Remarkable advances in molecular genetics that have occurred during past decades have resulted in numerous clinical applications for DNA analysis. Prenatal diagnosis has been enhanced markedly, both in terms of improvement in diagnostic accuracy for previously detectable genetic disorders, and in terms of the number of previously undetectable conditions that now may be accurately identified in the fetus. As a result of the Human Genome Project, the list of diagnosable conditions grows daily. At the present time, however, because of cost, complexity, and resource limitations, DNA analysis is generally not performed for prenatal population screening purposes but is used only if there is an increased risk of a specific genetic condition known to be present in a family as a result of the birth of an affected child or other family member. Improvements in technology and reductions in cost, however, may eventually result in certain DNA diagnostic tests becoming incorporated into routine prenatal care.

The ideal DNA analysis is a direct test for the presence of a mutation in an affected individual subject. The molecular basis of most disorders is caused by more than one mutation in the relevant gene. Therefore, the mutation must first be characterized in a particular family before any individual person at risk can be tested or a direct prenatal test offered. In many instances, a direct test is not available because the mutation in the patient's family is unknown or the gene has not yet been cloned. In these situations, indirect tests (linkage analysis) may be possible using the pattern of inheritance of DNA restriction fragments that are very close to the abnormal gene on the chromosome and are usually inherited together (linked) with the disease gene.<sup>22 Dahl H.-H.M. Elements of molecular genetics Med J Aust 1993 ;  158 : 195

Cliccare qui per andare alla sezione Riferimenti</sup> The presence or absence of the disease-producing mutation may then be inferred by comparing the DNA marker pattern present in fetal cells to that of the parents or affected offspring.