EXPANSION OF A (CAG)N REPEAT REGION IN A SPORADIC CASE OF HD

The genetic mutation underlying Huntington's disease (HD) has been ide ntified as an expansion and instability of a specific CAG repeat seque nce in a gene on chromosome 4. A simple polymerase chain reaction assa y has been used for the assessment of the (CAG)n expansion in a 72-yea r-old woman with typical HD symptoms, but no family history of the dis order. The DNA analysis showed that the patient had an allele with 41 repeat units, in the size range seen in HD chromosomes. Therefore, HD diagnosis is confirmed in this seemingly sporadic case and the disease is newly diagnosed in a large family. The risk of inheriting this uns table expanded allele is discussed.