Huntington disease inheritance pattern?

• A. Autosomal recessive HTT mutation
• B. X-linked recessive
• C. Autosomal dominant CAG repeats in HTT gene
• D. Mitochondrial inheritance

Answer: (C)

Huntington disease is caused by a trinucleotide (CAG) repeat expansion in the HTT gene, and it follows autosomal dominant inheritance. That means a single mutated allele is enough to cause disease, so an affected parent has a 50% chance of passing it to each child, regardless of sex. The disease mechanism is a toxic polyglutamine-containing huntingtin protein produced by the expanded CAG repeats; the length of the repeats correlates with how soon and how severely the disease presents. This leads to anticipation, especially when transmitted from the father, with earlier onset in later generations. It’s not X-linked, not autosomal recessive, and not due to mitochondrial inheritance, which is why those patterns don’t fit Huntington disease.