SOMATIC MOSAICISM OF THE EXPANDED CAG TRINUCLEOTIDE REPEAT IN MESSENGER-RNAS 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 Ma chado-Joseph disease (MJD), dentatorubral-pallidoluysian atrophy (DRPL A), and X-linked spinal and bulbal muscular atrophy (SBMA) were examin ed in various neural and nonneural tissues of affected individuals. Th e tissue-specific variation of expanded CAG repeat alleles were appare nt 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 ne rvous 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 exp anded CAG repeats were detected in all tissues studied, and the tissue -specific variation in the CAG repeat size of the mRNA did not correla te with the tissue-specific severity of pathological involvement in th ese diseases.