Huntington's Disease Risk: Probability for Child Based on Parent Genetics

The probability of a first child developing Huntington's disease is 25%.

Huntington's is an autosomal dominant disorder – one mutated gene copy causes the disease. The man's father is unaffected (no mutation). His mother has Huntington's, so she carries the mutation. The man therefore has a 50% chance of inheriting the mutated gene. If he carries it, each child has a 50% chance of inheriting it. Combined probability: 0.5 × 0.5 = 0.25 (25%).