ANALYSIS OF THE VON WILLEBRAND FACTOR (vWF) GENE IN 6 PATIENTS WITH SEVERE TYPE III VON WILLEBRANDS DISEASE

DNA from 6 unrelated patients with severe type III von Willebrands disease (vWF antigen < 0.01u/dl) was studied with a cDNA probe for the 3' end of the vWF gene. DNA was extracted from peripheral blood leucocytes using standard techniques and was digested with a range of restriction enzymes. DNA fragments were separated by electrophoresis in 0.7% agarose and were southern blotted onto hybond-N (Amersham). The probe used was pvWF1100, a 1.1kb PstI fragment derived from the 2.28kb vWFcDNA insert of pvWF2280 isolated from a human endothelial cell cDNA expression library (Verweij et al, Nucleic Acids Res 13 (1985) 4699-4717). The probe corresponds to nucleotides 7083 to 8191 of the vWF cDNA (first nucleotide of initiator methionine as 1).

When digested with Bglll and probed with pvWF11000, normal DNA showed two invariant bands (13 and 4.9kb) and polymorphic bands of 9 and/or 7.4kb. This pattern was also seen in 5 of the 6 severe vWD patients DNA suggesting that in this 3' area of the gene they had no major deletions or rearrangements. In the 6th case however the band of 4.9kb was not seen and did not appear to be replaced by any novel fragments, suggesting a partial deletion including some of the 3' end of the gene. This patient had the clinically severest form of the condition in that the patient had developed, some 10 years ago, an antibody (inhibitor) to vWF as detected by the ability of the patients plasma to inhibit restocetin cofactor activity in normal plasma. His parents were related (his mother was his father's second cousin) and had levels of vWFAg, considerably lower than those of factor VIII activity. This situation has been previously reported in carriers of recessive severe vWD. vWD was also present in a second family member, but in a less severe form (vWFAg 3u/dl). This patient and all other members of the family have, to date, given normal restriction fragment patterns with the vWF probe and several enzymes, including BgIII.