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. How would you advise this couple?

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1. Explain the inheritance pattern of Duchenne Muscular Dystrophy (DMD), which is an X-linked recessive disorder. This means that the gene causing the disorder is located on the X chromosome and the condition manifests predominantly in males who have only one X chromosome.
2. Discuss the genetic background of the man. Since his brother had DMD and he is phenotypically normal, he could potentially be a carrier of the DMD gene mutation. This is because he may have inherited the mutated gene on his X chromosome from his mother, who would be an asymptomatic carrier.
3. Consider the genetic status of the fiancée. Since she has no family history of DMD, it is less likely (but not impossible) that she is a carrier of the DMD gene. Carrier testing could be recommended to determine her carrier status more definitively.
4. Discuss the implications for their offspring. If the man is a carrier and the fiancée is not, their daughters may be carriers (inheriting the mutated gene from the father), and their sons would not have DMD (as they inherit their X chromosome from their mother). If both are carriers, there is a risk their sons could have DMD and their daughters could either be carriers or have DMD if they inherit the mutated gene from both parents.
5. Recommend genetic counseling and possibly genetic testing for both the man and his fiancée to assess their carrier status and discuss the risks and implications in more detail. This will help them make informed decisions about family planning.