What are the differences between Bernard‑Soulier syndrome and von Willebrand disease?

Bernard-Soulier Syndrome vs Von Willebrand Disease: Key Differences

Bernard-Soulier syndrome (BSS) is a platelet disorder caused by defective GPIb-IX-V receptor complex on platelets, while von Willebrand disease (VWD) is a plasma protein deficiency affecting von Willebrand factor (VWF)—these are fundamentally different pathophysiologic entities that can be distinguished by platelet size, VWF levels, and specific laboratory testing.

Fundamental Pathophysiology

BSS is an inherited platelet function disorder resulting from mutations in genes encoding the GPIb-IX-V complex (GP1BA, GP1BB, or GP9), which serves as the platelet receptor for VWF 1, 2. The defect lies within the platelet itself—specifically the absence or dysfunction of GPIbα, which normally binds VWF, collagen, thrombin, and other ligands 2.

VWD results from deficiency or dysfunction of VWF, a large plasma glycoprotein that mediates platelet adhesion and protects Factor VIII from degradation 3. The defect is in the plasma protein, not the platelet. VWD is the most common inherited bleeding disorder with prevalence up to 1% in the general population 3.

Clinical Presentation Overlap and Distinctions

Both conditions present with mucocutaneous bleeding including epistaxis, easy bruising, gingival bleeding, menorrhagia, and prolonged bleeding after procedures 3, 4, 5. However:

• BSS typically presents earlier in childhood with more severe bleeding symptoms 4
• BSS patients have macrothrombocytopenia (giant platelets with low counts) visible on blood smear 4, 2
• VWD patients have normal-sized platelets with normal or slightly decreased counts 3

Critical Laboratory Distinctions

Platelet Morphology

• BSS: Giant platelets (macrothrombocytopenia) on peripheral smear—this is pathognomonic 4, 2, 5
• VWD: Normal platelet size 3

VWF Levels

• BSS: Normal VWF antigen (VWF:Ag), normal VWF activity, normal VWF multimers—the plasma protein is intact 1, 6
• VWD: Reduced VWF:Ag and/or VWF activity, abnormal VWF multimers in type 2 variants 3

Ristocetin-Induced Platelet Aggregation (RIPA)

• BSS: Absent or severely reduced RIPA despite normal plasma VWF—the platelet cannot respond to VWF 6, 4
• VWD: Reduced RIPA due to insufficient VWF in plasma 3

Flow Cytometry

• BSS: Absent or markedly reduced GPIb-IX-V expression on platelet surface 1, 2
• VWD: Normal platelet glycoprotein expression 3

Factor VIII Levels

• BSS: Normal Factor VIII:C 1, 4
• VWD: Often reduced Factor VIII:C (except type 2N which specifically affects FVIII binding) 3

Inheritance Patterns

• BSS: Typically autosomal recessive (classic form), though rare autosomal dominant variants exist 2, 7
• VWD: Autosomal dominant (types 1 and 2) or autosomal recessive (type 3) 3

Common Diagnostic Pitfall

BSS is frequently misdiagnosed as immune thrombocytopenic purpura (ITP) or VWD 4, 8. The presence of giant platelets and thrombocytopenia can mislead clinicians into treating with corticosteroids or IVIG (ineffective in BSS) or misattributing bleeding to VWD when VWF levels are normal 8. A case report documented a patient treated for VWD for 30 years before genetic sequencing revealed BSS 8.

Critical diagnostic step: Always examine the blood smear for platelet size when evaluating bleeding disorders. If giant platelets are present with thrombocytopenia, pursue BSS workup with flow cytometry for GPIb-IX-V expression and genetic testing 1, 8, 7.

Treatment Differences

• BSS: Platelet transfusions are the mainstay; VWF replacement (DDAVP or VWF concentrates) is ineffective since the platelet receptor is defective 4, 8, 9
• VWD: DDAVP (for types 1 and some type 2) or VWF/FVIII concentrates are effective since platelets are functional 3

Definitive Diagnosis

• BSS: Genetic sequencing showing mutations in GP1BA, GP1BB, or GP9 genes 1, 7
• VWD: Reduced VWF levels with personal/family bleeding history and genetic testing of VWF gene when indicated 3

The key to distinguishing these disorders is recognizing that BSS is a platelet receptor defect with normal plasma proteins and giant platelets, while VWD is a plasma protein deficiency with normal platelet structure and function 1, 6, 2.