Paradominant inheritance, a hypothesis explaining occasional familial occurrence of sporadic syndromes<FNR HREF="fn1"></FNR><FN ID="fn1">Presented in part at the International Symposium “Mosaicism in Human Skin” on the occasion of the 60th birthday of Rudolf Happle, Marburg, Germany, 22–23 May, 1998</FN>

Heterozygous individuals carrying a “paradominant” mutation, as a rule, are phenotypically normal. Therefore, the mutation can be transmitted unperceived through many generations. The trait becomes manifest when a somatic mutation occurs during embryogenesis giving rise to loss of heterozygosity and forming a mutant cell population, being either homozygous or hemizygous for the mutation. This concept explains the occasional familial occurrence of usually sporadic traits like the Klippel-Trenaunay syndrome and others. Am. J. Med. Genet. 85:359–360, 1999. &#169; 1999 Wiley-Liss, Inc.