Huntington's disease is inherited in which pattern?

• A. Autosomal recessive
• B. Autosomal dominant
• C. X-linked recessive
• D. Mitochondrial inheritance

Answer: (B)

Huntington's disease is inherited in an autosomal dominant pattern: a single mutant allele is enough to cause the disease, so each child of an affected parent has about a 50% chance of inheriting it, regardless of sex. The mutation is a CAG trinucleotide repeat expansion in the HTT gene on an autosome, which explains why both men and women are affected equally and why the condition often appears in adulthood. This pattern also allows anticipation, where disease onset can occur earlier in subsequent generations due to increasing repeat length. Because the mutation is on an autosome and not on a sex chromosome or mitochondria, it is not autosomal recessive, X-linked recessive, or mitochondrial inheritance.