Somatic mosaicism of the expanded CAG trinucleotide repeat in mRNAs for the responsible gene of Machado-Joseph disease (MJD), dentatorubral-pallidoluysian atrophy (DRPLA), and spinal and bulbar muscular atrophy (SBMA).

The CAG trinucleotide repeats in mRNAs for the responsible genes of Machado-Joseph disease (MJD), dentatorubral-pallidoluysian atrophy (DRPLA), and X-linked spinal and bulbal muscular atrophy (SBMA) were examined in various neural and nonneural tissues of affected individuals. The tissue-specific variation of expanded CAG repeat alleles were apparent for mRNAs of all three genes. The expanded CAG repeats of the mRNA were shorter in the cerebellum than in other regions of the central nervous system in DRPLA and MJD, but not in SBMA, and were longer in the liver and colon in MJD. Transcripts of the responsible genes with expanded CAG repeats were detected in all tissues studied, and the tissue-specific variation in the CAG repeat size of the mRNA did not correlate with the tissue-specific severity of pathological involvement in these diseases.