Genotypes of European and Iranian patients with type 3 von Willebrand disease enrolled in 3WINTERS-IPS

Abstract

Type 3 von Willebrand disease (VWD3) is a rare and severe bleeding disorder characterized by often undetectable von Willebrand factor (VWF) plasma levels, a recessive inheritance pattern, and heterogeneous genotype. The objective of this study was to identify the VWF defects in 265 European and Iranian patients with VWD3 enrolled in 3WINTERS-IPS (Type 3 Von Willebrand International Registries Inhibitor Prospective Study). All analyses were performed in centralized laboratories. The VWF genotype was studied in 231 patients with available DNA (121 [115 families] from Europe [EU], and 110 [91 families] from Iran [IR]). Among 206 unrelated patients, 134 were homozygous (EU/IR = 57/77) and 50 were compound heterozygous (EU/IR = 43/7) for VWF variants. In 22 patients, no or only one variant was found. A total of 154 different VWF variants (EU/IR = 101/58 [5 shared]) were identified among the 379 affected alleles (EU/IR = 210/169), of which 48 (EU/IR = 18/30) were novel. The variants p.Arg1659*, p.Arg1853*, p.Arg2535*, p.Cys275Ser, and delEx1_Ex5 were found in both European and Iranian VWD3 patients. Sixty variants were identified only in a single allele (EU/IR = 50/10), whereas 18 were recurrent (≥3 patients) within 144 affected alleles. Nine large deletions and one large insertion were found. Although most variants predicted null alleles, 21% of patients carried at least 1 missense variant. VWD3 genotype was more heterogeneous in the European population than in the Iranian population, with nearly twice as many different variants. A higher number of novel variants were found in the Iranian VWD3 patients.

Molecular pathogenesis and heterogeneity in type 3 VWD families in U.S. Zimmerman program

“…24 We confirmed an exon 1-3 deletion in one IC, however Europe in 3WINTERS-IPS, was only found in two families along with another variant. 10,26 The variant p. Pro2808Leufs*24, observed in the Canadian type 3 VWD study and associated with milder bleeding, was found in one family, however our IC presented with a more severe bleeding phenotype (ISTH BS 15). 27 While some of the variants identified were previously reported and frequently occurring in other populations, we also identified 34 novel variants (Figure 2).…”

“…Causative VWF variants were identified in all 44 type 3 subjects with 93% of the mutant alleles accounted for, which is consistent with other type 3 VWD studies that have reported between 80%-95% of cases with pathogenic variants. 4,[7][8][9][10] Of the variants identified, 9% were large heterozygous deletions of exon 1-3, exon 4-5, exon 18 and exon 35-38. The exon 4-5 in-frame deletion has been previously reported as the most common deletion in the VWF gene occurring in both type 1 and type 3 VWD.…”

“…and Iranian (84%) type 3 VWD, which may reflect a higher rate of consanguinity in those populations. 10 Nine of the genetic variants were found in multiple families where OC displayed heterogeneity from normal to low VWF to type 1 as well as varied bleeding scores (Table 5). This exemplifies the complexity when correlating the genotype and phenotype and suggests that in addition to the unaffected allele, other factors including age, blood group, carbohydrate modifications and modifying genes contribute to VWF levels and bleeding.…”

“…[28][29][30][31] Missense variants accounted for 13% of the type 3 VWF variants identified, which is slightly lower than those found in the Canadian (19%) and 3WINTERS-IPS (21%) studies. 4,10 The underlying mecha- along with a splice site region variant (c.6256+2dup) that resulted in absence of VWF. 12 The mother with p. Two of the type 3 cases had splice site variants that were only identified upon re-analysis of the Sanger sequencing results.…”

“…A thorough genetic evaluation included VWF Sanger sequencing, comparative genomic hybridization (aCGH) and in silico prediction programs. While several large type 3 studies have been previously reported, 4,[7][8][9][10] the results provided here from the Zimmerman Program represents a cohort of VWD families in the U.S. with extensive phenotypic and genotypic data and provides additional insight into the bleeding tendencies, inheritance and phenotypic heterogeneity in families with type 3 VWD.…”