A 55-year-old man presents with progressive involuntary choreiform movements, personality changes, and cognitive decline over 8 years. His father had similar symptoms. Genetic testing reveals a trinucleotide repeat expansion. The affected gene is located on which chromosome?

• A Chromosome 19
• B Chromosome 20
• C Chromosome 21
• D Chromosome 4 ✓

Explanation

Huntington disease is an autosomal dominant disorder caused by CAG trinucleotide repeat expansion in the huntingtin (HTT) gene on chromosome 4p16.3. It causes selective degeneration of GABAergic medium spiny neurons in the caudate and putamen. Chromosome 20 causes familial Creutzfeldt-Jakob disease. Chromosome 21 is associated with early-onset Alzheimer's in Down syndrome. Chromosome 19 carries APOE4.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.