Which type of von Willebrand disease has four subtypes and is autosomal dominant?

Which type of von Willebrand disease has four subtypes and is autosomal dominant?

• A. Type 1
• B. Type 2
• C. Type 3
• D. Type 4

Answer: (B)

The key idea is that von Willebrand disease type 2 represents qualitative defects in von Willebrand factor function, and it has four distinct subtypes based on how that function is impaired. In contrast to type 1, which is a partial quantitative deficiency, and type 3, which is a near-complete deficiency, type 2 features abnormal VWF activity with often normal or near-normal VWF levels. Those four subtypes—2A, 2B, 2M, and 2N—reflect different mechanisms: 2A loses high molecular weight multimers and thus has impaired platelet adhesion; 2B has increased affinity for the platelet receptor GP Ib, which can cause platelet clumping and sometimes low platelet counts; 2M shows reduced platelet adhesion despite normal multimers; and 2N has reduced binding of VWF to factor VIII, leading to lower FVIII activity. Importantly, the pattern of inheritance for type 2 is typically autosomal dominant, distinguishing it from type 3 (autosomal recessive) and helping explain why this type is described as having multiple subtypes with a dominant inheritance tendency. Therefore, the type with four subtypes and the common autosomal dominant inheritance is type 2.

The key idea is that von Willebrand disease type 2 represents qualitative defects in von Willebrand factor function, and it has four distinct subtypes based on how that function is impaired. In contrast to type 1, which is a partial quantitative deficiency, and type 3, which is a near-complete deficiency, type 2 features abnormal VWF activity with often normal or near-normal VWF levels. Those four subtypes—2A, 2B, 2M, and 2N—reflect different mechanisms: 2A loses high molecular weight multimers and thus has impaired platelet adhesion; 2B has increased affinity for the platelet receptor GP Ib, which can cause platelet clumping and sometimes low platelet counts; 2M shows reduced platelet adhesion despite normal multimers; and 2N has reduced binding of VWF to factor VIII, leading to lower FVIII activity. Importantly, the pattern of inheritance for type 2 is typically autosomal dominant, distinguishing it from type 3 (autosomal recessive) and helping explain why this type is described as having multiple subtypes with a dominant inheritance tendency. Therefore, the type with four subtypes and the common autosomal dominant inheritance is type 2.