Genetic Testing for Children Who Have JHD Symptoms

This article shows that not every child at risk for Huntington's Disease who appears to be symptomatic actually has the disease.
This is an older article, but an important one we wanted to have on the site. It shows that not every child at risk for Huntington's Disease who appears to be symptomatic actually has the disease.

Of the eleven children who were clinically diagnosed with Huntington's disease who did not have a repeat expansion, five presented with movement symptoms alone, two with chorea, two with involuntary movements, and one with tremors. Three of the children presented with rigidity; two also had declining school performance and the other had EEG abnormalities. One child presented with psychiatric symptoms. Another had Pelizaeus-Merzbacher disease, another rare movement disorder. Another child presented with Tourette's syndrome and developmental delay. Six of the children had no known history of HD in the family.

Of the fifteen children who did have the CAG expansion and became symptomatic in the first decade, all had an affected parent. Twelve had CAG repeats of 80 or more and two of the following symptoms: declining school performance, seizures, oral motor dysfunction, rigidity, and gait disorder. There were three children who presented with one symptom and who had CAG epansions less than 80 repeats.

The eighteen children with CAG expansions who became symptomatic at ten or older presented with a more diverse groups of symptoms. Only one fit the adult pattern of symptoms. Some presented with rigidity and declining school performance and some with severe behavioral symptoms. Another group had lifelong cognitive problems with onset associated with behavioral then movement problems.

Marsha L. Miller, Ph.D.
Martha Nance, M.D.
Genetic Testing of Children At Risk for Huntington's Disease. US Huntington Disease Genetic Testing Group.
Martha Nance, M.D.
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.
Neurology 1997 Oct;49(4):1048-53.