Von Willebrand Disease (VWD) is the most common inherited bleeding disorder. It is characterized by a deficiency or dysfunction of von Willebrand factor (VWF), a protein that plays a role in blood clotting. This condition can lead to prolonged bleeding after an injury or surgery, and sometimes even spontaneous bleeding. This article explores VWD prevalence, its influencing factors, and reasons for underestimation.
Global and Reported Prevalence
Von Willebrand Disease is estimated to affect approximately 0.6% to 1.3% of the general population. However, the prevalence of clinically significant VWD is considerably lower, estimated at about 1 in 10,000 people.
The variation in reported prevalence figures stems from the distinction between asymptomatic cases and those with noticeable bleeding symptoms. Studies that screen healthy individuals, such as school-aged children, tend to report higher prevalence rates, closer to 1% of the population. Conversely, data collected from specialized bleeding clinics or patient registries show lower figures, reflecting only diagnosed symptomatic cases. For instance, a 2019 global survey reported a referral-based estimate of 1.5 per 100,000 individuals.
Factors Influencing Prevalence Rates
The reported prevalence of VWD is influenced by the different types of the disorder, along with demographic and genetic factors. VWD is classified into three main types based on the nature of the von Willebrand factor defect. Type 1 VWD, which involves a partial quantitative deficiency of VWF, is the most common, accounting for 60% to 80% of all cases. Type 2 VWD, characterized by qualitative defects where the VWF does not function properly, makes up 15% to 30% of cases and includes four subtypes (2A, 2B, 2M, and 2N).
Type 3 VWD, resulting from a near-total or total absence of VWF, is the rarest and most severe form, representing less than 5% of cases, with a global prevalence estimated at approximately 1 in 1,000,000 people. While VWD affects males and females equally, women are more frequently diagnosed due to increased bleeding symptoms during menstruation, pregnancy, and childbirth. For example, heavy menstrual bleeding is reported by 93% of women with Type 1 VWD.
VWD is an inherited disorder. Type 1 and most Type 2 VWD are inherited in an autosomal dominant pattern, meaning only one copy of the altered gene is needed to express the condition. However, Type 3 VWD and some Type 2 subtypes are inherited in an autosomal recessive manner, requiring two copies of the altered gene for the condition to manifest. Age of onset can vary, with earlier onset associated with more severe VWF deficiency.
Why Prevalence is Underestimated
Despite its relatively high estimated prevalence, VWD is often underdiagnosed or misdiagnosed, leading to a significant underestimation of its true occurrence. One major reason for this is the mild or non-specific nature of symptoms in many individuals. Common symptoms like easy bruising, frequent nosebleeds, or prolonged bleeding from minor cuts can be overlooked by individuals and healthcare providers alike, as they may be dismissed as normal occurrences.
A general lack of awareness about VWD among the public and even some healthcare professionals also contributes to underdiagnosis. Many practitioners may not consider VWD as a potential diagnosis, particularly when symptoms are subtle or a patient does not have a clear family history of the disorder. This knowledge gap can delay appropriate diagnostic investigations.
Diagnostic challenges further complicate accurate prevalence reporting. The diagnosis of VWD requires specialized laboratory tests that measure both the quantity and function of VWF. These tests can be complex and may not be routinely performed. Standard coagulation tests may not always reveal abnormalities, especially in mild cases, potentially leading to false negatives.
The variability in laboratory test results, influenced by factors like stress or hormonal changes, can also necessitate repeated testing, prolonging the diagnostic journey. This underestimation means many individuals with the condition may not receive proper diagnosis and management, potentially leading to preventable bleeding complications and impacting their quality of life.