2001, 2002; Jilma-Stohlawetz et al., 2003). In the present study, the a/b genotype of HPA-5a/5b was signiﬁcantly lower in type 2 diabetes and non-diabetic ASO patients than in controls. The Lys505Glu amino acid substitution located in the cation-binding domain of α2 is responsible for HPA-5b (Bra) and HPA-5a (Brb) epitope formation (Santoso et al., 1993). In a large study, Kroll et al. (2000) found an association between HPA-5 dimorphism in a low-risk patient subgroup with coronary artery disease. In this population, the frequency of Brb homozygous individ- uals was overrepresented. This ﬁnding suggests that the allele 3 (807C; Bra) may increase the risk for thrombotic disease through a quantitative effect on the function that is independent of the genetic effects on expression levels. However, the frequency of phenotype HPA-5b in Japa- nese is lower than that in Caucasian (8.7 vs. 20.6%). In addition, it has been reported that the probability of HPA- related immunization is strongly associated with HLA class II DR types (Gonzalez-Conejero et al., 1998). A larger number of patients will need to be examined to conﬁrm this possibility. In conclusion, we performed a genetic analysis of HLA, and HPA in Japanese control subjects and type 2 dia- betes patients with and without ASO. The incidence of HLA-DRB1*1501 was found to be signiﬁcant in type 2 diabetes and non-diabetic ASO-positive patients com- pared with controls, and the frequency of this allele was signiﬁcant in patients with ASO. The frequency of NA2/ NA2 in ASO-positive diabetes and non-diabetic ASO- positive patients was signiﬁcantly higher than in controls. The a/b genotype of HPA-5a/5b was signiﬁcantly lower in type 2 diabetes and non-diabetic ASO-positive patients than in controls. 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