Genetic testing of children at risk for Huntington's disease. US Huntington Disease Genetic Testing Group.

We reviewed 44 symptomatic children tested for CAG repeat expansions in the gene responsible for Huntington's disease (HD). Thirty-three patients had CAG repeat expansions, and 11 did not. No patient with a CAG repeat expansion had a negative family history of HD. Of the 15 patients presenting in the first decade, 12 had greater than 80 CAG repeats and a clinical profile at the time of the test that included two or more of the following: declining school performance, seizures, oral motor dysfunction, rigidity, and gait disorder. Three patients with smaller CAG repeat expansions had incomplete or atypical symptom profiles. Symptom patterns in patients presenting in the second decade were more varied but usually included behavioral and motor symptoms. Patients without CAG expansions had incomplete or atypical symptom profiles. We define the historical and clinical profiles of HD presenting in the first two decades and suggest that physicians exercise restraint in using a "diagnostic" gene test for HD in the evaluation of at-risk children with incomplete or atypical symptom profiles or no family history of HD, in whom test results are very likely to be normal or unrelated to the patient's symptoms.