Friedreich AtaxiainLouisiana Acadians: Demonstration ofa FounderEffect byAnalysis ofMicrosatellite-g enerated Extended Haplotypes

Summary Eleven Acadian families withFriedreich ataxia (FA)whowere fromsouthwest Louisiana were studied with a series ofpolymorphic markers spanning 310kbintheD9S5-D9S15 region previously showntobetightly linked tothedisease locus. Inparticular, three veryinformative microsatellites were tested. Evidence fora strongfounder effect was found, since aspecific extended haplotype spanning 230kbfrom26P(D9S5) to MCT112(D9S15) was present on 70%ofindependent FAchromosomes andonly once (6%)on thenormal ones.There was no evident correlation between haplotypes andclinical expression. Thetyping ofan additional microsatellite (GS4) located 80kbfromMCT112created adivergence ofthemainFA-linked haplotype, generating fourminorandone major haplotype. A similar split was observed withGS4ina patient homozygous for a rare26P-to-MCT112 haplotype. These results suggest that GS4isaflanking marker forthedisease locus, although other interpretations arepossible.