Detection of haemophilia carriers: multivariate analysis compared with discriminant analysis using up to five factor VIII variates

Rapid polymerase chain reaction analysis of St14 (DXS52) VNTR: carrier detection of hemophilia A

OBJECTIVE

To determine the frequency of St14 VNTR allele in Koreans as a marker of the hemophilia A and to evaluate the efficacy of this marker for carrier detection of hemophilia A METHODS: PCR amplified RFLP analysis of St14 VNTR was done in 312 X-chromosomes of 122 unrelated Korean males and 95 females and the same method was applied to carrier detection in the 2 hemophilia A families.

RESULTS

There were 13 alleles of different sizes of St14 VNTR locus appeared in 312 X-chromosomes of unrelated Koreans. For carrier detection of hemophilia A, in the family A, the mother showed 1390/ 1330 bp alleles and the father showed 700 bp allele. The affected son has inherited 1390 bp allele from his mother. The daughter at risk showed 1330/700 bp alleles. In family B, the mother showed 1280/700 bp alleles and the stepfather showed 1390 bp allele. The affected son has inherited 1280 bp allele. The daughter at risk showed 1390/700 bp alleles. And so the daughters of the 2 families were not carriers for hemophilia A.

CONCLUSION

PCR analysis of St14 VNTR was a useful tool for carrier detection of hemophilia A.

Detection of carriers of haemophilia A: use of bioassays and restriction fragment length polymorphisms (RFLP)

BACKGROUND

Haemophilia A is a sex-linked bleeding disorder carried by unaffected females. Currently, the two main methods used for the determination of carrier status in women from families with haemophilia A are bioassays and DNA-based assays using restriction fragment length polymorphisms (RFLP).

AIM

The aim of this paper was to assess the current usefulness of these two methods.

METHODS

Bioassays measured factor VIII coagulation activity by a two-stage coagulation assay and von Willebrand antigen by immunoelectrophoresis. RFLP were determined with two intragenic probes (p114 and p486) and two linked probes (St14 and DX13). Data were analysed using a Bayesian analysis to allow for all possible recombination events. We also incorporated an estimate for the risk of mosaicism into calculations in isolated haemophilia families. Both bioassays and RFLP were used to determine carrier status in 63 women, 31 from known haemophilia families and 32 from families of isolated cases. The techniques were assessed for their ability to classify the patients as normal (p < 0.2) or carrier (p > 0.7). Where applicable, intron 22 inversion was also tested.

RESULTS

In the known families, six women could not be classified after bioassay, but all could be classified by RFLP. Of the 32 women from families of isolated cases, eight were unclassified by bioassay and 12 were not definitely classified using RFLP. However, RFLP was useful in determining that a recent mutation had occurred in six of the eight families in which DNA from the grandparents was available.

CONCLUSION

For diagnosis of carriers of haemophilia, RFLP is the preferred method in familial haemophilia, but is less useful in isolated haemophilia.

Familial discrepancy between the one-stage and two-stage factor VIII methods in a subgroup of patients with haemophilia A

A higher result for plasma factor VIII:C measured by the one-stage as compared with the two-stage method has been described in some patients with haemophilia A or with von Willebrand's disorder. We used both methods to measure FVIII:C in 95 patients with haemophilia A. The results were equivalent in all 21 patients with severe haemophilia (16 families) and in 45 of the patients with mild or moderate haemophilia (18 families). However, the results were discrepant (FVIII:C by one-stage assay 2-7-fold higher than by two-stage assay) in the other 29 patients with mild or moderate haemophilia (12 other families). For each patient with discrepant FVIII:C results the classification was the same for all other affected members of his family. In some families with haemophilia A the gene defect leads to a discrepancy between the one-stage and two-stage FVIII:C results and may be more widespread than previously recognized.

Carrier detection and prenatal diagnosis of hemophilia A: 5-years experience at a hemophilia center

The identification of carriers and the prenatal diagnosis of hemophilia A have greatly improved with knowledge of the structure of the factor VIII gene. This has permitted the defect to be traced in families by using restriction fragment length polymorphisms. This study summarizes 5 years' experience at A. Bianchi Bonomi Hemophilia and Thrombosis Center and the problems encountered. One hundred and forty-four women at risk of hemophilia A from 93 families were referred to our center for DNA analysis. Carrier detection was performed in 95 women, including 11 who were pregnant. Prenatal diagnosis was performed at 7-14 weeks' gestation in 56 pregnant women. We employed two intragenic restriction fragment length polymorphisms (XbaI and BclI) and the two extragenic restriction fragment length polymorphisms (TaqI and BglII). Combining the results of intra and extragenic restriction fragment length polymorphisms with pedigree analysis, a diagnosis was reached in approximately 90% of cases. Of the 33 male fetuses, 11 were affected and 19 not affected. Two cases of recombination between extragenic restriction fragment length polymorphisms and the factor VIII locus were found.

Application of DNA-based diagnosis to patient care: the example of hemophilia A

DNA-based carrier testing and prenatal diagnosis are rapidly expanding medical applications of recombinant-DNA technology. The ultimate goal of DNA-based diagnosis is the determination of the causative mutation, but, in general, this is possible only for large deletions, insertions, or certain nonsense mutation that, in most diseases, involve only a few percent of affected families. If direct diagnosis of the carrier state or fetal disease state is not feasible, indirect diagnosis can be performed by following the segregation of linked polymorphisms through the family pedigree. For such indirect diagnosis, DNA from multiple family members must be analyzed. Although this procedure is highly accurate in many families, errors can potentially occur because of meiotic recombination, genetic heterogeneity, new mutations, and nonpaternity. In this review, a general introduction to DNA-based diagnosis of mendelian diseases is presented and the methods and strategy are outlined. The use of these techniques for the diagnosis of hemophilia A is then described to illustrate the principles of diagnosis and to highlight some of the complexities encountered. DNA-based diagnosis is in its infancy and has the potential to revolutionize preventive medicine.