Scientists are still searching for more genes and mutations. In many cases, direct testing is possible for ADRP, Usher syndrome type I B, some macular dystrophies, choroideremia, and gyrate atrophy. Direct testing may take a period of weeks to be completed by the laboratory service. Indirect Testing Indirect tests take advantage of the fact that genes and other DNA regions that lie close together on the same chromosome are usually inherited together. To find the links between genes, scientists perform a specific type of study using markers.
Markers are DNA fragments with harmless variations that are unique to families.
If the disease gene is linked to a marker, scientists can detect where that gene is located. Because all individuals inherit markers from both parents, researchers must compare markers from affected and unaffected individuals to sort out which ones are associated with the disease. Therefore, several family members are needed from more than one generation. The certainty of indirect testing results depends on how close the disease gene is linked to markers. Sometimes, markers cannot be readily identified and a disease gene cannot be traced through a family.