Question

Which of the following is a true statement regarding Huntington's chorea?

• A. There is a loss of function type of mutation
• B. It is an autosomal recessive disorder
• C. It is a trinucleotide repeat expansion type of disorder
• D. There is an increased number of CAA repeats

Hint:

Caudate atrophy, autosomal dominant, and an unstable CAG triplet.

Answer 1

The Correct Option is C

Option-elimination works cleanly here. Statement (b) calls Huntington's autosomal recessive, but it is autosomal dominant, so out. Statement (a) calls it a loss-of-function mutation, but the expanded huntingtin protein gains a toxic function (a toxic polyglutamine tract that damages striatal neurons), so out. Statement (d) names CAA repeats, but the expanded triplet in HTT is CAG, so that detail is wrong. That leaves statement (c): Huntington's is one of the classic trinucleotide repeat expansion disorders, where an unstable CAG repeat lengthens beyond about 36 to 40 copies and triggers disease, with longer repeats giving earlier, more severe disease (anticipation). So (c) is the true statement. Clinical recall to anchor it: choreiform involuntary movements, psychiatric and mood changes, and progressive dementia, with caudate nucleus atrophy on imaging.