Huntington disease in a 9-year-old boy: clinical course and neuropathologic examination.

Huntington disease is a dominantly inherited, neurodegenerative disorder, usually with onset in the fourth to fifth decade of life but in a small proportion of patients before the age of 20 years. The early-onset form, juvenile Huntington disease, is clinically different from that of more common adult-onset forms and includes cognitive decline, parkinsonism, myoclonus, and seizures. We report a case of a boy with juvenile Huntington disease with a very early age at disease onset (3 years). The suspected clinical diagnosis was confirmed by DNA analysis, which revealed (CAG)(n) expansion into the range characteristic of juvenile Huntington disease (95 repeats). The clinical course of the disease was typical for the juvenile form of Huntington disease, but the diagnosis was not so obvious because there was no history of any neurodegenerative disorder in the family. The child died at the age of 11 years. The detailed neuropathologic investigations performed postmortem showed the characteristic features of Huntington disease. As the patient's de novo mutation was very unlikely to occur, genetic counseling and the possibility of predictive testing were proposed to the family. Indirect molecular data indicate the familial character of the disease, with strong anticipation of transmission.