Syndrome of multiple mucosal neuromas, medullary thyroid carcinoma, and pheocromocytoma: cause of colon diverticula in children

Pathogenesis of Hirschsprung's disease

Hirschsprung's disease is an inherited disorder showing incomplete penetrance and variable expressivity. Genetic mapping and mutation screening of candidate genes, together with the study of several natural and knockout animal models, clearly have shown the involvement of several different genes in the pathogenesis of Hirschsprung's disease. Among these genes, the RET proto-oncogene accounts for the highest proportion of both familial and sporadic cases, with a wide range of mutations scattered along its entire coding region. The low detection rate of RET mutations in Hirschsprung patients also led to different hypotheses, such as the existence of additional Hirschsprung genes. Different animal and human genetic studies have identified 6 Hirschsprung genes: RET proto-oncogene (RET), endothelin 3 (EDN3), endothelin B receptor gene (EDNRB), glial-cell-line-derived neurotrophic factor (GDNF), endothelin converting enzyme (ECE1), gene encoding the Sry-related transcription factor SOX10 (SOX10). Microenvironmental factors also can play a role in the pathogenesis of aganglionosis. The developmental process of the crest-derived progenitor cells is sensitive to the level of different molecules. The expression deficit of different factors (GDNF, NTN) in the hindgut, in the absence of genetic mutations, could determine a missed activation of the receptor system, causing enteric neuroblast migration arrest.

Association of multiple endocrine neoplasia type 2 and Hirschsprung disease

In a few patients with Hirschsprung disease (HSCR) and no clinical symptoms of multiple endocrine neoplasia type 2 (MEN-2A) or medullary thyroid carcinoma (MTC), missense mutations in the cysteine residues 609 and 620 of the Ret gene have been identified. In several pedigrees with either MEN-2A or familial MTC (FMTC) a documented germline mutation in cysteine 618 or 620 follows the segregation of the disease phenotype. The appearance of the HSCR phenotype in such patients and pedigrees cannot be easily reconciled with the gain of function which is associated with the dominant oncogenic effect of MEN-2A mutations. Gastrointestinal manifestations are known to occur also in association with MEN-2B but, to the best of our knowledge, in only very few cases the intestinal phenotype of MEN-2B has been investigated by enzymo-histochemical techniques, as in the present work. We report an extensive molecular study of patients, two with HSCR and FMTC carrying a Cys620Arg or Ser mutation and two with MEN-2B and gastrointestinal symptoms carrying a Met918Thr mutation. One of the latter two patients showed aganglionosis of the last 5 cm of rectum which caused a congenital megacolon leading to the diagnosis and operation for HSCR. The mutation screening of all the exons of Ret in 3 of these patients did not reveal any additional mutation. Therefore these results do not support the hypothesis of additional constitutional Ret mutations in patients showing association of MEN-2 and HSCR, whilst the histochemical and clinical data in one of these patients indicate that MEN-2B can be associated with a true form of short segment HSCR.

Intestinal ganglioneuromatosis: mucosal and transmural types. A clinicopathologic and immunohistochemical study of six cases

Six cases of intestinal ganglioneuromatosis (GN) included in this study reveal the occurrence of two morphologic patterns. Transmural GN was characterized by neural hyperplasia in all layers of the bowel wall with predominant involvement of the myenteric plexus. It was found in three patients affected by multiple endocrine neoplasia IIb. Mucosal GN, having predominant involvement of the mucosa without concomitant hyperplasia of the myenteric plexus, was associated with von Recklinghausen's disease, adenocarcinoma of the colon, and multiple adenomas with megacolon in one case each. Clinicopathologic correlations and review of the literature suggest that mucosal GN might represent a distinct entity with a lower morbidity rate than the transmural variant. Immunohistochemical stains reveal considerable heterogeneity. S-100 protein, neuron-specific enolase, and synapto-physin immunostaining followed the distribution of the nervous hyperplasia in the different intestinal layers as identified morphologically and allowed precise determination of the proliferating cells. Increased reactivity for vasoactive intestinal polypeptide, opioid peptides leu-enkephalin and met-enkephalin, and substance P was present in all cases with transmural involvement; mucosal GN showed normal reactivity for opioid peptides and focal increased staining for substance P (one case) and vasoactive intestinal polypeptide (two cases) in the lamina propria. Mild increased immunoreactivity for tyrosine hydroxylase was present in the myenteric plexus of four out of four cases. Histochemical determination of acetylcholinesterase, performed in one case of transmural type, demonstrated hyperplasia of parasympathetic fibers and neurons. Electron microscopic study of another case suggested the presence of several neurotransmitters. These results indicate that the physiopathology of GN is related to a complex hyperplasia of several peptidergic, cholinergic, and probably adrenergic nerve fibers instead of a selective overgrowth of one type of nerve fiber.