IDENTIFICATION OF AN EXPANDED CAG REPEAT IN THE HUNTINGTONS-DISEASE GENE (IT15) IN A FAMILY REPORTED TO HAVE BENIGN HEREDITARY CHOREA

Benign hereditary chorea (BHC) is a rare autosomal dominant disorder c haracterised by the onset of non-progressive chorea in childhood and t he absence of cognitive impairment. Using primers flanking the (CAG)n repeat in ITIS, expansion of which is associated with HD, we have dete cted an abnormal PCR product in four affected members from one family where affected subjects were originally reported to have BHC. The expa nded allele contains 38 repeats in the affected parent and this underg oes further enlargement to 39 and 45 repeats in the two affected offsp ring. We conclude that the diagnostic criteria for BHC should include a normal result from analysis for the (CAG)n expansion identified in H D.