The DNA testing has demonstrated that all individuals who demonstrate the fragile X syndrome have a parent who is a carrier. If the person affected by fragile X is a male, the carrier is always his mother. Since the carrier mother has two X chromosomes the chance of passing on the fragile X chromosome is 50 percent. The DNA testing can document the degree of amplification of the CGG repeat in the carrier. A higher level of amplification in a carrier female will increase the risk that the gene will amplify further in an affected child.
Amplification only occurs from the carrier status when the gene passes through a female.
Carrier males who are unaffected by the syndrome will pass the gene to all of their daughters but to none of their sons. The gene, however, will not amplify when passed on by a father so that daughters of carrier males are almost always unaffected carriers. Since the inheritance pattern in fragile X is complex, it is important for family members to receive genetic counseling concerning their risks of carrying the fragile X gene and passing it on to their children. It provides services including responding to requests for information, maintaining a resource center of educational materials, and publishing a variety of guides, directories, bibliographies and newsletters. It publishes A Guide to Selected National Genetic Voluntary Organizations.