CAG repeat analyses in frozen and formalin-fixed tissues following primer extension preamplification for evaluation of mitotic instability of expanded SCA1 alleles.
Neurodegenerative disorders, including spin-ocerebellar ataxias (SCA), Huntington disease (HD) and dentatorubral-pallidoluysian atrophy (DRPLA), are associated with unstable CAG repeats. To investigate the mitotic stability of the repetitive element in the genes for SCA1, SCA3, HD, and DRPLA we extracted DNA from up to 13 tissue samples from four deceased individuals with progressive neurological disorders and neuropathological signs. Due to the formalin fixation of some tissues the genomic DNA was highly degraded and unsuitable for amplification of fragments longer than 150 bp. After size selection and primer extension preamplification, specific analyses could be performed even for expanded alleles. In all four patients the SCA1 mutation could be demonstrated, in one case with remarkable somatic heterogeneity of the elongated allele, whereas alleles of the normal range were stable in all tissues examined.