If so, testing for that defect can be offered to other family members. This is called direct DNA testing. The defect is always in the dystrophin gene but there are many ways in which the gene may be defective. In such families the laboratory may be able to trace the defective gene and the normal gene through the generosity by following markers called DNA polymorphisms. This is called indirect DNA testing.
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 best to combine information from all available tests. Used with permission.