Which condition is typically autosomal dominant?

• A. Huntington disease
• B. Cystic fibrosis
• C. Sickle cell disease
• D. Tay-Sachs disease

Answer: (A)

Autosomal dominant inheritance means that one mutated allele is enough to cause the disorder, and affected individuals typically have an affected parent with a 50% chance of passing it to each child. Huntington disease fits this pattern because it is caused by a pathogenic expansion in the HTT gene and is inherited in an autosomal dominant manner with high penetrance. This results in disease in individuals who inherit just one mutated allele, and it often appears across generations with affected men and women equally, though onset is usually in midlife and can appear earlier in later generations due to anticipation.

The other conditions listed are inherited in an autosomal recessive pattern, meaning two mutated copies are typically required for disease to manifest. Cystic fibrosis, sickle cell disease, and Tay-Sachs disease usually have carriers who are asymptomatic and only show disease when both copies are mutated.