An autopsy brain from a patient who died of a chronic progressive movement disorder shows symmetric atrophy of the head of the caudate nucleus with marked neuronal loss in the striatum and gliosis. The cortex is relatively preserved. The underlying mutation involves:

• A GAA trinucleotide expansion in the frataxin gene
• B Trinucleotide CAG repeat expansion encoding polyglutamine tract in huntingtin ✓
• C Point mutation in the parkin gene
• D Hexanucleotide repeat expansion in C9orf72

Explanation

Huntington disease shows striking atrophy of the caudate and putamen with selective loss of striatal GABAergic medium spiny neurons, particularly those expressing enkephalin projecting to the external globus pallidus. It results from CAG repeat expansion in HTT producing an expanded polyglutamine tract with toxic gain of function. GAA expansion in frataxin causes Friedreich ataxia, which kills option A.

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.