Hirschsprung Disease Overview

[Aganglionic Megacolon, HSCR]

Syndromic HSCR

Syndromes associated with HSCR are listed in alphabetical order; the prevalence of HSCR in each syndrome varies widely and is estimated in Table 2.

Bardet-Biedl syndrome (BBS). BBS includes the features of progressive pigmentary retinopathy, obesity, postaxial polydactyly, hypogenitalism, and renal abnormalities, with variable but generally mild mental retardation. HSCR has been reported in approximately 2% of individuals with BBS [Beales et al 1999]. In approximately 10% of affected individuals, BBS overlaps with HSCR and McKusick-Kaufman syndrome (MKKS), which includes hydrometrocolpos and heart disease [Davenport et al 1989]. A total of 11 genes have been identified for BBS, including the MKKS that causes McKusick-Kaufman syndrome [Stone et al 2000]. Specific genotype-phenotype correlations with HSCR have not been established. Inheritance is autosomal recessive.

Cartilage-hair hypoplasia. This skeletal dysplasia, prevalent among the Old Order Amish and Finnish populations, is characterized by short-limbed dwarfism, sparse hair, hypoplastic anemia, and a variety of immune defects. HSCR occurs in roughly 7%-9%, and is more likely to be associated with severe manifestations of the disorder [Makitie & Kaitila 1993, Makitie et al 2001]. The causative gene is the endoribonuclease RNase MRP (RMRP), important in processing of nuclear ribosomal RNA and in mitochondrial DNA synthesis [Ridanpaa et al 2001]. Inheritance is autosomal recessive.

Congenital central hypoventilation syndrome (CCHS). Classic CCHS is characterized by adequate ventilation while the affected individual is awake and by hypoventilation with normal respiratory rates and shallow breathing during sleep; more severely affected individuals hypoventilate when both awake and asleep. Both of these phenotypes present in the newborn period. Children with CCHS often have physiologic and anatomic manifestations of a generalized autonomic nervous system dysfunction, tumors of neural crest origin including neuroblastoma, ganglioneuroma, and ganglioneuroblastoma-altered development of neural crest-derived structures (i.e., Hirschsprung disease). Approximately 20% of individuals with CCHS have HSCR [Trang et al 2005], a combination known as Haddad syndrome.

De novo heterozygous mutations in PHOX2B have been found in 90% of individuals with CCHS [Amiel et al 2003, Matera et al 2004]. A subset of individuals with CCHS have a heterozygous mutation in RET, EDN3, GDNF, or BDNF (Table 3) [Bolk et al 1996, Amiel et al 1998, Sakai et al 1998, Weese-Mayer et al 2002]. In one study, RET was shown to act as a modifier gene for the development of HSCR in persons with CCHS [de Pontual et al 2006].

Familial dysautonomia (FD, Riley-Day syndrome). FD affects the development and survival of sensory, sympathetic, and parasympathetic neurons. It is a debilitating disease present from birth. Progressive neuronal degeneration continues throughout life. Affected individuals have gastrointestinal dysfunction, vomiting episodes, recurrent pneumonia, altered sensitivity to pain and temperature, and cardiovascular instability. About 40% of affected individuals have autonomic crises. FD occurs with relatively high frequency within the Ashkenazi Jewish population (1:3700 live births). FD has been associated with HSCR in some individuals [Azizi et al 1984].

Inheritance is autosomal recessive. The causative gene IKBKAP, a molecule with an immune modulatory role [Anderson et al 2001, Slaugenhaupt et al 2001], maps to 9q31, the location for a presumed genetic modifier locus identified in several families with HSCR [Bolk et al 2000].

Fryns syndrome. Fryns syndrome is characterized by hypoplasia of the distal digits, coarse facial features, variable diaphragmatic hernia, and a variety of other anomalies of the cardiac, gastrointestinal, genitourinary, and central nervous systems [Slavotinek 2004]. At least six persons have had HSCR in addition to features of Fryns syndrome, suggesting that Fryns syndrome may represent a neurocristopathy, like HSCR [Alkuraya et al 2005]. Although a specific genetic etiology has not been identified for Fryns syndrome, inheritance is generally presumed to be autosomal recessive.

Goldberg-Shprintzen syndrome. This disorder shares many of the clinical features of Mowat-Wilson syndrome including microcepthaly, mental retardation, facial dysmorphism, and HSCR, but affected individuals may also have cleft palate and colocoma, and the condition is presumed to be inherited in an autosomal recessive manner on the basis of several affected sibling pairs [Goldberg & Shprintzen 1981, Hurst et al 1988, Brooks et al 1999]. Two families with features of microcephaly, mental retardation, generalized polymicrogyria, and variable HSCR were identified as having homozygous mutations in the KIAA1279 gene, thereby suggesting that this is the Goldberg-Shprintzen gene [Brooks et al 2005].

Note: Goldberg-Shprintzen syndrome is distinct from the Shprintzen-Goldberg syndrome.

Intestinal neuronal dysplasia, type B (IND). IND is associated with severe symptoms of bowel obstruction and may be clinically indistinguishable from HSCR, although age of onset tends to be later (six months to six years) [Kapur 1999, Kapur 2001]. In contrast to HSCR, the pathologic findings include hyperplasia of enteric ganglia (vs absent ganglion cells in HSCR) and other features such as "giant ganglia" that many pathologists find controversial [Kapur 2003]. IND can be found in isolation or proximal to aganglionic bowel in approximately 20% of individuals with HSCR. Attempts to identify mutations in known HSCR-associated genes have been unsuccessful in at least one series of individuals with IND or mixed IND/HSCR [Gath et al 2001].

L1 syndrome Seven individuals with HSCR and X-linked aqueductal stenosis with documented mutations in L1CAM have been reported [Okamoto et al 1997, Vits et al 1998, Parisi et al 2002, Okamoto et al 2004, Basel-Vanagaite et al 2006]. No mutation was identified in RET in the one individual examined [Parisi et al 2002], although it is unknown whether mutations in other HSCR-associated genes may be implicated in the development of this condition. The association of hydrocephalus and HSCR suggests that the neuronal cell adhesion molecule, L1CAM, may be important for ganglion cell population of the gut. In addition, reduced L1CAM expression has been described in the extrinsic innervation of aganglionic gut from individuals with HSCR [Ikawa et al 1997]. Although HSCR is documented as having a male predominance, L1CAM is the only X-linked gene identified in association with HSCR; however, in one series of males with HSCR, no pathogenic L1CAM mutations were identified [Hofstra et al 2002].

Mowat-Wilson syndrome (Hirschsprung disease - mental retardation syndrome). Clinical features include microcephaly, mental retardation, seizures, and distinctive facial features (ocular hypertelorism, broad eyebrows, saddle nose, small rotated ears with upturned lobes, and pointed chin) [Lurie et al 1994, Mowat et al 1998]. HSCR has been reported in 41%-71% of affected individuals depending on the series [Mowat et al 2003, Zweier et al 2003, Cerruti Mainardi et al 2004, Zweier et al 2005]. Many individuals also demonstrate short stature, ocular anomalies, agenesis of the corpus callosum, congenital heart defects, and/or genitourinary abnormalities. Mowat-Wilson syndrome is associated with deletions or heterozygous mutations in the ZFHX1B (zinc finger homeobox 1B) gene localized to 2q22 (see Table 1) [Amiel et al 2001, Cacheux et al 2001, Wakamatsu et al 2001].

Multiple endocrine neoplasia type 2 (MEN 2)

• MEN 2A is an autosomal dominant disorder characterized by neoplastic transformation of C cells in the thyroid (medullary thyroid carcinoma, MTC), parathyroid hyperplasia, and adrenal medullary tumors (pheochromocytoma). In familial MTC (FMTC), development of medullary thyroid cancer in at least four family members is observed, without the other manifestations of MEN 2A. In the majority of individuals and families with MEN 2A or FMTC, the disease is caused by a single base-pair substitution in one of five codons of the RET gene, which results in an amino acid substitution for a cysteine residue that confers constitutive activity by dimerization of the receptor [Eng et al 1996, Eng & Mulligan 1997, Sijmons et al 1998]. In some families with RET mutations in the cysteine codons 609, 611, 618, or 620, MEN 2A or FMTC is associated with HSCR [Sijmons et al 1998, Eng 1999, Hansford & Mulligan 2000], although in one series, this association was found in only 1% of individuals [Yip et al 2003].
  
  While most individuals with MEN 2A do not have aganglionosis, and vice versa, in some series an estimated 2.5%-5% of individuals with HSCR have a MEN 2A-associated RET mutation. As HSCR may be the initial finding in such individuals, molecular genetic testing could lead to recognition of RET mutations associated with MEN 2A and a cancer predisposition, with significant impact on care of the affected individual and family members [Amiel & Lyonnet 2001, Pakarinen et al 2005].

• MEN 2B manifests as diffuse ganglioneuromas of the alimentary canal, marfanoid skeletal abnormalities, MTC, and pheochromocytoma. A heterozygous mutation in RET (p.M918T) that alters its substrate specificity has been identified in more than 90% of individuals with MEN 2B. Individuals with MEN 2B may present in the newborn period with intestinal obstruction that clinically resembles HSCR but is caused by diffuse ganglioneuromatosis [Smith et al 1999]. Aside from one report of coincident HSCR in an individual with MEN 2B and the p.M918T mutation [Romeo et al 1998], the majority of these individuals do not have HSCR.

Neurofibromatosis 1 (NF1) is an autosomal dominant condition characterized by café-au-lait spots, skin-fold freckling, and neurofibromas, among other neuroectodermal features. Gastrointestinal involvement includes findings described as intestinal neuronal dysplasia with myenteric plexus hypertrophy [Saul et al 1982] as well as HSCR [Clausen et al 1989]. In one family, cosegregation of the NF1 and megacolon phenotypes was associated with inheritance of both an abnormal NF1 allele from one parent and an abnormal GDNF allele from the other parent [Bahuau et al 2001], thus reinforcing the role of multiple gene interactions in the development of HSCR.

Smith-Lemli-Opitz syndrome (SLOS) is characterized by microcephaly, congenital heart disease, growth and developmental delays, distinctive facial features, undermasculinization with hypospadias in males, and characteristically, syndactyly of toes two or three. HSCR has been described in several individuals with this disorder, generally with more severe manifestations [Curry et al 1987, Cass 1990], although mild phenotypes of SLOS may be associated with HSCR [Mueller et al 2003]. SLOS is caused by mutations in the gene encoding the enzyme that catalyzes the final step in cholesterol biosynthesis. Inheritance is autosomal recessive.

Waardenburg syndrome type 4 (WS4, Waardenburg-Shah syndrome). Clinical features include HSCR, sensorineural deafness, and pigmentary anomalies (e.g., heterochromic irides, piebaldism). Since melanocytes and the inner hair cells critical for cochlear function are both derived from neural crest cells, WS4 is considered a generalized neurocristopathy.

No evidence for RET mutations as a cause of WS4 exists, although mutations in EDN3, EDNRB, and SOX10 [SRY (sex-determining region Y)-box 10] have been reported in affected individuals. In general, WS4 results from homozygosity for EDN3 or EDNRB mutant alleles, whereas heterozygotes exhibit isolated HSCR without the other features, although this correlation is not always straightforward [Edery et al 1996, Hofstra et al 1996, Syrris et al 1999]. In contrast, all the mutant SOX10 alleles reported in individuals with WS4 to date have been de novo or inherited in an autosomal dominant manner [Pingault et al 1998, Southard-Smith et al 1999]. SOX10 encodes a transcription factor that is expressed by hindbrain neural crest cells from the stage at which they leave the neural tube and throughout the colonization process [Bondurand et al 1998]. Defects in the SOX10 gene have been reported in only a small number of individuals with HSCR, and in none with isolated HSCR [Sham et al 2001]. Some individuals with WS4 and SOX10 mutations in the terminal exon exhibit the additional neurologic symptoms of peripheral neuropathy with central nervous system myelination abnormalities and developmental delays, termed PCWH (peripheral demyelinating neuropathy, central dysmyelinating leukodystrophy, Waardenburg syndrome, and HSCR) [Inoue et al 2000, Pingault et al 2000, Inoue et al 2004].

Nonsyndromic HSCR

Nonsyndromic HSCR (in which HSCR occurs without other anomalies) has been associated with mutations in at least six genes [Wartiovaara et al 1998, Kapur 1999, Parisi & Kapur 2000] (Table 3).

Table 3. Genes Associated with Nonsyndromic HSCR

Gene Symbol	Protein Name	Chromosomal Locus	Inheritance	Frequency	Type of HSCR	Syndromic? 1
RET	Proto-oncogene tyrosine-protein kinase receptor ret	10q11.2	AD	17%-38%	Short segment	Yes
				70%-80%	Long segment 2
				50%	Familial
				3%-10% 3	Simplex
GDNF 4	Glial cell line-derived neutrotrophic factor	5p13.1-p12	AD	<1% 5	Variable	Yes
NRTN 4	Neurturin	19p13.3	AD	<1% 5	Variable	Unknown
EDNRB	Endothelin B receptor	13q22	AD/AR	3%-7%	Variable	Yes 6
EDN3	Endothelin-3	20q13.2-q13.3	AD/AR	5%	Variable	Yes 6
ECE1	Endothelin-converting enzyme 1	1p36.1	AD 5	<1% 5	Variable	Unknown

1. Mutations in the gene have also been reported with syndromic forms of HSCR (see Table 2).

2. Homozygous mutations have been associated with total colonic aganglionosis in some cases.

3. RET mutations are reported to be higher (10%-35%) in simplex HSCR (HSCR in a single family member) in some referral series (see following text).

4. A mutation in this gene is insufficient by itself to cause disease in most cases (see following text).

5. Limited data are available.

6. The syndromic form is usually associated with homozygous mutations in this gene.

The genes associated with isolated HSCR fall into two major groups:

Genes for RET and its ligands. The tyrosine kinase receptor, RET (proto-oncogene tyrosine-protein kinase receptor; rearranged during transfection), is expressed by enteric neural precursors shortly after they leave the neural plate and throughout their colonization of the entire gut. GDNF (glial cell line-derived neurotrophic factor) and NRTN (or NTN; neurturin) are two of the ligands for RET expressed by adjacent mesenchymal cells. Although coreceptors for RET and its ligands exist, testing for mutations in the specific coreceptor associated with GDNF (GFR alpha-1) has not revealed any causative mutations in humans [Myers et al 1999].

Mutations in RET appear to be dominant loss-of-function mutations with incomplete penetrance and variable expressivity.

RET mutations alone are estimated to account for 7%-41% of all individuals with HSCR and 70%-80% of those with long-segment disease [Angrist et al 1995, Seri et al 1997, Sancandi et al 2000]. Homozygous RET mutations have been associated with total colonic aganglionosis in some individuals [Inoue et al 2000, Shimotake et al 2001].

RET is implicated in up to 50% of all familial HSCR [Attie et al 1995, Hofstra et al 2000]. The involvement of RET has been estimated to occur in 10%-35% of simplex cases of HSCR (i.e., HSCR in a single family member) in several referral series, which may be biased toward more severe or familial cases [Angrist et al 1995, Attie et al 1995, Eng & Mulligan 1997]; in the few population-based series reported, the incidence is 3%-10% [Svensson et al 1999, Borrego et al 2000, Sancandi et al 2000].

The penetrance of RET mutations is approximately 50%-70% [Bolk et al 2000]. Several candidate loci that may be responsible for the incomplete penetrance and variable expressivity observed in individuals with RET mutations have already been identified [Bolk et al 2000, Gabriel et al 2002].

Common polymorphisms in RET that do not cause amino acid changes appear to be over-represented within a population of individuals with HSCR [Borrego et al 1999, Fitze et al 1999, Borrego et al 2000], adding further complexity to the task of determining if a sequence variant is a disease-causing mutation. In addition, specific RET haplotypes, including polymorphisms in promoter elements and 5' introns, may also modify the risk of developing HSCR based on differences in RET protein expression, even in the absence of a pathogenic RET gene mutation [Fitze et al 2003a, Fitze et al 2003b, Sancandi et al 2003, Burzynski et al 2005, Lantieri et al 2006]. Specific RET promoter single nucleotide polymorphisms that decrease transcription may predispose to the development of HSCR in some populations [Garcia-Barcelo et al 2005], and one enhancer variant with differential effects in males and females may explain the increased occurrence in males, at least in part [Emison et al 2005].

Mutations in GDNF and NRTN have been identified in only a small minority of individuals with HSCR, and in almost all of those individuals, a mutation was also identified in RET or another HSCR gene, suggesting that mutation in one of the ligands is not sufficient by itself to cause disease [Angrist et al 1996, Hofstra et al 1996, Ivanchuk et al 1996, Salomon et al 1996, Doray et al 1998, Eketjall & Ibanez 2002].

EDNRB and related genes. Components of another cell signaling pathway that probably interacts with the RET pathway during enteric neural crest-colonization have been implicated in HSCR [Carrasquillo et al 2002]; these include the endothelin receptor type B (EDNRB) and its ligand, endothelin-3 (EDN3). Synthesis of the mature active form of endothelin-3 requires post-translational modification by endothelin-converting enzyme 1 (encoded by ECE1). EDNRB and EDN3 mutations probably account for approximately 10% of individuals with HSCR [Amiel et al 1996, Kusafuka et al 1996, Svensson et al 1999]. Within the Mennonite community, however, a significant proportion of affected individuals have a missense mutation in the EDNRB gene, representing a founder mutation, and some of these individuals have manifestations of Waardenburg syndrome type 4 (WS4) [Puffenberger et al 1994]. In general, individuals with a heterozygous mutation in EDNRB or EDN3 present with HSCR or occasionally features of WS4, while those with homozygous mutations in either gene are more likely to have more severe manifestations of WS4 [Verheij et al 2002]. A mutation in ECE1 has been reported in only one individual, who also had craniofacial anomalies and a heart defect [Hofstra et al 1999].