USMLE Step 1 Question 350

Question:

A patient with chorea and dementia is diagnosed with Huntington’s Disease. Which of the following correctly describes the genetic abnormality present in this patient?

Correct Answer: B.  Expansion of CAG repeats on Chromosome 4

Huntington’s Disease is a classic trinucleotide repeat disorder (B), where there is an expansion of CAG repeats on Chromosome 4.

Huntington’s is inherited autosomal dominantly (not X-linked [E]) and involves atrophy of cholinergic and GABAergic neurons in the caudate.

HOX genes (A) are responsible for general anterior-posterior patterning of the nervous system; diruption of proper HOX regulation would result in developmental disorders.

The APOE4 allele (C) and p-App (D) genes are both associated with the familial form of Alzheimer’s disease.