Genotyping was performed for DNA microsatellite markers D3S1558, D3S1769, GGAA8B03, D3S1267, D3S1551, D3S1290, GATA4A10, and D3S1744. These markers map to the chromosome region 3q13-q22 and are linked to the HMSN 2B phenotype.5 Genotyping also was performed for microsatellite markers mapped to 7p14 (D7S1808, D7S1869, D7S435, and D7S1806), linked to the HMSN 2D phenotype,6 and for markers situated proximally (D7S2201) and distally (D7S526 and D7S1830) to 7p14. The markers (Research Genetics, Huntsville, Ala) were amplified by polymerase chain reaction in a final volume of 15 µL containing 50 ng of genomic template DNA, 2 pmol of each oligonucleotide microsatellite primer, 200 µM concentrations of dATP, dGTP, and dTTP, 50 mM of dCTP (Boehringer Mannheim, Indianapolis, Ind), 0.5 µCi of α-32P dCTP (Amersham Life Science, Arlington Heights, Ill), and 0.5 U of Taq DNA polymerase (Boehringer Mannheim) in a 1 × Taq buffer containing 10-mmol/L Trishydrochloride (pH 8.3 at 20°C), 50-mmol/L potassium chloride, and 1.5-mmol/L magnesium chloride. Amplification was performed for 35 cycles of denaturation at 94°C for 15 seconds, annealing at 55°C for 1 minute, and extension at 72°C for 15 seconds, with a final elongation cycle at 72°C for 10 minutes. After 10 µL of loading buffer (95% formamide, 10-mmol/L EDTA, 0.1% bromophenol blue, and 0.1% xylene cyanol) was added, the amplified products were denatured at 94°C for 10 minutes and then cooled rapidly to 4°C and placed on ice. Three microliters of each sample was electrophoresed on 6% denaturing polyacrylamide sequencing gels at 75 W for 2 to 3 hours. Gels were vacuum dried and autoradiographed overnight at −70°C. Base-pair sizes of the polymerase chain reaction products were calculated using a double-strand DNA cycle sequencing system (Gibco BRL, Grand Island, NY).