g. Promega Powerplex 16) [26]. The investigation can be conducted concurrently with foetal mutation analysis. Mutations in type 2 VWD are predominantly missense changes affecting specific functional domains and can be sought by targeted analysis of exons encoding these domains. This is simplest for type 2B and most complex for type 2A. Patients may be referred for genetic testing when they have a discrepancy between VWF:RCo and VWF:Ag (≤0.6) indicating reduced platelet-binding activity, but without disease type having been clarified. In these cases, exon 28 is the best starting

point for analysis. As further work is undertaken to understand the molecular basis of type 2A VWD, additional mutation locations are being identified. The majority of mutations are found in the A2 and A1 domains encoded by exon 28. The D3 domain (exons 22 and EX 527 concentration 25–27) has recently been recognized as the site of >25% of 2A mutations [27]. Rarer mutations are found in the cysteine knot (CK, exon 52) and the D2 domain (exons 11–17), with occasional mutations elsewhere in the

gene [28, 29]. Targeted analysis of exon 28 is commonly available, but diagnostic laboratories may not analyse further exons. This gain-of-function mutation type is characterized by enhanced RIPA. Ivacaftor cost Conformational changes induced by the mutation result in spontaneous VWF- GPIb binding. Type 2B VWD mutations have a restricted location within the A1 domain encoded by the 5′ end of exon 28. Platelet-type pseudo VWD, resulting from mutations in the GP1BA gene, is responsible for a similar phenotype and can be discriminated from type 2B VWD by analysis of exon 2 of that gene [30]. Mutations can affect either/both binding to GPIb/collagen. They are largely located in the A1 domain where they impair binding to GPIb, and the A3 domain where they may affect binding only to collagen or to both collagen and GPIb. Targeted analysis of exons 28–32

identifies most reported mutations [31]. Patients with this recessively inherited type of VWD, which mimics mild haemophilia A, may have reduced FVIII coagulant activity with normal or reduced VWF levels. Mutations reduce the binding of FVIII by VWF, thus reducing its plasma half-life until and level. The missense mutations that are responsible lie predominantly in the D’ domain encoded by exons 18–20. There are also reports of missense mutations that influence FVIII binding close to the propeptide cleavage site (exon 17) and in the D3 domain (exons 24–25) [29]. Putative type 2N patients with no mutation in these VWF exons should be investigated for F8 mutations. Parallel reductions in VWF:RCo and VWF:Ag indicate likely type 1 VWD. Genetic analysis may be requested in two situations. (i) To help understand disease pathogenicity in patients that have particularly low VWF levels.