Von Willebrand factor 1 and factor 2 alleles (intron 40) are suitable markers for carrier detection in von Willebrand disease families in the Indian population

Genetic heterogeneity in a large cohort of Indian type 3 von Willebrand disease patients

Background

Though von Willebrand disease (VWD) is a common coagulation disorder, due to the complexity of the molecular analysis of von Willebrand factor gene (VWF), not many reports are available from this country. Large size of the gene, heterogeneous nature of mutations and presence of a highly homologous pseudogene region are the major impediments in the genetic diagnosis of VWD. The study is aimed at unravelling the molecular pathology in a large series of VWD patients from India using an effective strategy.

Method

We evaluated 85 unrelated Indian type 3 VWD families to identify the molecular defects using a combination of techniques i.e. PCR-RFLP, direct DNA sequencing and multiple ligation probe amplification (MLPA).

Results

Mutations could be characterized in 77 unrelated index cases (ICs). 59 different mutations i.e. nonsense 20 (33.9%), missense 13 (22%), splice site 4 (6.8%), gene conversions 6 (10.2%), insertions 2 (3.4%), duplication 1 (1.7%), small deletions 10 (17%) and large deletions 3 (5.1%) were identified, of which 34 were novel. Two common mutations i.e. p.R1779* and p.L970del were identified in our population with founder effect. Development of alloantibodies to VWF was seen in two patients, one with nonsense mutation (p.R2434*) and the other had a large deletion spanning exons 16–52.

Conclusion

The molecular pathology of a large cohort of Indian VWD patients could be identified using a combination of techniques. A wide heterogeneity was observed in the nature of mutations in Indian VWD patients.

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.

Robustness of factor assays following cordocentesis in the prenatal diagnosis of haemophilia and other bleeding disorders

Prenatal diagnosis is the generally accepted option for genetic disorders including haemophilias and other bleeding disorders. Cord blood analysis between 17.4 and 20.6 weeks of gestation was performed in 172 confirmed carriers belonging to families of haemophilia A, haemophilia B, von Willebrand disease (VWD), factor VII and X deficiency; 133 were carriers for haemophilia A, 30 for haemophilia B, six for type 3 VWD, two for FX deficiency and one for FVII deficiency. The approach to the cord was either transabdominal or transamniotic. The volume of blood collected varied between 1 and 2 mL. In case of haemophilias, the diagnosis was offered by factor VIII/IX:C activity and antigen assays wherever required. In case of VWD, the diagnosis was based on von Willebrand factor antigen assays as detected by ELISA along with FVIII:C assay while in cases of FVII and FX deficiency, the diagnosis was based on FVII:C and FX:C respectively. The factor levels were compared with the normal range established in the laboratory for different coagulation factors between 18 and 21 weeks of gestation in women tested for other haematological disorders. Only in two cases, the procedure had to be repeated for reasons of extensive maternal contamination. All the deliveries have been followed up and the diagnoses reconfirmed by repeat clotting factor assays and DNA analysis whenever informative. Simple precautions like collection of fetal blood samples in smaller volumes in separate tubes, assaying multiple coagulation factors in the fetal blood samples helped us to offer diagnoses in all the women analysed. No fetal death or abortion was reported following the procedure. We suggest that accurate fetal blood sampling is a safe technique for the diagnosis of many of the bleeding disorders in places where genetic diagnostic services are not available.