Suitability of four polymorphic DNA markers for indirect genetic diagnosis of haemophilia A in Japanese subject

Abstract

Indirect genetic diagnosis using polymorphic DNA markers can detect carriers of haemophilia A (HA). These markers include CA repeat polymorphisms at intron 13 (CA-13) and CT-AG at intron 22 of the coagulation factor VIII (FVIII) gene, and also certain restriction fragment length polymorphisms (RFLPs) such as HindIII at intron 19 and BclI at intron 18. Recently, CA repeat polymorphism at intron 6 (CA-6) was also reported. We compared usefulness of the BclI RFLP, the HindIII RFLP, and CA-13 to that of CA-6. Heterozygosity of markers was examined in 282 X chromosomes obtained from 205 subjects including HA patients. Expected heterozygosity of the HindIII and BclI RFLPs was 30.0% and 27.9%, while observed heterozygosity was 28.0% and 26.5%. Expected heterozygosity of CA-13 was 45.6%, and observed heterozygosity was 40.0%. CA-6 showed two alleles with repeat numbers of 13 and 14, expected and observed heterozygosity were low (1.4% and 2.6%, respectively). When we used these markers in a HA lineage where the mother was a carrier according to coagulation factor assays, carrier diagnosis was possible using CA-13, the HindIII RFLP, and the BclI RFLP. This was not true for CA-6, for which the mother was homozygous. Although CA-13, and the HindIII and BclI RFLPs were useful for indirect genetic diagnosis of HA, CA-6 proved less useful because of low heterozygosity.