DNA polymorphisms for carrier detection of hemophilia in Thailand.

The assessment of carrier state based on the pedigree and laboratory testing in 55 females from 34 Thai hemophilia families (24 affected by hemophilia A, 10 by hemophilia B) was studied. The laboratory testing included phenotypic analysis (FVIII:C/vWF: Ag ratio, FIX:C) and two types of DNA polymorphisms, restriction fragment length polymorphisms (RFLP) and variable number tandem repeats (VNTR) in/and close to the factor VIII genes (Bcl I, Xba I RFLP, St 14 VNTR) and factor IX genes (Mse I, Dde I RFLP). Fifteen out of seventeen (88%) obligate hemophilia A carriers and one out of five (20%) obligate hemophilia B carriers were diagnosed by phenotypic analysis. All hemophilia A carriers were informative for at least one polymorphism (Bcl I, Xba I or St 14) while 42% of hemophilia B carriers were informative for Mse I RFLP only. DNA polymorphism analysis has advantage over phenotypic analysis since it generally gives an absolute diagnosis when informative. Most DNA polymorphism analyses are performed by PCR technique which is a simple, inexpensive and quick procedure. However, it is limited by non-informativeness and high incidence of new mutations.

Detection of carriers and prenatal diagnosis of bleeding disorders.

Carrier detection and prenatal diagnosis in the three commonest bleeding disorders (hemophilia A and B and von Wilebrands disease) can be performed either phenotypically or genotypically. Phenotypic analysis for carrier detection results only in a probabilistic assessment whereas DNA analysis, either by direct defect detection or by DNA polymorphism based gene tracking, can result in an accuracy of effectively 100%. Direct defect detection is the method of choice but can be technically demanding. Polymorphism analysis is much simpler and is now being used in family studies world wide.