Analysis of clinical phenotype and genotype in patients with VWD2B, in a single institution of Argentina

WOODS AI; BERMEJO EI; SANCHEZ LUCEROS A; KEMPFER AC; CALDERAZZO JC; MESCHENGIESER S.S; LAZZARI MA

Amsterdam

Congreso; CONGRESS OF THE INTERNATIONAL SOCIETY ON THROMBOSIS AND HAEMOSTASIS; 2013

INTERNATIONAL SOCIETY ON THROMBOSIS AND HAEMOSTASIS

Abstr. code: PB 4.43-6 Analysis of clinical phenotype and genotype in patients with VWD2B, in a single institution of Argentina Adriana I Woods, Emilse Bermejo, Analía Sánchez-Luceros, Ana C Kempfer, Julio C Calderazzo, Susana S Meschengieser, María A Lazzari Laboratorio de Hemostasia y Trombosis, IMEX-CONICET, Instituto de Investigaciones Hematológicas, Academia Nacional de Medicina de Buenos Aires, Buenos Aires, Argentina Background Type 2B von Willebrand disease (VWD2B) is characterized by gain-of-function mutations in the A1 domain of von Willebrand factor (VWF) inducing a greater affinity for platelet GPIb, associated with the disappearance of large forms of multimers (HMWM), thrombocytopenia, positive ristocetin induced platelet aggregation (RIPA) at low concentrations, and VWF:RCo/VWF:Ag<0.6. An atypical form of VWD2B was also described, characterized by both normal platelet count (PC) and multimers, but positive RIPA at low concentrations (Casonato A, 2010). It is extremely important to determine the degree of severity of the disease, correlating in each patient the phenotype with genotype. This could help to decide for example, the input to the patient prophylactic treatment, prophylaxis of bleeding in a challenge as surgery, childbirth, etc. Aims We tried to find a relationship between the mutations identified, the BSS, PC, multimeric pattern, lower minimal aggregating ristocetin concentration, and propeptide/VWF:Ag ratio (VWFpp ratio) in 19 patients (pts) with VWD2B with candidate mutations. Methods The exon 28 was amplified and sequenced (ABI Prism310). BSS was calculated in each pts. Pts were grouped according to their mutation. Results The following mutations were described in our pts: p.R1304V (n=3; females=2); BSS=4.3±0.9; all pts with both normal PC, and multimers, and positive RIPA at 0.5 mg/mL. VWFpp ratio (normal value=1.5±0.5)=2.5±0.3. p.R1306W (n=4; females=2); BSS=6.3±1.9; low PC and absence HMWM=all of pts; positive RIPA at 0.3 mg/ml=25% of pts, at 0.5 mg/mL=75% of pts. VWFpp ratio=2.21±0.4. p.R1308C (n=4; females=4), BSS=4.3±1.8; low PC=50% of pts; absence of HMWM=all pts; positive RIPA at 0.3 mg/ml=25% of pts, at 0.7 mg/mL=75% of pts. VWFpp ratio=2.1±0.5. p.V1316M (n=8; females=5) was the most frequent mutation in our pts. BSS=4.6±1.0; low PC= 87.5% of pts; absence of HMWM=all of pts; positive RIPA at 0.3 mg/ml=25% of pts, at 0.5 mg/mL=62.5% of pts, at 0.6 mg/mL=12.5% of pts. VWFpp ratio=2.5±0.4. Conclusion Phenotypic profile of p.R1304V revealed atypical VWD2B, given the presence of both normal PC and multimers in those pts. Considering the other 16 pts with typical VWD 2B, all of them had absence of HMWM, and 81.25% had low PC. Pts with p.R1306W had BSS higher than the other pts, although the difference was not statistically significant (p=0.158); all those pts also had low PC and absence of HMWM. These findings could indicate a higher tendency to more severe clinical symptoms associated with this mutation. No differences were observed in the BSS with the other pts. It is important to take into account that only 15.8% of our 19 pts showed positive RIPA at 0.7 mg/mL. In contrast, a 75% of pts with p.R1308C had positive RIPA at 0.7 mg/mL. According to these results, we agree with the recommendations of using 0.5-0.7 mg/mL RIPA for diagnosing VWD2B (SSC, ISTH 2010).  VWFpp ratio was slightly high in all our pts with typical and atypical VWD2B, but unrelated to the different mutations, the BSS, the PC, and the lower aggregating concentrations of RIPA.