Radioactive probes

Hemophiliacs suffer from defective Factor VIII, which can be detected in fetuses 20 weeks old. A more accurate test, which can also be administered earlier during pregnancy, involves the use of a radioactive probe (36 nucleotide RNA fragment) which hybridizes restriction fragments. The gene for hemophilia is 186,000 base pairs, and has 26 exons separated by 25 introns. Mutations in the gene can be detected by RFLPs. This technology has also been used to detect the single base-pair difference between normal and mutated beta-chains, a screen for sickle-cell anemia. A DNA probe has been developed that hybridizes with the gene for dystrophin. The previous screening for Duchenne Muscular Dystrophy was a sex screen, with option to abort a male. The new technique allows differentiation between the healthy and diseased male fetus, so parents have more information with which to make an informed choice (if they chose). The hybridization only occurs if the normal dystrophin gene is present, no hybridization occurs in the DMD sufferer.