[Genetic diagnostics using linkage analysis--when and why?].

Prenatal diagnosis in certain genetic diseases can be achieved by direct DNA testing if the population at risk has a limited number of relatively common mutations, or if the gene being tested is small. In the case of other genetic diseases, this possibility is unfeasible. The use of polymorphic markers very close to a given gene can identify patients and carriers indirectly and may be used for early diagnosis in pregnancy.