Genetic analysis of a dentatorubral-pallidoluysian atrophy family: relevance to apparent sporadic cases.

Dentatorubral-pallidoluysian atrophy (DRPLA) is associated with an unstable CAG trinucleotide sequence. We describe a DRPLA family whose members have an allele containing an expanded CAG repeat, even in an elderly neurologically normal individual. The proband developed DRPLA at age 14. She was initially considered a sporadic case, but later her sister became symptomatic. Investigation of the number of CAG repeat units in her family revealed the 81-year-old father to have an expanded CAG repeat of 51 units. To our knowledge, such an advanced aged unaffected patient has not been previously documented. The present example may explain apparent sporadic cases.