The Copenhagen founder variant GP1BAc.58T>G is the most frequent cause of inherited thrombocytopenia in Denmark

The classic Bernard‐Soulier syndrome (BSS) is a rare inherited thrombocytopenia (IT) associated with severe thrombocytopenia, giant platelets, and bleeding tendency caused by homozygous or compound heterozygous variants in GP1BA, GP1BB, or GP9. Monoallelic BSS (mBSS) associated with mild asymptomatic macrothrombocytopenia caused by heterozygous variants in GP1BAor GP1BBmay be a frequent cause of mild IT.