A 40-year-old woman whose father had Huntington disease currently shows no symptoms of the disease. She is newly pregnant with her first child and seeks your best estimate of the chance her child will inherit the disease. What is your estimate and how did you arrive at it? (Hint: See Figure 4.11)

Key Concepts

Huntington Disease Genetics

Huntington disease is an autosomal dominant disorder caused by a mutation in the HTT gene. This means that only one copy of the mutated gene, inherited from an affected parent, is sufficient to cause the disease. If a parent has the disorder, there is a 50% chance of passing the mutated gene to each child, regardless of the child's gender.

Penetrance

Penetrance refers to the proportion of individuals with a specific genotype who exhibit the associated phenotype. In the case of Huntington disease, while the mutation guarantees a 50% chance of inheritance, the penetrance is nearly complete, meaning that most individuals who inherit the mutation will eventually develop symptoms, typically in mid-adulthood.

Risk Assessment in Genetic Counseling

Genetic counseling involves assessing the risk of genetic disorders in offspring based on family history and genetic testing. In this scenario, the woman has a 50% chance of passing the Huntington mutation to her child, but since she currently shows no symptoms, it is crucial to consider whether she carries the mutation, which can be determined through genetic testing.