[Collagen adhesion-aggregation abnormality (2nd report)--congenital platelet membrane glycoprotein VI deficiency].

Previously, we reported a case of 26-year-old woman with a mild bleeding tendency whose platelets specifically lacked collagen-induced aggregation and adhesion to collagen fibrils. In this report, we investigated the membrane glycoproteins of this patient's platelets and found that her platelets were absent in a 61-kDa glycoprotein, which was identified to be glycoprotein VI (GP VI) of the platelet membrane. Her parents platelets contained about 50% the normal amount of GP VI. These results indicate that our patient has a congenital homozygous GP VI deficiency and that GP VI functions as a collagen receptor.