Friedreich's ataxia (FRDA), the most common autosomal recessively inherited ataxia, is due to a homozygous GAA triplet repeat expansion in the first intron of the FRDA gene in about 96% of patients. Approximately 4% of FRDA patients are compound heterozygotes with a GAA repeat expansion in one allele and a point mutation in the coding region of the second allele. To reinvestigate the mutation spectrum, we searched for mutations including exon deletions in six patients heterozygous for the GAA repeat expansion and found two unknown missense mutations, p.Asn146Lys and p.Leu186Arg, in trans to the expanded FRDA allele. Interestingly, we detected a heterozygous 2776 bp deletion including exon 5a in one of our patients. This deletion removes 50 of the 210 residues of the frataxin. Furthermore, since no FRDA case with two-point mutations is known, we screened eight patients with FRDA phenotype but GAA alleles within the normal range but did not reveal a mutation within the FRDA gene. In addition, DNA polymorphisms have been found in four out of 100 control individuals in this study.

Aprataxin (APTX) mutations are the cause of ataxia with ocular motor apraxia type 1(AOA1), an autosomal recessive disorder linked to chromosome 9p13.AOA1 seems to be one of the most frequent causes of recessive ataxia in Japan and Portugal. We screened a group of 165 early onset ataxia patients for APTX mutations and detected two non-related patients homozygous for the W293X nonsense mutation. Additionally, we describe several new transcript variants of the APTX gene and discuss their relevance for a sufficient mutation screening.