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)

Verified step by step guidance

1. Step 1: Understand the inheritance pattern of Huntington's disease. Huntington's disease is an autosomal dominant disorder, meaning that only one copy of the mutated gene is needed for an individual to be affected.
2. Step 2: Determine the genetic status of the woman. Since her father had Huntington's disease, he must have had at least one copy of the mutated gene. The woman has a 50% chance of having inherited the mutated gene from her father.
3. Step 3: Assess the woman's current health status. The woman is 40 years old and currently shows no symptoms. While late-onset is possible, the absence of symptoms at this age may suggest she did not inherit the mutated gene, but it is not definitive.
4. Step 4: Calculate the probability of the child inheriting the disease. If the woman did inherit the mutated gene, there is a 50% chance she will pass it on to her child. If she did not inherit the gene, the chance is 0%.
5. Step 5: Combine probabilities to estimate the risk for the child. Since the woman has a 50% chance of being a carrier and, if she is, a 50% chance of passing it to her child, the overall probability of the child inheriting the disease is 25%.

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.