(i) Pedigrees of family A and family B. Squares denote males; circles denote females. In family A (A[i]), the intron 40 VNTR-1 is shown as number of ATCT repeat units.17,18 In family B (B[i]), the intron 40 VNTR-2 is shown as number of TCTA repeat units.19(ii) Multimer analysis of vWF from plasma of members of family A and family B. Plasma samples were electrophoresed on 2% (A[ii], lanes 1-6; B[ii], lanes 5 and 6) or 3% (B[ii], lanes 1-4) SDS-agarose gels. Lanes 1 through 4 of A(ii) and B(ii) contain equal volumes of plasma (2 μL). Lanes 5 and 6 of A(ii) and B(ii) contain the appropriate volume of plasma containing 0.5 mU vWF as determined by ELISA. The vWF was transferred onto nitrocellulose by electroblotting. Lanes 1 through 4 of A(ii) and B(ii) were developed with the use of polyclonal rabbit anti-human vWF antibody and a secondary alkaline phosphatase-conjugated swine anti-rabbit IgG polyclonal antibody and colorimetric staining. Lanes 5 and 6 of A(ii) and B(ii) were developed with the use of rabbit anti-human vWF polyclonal antibody and a secondary horseradish peroxidase–conjugated swine anti-rabbit IgG polyclonal antibody and enhanced chemiluminescence. NP denotes plasma pooled from 20 normal individuals. (iii) Factor VIII binding to vWF from plasma of members of family A and family B. Mouse anti-vWF monoclonal RFF-VIII R/1 was used to coat the wells of a 96-well microtitre plate. Serial dilutions of patient plasma of known vWF:Ag (U/dL) were incubated in the wells. Then 5 mU of recombinant factor VIII was added, and the amount of factor VIII bound was determined by means of a chromogenic assay. Factor VIII binding expressed as absorbance at 405 nm was plotted against the concentration of vWF. Plasma from a patient with no factor VIII binding to vWF owing to homozygosity for the type 2N vWD mutation T791M.