Hirschsprung disease - genetics and development

Hirschsprung disease (HSCR) is a complex genetic disorder that is characterized by the lack of the Enteric Nervous System (ENS) in the myenteric and submucosal plexuses of the gastrointestinal tract. HSCR is a neurocristopathy and can result from aberrant migration, proliferation or differentiation of vagal neural crest cells. The length of the affected intestine classifies HSCR. The most common form of the disease (~80% of patients) is called shortsegment HSCR (S-HSCR), where aganglionosis does not extend beyond the sigmoid colon. Approximately 20% of the patients is diagnosed with long-segment HSCR (L-HSCR), in which aganglionosis extents proximal to the sigmoid. The population incidence is generally assumed to be 1/5000 live births, though it varies among patients of distinct ethnic origin. A sex bias is also present in this disorder as approximately three times more males are affected. The pattern of inheritance for L-HSCR is autosomal dominant with low penetrance whereas the inheritance of the much more common S-HSCR is believed to be multifactorial. The major gene in HSCR is RET. Nevertheless, mutations in the coding sequence of RET are hardly being found in the main classes of patients. The work included in this thesis had two main goals. Firstly, to elucidate further the role of RET in those cases where no coding sequence mutations were found. We focused on the most common group of patients, namely those with S-HSCR who lack a disease history in the family. We found, that the RET gene is involved in nearly all HSCR cases and that the majority of mutations are not lying within the coding regions, but in the regulatory sequences of the RET locus. Secondly, baring in mind that HSCR is genetically complex disease, we attempted to find new genes and loci involved in HSCR development and more generally genes encoding proteins, Scope which contribute to ENS development. In a collaborative effort with the Rotterdam group a new HSCR susceptibility locus was identified in a multigenerational HSCR family. Further, ENS precursors cells, isolated from mouse embryos’ intestines were studied and expression profiling was performed. Genes encoding proteins belonging to the RET pathway or genes encoding proteins affected by RET signaling in these cells, were identified. By this approach we hope to get a better insight in ENS development, and HSCR susceptibility