How is von Willebrand disease passed on?
Von Willebrand disease is mostly a genetic disorder. This means it is passed down through the genes from parent to child. The altered gene in von Willebrand disease is on one of the regular chromosomes (autosomal), not on one of the sex chromosomes (like haemophilia). This means that, unlike haemophilia which affects more males, von Willebrand disease affects males and females in equal numbers.
There are two main inheritance patterns for VWD:
In most type 1 and type 2A, 2B and 2M VWD, the VWD gene is dominant. This means that if one parent has a VWD gene, they have a 1 in 2 (50%) chance of passing the gene on to each of their children. They or their children may or may not have symptoms.
If a child who has inherited autosomal dominant VWD (eg, has type 1 and type 2A, 2B and 2M VWD) has children, each of their children has a 1 in 2 (50%) chance of inheriting the altered VWF gene. Their children would typically have a symptom pattern similar to their affected parent.
In type 3 and type 2N and some type 1 and 2A VWD, the VWD gene is recessive. If both parents carry this type of VWD, they may have no or mild symptoms.
With their children:
- There is a 1 in 4 (25%) chance that their children could inherit a copy of the VWD gene from both of them and have symptoms, usually moderate to severe.
- There is a 1 in 2 (50%) chance that their children will inherit only one copy of the VWD gene from them and carry the gene but may have no or only mild symptoms, like their parents.
- There is also a 1 in 4 (25%) chance that their children will not inherit the VWD gene at all.
If a child has inherited autosomal recessive VWD (eg, has type 3 or type 2N VWD), their children will ALL
inherit a copy of the altered VWF gene and are known as obligate carriers.
Their children may or may not have symptoms.
If one member of a family is diagnosed with VWD, the doctor may recommend testing other members to see whether they have VWD as well.