A case of juvenile huntington disease in a 6-year-old boy.

Huntington disease is a neurodegenerative disorder distinguished by the triad of dominant inheritance, choreoathetosis and dementia, usually with onset in the fourth and fifth decades. It is caused by an unstable cytosine-adenine-guanine (CAG) trinucleotide repeat expansion in the gene IT15 in locus 4p16.3. Juvenile HD that constitutes about 3% to 10% of all patients is clinically different from adult-onset form and characterized by a larger number of CAG repeats typically exceeding 60. We report a case of a 6-year-old boy with myoclonic seizure and 140 CAG repeats confirmed by molecular genetic analysis.