The conventional neuropathologic approach to Huntington's disease culm
inated in the classification developed by Vonsattel. Molecular biology
studies of human and experimental material have provided new insight
into the lesions of this disease characterized by an abnormally large
number of CAG triplet repeats in a mutant gene, a mechanism also known
to occur in ten or so other ''molecular'', neurologic diseases. The p
rotein encoded by the HD locus (huntingtin) is associated with another
protein (HAP-I), which enhances its toxic potential; huntingtin inter
acts with the enzyme GADPH, and its cleavage by apopain may lead to in
appropriate apoptosis. Interactions between huntingtin, HAP-1, GADPH,
and apopain may be modulated by the presence of polyglutamines.