Hirschsprung disease (HRSD), or aganglionic megacolon, is a disorder associated with the lack of intrinsic ganglion cells in the myentric and submucosal plexuses in the gastrointestinal tract. Clinically, the phenotype may be mild, intermediate or severe. The incidence of severe HRSD is 1/5,000 livebirths, and males are more likely to be affected than females. The etiologies of this developmental disorder are unknown, but failure of neural crest cells or preenteric/enteric ganglion cells to migrate, differentiate or colonize the gut could result in HRSD. The postulated defects are in cell-cell or cell-substrate adhesion of ganglion cells. It is assumed that HRSD is a sex-modified multifactorial disorder. Our recent studies, however, demonstrate dominant inheritance for long segment HRSD (aganglionosis of the transverse colon and beyond), dominant inheritance for short segment HRSD (aganglionosis of the splenic flexure and descending colon) and multifactorial/recessive inheritance for the """"""""classic"""""""" type HRSD (aganglionosis up to and including the sigmoid colon). The penetrances of these genes are incomplete. To identify genetic factors leading to HRSD three studies are proposed. First, we shall perform high resolution prophase banding and cytogenetic analysis on 20 probands with multiple anomalies to identify consistent chromosomal aberrations. Second, we shall use highly polymorphic DNA probes to search for microdeletions within chromosome 13q22 in 50 simplex families. Third, we shall study highly polymorphic DNA markers and perform linkage in a minimum of 6 large pedigrees and in 60 affected sib and other relative pairs, to identify regions of the human genome that contain genes predisposing to HRSD. The genetic markers to be used will be selected on the basis of three criteria: localizations of known chromosomal aberrations; candidate genes responsible for cell-cell and cell-substrate adhesion; and, human chromosomal segments homologous to mouse chromosomal segments containing mutations causing aganglionosis in the mouse. Specifically, our aim is to identify genetic etiologies of HRSD and study the effects of abnormalities of cell adhesion on human pathology. Also, we aim to elucidate the relationship between the genes identified, extent of aganglionosis and severity of symptoms. Generally, our studies have the long-term objective of providing a logical approach to identifying the genes predisposing to complex, """"""""multifactorial"""""""" disorders.
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