Prenatal diagnosis for haemophilia: the Thai experience

BACKGROUND

Haemophilia is a lifelong X-linked recessive inherited bleeding disorder. Since the haemophilia management in economically less-developed countries is inadequately provided, prevention of new cases of haemophilia is essentially required.

SUBJECTS AND METHODS

A total of 42 pregnancies in 37 women at risk for severe and moderate haemophilia (A = 33, B = 4) were enrolled. The prenatal diagnostic (PND) procedure was performed in 32 women, while 10 women refused further PND procedure after knowing their foetuses were female (n = 8) and male (n = 2). The foetal specimen was obtained through chorionic villus sampling (n = 14), amniocentesis (n = 1) and cordocentesis (n = 17). The status of haemophilia was determined using informative RFLP markers and inversion of intron 22 of the F8 gene, and/or foetal FVIII:C or FIX:C.

RESULTS

The final diagnosis revealed normal males (n = 18), haemophilia A males (n = 9), normal females (n = 3) and haemophilia A carrier females (n = 2). All women with affected haemophilia sons requested to terminate their pregnancies except one woman. One of 32 pregnancies (3.1%) had spontaneous abortion. At follow-up after birth, the PND was accurately confirmed in one haemophilia A male, three normal females and two carrier females by laboratory testing, and 18 unaffected normal males by history taking of no bleeding manifestations. However, 10 women who continued their pregnancies after knowing foetal sex turned out to have two haemophilia A males, one normal female, one haemophilia A carrier female and six normal or carrier females.

CONCLUSION

The PND of haemophilia could be accurately determined but it was not well accepted by all couples at risk.

Allele frequencies of two polymorphisms associated with the factor IX gene in Iranian population

Indirect genetic diagnosis using polymorphic DNA markers can be useful in large-scale screening programs, which is technically simpler, more rapid and amenable. The main objective of this study was to test the informativeness of two common intragenic markers (TaqI and XmnI) in Iranian haemophilia B families to detect the carriers by using a strategy that would be accurate and informative, yet less expensive compared to direct mutation analysis. The efficacy of these sites has been examined in 50 unrelated Iranian haemophilia B families and 50 normal females. The method used was polymerase chain reaction/restriction fragment length polymorphism (PCR/RFLP), which is economical and the enzymes XmnI and TaqI are cheap enough to be accessible in most of laboratories in developing countries. Our results show that 25% of X-chromosomes had the restriction site for TaqI enzyme. The XmnI site was 21%. The heterozygosity rates for TaqI and XmnI polymorphisms were 37% and 38%, respectively. Using the two polymorphisms together, the informative rate reached 46%. Taking advantage of TaqI and XmnI polymorphisms, carrier detection was performed for seven females with unknown status in five haemophilia B families (including one large extended family) with positive history. Six of the girls were normal and one was haemophilia B carrier. Therefore, carrier detection might be possible for informative Iranian haemophilia B families in the familial cases. Additionally, similarities in term of heterozygosity rates for these two polymorphic sites were seen between some European and Iranian populations.