Is the assessment of von Willebrand disease prevalence an achievable challenge? The example of the French Basque Country where blood group O and factor XI deficiency are highly prevalent.

The diagnosis of type I von Willebrand disease (VWD) is not straightforward because of the absence of a single clear-cut biological criteria and the interference of several acquired conditions on phenotype expression. We illustrate here this challenge with the French Basque population characterised by a marked high frequency in both blood group O and factor XI deficiency. From this example one may question the validity of epidemiological studies reporting on VWD prevalence.