The levels of von Willebrand factor (VWF) in plasma are influenced by several variables, such as age, blood group, pregnancy, hormones, and smoking. The VWF levels may vary greatly on repeated laboratory testing in the same subject.1 About 60% of the variation in plasma VWF is caused by genetic factors, with ABO blood group accounting for only 30% of this.2 Indeed, in the normal population VWF levels are 25%-35% lower in individuals with blood group O than in individuals with non-O blood groups.3 Based on the results of epidemiologic studies, blood group–specific reference ranges have been suggested for diagnosis in von Willebrand disease (VWD).4,5 This biologic variation in VWF concentration may cause pitfalls when diagnosing mild cases of VWD.

There are no reports on the effect of ABO blood group in subjects heterozygous for VWF null alleles or heterozygous for some specific missense mutations. The influence of the ABO blood group in these individuals would be worthy of reporting since in several of these cases bleeding is rare despite the presence of clearly reduced VWF levels in plasma.

We have compared the VWF antigen (VWF:Ag) levels, according to blood group, of the heterozygous subjects from our families with recessive VWD. These individuals are heterozygous for VWF null alleles (splice site mutation, stop codon, frameshift, gene deletion), the type 2N mutation Arg854Gln, or the recessive missense mutation 7085G>T (Cys2362Phe) in exon 42 of the VWF gene6-8 (and unpublished data, 1999). Cys2362Phe is a true recessive mutation since it causes bleeding in compound heterozygous or homozygous states only.7,8 

All heterozygous subjects carrying blood group O have significantly lower VWF:Ag levels regardless of the type of mutation (Table1). Interestingly, subjects heterozygous for Cys2362Phe showed VWF:Ag values almost indistinguishable from those observed in carriers of a null allele. Subjects with the type 2N mutation Arg854Gln seem to have values roughly similar to those of healthy individuals.3,4 The same analysis was carried out also for factor VIII procoagulant activity (FVIII:C), but no significant differences in FVIII:C levels between subjects with O and non-O blood groups, according to the different types of mutations, were observed (data not shown).

Table 1.

Von Willebrand factor antigen levels in subjects heterozygous for the Cys2362Phe mutation, null alleles, or Arg854Gln (type 2N) according to blood group

Subjects Mean VWF:Ag ± SD, U/dL Range, U/dL  
Cys2362Phe*   
 O blood group (n = 8) 35.2 ± 16.2 25-55 
 Non-O blood group (n = 15) 61.5 ± 26.6 30-140  
Null allele   
 O blood group (n = 15) 43.2 ± 10.8 30-66  
 Non-O blood group (n = 15) 61.3 ± 23.6 25-98 
Arg854Gln   
 O blood group (n = 10) 75.4 ± 31.4 50-142  
 Non-O blood group (n = 7) 105.3 ± 24.3 74-153 
Subjects Mean VWF:Ag ± SD, U/dL Range, U/dL  
Cys2362Phe*   
 O blood group (n = 8) 35.2 ± 16.2 25-55 
 Non-O blood group (n = 15) 61.5 ± 26.6 30-140  
Null allele   
 O blood group (n = 15) 43.2 ± 10.8 30-66  
 Non-O blood group (n = 15) 61.3 ± 23.6 25-98 
Arg854Gln   
 O blood group (n = 10) 75.4 ± 31.4 50-142  
 Non-O blood group (n = 7) 105.3 ± 24.3 74-153 

P values determined by Mann-Whitney test and indicate the differences between blood groups.

*

P = .01.

P = .03.

P = .03.

Zhang et al9 reported phenotypic data in 3 groups of subjects heterozygous for null alleles (2430delC, Arg1659Xaa, and Arg1853Xaa). Subjects with Arg1853Xaa showed significantly lower VWF:Ag levels than did subjects heterozygous for 2430delC. But an excess of subjects with a non-O blood group (21, versus 9 with blood group O) was present in the group of subjects with 2430delC, compared to the group of subjects with Arg1853Xaa (1, versus 5 with blood group O). Thus the discrepant VWF:Ag levels between the 2 groups could be simply due to the different prevalence of blood groups. We have calculated VWF:Ag levels of subjects heterozygous for null alleles reported by Zhang et al.9 The mean VWF:Ag value for blood group O subjects (n = 17) was 32.3 ± 17. 3 U/dL, in comparison with 48.8 ± 25.9 U/dL in non-O blood group subjects (n = 25; P = .05), thus confirming our results. As a further confirmation of the present findings, also in the study of Zhang et al,9 no differences were observed as to FVIII:C.

It has been recently suggested that VWF levels in carriers of blood group O are presumably lower due to increased clearance of VWF.10 The present results show that blood group–associated VWF difference still exists despite the fact that individuals with null alleles (and possibly Cys2362Phe) have a clear defect in synthesis. This defect causes a 50% reduction of VWF which is larger than the blood group–dependent variation. The fact that in addition to the synthetic defect of the null allele, the VWF synthesized by the second normal allele still shows variation due to blood group may suggest that the effect of blood group is independent of the synthesis and occurs after VWF is secreted into bloodstream. This hypothesis is supported also by the demonstration that platelet VWF content, which reflects endothelial synthesis and storage of VWF,11 is similar in subjects with O and non-O blood groups.

In conclusion, blood group significantly influences VWF:Ag level not only in normal subjects but also in heterozygous subjects with a null allele, Arg854Gln, or Cys2362Phe missense mutation. The contribution of blood group may explain in itself, at least in part, the heterogeneity of plasma phenotypes observed in heterozygous carriers for type 3 VWD.12 A puzzling, still unanswered question is why subjects with absolute reduction of VWF in plasma associated with heterozygosity for null alleles or, for instance, Cys2362Phe mutation are almost asymptomatic.

References

References
1
Mohlke
KL
Ginsburg
D
von Willebrand disease and quantitative variation in von Willebrand factor.
J Lab Clin Med.
130
1997
252
261
2
Orstavik
KH
Magnus
P
Reisner
H
Berg
K
Graham
JB
Nance
W
Factor VIII and factor IX in a twin population: evidence for a major effect of ABO locus on factor VIII level.
Am J Hum Genet.
37
1985
89
93
3
Gill
JC
Endres-Brooks
J
Bauer
PJ
Marks
WJ
Montgomery
RR
The effect of ABO blood group on the diagnosis of von Willebrand disease.
Blood.
69
1987
1691
1695
4
Rodeghiero
F
Castaman
G
Dini
E
Epidemiological investigation of the prevalence of von Willebrand's disease.
Blood.
69
1987
454
459
5
Werner
EJ
Broxson
EH
Tucker
EL
et al. 
Prevalence of von Willebrand disease in children: a multiethnic study.
J Pediat.
123
1993
893
898
6
Eikenboom
JCJ
Ploos Van Amstel
HK
Reitsma
PH
Briët
E
Mutations in severe, type III von Willebrand's disease in the Dutch population: candidate missense and nonsense mutations associated with reduced levels of von Willebrand factor messenger RNA.
Thromb Haemost.
68
1992
448
454
7
Eikenboom
JCJ
Castaman
G
Vos
HL
Bertina
RM
Rodeghiero
F
Characterization of the genetic defects in recessive type 1 and type 3 von Willebrand disease patients of Italian origin.
Thromb Haemost.
79
1998
709
717
8
Castaman
G
Novella
E
Castiglia
E
Eikenboom
JCJ
Rodeghiero
F
A novel family with recessive von Willebrand disease due to compound heterozygosity for a splice site mutation and a missense mutation in the von Willebrand factor gene.
Thromb Res.
105
2002
135
138
9
Zhang
ZP
Lindstedt
M
Blombäck
M
Anvret
M
Effects of the mutant von Willebrand factor gene in von Willebrand disease.
Hum Genet.
96
1995
388
394
10
Vlot
AJ
Maser-Bunschoten
EP
Zarkova
AG
et al. 
The half-life of infused factor VIII is shorter in hemophiliac patients with blood group O than in those with blood group A.
Thromb Haemost.
83
2000
65
69
11
Rodeghiero
F
Castaman
G
Ruggeri
M
Tosetto
A
The bleeding time in normal subjects is mainly determined by platelet von Willebrand factor and is independent from blood group.
Thromb Res.
65
1992
605
615
12
Mannucci
PM
Lattuada
A
Castaman
G
et al. 
Heterogeneous phenotypes of platelet and plasma von Willebrand factor in obligatory heterozygotes for severe von Willebrand's disease.
Blood.
74
1989
2433
2437