Question

A couple has come to the genetic counseling office. They have a child affected by the genetic disorder cystic fibrosis. The genetic counselor tells the couple that the risk of having a child affected by cystic fibrosis is 1/4 or 25 percent. Since the couple already has a child with cystic fibrosis, can they have three more children without worrying that any of them will be affected by the disorder? Explain your answer.

Answer 1

When a genetic disorder is diagnosed in a family, family members often want to know the likelihood that they or their children will develop the condition. This can be difficult to predict in some cases because many factors influence a person's chances of developing a genetic condition. One important factor is how the condition is inherited. For example:

Autosomal dominant inheritance: A person affected by an autosomal dominant disorder has a 50 percent chance of passing the altered gene to each child. The chance that a child will not inherit the altered gene is also 50 percent. However, in some cases an autosomal dominant disorder results from a new (de novo) variant that occurs during the formation of egg or sperm cells or early in embryonic development. In these cases, the child's parents are unaffected, but the child may pass on the condition to his or her own children.