Genetic determination of the VNTR and HPA-2 regions of GPIb. PCR analysis of the VNTR polymorphism was performed with two different sets of primers: VNTR F3/B4 (A) and VNTR F2/B5 (B). HPA-2 identification was performed by PCR-ASRA–BsaHI digestion (C) and confirmed by SSCP (D). Amplified products were resolved by acrylamide gel electrophoresis and stained with AgNO₃. The genotype of the VNTR and HPA-2 polymorphisms is indicated at the top of each lane. MW represents the 1-kb marker ladder (GIBCO-BRL, Life Technologies, Barcelona, Spain).