Evidence for a common Spinocerebellar ataxia type 7 (SCA7) founder mutation in Scandinavia

Spinocerebellar ataxia type 7 (SCA7) is a neuro-degenerative disorder chara cterised by progressive cerebellar ataxia and macular degeneration. SCA7 is one of the least common genetically verified autosomal dominant cerebellar ataxias (ADCAs) in the world (4.5 to 11.6%), but in Sweden and Finland SCA 7 is the most commonly identified form of ADCA. In an inventory of heredita ry ataxias in Scandinavia (Sweden, Norway, Denmark and Finland) we identifi ed 15 SCA7 families, eight in Sweden and seven in Finland, while no cases o f SCA7 could be found in Norway or Denmark. We examined whether the relativ ely high frequency of SCA7 families in Sweden and Finland was the result of a common founder effect. Only two out of 15 families could be connected ge nealogically. However, an extensive haplotype analysis over a 10.2 cM regio n surrounding the SCAI gene locus showed that all 15 families studied share d a common haplotype over at least 1.9 cM. This strongly suggests that all Scandinavian SCA7 families originate from a common founder pre-mutation.