All linkage analyses were undertaken assuming that FPD-AML is caused by a mutation in a single diallelic autosomal dominant gene with a population frequency of 0.0001, and that the phenotype is incompletely penetrant (90% lifetime probability of manifesting disease in carriers, and no chance of manifesting disease in noncarriers). The map-specific multipoint lod scores above were calculated at each marker interval between D21S263 andD21S211 using the MLINK and LINK-MAP programs as implemented in FASTLINK v 2.3P.8 These analyses assumed 1 cM distance between markers (except 2 cM between D21S65 andD21S211) and that there was no interference or sex differences in the recombination fractions. The five recombination fractions were estimated from the genotype data and indicate that there was only one recombinant haplotype (in one unaffected individual).