The apparent enlargement of the ventricles seen here is due to atrophy of the head of the caudate from neuronal loss with Huntington disease (HD), an autosomal dominant condition characterized clinically by choreiform movements.

The autosomal dominant inheritance pattern of HD is shown below, with reduced penetrance in the second generation (a male with the abnormal gene who does not express the disease but who can pass the trait onto offspring). HD also exhibits delayed expression, with onset of the disease in mid-life, usually in the 40's.