neurogenesis and vasoregulation in foetal development. Its dysfunction was known to cause HSCR, an aganglionic colonic disorder with syndromic forms reported to associate with both small heads and developmental delay. We therefore asked, "is CNS maldevelopment a more general feature of ET_B mutation?" To investigate, we reviewed the micro-CT scans of an ET_B^−/− model animal, sl/sl rat, and quantitatively evaluated the structural changes of its brain constituents.

Methods

Eleven neonatal rats generated from ET_B^+/− cross breeding were sacrificed. Micro-CT scans were completed following 1.5% iodine-staining protocols. All scans were reviewed for morphological changes. Selected organs were segmented semi-automatically post-NLM filtering: TBr, T-CC, T-CP, OB, Med, Cer, Pit, and S&I Col. Volumetric measurements were made using Drishti rendering software. Rat genotyping was completed following analysis. Statistical comparisons on organ volume, organ growth rate, and organ volume/bodyweight ratios were made between sl/sl and the control groups based on autosomal recessive inheritance. One-way ANOVA was also performed to evaluate potential dose-dependent effect.

Results

sl/sl rat has 16.32% lower body weight with 3.53% lower growth rate than the control group. Gross intracranial morphology was preserved in sl/sl rats. However, significant volumetric reduction of 20.33% was detected in TBr; similar reductions were extended to the measurements of T-CC, T-CP, OB, Med, and Pit. Consistently, lower brain and selected constituent growth rates were detected in sl/sl rat, ranging from 6.21% to 11.51% reduction. Lower organ volume/bodyweight ratio was detected in sl/sl rats, reflecting disproportional neural changes with respect to body size. No consistent linear relationships exist between ET_B copies and intracranial organ size or growth rates.

Conclusion

Although ET_B^−/− mutant has a normal CNS morphology, significant size reductions in brain and constituents were detected. These structural changes likely arise from a combination of factors secondary to dysfunctional ET-1/ET-3/ET_B signalling, including global growth impairment from HSCR-induced malnutrition and dysregulations in the neurogenesis, angiogenesis, and cerebral vascular control. These changes have important clinical implications, such as autonomic dysfunction or intellectual delay. Although further human study is warranted, our study suggested comprehensive managements are required for HSCR patients, at least in ET_B^−/− subtype.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12868-021-00646-z.

The advances of genetics research on Hirschsprung's disease

Hirschsprung's disease (HSCR) is a rare and complex congenital disorder characterized by the absence of the enteric neurons in lower digestive tract with an incidence of 1/5 000. Affected infant usually suffer from severe constipation with megacolon and distended abdomen, and face long-term complications even after surgery. In the last 2 decades, great efforts and progresses have been made in understanding the genetics and molecular biological mechanisms that underlie HSCR. However, only a small fraction of the genetic risk can be explained by the identified mutations in the previously established genes. To search novel genetic alterations, new study designs with advanced technologies such as genome/exome-wide association studies (GWASs/EWASs) and next generation sequencing (NGS) on target genes or whole genome/exome, were applied to HSCR. In this review, we summaries the current development of the genetics researches on HSCR based on GWASs/EWASs and NGS, focusing on the newly discovered variants and genes, and their potential roles in HSCR pathogenesis.

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.

Gli family zinc finger 1 is associated with endothelin receptor type B in Hirschsprung disease

Hirschsprung disease (HSCR) is a newborn colorectal disease characterized by an absence of ganglia in the distal gut. Hedgehog (Hh) and endothelin signaling serve important roles in gastrointestinal tract formation. Alterations in the signaling pathways disrupt the development of enteric neural crest cells (ENCCs). It is not known whether there is any coordination between these pathways in the pathogenesis of HSCR. In the present study, tissue samples from 35 patients with HSCR, including stenotic aganglionosis gut and normal ganglionic gut, were obtained. The expression of Gli family zinc finger 1 (Gli1) and endothelin receptor type B (EDNRB) was determined using reverse transcription-quantitative polymerase chain reaction, immunohistochemistry and western blotting. In addition, the SK-N-SH cell line was used to investigate the association between Hh signaling and the expression of EDNRB. The results revealed aberrant expression of Gli1 in the aganglionic segments, as well as decreased expression of Gli1 in tissues from 7 patients with HSCR exhibited, whereas tissues from 9 patients with HSCR exhibited increased Gli1 expression compared with the expression in the normal tissues. There was a negative association between EDNRB expression and Gli1 expression in the same sample. Knockdown of Gli1 by small interfering RNA and inhibition of Hh signaling by Vismodegib in SK-N-SH cells increased EDNRB expression. By contrast, upregulation of Gli1 expression by plasmids and activation of Hh signaling by Purmorphamine decreased EDNRB expression. Furthermore, premature enteric ganglia were observed in 4 patients with HSCR with decreased Gli1 expression. Thus, the results of the present study suggest that altered Gli1 expression negatively regulates EDNRB expression in patients with HSCR. The increased expression of EDNRB induced by decreased Gli1 expression may represent a novel mechanism in HSCR.

Gene-environment interactions and the enteric nervous system: Neural plasticity and Hirschsprung disease prevention

Intestinal function is primarily controlled by an intrinsic nervous system of the bowel called the enteric nervous system (ENS). The cells of the ENS are neural crest derivatives that migrate into and through the bowel during early stages of organogenesis before differentiating into a wide variety of neurons and glia. Although genetic factors critically underlie ENS development, it is now clear that many non-genetic factors may influence the number of enteric neurons, types of enteric neurons, and ratio of neurons to glia. These non-genetic influences include dietary nutrients and medicines that may impact ENS structure and function before or after birth. This review summarizes current data about gene-environment interactions that affect ENS development and suggests that these factors may contribute to human intestinal motility disorders like Hirschsprung disease or irritable bowel syndrome.

Fluorescence Visualization of the Enteric Nervous Network in a Chemically Induced Aganglionosis Model

Gastrointestinal motility disorders, severe variants in particular, remain a therapeutic challenge in pediatric surgery. Absence of enteric ganglion cells that originate from neural crest cells is a major cause of dysmotility. However, the limitations of currently available animal models of dysmotility continue to impede the development of new therapeutics. Indeed, the short lifespan and/or poor penetrance of existing genetic models of dysmotility prohibit the functional evaluation of promising approaches, such as stem cell replacement strategy. Here, we induced an aganglionosis model using topical benzalkonium chloride in a P0-Cre/GFP transgenic mouse in which the neural crest lineage is labeled by green fluorescence. Pathological abnormalities and functional changes in the gastrointestinal tract were evaluated 2–8 weeks after chemical injury. Laparotomy combined with fluorescence microscopy allowed direct visualization of the enteric neural network in vivo. Immunohistochemical evaluation further confirmed the irreversible disappearance of ganglion cells, glial cells, and interstitial cell of Cajal. Remaining stool weight and bead expulsion time in particular supported the pathophysiological relevance of this chemically-induced model of aganglionosis. Interestingly, we show that chemical ablation of enteric ganglion cells is associated with a long lifespan. By combining genetic labeling of neural crest derivatives and chemical ablation of enteric ganglion cells, we developed a newly customized model of aganglionosis. Our results indicate that this aganglionosis model exhibits decreased gastrointestinal motility and shows sufficient survival for functional evaluation. This model may prove useful for the development of future therapies against motility disorders.

Ibuprofen slows migration and inhibits bowel colonization by enteric nervous system precursors in zebrafish, chick and mouse

Hirschsprung Disease (HSCR) is a potentially deadly birth defect characterized by the absence of the enteric nervous system (ENS) in distal bowel. Although HSCR has clear genetic causes, no HSCR-associated mutation is 100% penetrant, suggesting gene-gene and gene-environment interactions determine HSCR occurrence. To test the hypothesis that certain medicines might alter HSCR risk we treated zebrafish with medications commonly used during early human pregnancy and discovered that ibuprofen caused HSCR-like absence of enteric neurons in distal bowel. Using fetal CF-1 mouse gut slice cultures, we found that ibuprofen treated enteric neural crest-derived cells (ENCDC) had reduced migration, fewer lamellipodia and lower levels of active RAC1/CDC42. Additionally, inhibiting ROCK, a RHOA effector and known RAC1 antagonist, reversed ibuprofen effects on migrating mouse ENCDC in culture. Ibuprofen also inhibited colonization of Ret+/- mouse bowel by ENCDC in vivo and dramatically reduced bowel colonization by chick ENCDC in culture. Interestingly, ibuprofen did not affect ENCDC migration until after at least three hours of exposure. Furthermore, mice deficient in Ptgs1 (COX 1) and Ptgs2 (COX 2) had normal bowel colonization by ENCDC and normal ENCDC migration in vitro suggesting COX-independent effects. Consistent with selective and strain specific effects on ENCDC, ibuprofen did not affect migration of gut mesenchymal cells, NIH3T3, or WT C57BL/6 ENCDC, and did not affect dorsal root ganglion cell precursor migration in zebrafish. Thus, ibuprofen inhibits ENCDC migration in vitro and bowel colonization by ENCDC in vivo in zebrafish, mouse and chick, but there are cell type and strain specific responses. These data raise concern that ibuprofen may increase Hirschsprung disease risk in some genetically susceptible children.

Hirschsprung's disease, Down syndrome, and missing heritability: too much collagen slows migration

Hirschsprung's disease (HSCR) causes functional intestinal obstruction due to the absence of the enteric nervous system (ENS) in the distal bowel and is usually diagnosed shortly after birth or during childhood. While several genetic and nongenetic factors have been linked to HSCR, the underlying mechanisms that prevent ENS precursors from colonizing distal bowel during fetal development are not completely understood in many affected children. In this issue of the JCI, Soret and colleagues identify a new mechanism that causes HSCR-like disease in mice and involves deposition of excess collagen VI in the intestine by migrating ENS precursors as they colonize fetal bowel. Remarkably, their findings may explain some of the so-called missing heritability of HSCR and suggest a mechanism for increased HSCR incidence in children with Down syndrome (trisomy 21).

QTL analysis identifies a modifier locus of aganglionosis in the rat model of Hirschsprung disease carrying Ednrb(sl) mutations

Hirschsprung disease (HSCR) exhibits complex genetics with incomplete penetrance and variable severity thought to result as a consequence of multiple gene interactions that modulate the ability of enteric neural crest cells to populate the developing gut. As reported previously, when the same null mutation of the Ednrb gene, Ednrb^sl, was introgressed into the F344 strain, almost 60% of F344-Ednrb^sl/sl pups did not show any symptoms of aganglionosis, appearing healthy and normally fertile. These findings strongly suggested that the severity of HSCR was affected by strain-specific genetic factor (s). In this study, the genetic basis of such large strain differences in the severity of aganglionosis in the rat model was studied by whole-genome scanning for quantitative trait loci (QTLs) using an intercross of (AGH-Ednrb^sl×F344-Ednrb^sl) F₁ with the varying severity of aganglionosis. Genome linkage analysis identified one significant QTL on chromosome 2 for the severity of aganglionosis. Our QTL analyses using rat models of HSCR revealed that multiple genetic factors regulated the severity of aganglionosis. Moreover, a known HSCR susceptibility gene, Gdnf, was found in QTL that suggested a novel non-coding sequence mutation in GDNF that modifies the penetrance and severity of the aganglionosis phenotype in EDNRB-deficient rats. A further identification and analysis of responsible genes located on the identified QTL could lead to the richer understanding of the genetic basis of HSCR development.

Genetic background strongly modifies the severity of symptoms of Hirschsprung disease, but not hearing loss in rats carrying Ednrb(sl) mutations

Hirschsprung disease (HSCR) is thought to result as a consequence of multiple gene interactions that modulate the ability of enteric neural crest cells to populate the developing gut. However, it remains unknown whether the single complete deletion of important HSCR-associated genes is sufficient to result in HSCR disease. In this study, we found that the null mutation of the Ednrb gene, thought indispensable for enteric neuron development, is insufficient to result in HSCR disease when bred onto a different genetic background in rats carrying Ednrb^sl mutations. Moreover, we found that this mutation results in serious congenital sensorineural deafness, and these strains may be used as ideal models of Waardenburg Syndrome Type 4 (WS4). Furthermore, we evaluated how the same changed genetic background modifies three features of WS4 syndrome, aganglionosis, hearing loss, and pigment disorder in these congenic strains. We found that the same genetic background markedly changed the aganglionosis, but resulted in only slight changes to hearing loss and pigment disorder. This provided the important evidence, in support of previous studies, that different lineages of neural crest-derived cells migrating along with various pathways are regulated by different signal molecules. This study will help us to better understand complicated diseases such as HSCR and WS4 syndrome.

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.

Vitamin A facilitates enteric nervous system precursor migration by reducing Pten accumulation

Hirschsprung disease is a serious disorder of enteric nervous system (ENS) development caused by the failure of ENS precursor migration into the distal bowel. We now demonstrate that retinoic acid (RA) is crucial for GDNF-induced ENS precursor migration, cell polarization and lamellipodia formation, and that vitamin A depletion causes distal bowel aganglionosis in serum retinol-binding-protein-deficient (Rbp4(-/-)) mice. Ret heterozygosity increases the incidence and severity of distal bowel aganglionosis induced by vitamin A deficiency in Rbp4(-/-) animals. Furthermore, RA reduces phosphatase and tensin homolog (Pten) accumulation in migrating cells, whereas Pten overexpression slows ENS precursor migration. Collectively, these data support the hypothesis that vitamin A deficiency is a non-genetic risk factor that increases Hirschsprung disease penetrance and expressivity, suggesting that some cases of Hirschsprung disease might be preventable by optimizing maternal nutrition.

Adult segmental Hirschsprung disease

Hirschsprung disease (HD) is characterized by aganglionosis, which mainly occurs in the rectum and distal sigmoid colon. Typical HD is seldom diagnosed in adulthood, and segmental involvement is very rare. A 37-year-old man suffered from refractory constipation for 20 years. He could only defecate once a week and frequently needed an enema for defecation. A barium enema showed an annular stenotic segment of the rectosigmoid colon of 8 cm in length, which started 10 cm above anal circulation and showed dilated colon above the stenotic segment. The distal rectum was normal. The narrowed segment of the rectum was resected. At one-year follow up, the patient had normal defecation without laxatives.

Retinoic acid regulates murine enteric nervous system precursor proliferation, enhances neuronal precursor differentiation, and reduces neurite growth in vitro

Enteric nervous system (ENS) precursors undergo a complex process of cell migration, proliferation, and differentiation to form an integrated network of neurons and glia within the bowel wall. Although retinoids regulate ENS development, molecular and cellular mechanisms of retinoid effects on the ENS are not well understood. We hypothesized that retinoids might directly affect ENS precursor differentiation and proliferation, and tested that hypothesis using immunoselected fetal ENS precursors in primary culture. We now demonstrate that all retinoid receptors and many retinoid biosynthetic enzymes are present in the fetal bowel at about the time that migrating ENS precursors reach the distal bowel. We further demonstrate that retinoic acid (RA) enhances proliferation of subsets of ENS precursors in a time-dependent fashion and increases neuronal differentiation. Surprisingly, however, enteric neurons that develop in retinoid deficient media have dramatically longer neurites than those exposed to RA. This difference in neurite growth correlates with increased RhoA protein at the neurite tip, decreased Smurf1 (a protein that targets RhoA for degradation), and dramatically decreased Smurf1 mRNA in response to RA. Collectively these data demonstrate diverse effects of RA on ENS precursor development and suggest that altered fetal retinoid availability or metabolism could contribute to intestinal motility disorders.

Diminished Ret expression compromises neuronal survival in the colon and causes intestinal aganglionosis in mice

Mutations in the RET gene are the primary cause of Hirschsprung disease (HSCR), or congenital intestinal aganglionosis. However, how RET malfunction leads to HSCR is not known. It has recently been shown that glial cell line-derived neurotrophic factor (GDNF) family receptor alpha1 (GFRalpha1), which binds to GDNF and activates RET, is essential for the survival of enteric neurons. In this study, we investigated Ret regulation of enteric neuron survival and its potential involvement in HSCR. Conditional ablation of Ret in postmigratory enteric neurons caused widespread neuronal death in the colon, which led to colonic aganglionosis. To further examine this finding, we generated a mouse model for HSCR by reducing Ret expression levels. These mice recapitulated the genetic and phenotypic features of HSCR and developed colonic aganglionosis due to impaired migration and successive death of enteric neural crest-derived cells. Death of enteric neurons was also induced in the colon, where reduction of Ret expression was induced after the period of enteric neural crest cell migration, indicating that diminished Ret expression directly affected the survival of colonic neurons. Thus, enteric neuron survival is sensitive to RET dosage, and cell death is potentially involved in the etiology of HSCR.

Adult Hirschsprung's Disease Diagnosed During Forensic Autopsy

We report a case of fatal Hirschsprung's disease (HD) discovered at autopsy. A 20-year-old man collapsed at home. Emergency medical personnel found him in cardiac arrest and all resuscitative efforts failed. He had a past history of chronic constipation since infancy. Forensic autopsy revealed a megacolon full of gas and stools. Microscopic examination showed absence of ganglion cells in a short segment of the rectum and enterocolitis in the left and transverse colon. HD is rarely described in adults. In many cases, patients complained of constipation since infancy but the affection remained misdiagnosed. The relative good tolerance of the disease is usually due to a short aganglionic bowel segment. Enterocolitis is a frequent and severe complication of HD in children but is rarely described in adults. This case suggests the importance of HD diagnosis in childhood in order to avoid fatal complications with forensic consequences.

Reduced endothelin converting enzyme-1 and endothelin-3 mRNA in the developing bowel of male mice may increase expressivity and penetrance of Hirschsprung disease–like distal intestinal aganglionosis

Hirschsprung disease (distal intestinal aganglionosis, HSCR) is a multigenic disorder with incomplete penetrance, variable expressivity, and a strong male gender bias. Recent studies demonstrated that these genetic patterns arise because gene interactions determine whether enteric nervous system (ENS) precursors successfully proliferate and migrate into the distal bowel. We now demonstrate that male gender bias in the extent of distal intestinal aganglionosis occurs in mice with Ret dominant-negative mutations (RetDN) that mimic human HSCR. We hypothesized that male gender bias could result from reduced expression of a gene already known to be essential for ENS development. Using quantitative real-time polymerase chain reaction (PCR) we demonstrated reduced levels of endothelin converting enzyme-1 and endothelin-3 mRNA in the male mouse bowel at the time that ENS precursors migrate into the colon. Other HSCR-associated genes are expressed at comparable levels in male and female mice. Testosterone and Mullerian inhibiting substance had no deleterious effect on ENS precursor development, but adding EDN3 peptide to E11.5 male RetDN heterozygous mouse gut explants in organ culture significantly increased the rate of ENS precursor migration through the bowel.

Enteric neuroblasts require the phosphatidylinositol 3-kinase/Akt/Forkhead pathway for GDNF-stimulated survival

Glial cell line-derived neurotrophic factor (GDNF)/Ret signaling is required for enteric neural crest survival, proliferation, migration and process extension, but signaling pathways that mediate enteric nervous system (ENS) precursor development are poorly understood. We therefore examined GDNF effects on immunoselected ENS precursor survival and neuronal process extension in the presence of phosphatidylinositol 3-kinase and mitogen-activated protein kinase pathway inhibitors. These studies demonstrated that GDNF promotes ENS precursor survival through phosphatidylinositol-3-kinase. Specifically, GDNF induces phosphorylation of Akt and loss of the Akt substrates FOXO1 and FOXO3a from the nucleus of ENS precursors. Furthermore, dominant negative Akt or active FOXO1 constructs promote ENS precursor cell death while a dominant negative FOXO1 construct prevents cell death. In contrast, the MAPK kinase inhibitor PD98059 did not influence ENS precursor survival or neurite extension. These data demonstrate a critical role for PI-3 kinase/Akt/FOXO signaling, but not for MAPK in ENS precursor survival and neurite extension.

Long-term results of treatment of Hirschsprung's disease

Many children with Hirschsprung's disease (HD) have a good outcome following surgical treatment, but long-term follow-up studies have identified a number of concerns. Analysis of long-term function in children after surgical management is difficult. The most commonly encountered problems include constipation, incontinence, enterocolitis and the overall impact of the disease on lifestyle (quality of life). Other complications are less frequent. Each of these problems will be discussed.

Management of Hirschsprung's disease: a comparison of Soave's and Duhamel's pull-through methods

The aim of this study was to compare the safety and benefits of Soave's and Duhamel's pull-through procedures for the management of Hirschsprung's disease (HD). The patients consisted of 33 boys (85%) and six girls (15%), a ratio of 5.5:1. Their ages ranged from 1 day to 8 years. Rectal biopsy was performed to confirm the diagnosis of HD. Twenty-five patients (64%) underwent Soave's pull-through, and 13 patients (33%) underwent Duhamel's pull-through. Twenty children (80%) out of the 25 undergoing Soave's pull-through recovered uneventfully, compared with 11 out of the 13 (84%) undergoing Duhamel's pull-through. The complications following Soave's procedure included strictures in two patients (8%), enterocolitis in another two (8%), and anastomotic leakage in one (4%). Additional operations were required in two patients (8%). The complications following Duhamel's procedure included stricture in one patient (7.6%) and enterocolitis in another (7.6%). An additional operation was required in one patient (7.6%). The rate of constipation was 16% after the Soave's pull-through compared with 15% after the Duhamel's pull-through. There was no significant difference between the two procedures in postoperative surgical morbidity or in long-term risk of enterocolitis. In the light of present findings, both procedures appear comparable in terms of efficiency and associated complications.

[Necrotizing enterocolitis during pregnancy in a woman operated on at six months of Hirschsprung's disease]

Necrotizing enterocolitis is a rare and severe complication of Hischsprung's disease. Aggravation of unknown or undertreated Hischsprung's disease may be seen during pregnancy. To our knowledge, the following case is the first combining those two elements: necrotizing enterocolitis in a 20 years old women operated on of Hischsprung's disease when she was six months. The final diagnosis was made 24 hours later. Definitive treatment was a three-stage ileal pouch-anal anastomosis.

GDNF availability determines enteric neuron number by controlling precursor proliferation

To clarify the role of Ret signaling components in enteric nervous system (ENS) development, we evaluated ENS anatomy and intestinal contractility in mice heterozygous for Ret, GFRalpha1 and Ret ligands. These analyses demonstrate that glial cell line-derived neurotrophic factor (GDNF) and neurturin are important for different aspects of ENS development. Neurturin is essential for maintaining the size of mature enteric neurons and the extent of neuronal projections, but does not influence enteric neuron number. GDNF availability determines enteric neuron number by controlling ENS precursor proliferation. However, we were unable to find evidence of programmed cell death in the wild type ENS by immunohistochemistry for activated caspase 3. In addition, enteric neuron number is normal in Bax(-/-) and Bid(-/-) mice, suggesting that, in contrast to most of the rest of the nervous system, programmed cell death is not important for determining enteric neuron numbers. Only mild reductions in neuron size and neuronal fiber counts occur in Ret(+/-) and Gfra1(+/-) mice. All of these heterozygous mice, however, have striking problems with intestinal contractility and neurotransmitter release, demonstrating that Ret signaling is critical for both ENS structure and function.

Gastrointestinal manifestations of multiple endocrine neoplasia type 2

OBJECTIVE

To determine the clinical features, natural history, and role of surgery for gastrointestinal manifestations of the multiple endocrine neoplasia type 2 (MEN 2) syndromes.

SUMMARY BACKGROUND DATA

The MEN 2 syndromes are characterized by medullary thyroid carcinoma and other endocrinopathies. In addition, some patients with MEN 2A develop Hirschsprung's disease (HD), and all patients with MEN 2B have intestinal neuromas and megacolon that can cause significant gastrointestinal problems.

METHODS

From 83 families with MEN 2A, eight patients with HD were identified (MEN 2A-HD). These and all patients with MEN 2B followed at the authors' institution (n = 53) were sent questionnaires to describe the onset and type of gastrointestinal symptoms and treatment they had before the diagnosis of MEN 2. Records of all patients responding were reviewed, including radiographic imaging, histology, surgical records, and genetic testing.

RESULTS

Thirty-six of the 61 patients (59%) responded (MEN 2A = 8, MEN 2B = 28) to the questionnaires. All patients with MEN 2A-HD were operated on for HD 2 to 63 years before being diagnosed with MEN 2. All patients responding were underweight as infants and had symptoms of abdominal pain, distention, and constipation. Eighty-eight percent had hematochezia, 63% had emesis, and 33% had intermittent diarrhea before surgery. All patients with MEN 2A-HD had rectal biopsies with a diverting colostomy as the initial surgical procedure. This was followed by a colostomy takedown and pull-through procedure at a later interval. Ninety-three percent of patients with MEN 2B had gastrointestinal symptoms 1 to 24 years before the diagnosis of MEN 2. Symptoms included flatulence (86%), abdominal distention or being underweight as a child (64%), abdominal pain (54%), constipation or diarrhea (43%), difficulty swallowing (39%), and vomiting (14%). Seventy-one percent of patients with MEN-2B with gastrointestinal symptoms had radiographic imaging, 32% were admitted to the hospital, and 29% underwent surgery.

CONCLUSIONS

Patients with MEN 2A-HD had a typical HD presentation and always required surgery. Patients with MEN 2B have significant gastrointestinal symptoms, but less than a third had surgical intervention. Understanding the clinical course and differences in these patients will improve clinical management.

Increased smooth muscle contractility of intestine in the genetic null of the endothelin ETB receptor: a rat model for long segment Hirschsprung's disease

BACKGROUND AND AIMS

The endothelin ETB receptor null rat (ETB(-/-)R) has an intestinal segment without ganglia, and this rat is characterised by intestinal obstruction similar to that observed in human Hirschsprung's disease. In the present study, we have examined the myogenic mechanism responsible for obstruction in the ETB(-/-)R.

RESULTS

The ETB(-/-)R had an enlarged belly and the average lifespan was 18.1 days. The bowel from the rectum to the lower part of the small ileum was constricted whereas the upper region was dilated with faecal stasis and thus presented as megaileum. The constricted muscle segments without ganglia had a greater increase in absolute force when stimulated by carbachol, high K+, and endothelin-1 compared with that of normal siblings. In contrast, in the dilated part with ganglia, the absolute contractile force due to these stimulants in the ETB(-/-)R was not different from that in the ETB(+/+)R. Such a functional hypertrophy of the musculature was observed in parts of the colon, caecum, and distal ileum without ganglia but not in the part of the proximal ileum and jejunum with ganglia. Morphological study demonstrated that the thickness of the circular and longitudinal muscle layers was greater in the constricted part of the intestine in the ETB(-/-)R, and these changes were associated with an increase in the number of smooth muscle cells.

CONCLUSIONS

Our findings suggest that both increased contractility of smooth muscle and increased thickness of the intestinal muscular wall may contribute to the intestinal obstruction in the ETB(-/-)R.

Lessons from genetically engineered animal models. II. Disorders of enteric neuronal development: insights from transgenic mice

Understanding the development of congenital defects of the enteric nervous system, such as Hirschsprung's disease, was, until recently, an intractable problem. The analysis of transgenic mice, however, has now led to the discovery of a number of genetic abnormalities that give rise to aganglionic congenital megacolon or neuronal intestinal dysplasia. The identification of the responsible genes has enabled the developmental actions of their protein products to be investigated, which, in turn, has made it possible to determine the causes of aganglionoses. Two models of pathogenesis have emerged. One, associated with mutations in genes encoding endothelin-3 or its receptor, endothelin B, posits the premature differentiation of migrating neural crest-derived progenitors, causing the precursor pool to become depleted before the bowel has been fully colonized. The second, associated with mutations in genes encoding glial cell line-derived neurotrophic factor (GDNF), its preferred receptor GFRalpha1, or their signaling component, Ret, appears to deprive a GDNF-dependent common progenitor of adequate support and/or mitogenic drive. In both cases, the terminal bowel becomes aganglionic when the number of colonizing neuronal precursors is inadequate.

Long-term outcome after Hirschsprung's disease: patients' perspectives

BACKGROUND

The results of treatment of Hirschsprung's disease (HD) are not uniformly successful, and the parents' and child's interpretation of the outcome may be different from that of the surgeon.

METHODS

One hundred seven children treated for HD over 22 1/2 years were reviewed retrospectively. Adequate clinical data regarding functional outcomes were available in 78, of which, an additional questionnaire was completed by 69. Follow-ups were divided into type of pull-through (PT), age at time of PT (< 4 months and > 4 months) and age at last follow-up (< 5 years, 5 to 15 years and > 15 years). Degrees of constipation and incontinence were determined using standard scoring systems.

RESULTS

The median age at presentation was 9 days (range, 1 day to 9.4 years), and 41% presented within the first 72 hours of life. Aganglionosis extended to the rectosigmoid region in 75%, proximal to the splenic flexure in 11%, and total colon in 6.5%. Treatments included a Soave procedure in 57, Duhamel in 31, Swenson in 10, and sphincterotomy-myectomy in two. No surgical treatment or only a decompressing enterostomy was performed in two and three children, respectively, and two underwent a PT elsewhere. Complications related to the enterostomy occurred in 39 patients. Postoperative enterocolitis and bowel obstructions occurred in nine and 13 patients, respectively. Staple-line fusion, anastomotic stenosis, and anastomotic leak occurred in nine, 17, and two patients, respectively. Seven children died, only one directly related to the PT. Aside from more constipation associated with the Duhamel procedure, functional outcomes were not significantly different among the types of PTs. No differences were found between patients who underwent a PT at less than 4 months of age and those at greater than 4 months of age. Significantly, however, fecal continence was relatively poor in those less than 15 years of age (50% with only fair to poor continence), but improved markedly once the child reached later adolescence (8%, P < .0002). Correspondingly, the negative impact on the child's social life was much greater in the younger age groups compared with later adolescence (50% of those aged 5 to 15 years v 18% of those > 15 years; P = .007). The effect on the families' lives mirrored this. Finally, only 64% of patients were interpreted as having "normal" stooling habits, yet 90% of parents were moderately or very satisfied with their child's outcome, with no differences found among the three sets of comparison groups.

CONCLUSIONS

The outcomes for HD are not always as good as surgeons may perceive; long term follow-up is important. With time, most children significantly improve with respect to fecal continence, but this may not be until later adolescence. In the meantime, the impacts on their social and family lives may be significant. Despite high complication rates, often poor continence, and relative infrequency of normal stooling habits, most parents are satisfied with their child's outcome and adapt to their functional abnormalities along with them.

Development of the human gastrointestinal tract: twenty years of progress

A combination of approaches has begun to elucidate the mechanisms of gastrointestinal development. This review describes progress over the last 20 years in understanding human gastrointestinal development, including data from both human and experimental animal studies that address molecular mechanisms. Rapid progress is being made in the identification of genes regulating gastrointestinal development. Genes directing initial formation of the endoderm as well as organ-specific patterning are beginning to be identified. Signaling pathways regulating the overall right-left asymmetry of the gastrointestinal tract and epithelial-mesenchymal interactions are being clarified. In searching for extrinsic developmental regulators, numerous candidate trophic factors have been proposed, but compelling evidence remains elusive. A critical gene that initiates pancreas development has been identified, as well as a number of genes regulating liver, stomach, and intestinal development. Mutations in genes affecting neural crest cell migration have been shown to give rise to Hirschsprung's disease. Considerable progress has been achieved in understanding specific phenomena, such as the transcription factors regulating expression of sucrase-isomaltase and fatty acid-binding protein. The challenge for the future is to integrate these data into a more complete understanding of the physiology of gastrointestinal development.