A 48-year-old man is referred for personality change, irritability, and declining work performance over two years. Examination reveals slow, writhing involuntary movements of the limbs and face. His father died with a similar illness. MRI shows disproportionate atrophy of the caudate nuclei. This subcortical dementia is caused by:

• A X-linked mutation in the dystrophin gene
• B Autosomal recessive mutation in the parkin gene
• C Mitochondrial DNA mutation with maternal inheritance
• D Autosomal dominant CAG trinucleotide repeat expansion in the huntingtin gene ✓

Explanation

The combination of midlife behavioural change, choreiform movements, paternal transmission history, and caudate atrophy is diagnostic of Huntington disease, an autosomal dominant disorder due to unstable CAG trinucleotide repeat expansion in the huntingtin gene, with anticipation on paternal transmission. Parkin mutations cause early-onset parkinsonism without dementia, mitochondrial mutations show maternal inheritance, and dystrophin defects cause Duchenne muscular dystrophy, not dementia.

Reference: Kaplan and Sadock's Synopsis of Psychiatry, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.