An interrupted 34-CAG repeat SCA-2 allele in patients with sporadic spinocerebellar ataxia

In spinocerebellar ataxia type 2 (SCA-8), a difference of three CAG repeats distinguishes normal alleles (14 to 31 repeats) from pathogenic alleles (3 4 to 57 repeats). All sequenced pathogenic alleles have a pure CAG repeat s tructure, whereas interrupted repeats have been seen exclusively in normal alleles. The authors present two patients with sporadic SCA with an interru pted 34-CAG repeat allele, (CAG)(24)(CAA)(CAG)(9), who showed a phenotype c ompatible with SCA-2. The interrupted allele coding for a 34 pure polygluta mine tract may cause the SCA phenotype.