The type II multiple endocrine neoplasia syndromes, familial medullary thyroid carcinoma syndrome and Hirschsprung's disease result from different lesions at a common genetic locus.
MEN-IIa, MEN-IIb and FMTC are all inherited in an autosomal dominant manner with variable penetrance. The candidate gene in each case has been mapped to chromosome 10q11.2.
Hirschsprung's disease is an autosomal trait but has less clear inheritance.
All four conditions are associated with mutations in the the receptor tyrosine kinase gene RET. In MEN-IIa, MEN-IIb and FMTC there are point mutations which may result in gain of function. Hirschsprung's disease is associated with large loss of function mutations.
RET-knockout transgenic mice show complete absence of parasympathetic ganglion cells in the gut with renal agenesis.
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