A clinically useful DNA probe closely linked to haemophilia A

Genetic linkage studies were done in families segregating for haemophilia A with an X-chromosome-specific probe, DX13, which has been localised to band Xq28. When DNA is digested with the restriction enzyme Bg1 II, this probe recognises a restriction fragment length polymorphism, for which 50% of females are heterozygous. No crossovers were seen between the haemophilia A locus and the DX13 locus (lod score = 5.4 at recombination fraction [theta] 0.0; 95% confidence limits of theta, 0-12%). This indicates that the DX13 probe is closely linked to the haemophilia A locus and is likely to prove useful in carrier detection and prenatal diagnosis.