As a genetic counselor, you advise couples about the possibility of genetic disease in their offspring. Today you met with an engaged couple, both of whom are phenotypically normal. The man, however, has a brother who died of Duchenne-type muscular dystrophy, an X-linked recessive condition. His fiancée, whose family has no history of the disease, is worried that the couple's sons or daughters might be afflicted. The sister of this man is planning to marry his fiancée's brother. How would you advise this second couple?

Verified step by step guidance

1. Understand that Duchenne muscular dystrophy is an X-linked recessive disorder, meaning the gene causing the disease is located on the X chromosome and two copies of the recessive allele are needed for females to express the disease, while only one is needed for males.
2. Since the man has a brother with the disease, it indicates that his mother is at least a carrier of the disease allele (X^d). The man himself could either be a carrier (X^dY) or not (XY).
3. The man's sister, who is planning to marry the fiancée's brother, has a 50% chance of being a carrier (X^dX) because she could have inherited the X^d from her mother.
4. The fiancée's brother, who is marrying the man's sister, has no family history of the disease, so he is likely not a carrier (XY).
5. Advise the second couple that if the man's sister is a carrier, there is a 50% chance their sons could have the disease and a 50% chance their daughters could be carriers. Genetic testing can provide more information about the sister's carrier status.

Key Concepts

X-linked Recessive Inheritance

X-linked recessive inheritance refers to genetic conditions associated with mutations in genes on the X chromosome. Males are more frequently affected because they have only one X chromosome, while females have two. A female carrier can pass the mutated gene to her sons, who will be affected, or to her daughters, who may become carriers.

Carrier Status

Carrier status in genetics indicates that an individual has one copy of a recessive allele that can cause disease in offspring if inherited. In X-linked recessive conditions, females can be carriers without showing symptoms, as they have a second, normal X chromosome. Understanding carrier status is crucial for assessing the risk of passing genetic conditions to children.

Genetic Counseling

Genetic counseling involves providing information and support to individuals or families about genetic conditions. Counselors assess the risk of inherited diseases, explain inheritance patterns, and discuss potential outcomes and options. This helps couples make informed decisions about family planning and managing genetic risks.