Prenatal diagnosis of hemophilia involving grandpaternal mosaicism.

Our Factor VIII and RFLP analyses identified previously unreported grandpaternal hemophilia A mosaicism in a male who transmitted the disease allele to 2 of 4 daughters and 2 of 4 grandsons. An uncommon flanking polymorphic DXS52 allele cosegregated with this grandpaternal mutant allele. This and other reports of mosaic hemophilia A carriers indicate that parental mosaicism can explain unusual segregation of low Factor VIII activities and DNA polymorphisms in about 1% of hemophilia A pedigrees.