Intestinal neuronal dysplasia is seen in about 25% to 35% of patients with HD, and HD occurs in 17.9% of patients with IND.4
Alternatively, structural anomalies also occur roughly in one in every 5000 live births with a slight male preponderance. The most common anomaly is an imperforate anus, which is a term used to denote all anorectal malformations ranging from simple to complex defects. These are often associated with anomalies of the urinary tract, trachea, esophagus, heart, gas- trointestinal tract, and skeletal system. The other anomalies are duplications and malrotation, which are manifested in the neonatal period.
Evolution of the Enteric Nervous System
The enteric nervous system (ENS) is unique, as it can function without input from the brain or spinal cord. It also has all the neurotransmitters that are found in the central nervous system (CNS).5,6The evolution of the ENS has been long debated. Okamoto and Ueda7 showed that the extramural parasympathetic innervation devel- ops in the 5th and 6th weeks of embryogenesis.
Studies in the chick and quail embryos have defined the embryogenesis of the ENS.8The ENS develops as a result of the migration of cells along defined pathways from the neural crest in a craniocaudal direction. These cells migrate to the vagal and sacral crest.8,9The vagal crest col- onizes almost the entire bowel, whereas the sacral crest is responsible for the postumbilical bowel. In the absence of the vagal crest cells, the sacral neural crest cells are not capable of giving Developmental disorders related to colorectal
disease are for the most part identified with Hirschsprung’s disease (HD) in children and adults, and hereditary conditions related to chronic megacolon. Other disorders result from structural abnormalities that manifest as ano- rectal malformations. Conditions that are rare and others that arise from surrounding struc- tures are listed in Table 2.1.
Incidence
The incidence of HD is reported as approxi- mately 1 in 5000 live births.1 The disease has a male-to-female ratio of 4.1 : 1, though this ratio is decreased as the length of the aganglionic segment increases. Familial incidence has been reported in 15% to 20% of the patients with total aganglionosis of the colon and 50% of those with total aganglionosis of the intestine. Agangliono- sis has been confined to the rectosigmoid in 75%
of the patients and to the sigmoid, splenic flexure, and the transverse colon in 17%.2 No clear genetic inheritance patterns have been identified in spite of the genetic factors that have been implicated. There is an increased risk for siblings of affected persons at 4% as compared with that of the general population, and also association with other genetic abnormalities and syndromes. There has been no racial pre- dominance of the disease. Intestinal neuronal dysplasia (IND) described by Meier-Ruge in 1971,3resembles HD in the clinical presentation;
however, it differs in histology, which shows hyperplasia of the submucosal and myenteric plexus4 as opposed to aganglionosis in HD.
2
Etiology of Congenital Colorectal Disease
Massarat Zutshi and Tracy L. Hull
9
rise to the enteric ganglia. This migration takes place during the 9th to 12th week, which is much later than that which occurs in the small bowel in the 7th week. The selection of the pathway is most likely achieved by a balanced combina- tion of molecules that promote and reduce cell adhesion.10Aganglionosis and hypoganglionosis are a result of factors that govern the migration, differentiation, and colonization of the sacral crest cells and is also due to the premature dif- ferentiation and early cessation of migration.
Cessation of migration correlates with cell–cell and cell–matrix adhesion molecules, consistent with an adhesive basis.11–13The timing of inhibi- tion of migration results in aganglionosis of dif- ferent parts of the bowel. If the crest cells are inhibited in the 8th week, only the colon is affected and the ileum remains unaffected. Inhi- bition in the 9th week results in aganglionosis of the descending colon and rectosigmoid, and only the rectosigmoid is affected when it occurs between the 10th and 12th weeks.
Neurons are nonmigratory, and thus for ganglia to develop the bowel the neurons must be colonized by crest-derived neural precursors.
The process of homing in of the neural crest pre- cursors is dependent on the microenvironment of the smooth muscle cells, which are the ulti- mate target of the crest cells and tell the cells where to stop migration and form enteric ganglia.14 This process is associated with an extracellular matrix called laminin, which is present in the mucosal and serosal epithelium of the smooth muscle cells and is the target for the neural crest cells.15The neural crest cells acquire a receptor for laminin asynchronously, which directs this homing process. This receptor is called laminin binding protein (LBP 110) and is
necessary for laminin binding. Laminin pro- motes neuritic extension and axonal growth.16 Laminin 1 promotes development of neurons from enteric cells of neural crest cells. There is a histologic difference between aganglionosis and denervation. An aganglionic segment is not den- ervated; what are missing are the cell bodies of the enteric neurons, which mediate the reflexes.
An aganglionic segment may be hypernervated, and this is seen in HD, wherein an abundance of laminin 1 is seen. The ENS is essential for normal propulsive intestinal motility. The peristaltic reflex has long been recognized as one that is evoked by increased luminal pressure and results in a wave of excitation and relaxation that descends the bowel and is propulsive; how- ever, its net effect is as a relaxant. This feature accounts for the contraction and narrowing that occurs in the hypoganglionic segment of bowel.
Etiology in Hirschsprung’s Disease and Allied Disorders
The diseases grouped under this heading are defined as a congenital absence of neurons in the terminal portion of the gut. It encompasses HD, in which a segment of the bowel is totally agan- glionic, and other diseases where the pathology is dysganglionosis. The diseases grouped under dysganglionosis include hypoganglionosis or hyperganglionosis as seen in intestinal neuronal dyplasias. Hirschsprung’s disease is a multigene abnormality with a wide variety of mutations.
The widely differing phenotypes, however, cannot account for the known mutations. Each gene involvement adds to the final HD disease phenotype and many of these abnormalities are as yet unknown. No one mechanism can explain the pathogenesis in HD due to the complexity of the mechanisms and multigenic nature of its evo- lution. Some of the gene abnormalities and their phenotype are listed in Table 2.2.
The animal models of aganglionosis are studied in lethal spotted (ls/ls) and piebald lethal mutant (sl/sl) mice. These mutations are inher- ited as autosomal recessive traits and provide the best models of HD.17,18Many observations have pointed to the role of inheritance in HD. The male-to-female ratio of 4 : 1, which is clearly imbalanced, the high rate of recurrences seen in siblings of affected individuals, the association of other genetic diseases with other genetic abnormalities, and the demonstration of the
Table 2.1. Classification of congenital colorectal disease 1. Structural and developmental malformations
Hirschsprung disease Anorectal malformations Congenital colonic varices Rectal arteriovenous malformations 2. Myopathies
Familial and degenerative myopathy mimicking Hirschsprung’s disease
Hereditary internal sphincter myopathy Spastic pelvic floor syndrome 3. Retrorectal tumors
Developmental cysts Chordoma
Anterior sacral meningocele
The ret proto-oncogene is mapped on chro- mosome 10 and plays a role in the control of proliferation, differentiation, and migration of subsets of the neural crest cells. The location of the Ret protein was reported by Martucciello et al22 in 1995, and this study supports the hypothesis that HD may be due to a loss in func- tional effect of Ret. In HD the autosomal domi- nant form has been demonstrated with functional loss of one copy of ret. Only a small number of HD patients, however, present a total deletion or disruption of the ret proto-oncogene.
Identical ret abnormalities, however, can result in dissimilar lengths of involvement of aganglionosis.
Other gene abnormalities are linked to genes encoding endothelin 3 (EDN3) or its receptor endothelin B (EDNRB). These genes are located on chromosome 13 and play a critical role in the development of ENS. The detection of this abnormality was a result of the analysis of the effect of knockout of the gene that encodes these molecules in mice.23When EDNRB is knocked out, an agangliosis develops that is similar to that seen in sl/sl mice.24 When EDN3 is mutated in ls/ls mice, arginine is replaced with a tryptophan residue in the C terminus of big EDN3.23 This results in a more localized abnormality wherein only the terminal colon is aganglionic. This effect is not well understood, and it is postulated that because EDN1/N2 do not compensate for the loss of EDN3, its effect must be quite local. The effect of EDN3 on crest-derived precursors by itself does not result in aganglionosis; however, in combination with factors controlling the microenvironment it may cause premature dif- ferentiation of the precursors as neurons, result- ing in distal aganglionosis.
Ret mutations account for 50% of all familial mutations and 15% to 20% of the sporadic cases of HD. Currently it is estimated that 50 ret25and 13 EDRNB26mutations have been reported. Of these 95% of EDRNB and 25% of ret mutations result in short segment aganglionosis.
Etiology of Other Congenital Diseases Mimicking Hirschsprung’s Disease
Hypoganglionosis in adults is acquired or inflammatory in its origin and is rare as an isolated condition. The acquired form can be disease in several animal models are pointers of
the pattern of inheritance. This pattern has been studied in the autosomal dominant form with incomplete penetrance and also in the autoso- mal recessive form. Badner et al19have studied the inheritance patterns and found that with aganglionosis beyond the sigmoid colon the mode of inheritance was that of a dominant gene with incomplete penetrance, while in those with aganglionosis that did not extend beyond the sigmoid colon the pattern was likely to be due to a recessive gene with very low penetrance.
C-ret (Rearranged During Transfection) and Glial Cell Line–Derived Neurotropic Factor (GNDF)
The c-ret proto-oncogene has been widely studied, and germline mutations have been responsible for HD and multiple endocrine neo- plasia type II (MEN II). The enteric neurons are dependant on the c-ret for survival.20This has prompted studies in lethal spotted mice and knockout mice that have targeted the c-ret proto- oncogene. This gene encodes for a Ret protein tyrosine kinase (TK) for which the GNDF has been defined as a ligand.21Activation of the Ret receptor by GNDF is therefore a very important step for formation of the ENS. The GNDF- independent Ret forms ENS of the rostral foregut and sympathetic chain, except for the sympathetic chain and superior cervical gan- glion.6 When c-ret is totally knocked out in transgenic mice, the ENS fails to develop in the entire bowel except the rostral foregut, when the gene is homozygous. However, the heterozygous mice have a normal ENS, and all ret mutations in humans are heterozygous and this could be explained by effects of additional genes or envi- ronmental factors.6
Table 2.2. Hirschsprung’s disease: genetic association
Gene Phenotype Chromosome
ret AD HSCR 10
GNDF HSCR 5
EDNRB AR HSCR* 13
EDN3 AR HSCR* 20
Sox 10 AD HSCR* 22
* Shah Waardenburg.
AD, autosomal dominant; AR, autosomal recessive.
caused by various conditions that include anox- emia or toxic or autoimmune processes, which result in neuronal depletion. The inflammatory type is also due to an autoimmune process, in which selective neurons are attacked by mononuclear cells.
Isolated intestinal neuronal dysplasia type B is found in 58.5% of constipated adults.27A milder form was seen in about 14.6% of all patients, and these patients may subsequently develop diverticulosis.27 Type A is rare, occur- ring in less than 5% of cases, and is character- ized by aplasia or hypoplasia of the adrenergic innervation.
The specific etiology of degenerative hollow visceral myopathy mimicking HD is unknown.
The inheritance pattern may be autosomal dom- inant with high or low penetrance.28The genetic defect is as yet unknown; however, a link with a defect in synthesis of a contractile protein29has been postulated. Involvement of the muscle layer that develops at 12 weeks of gestation may be an indication that the insult is during the first trimester. A mitochondrial DNA mutation has been postulated as a probable lesion in familial visceral myopathy.30
Diseases Associated with Hirschsprung’s Disease
Congenital anomalies associated with HD have been reported from various series and have an overall incidence of about 14.7% in 2856 patients.31Down syndrome is the most common chromosomal abnormality associated with HD, and the genetic modifiers have been located on chromosome 21q 22.32The diagnosis of HD in Down syndrome is often delayed because other associated anomalies take precedence and because constipation is often present in these patients due to hypotonia and hypothyroidism.
Cardiac abnormalities have been reported in the range of 0.5% to 1.0% of the general pop- ulation, and the incidence is increased in patients with Down syndrome. The common defects are endocardial cushion defects and patent ductus arteriosus. Hirschsprung’s disease is often associated with other neurocristopathy manifestations, such as pheochromocytoma, neuroblastoma, neurofibromatosis, and MEN II.
Waardenburg syndrome, caused by a gene on chromosome 2, is also associated and is charac-
terized by pigment abnormalities, cranial and spinal nerve anomalies, and bowel dysfunction.
Micro-ophthalmia and anophthalmia are also congenial disorders that are associated with HD. Associated gasterointestinal tract anomalies include malrotation, intestinal atresia anorectal malformations, Meckel’s diverticulum, and pyloric stenosis.
Conclusion
Hirschsprung first described HD in 1886, and since then many theories have been postulated to explain the genesis of this rather complex disease. Recent advances and studies in animal models have furnished a better understanding of the embryogenesis of the human enteric nervous system and the pathophysiology of HD. Genetic studies have identified various factors that can collectively influence the disease phenotype in HD. In humans ret, EDRNB, and EDN3 have been implicated in the etiology of HD. No one factor, however, can be singled out, as HD is a complex multigenic disorder. Future studies in identification of abnormal genes that cause dys- ganglionosis could help in the prevention and treatment of many of the disorders that have a genetic etiology. At this stage genetic counseling is still based on the length of the aganglionic segment. Future research will provide a better understanding of this complex genetic disorder and better means of counseling affected families.
Understanding of the pathophysiology and its link to the disease phenotype of HD and its related diseases will also modify treatment options and help future generations of affected families.
References
1. Passarge E. The genetics of Hirschsprung’s disease.
N Engl J Med 1967;276:138–143.
2. Kleinhaus S, Boley SJ, Sheran M, Sieber WK.
Hirschsprung’s disease: a survey of the members of the surgical section of the American Academy of Pediatrics.
J Pediatr Surg 1979;14:588–597.
3. Meier-Ruge W. Classification of malformations of col- orectal innervation. Vech Dtsch Ges Pathol 1971;506:55.
4. Puri P, Lake BD, Nixon HH, et al. Neuronal colonic dysplasia: an unusual association of Hirschsprung’s disease. J Pediatr Surg 1977;12:681–685.
5. Furness JB, Costa M. The enteric nervous system.
1987:65–69. New York Churchill Livingstone.
19. Badner JA, Sieber WK, Garver KL, Chakravarti A. A genetic study of Hirschsprung’s disease. Am J Hum Genet 1990;46:568–580.
20. Pachynis V, Mankoo B, Constantini F. Expression of c-ret protooncogene during mouse embryogenesis.
Development 1993;119:1005–1017.
21. Jing S, Wen D, Yu Y, et al. GDNF-induced activation of the Ret protein tyrosine kinase is mediated by GDNFR- alpha a novel receptor for GDNBF. Cell 1996;85:
1113–1124.
22. Martucciello G, Favre A, Takahashi M, Jasonni V.
Immunohistochemical localization of Ret protein in Hirschsprung’s disease. J Pediatr Surg 1995;30:433–436.
23. Baynash AG, Hosoda K, Giaid A, et al. Interaction of endothelin 3 with endothelin b receptor is essential for development of epidermal melanocytes and enteric neurons. Cell 1994;79:1277–1285.
24. Hosoda K, Hammer RE, Richardson JA, et al. Targeted and natural (piebald-lethal) mutation of endothelin-B receptor gene in mutagenic Hirschsprung’s disease. Cell 1994;79:1267–1276.
25. Charkravarty A. Endothelin receptor mediated sig- nalling in Hirschsprung’s disease. Hum Mol Genet 1996;5:303–307.
26. Kusafuka T, Wang YP. Novel mutation of the endothe- lin-B receptor gene in isolated patients wih Hirschs- prung’s disease. Hum Mol Genet 1996;5:347–349.
27. Stoss F, Meier-Ruge W. Experience with neuronal intes- tinal dysplasia (NID) in adults. Eur J Pediatr Surg 1994;4:298–302.
28. Schuffler MD, Pagon RB, Schwartz R, Bill AH. Visceral myopathy of the gastrointestinal tract. Gasteroenterol- ogy 1988;94:892–898.
29. Ionasescu V, Ionasescu R, Anuras S. Alterations in synthesis of contractile protein in fresh and cultured stomach smooth muscle in familial visceral myopathy.
Gasteroenterology 1981;80:1182.
30. Lowsky R, Davidson G,Wolman S, et al. Familial visceral myopathy associated with mitochondrial myopathy.
Gut 1993;34:279–283.
31. Brown RA. Disorders and Congenital Malformations Associated with Hirschsprung’s Disease. Harwood Aca- demic Publishers, Amsterdam, 2000.
32. Puffenberger EG, Hosada K, Washington SS. A missense mutation of the Endothelin-B receptor gene in multi- genic Hirschsprung’s disease. Cell 1994;79:1257–1266.
6. Gershon MD, Kirchgessner AL. Functional anatomy of the enteric nervous system. In Physiology of the gas- trointestinal tract. 3rdEd. Edited by Johnson LR, Alpers DH, Jocobson LR and Walsh JH. New York: Raven Press Vol. 1, 1994, 381–422.
7. Okamoto E, Ueda T. Embryogenesis of intramural ganglia of the gut and its relationship to Hirschsprung’s disease. J Pediatr Surg 1967;14:437–443.
8. LeDourin NM. Experimental analysis of the migration and differentiation of neuroblasts of the autonomous nervous system and neuroectodermal mesenchymal derivatives using a biochemical marking techniques.
Dev Biol 1973;41:162–184.
9. LeDourin NM. The migration of neural crest cells to the wall of the digestive tract in avian embryo. J Embryol Exp Morphol 1973;30:31–48.
10. Erickson CA. Control of neural crest cell migration in avian embryo. Dev Biol 1985;111:138–157.
11. Weston JA. The migration and differentiation of neural crest cells. Adv Morphol 1970;8:41–114.
12. Newgreen DF. Control of the directional migration of migration of mesenchyme cells and neurites. Semin Dev Biol 1990;1:301–311.
13. Akitaya T, Bronner-Fraser M. Expression of cell adhe- sion molecules during initiation and cessation of neural crest migration. Dev Dynam 1992;194:12–20.
14. Pomeranz HD, Sherman DI, Smalheiser NR, et al.
Expression of a neurally related laminin binding protein by neural crest-derived cells that colonize the gut: relationship to the formation of enteric ganglia.
J Comp Neurol 1991;313:625–642.
15. Bilozur ME, Hay ED. Neural crest migration in 3D extra- cellular matrix utilizes laminin, fibronectin or collagen.
Dev Biol 1988;125:19–33.
16. Engvall E, Davis GE, Dickerson K, et al. Mapping of domains in human laminin using monoclonal antibod- ies: localization of the neurite promoting site. J Cell Biol 1986;103:1321–1329.
17. Bolande RP. Animal model of human disease.
Hirschsprung’s disease, aganglionic or hypoganglionic megacolon: animal model. Aganglionic megacolon in piebald and spotted mutant mouse strains. Am J Pathol 1975;79:189–192.
18. Lane PW. Association of megacolon with recessive spotting genes in the mouse. J Hered 1966;108:29–
31.
