Reduction of CAG expansions in cerebellar cortex and spinal cord of DRPLA

Recent studies have identified an unstable expansion of a CAG repeat in a gene located on chromosome 12 as a cause of dentatorubropallidoluysian atrophy (DRPLA). To investigate whether the somatic heterogeneity may relate to the selective neuronal damage caused by the disease, genomic DNA from various tissues of an autopsied patient with DRPLA was examined to compare possible variations of expanded CAG repeats for the disease. Although the size of the expanded CAG repeat from many organs was almost the same as that from peripheral lymphocytes, those from cerebellar cortex and spinal cord were unexpectedly reduced and numbers of peaks within an expanded allele were relatively strict. These results suggest that the CAG repeat is not simply expanded in the genome of the tissues that are most involved in DRPLA, but that another mechanism might be responsible for the specific neuronal death.