If the mother of an affected boy is known to be a carrier and if her two dystrophin genes can be identified in this way, it can be determined whether the affected boy's sister received from their mother the same dystrophin gene as her brother. This indicates whether she has a high or a low probability of being a carrier. Using polymorphisms to track the gene defect through generations is called indirect DNA testing. Because of the way genes and chromosomes behave when eggs and sperm are made, the interpretation of indirect DNA testing is more complex than is described above. When indirect testing is to be used, this complexity should be explained to family members by a medical geneticist.
Direct testing is preferred so it is attempted first, if possible.
It is usually more time-consuming for the laboratory staff. Any one marker is informative in only some families. It is used to determine probabilities of carrier status and also for prenatal diagnosis. It is nearly always best to combine information from all available tests. So far research has proceeded along two paths.