title: Polymorphism of the fourth component of complement in Graves' disease and type I diabetes mellitus.
abstract: The distribution of major histocompatibility complex (MHC) phenotypes in unrelated patients with Graves' disease or Type I diabetes mellitus and healthy controls was examined. HLA-B8 was increased in both the Graves' disease patients (p = .0018) and diabetes mellitus patients (p = .0246) relative to controls. Although C4A*QO is known to show strong linkage disequilibrium with HLA-B8, we could not demonstrate a difference in the frequency of this allele between either group of patients and the controls because the null C4A*QO cannot be accurately estimated from phenotype data. An unusual variant C4B*3 occurred three times in 117 controls, 10 times in 61 Graves' disease patients (p = .0012) and 13 times in 48 diabetic patients (p = 0.74 X 10(-5]. Although C4B*3 is known to show strong linkage disequilibrium with HLA-B15, the frequencies of B15 in the two patient groups did not differ from that of the controls considered here. When 28 MHC haplotypes (supratypes) from 14 unrelated patients with Type I diabetes were compared with 27 non-diabetes supratypes occurring in the same families but not in the patients, 8/28 Type I diabetes supratypes were C4AQOB1+, HLA-B8+, and 4/28 were C4B*3+, whereas 1/27 non-diabetes supratypes was C4AQOB1+, B8+, and 0/27 was C4B*3+. Of the four C4B*3+ diabetes positive supratypes, two were HLA-B15, one was B5 and one was B40. Finally, the second haplotype of 11 diabetes mellitus patients known to carry one high risk C4 haplotype was investigated. The second haplotype was the common type C4A3B1 in only 3/11, whereas at least 5/11 had second haplotypes containing C4B*QO, C4B*3, C4B*2 or C4A*4.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000483:Alleles; D003181:Complement C4 / Q000235:genetics*; D003922:Diabetes Mellitus, Type 1 / Q000235:genetics* / Q000276:immunology; D008040:Genetic Linkage; D006111:Graves Disease / Q000235:genetics* / Q000276:immunology; D006680:HLA Antigens / Q000235:genetics; D015235:HLA-B Antigens; D006801:Humans; D008285:Major Histocompatibility Complex; D010641:Phenotype
chemical_list: D003181:Complement C4; D006680:HLA Antigens; D015235:HLA-B Antigens