Huntington disease in children: genotype-phenotype correlation.

Huntington disease is a neurodegenerative disorder of adulthood; however, a subset of early-onset patients exists, representing 1% of all HD patients. We reviewed a population of 155 HD-families to determine the frequency, molecular and clinical characteristics of children with an onset before the age of 10 years. In each case, a neurological evaluation was performed as well as molecular detection of the expanded CAG triplet in the affected child and both parents. The family history was also reviewed and updated. Seven children (1.92%) had onset of symptoms before the age of 10, two of them were dead by the time of the study. Large CAG expansions with intergenerational instability were identified, and in one case the child's allele was almost three times larger than the allele of the asymptomatic transmitting father, a situation reported only once before. Clinically, they showed preponderance of rigidity, seizures, learning disabilities and a rapid course of the disease. We attempted to use UHDRS. However, consistent results could not be obtained, suggesting that the scale should be revised for use in juvenile cases. HD should be considered in the differential diagnosis of neurodegenerative diseases in children, even in the absence of a positive family history.