Phenotypic and genetic characterizations of the Milan cohort of von Willebrand disease type 2

Abstract

von Willebrand disease (VWD) type 2 is caused by qualitative abnormalities of von Willebrand factor (VWF). This study aimed to determine the genotype and phenotype characterization of a large VWD type 2 cohort from Milan. We included 321 patients (54% females) within 148 unrelated families from 1995-2021. Patients were fully characterized using laboratory phenotype tests and the genotype diagnosis was confirmed by target genetic analysis using Sanger sequencing. Patients were diagnosed with type 2A (n= 98, 48 families), 2B (n= 85, 38 families), 2M (n= 112, 50 families), and 2N (n= 26, 12 families). Eighty-two unique VWF variants including 8 novels were found. The potential pathogenic effect of novel variants was assessed by in silico analysis. Most patients were heterozygous for a single variant (n= 259, 81%), whereas 37 cases (11%) had 2 variants (4 homozygous, 9 in trans and 24 in cis). Twenty-five patients (8%) had 3 or more variants, mainly due to gene conversions. Among the 82 distinct variants identified, five different types including missense (n= 64), gene conversion (n= 10), synonymous (n= 1), deletion (n= 4) and splice (n= 3) were observed. The results of this large cohort showed that VWD type 2 is invariably due to variants that do not prevent the synthesis of the protein and the vast majority of patients (88%) had missense variants. Given the complexity of type 2 diagnosis and the necessity of performing several phenotypic tests, genetic analysis for patients suspected of type 2 is beneficial to establish the correct diagnosis.

A comparative study in patients with type 2 von Willebrand disease using 4 different platelet-dependent von Willebrand factor assays

“…All the 5 groups of patients with VWD investigated showed reduced VWF:Ag median values, with patients with type 2M showing the lowest VWF levels. The type 2A group was the most heterogeneous because of the 11 different genetic variants, whereas almost all patients with type 2M/2A had the same variant (p.Arg1374His) [ 26 ]. The VWF activity/VWF:Ag ratio, which is crucial to distinguish VWD type 1 from most type 2 variants, was evaluated using the 4 different assays.…”

“…Each of these variants was mainly associated with either type 2M [ 20 , 21 , 22 ], 2A [ 23 , 24 , 25 ], or even as type 2A/2M (p.Arg1374Cys) [ 25 ]. In our center, these variants were classified as type 2M/2A [ 26 ]. Although the latter definition (2M/2A) is not included in the official VWD classification [ 3 ], we have extensively described the characteristics of these variants in a previous study [ 26 ].…”

“…In our center, these variants were classified as type 2M/2A [ 26 ]. Although the latter definition (2M/2A) is not included in the official VWD classification [ 3 ], we have extensively described the characteristics of these variants in a previous study [ 26 ]. In brief, patient diagnosis was based on markedly reduced VWF activity/VWF:Ag ratios with only mildly reduced VWF:CB/VWF:Ag ratios and a modest loss of HMWM due to a mutation in the A1 domain ( Supplementary Table 1 ).…”

Diagnóstico de la enfermedad de von Willebrand

“…Este índice es capaz de diferenciar la mayoría de los pacientes tipo 2 de los de tipo 1; si la relación es >0,7 (normal) se asocia al tipo 1, y si es <0,7 se asocia con el tipo 2, sin diferenciar sus subtipos excepto en el 2N, donde está normal. En este último, otra alternativa es la relación FVIII:C/FVW:Ag, que es el único donde está <0,7 [3,10,33,41,42], por lo tanto, esta relación baja asociada a un nivel de FVIII bajo con un FVW normal o casi normal, puede indicar EVW subtipo 2N o una hemofilia A leve [15,26,43].…”

Population-based prevalence and mutational landscape of von Willebrand disease using large-scale genetic databases

“…Qualitative defects result in four different type 2 VWD (2A, 2B, 2M and 2N) [11]. The genetic variants responsible for type 1 (mostly dominant) and 3 VWD (recessive) are spread across the 52 exons of VWF [12][13][14], whereas type 2 VWD variants are con ned to VWF functional domains [12,15].…”