Which description best fits Huntington disease?

• A. Autosomal dominant with CAG repeat expansion
• B. Autosomal recessive
• C. X-linked recessive
• D. Mitochondrial inheritance

Answer: (A)

Huntington disease is caused by a CAG trinucleotide repeat expansion in the HTT gene, and it is inherited in an autosomal dominant manner, meaning one mutated allele is enough to cause the disorder. The number of CAG repeats correlates with risk and age of onset, and these repeats can expand in transmission to offspring—especially from the father—leading to anticipation with earlier and more severe disease across generations. Clinically, it presents with chorea, psychiatric symptoms, and cognitive decline, usually starting in adulthood. This pattern is not consistent with autosomal recessive, X-linked recessive, or mitochondrial inheritance, which involve different transmission routes and patterns.