[Absence of linkage disequilibrium at amyloid precursor protein gene locus in Japanese familial Alzheimer's disease with 717Val-->Ile mutation].

To date, eleven independent early onset familial Alzheimer's disease (EOFAD) pedigrees with the 717Val-->Ile mutation of amyloid precursor protein (APP) gene have been identified. Interestingly, five pedigrees have been of Japanese origin. The apparent ethnic prediction of this mutation raises the possibility that there is a founder effect in Japan. If the hypothesis holds true, we can expect the presence of linkage disequilibrium at the APP locus. We did not, however, observe any significant linkage disequilibrium at any locus of APP or the adjacent GT12 locus in the five Japanese EOFAD probands with the 717Val-->Ile mutation. The result indicates that a founder effect would probably not be present in Japanese EOFAD pedigrees with the 717Val-->Ile mutation.