What is the pattern of inheritance for Huntington disease?

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

Answer: (A)

Huntington disease is inherited in an autosomal dominant pattern because just one mutated copy of the HTT gene is enough to cause the illness. The mutation is a CAG trinucleotide repeat expansion, and the number of repeats can increase in transmission to offspring, leading to later or earlier onset in successive generations (anticipation). This means each child of an affected parent has about a 50% chance of inheriting the condition, and both sexes are affected equally, since the gene is not on a sex chromosome.

This isn’t autosomal recessive, which would require two mutated copies for disease; it isn’t X-linked recessive, which would show a male-predominant pattern and transmission through carrier females; and it isn’t mitochondrial, which would be inherited strictly from the mother with maternal lineage transmission. The combination of dominant inheritance and a repeat expansion in a nuclear gene best fits Huntington disease.