CD9 and Alzheimer disease: In conclusion, the described GP1BA gene variant causes changes at the protein level, which may affect its protein conformation, expression, and thereby disturb the binding to its interacting partners and cause macrothrombocytopenia with decreased expression of GPIbα, GPIIa, GPIIIb, CD9 in this case of monoallelic BSS (AD macrothrombocytopenia).