A nurse is reinforcing education about the inheritance patterns of fragile X syndrome to a couple who have a family history of the disorder. Which of the following statements should the nurse make?

A. “Fragile X syndrome follows an autosomal recessive pattern, so both genetic parents must carry the gene mutation for a child to be affected.” Fragile X syndrome is not autosomal recessive; it is X-linked dominant, meaning it is associated with mutations in the FMR1 gene on the X chromosome. Only one copy of the mutated gene is needed to express the condition. B. "Since your child has fragile X syndrome, all of your future sons will also have the condition, but your daughters will not be affected." This is incorrect because not all sons will necessarily inherit the condition, and daughters can also be affected, though they often have milder symptoms due to having two X chromosomes. C. “Fragile X syndrome is inherited in a mitochondrial pattern which means it is passed from the pregnant individual to the child through mitochondrial DNA.” Mitochondrial inheritance involves genes from the mother’s mitochondria, but fragile X syndrome is not inherited this way—it is an X-linked disorder passed down through the X chromosome. D. “Fragile X syndrome is inherited in an X-linked dominant pattern, which means that if a pregnant client carries the gene mutation, each child has a 50% chance of inheriting the condition.” This is correct. Fragile X syndrome is X-linked dominant, and a parent who carries the full mutation has a 50% chance of passing it to each child. Males typically have more severe symptoms than females due to having only one X chromosome.