Paradominant inheritance, a hypothesis explaining occasional familial occurrence of sporadic syndromes

Heterozygous individuals carrying a "paradominant" mutation, as a rule, are phenotypically normal. Therefore, the mutation can be transmitted unpercei ved through many generations. The trait becomes manifest when a somatic mut ation occurs during embryogenesis giving rise to loss of heterozygosity and forming a mutant cell population, being either homozygous or hemizygous fo r the mutation. This concept explains the occasional familial occurrence of usually sporadic traits like the Klippel-Trenaunay syndrome and others, (C ) 1999 Wiley-Liss, Inc.