Carrier detection in severe von Willebrand?s disease

Germline de novo mutations and linkage markers vs. DNA sequencing for carrier detection in von Willebrand disease

Linkage analysis in autosomal inherited von Willebrand disease (VWD) is important to diagnose the carriers and reduce the burden of severe type VWD. The study was designed to identify the carriers and estimate the frequency of variable number of tandem repeats (VNTR) instability in VWD families. Carrier detection was performed in eight recessive type 3 VWD (VWD3) families using VNTRs VWF1 and VWF2, RsaI (789Thr/Ala) linkage markers, multimer analysis and DNA sequencing. Moreover, five dominant VWD families were studied through DNA sequencing and multimer analysis. Frequency of VWF VNTR instability was investigated in 20 VWD families. In VWD3 families, a total of 22 (81.5%) carriers were identified using VWF1 and VWF2 markers. However, only 13(48.1%) carriers were identified through RsaI markers. Mutation screening revealed 22(81.5%) carriers in VWD3 and 4 (33.3%) carriers in VWD2 families. In comparison to DNA sequencing, the accuracy of VWF1 and VWF2 markers in VWD3 was 85.7% while RsaI could identify 68.2% carriers accurately. Mutations p.R1205H and p.C1272R were identified as de novo in families. Multimer analysis confirmed the identified carriers in VWD2 families. Three VWD families were found to be carrying VNTR instability for VWF1 and VWF2 locus. VNTRs could be an effective linkage markers for carrier detection in VWD3 families. However, in the event of germline de novo mutations and VNTR instability, it may confound risk of misdiagnosis of carriers. Multimer analysis could be an alternative way of carrier detection in dominant type 2A and type 2B VWD families.

Prenatal diagnosis in severe von Willebrand disease families from India using combination of phenotypic and genotypic assays

OBJECTIVE

This study aimed to offer genetic diagnosis to affected type 3 severe von Willebrand disease families.

METHOD

Thirteen families were referred for prenatal diagnosis during the first and second trimesters of pregnancy. Prenatal diagnosis was offered by chorionic villus sampling between 11 and 12 weeks and by cordocentesis between 18 and 19.5 weeks of gestation. Phenotypic analysis included FVIII:C and von Willebrand factor antigen assays. A combination of molecular biological techniques which included PCR-restriction fragment length polymorphism technique using intron 40 variable number tandem repeat (VNTR) markers, conformation sensitive gel electrophoresis, direct DNA sequencing, and multiple ligation probe amplification (MLPA) were used to offer genotyic diagnosis in the remaining families.

RESULTS

Diagnosis was offered by intron 40 VNTR analysis in eight families. In one family, the diagnosis was given by direct mutation detection technique, whereas in another diagnosis was given by MLPA technique as the index case showed the presence of large deletion within von Willebrand factor. In three families, diagnosis was offered by cordocentesis on the basis of phenotypic assays, further confirmed by genotyping.

CONCLUSION

Both first and second-trimester prenatal diagnoses could be successfully offered using a combination of phenotypic and genotypic techniques to all severe von Willebrand disease families.

Spectrum of Von Willebrand disease and inherited platelet function disorders amongst Indian bleeders

Platelet function disorders (PFD) and Von Willebrand disease (VWD) are among the uncommon causes of bleeding in haematological practice. The inherited variety of PFD includes defects in platelet adhesion, aggregation, secretion and platelet procoagulant activities. VWD is classified into three major categories-type 1 and 3 (quantitative deficiency) and type 2 VWD (qualitative defect). In the present study, the profile and prevalence of inherited PFD and VWD in Indians are described. Two thousand eight hundred patients with history of muco-cutaneous bleeding and other bleeding disorders were investigated. The tests performed included platelet count, bleeding time, PT, APTT, F VIII assay, platelet factor 3 (PF3) availability, platelet aggregation studies, VWF:Ag, VWF:RCo and multimeric analysis. Out of 2,800 patients investigated, a total of 872 (31.1%) were characterized to have either inherited coagulation defects (64.2%) or inherited platelet function disorders (35.8%). Of these 872 patients, 312 (35.8%) cases were characterized to have inherited PFD and 94 (16.8%) patients as VWD. Among 312 inherited PFD patients, isolated PF3 availability defect (48.1%) was most common, followed by unclassified PFD (37.2%). Among 94 VWD patients, type 2 VWD was most common (44.7%), followed by type 3 VWD (34.5%) and type 1 VWD (21.3%), respectively. Bleeding manifestations included easy bruising (46%), undue prolonged bleeding from trivial injuries (50% in PFD and type 1 and type 2 VWD and 100% in type 3 VWD), menorrhagia (31%), gum bleeds (22%), epistaxis (55%), haematuria (6%), GI bleeds (11%) and rarely, haematomas and haemarthoses (4%). In conclusion, VWD and inherited platelet function disorders are not uncommon among Indian population presenting with bleeding disorders.