Founder effect in spinal and bulbar muscular atrophy (SBMA) in Scandinavia

We haplotyped 13 Finnish, 10 Swedish, 12 Danish and 2 Norwegian SBMA (spina l and bulbar muscular atrophy, Kennedy disease) families with a total of 45 patients and 7 carriers for 17 microsatellite markets spanning a 25.2 cM r egion around the androgen receptor gene on chromosome Xq11-q12 in search of a genetic founder effect. In addition, the haplotypes of 50 Finnish, 20 Da nish and 22 Swedish control males were examined. All the Scandinavian SBMA families shared the same 18 repeat allele for the intragenic GGC repeat, wh ich was present in only 24% of the controls. Linkage disequilibrium was als o seen for the closest microsatellite markers. In addition, extended haplot ypes of the Finnish, Swedish and Danish SBMA families revealed country-spec ific common founder haplotypes, which over time became gradually shortened by recombinations. No common haplotype was found among the controls. The da ta suggest that the SBMA mutation was introduced into western Finland 20 ge nerations ago. Haplotype analysis implies a common ancestor for the majorit y of Scandinavian SBMA patients.