title: Evidence that HLA class I and II associations with type 1 diabetes, autoantibodies to GAD and autoantibodies to IA-2, are distinct.
abstract: OBJECTIVE
  A major feature of type 1 diabetes is the appearance of islet autoantibodies before diagnosis. However, although the genetics of type 1 diabetes is advanced, the genetics of islet autoantibodies needs further investigation. The primary susceptibility loci in type 1 diabetes, the HLA class I and II genes, are believed to determine the specificity and magnitude of the autoimmune response to islet antigens. We investigated the association of glutamic acid decarboxylase autoantibodies (GADA) and insulinoma-associated antigen-2 autoantibodies (IA-2A) with the HLA region.
  
  
  METHODS
  Associations of GADA and IA-2A with HLA-DRB1, HLA-DQB1, HLA-B, HLA-C, HLA-A, MICA, and 3,779 single nucleotide polymorphisms (SNPs) were analyzed in 2,531 childhood-onset case subjects (median time since diagnosis 5 years). All analyses were adjusted for age-at-diagnosis and duration of diabetes.
  
  
  RESULTS
  GADA and IA-2A were associated with an older age-at-diagnosis (P < 10(-19)). For GADA, the primary association was with HLA-DQB1 (P = 9.00 × 10(-18)), with evidence of a second independent effect in the HLA class I region with SNP, rs9266722 (P = 2.84 × 10(-6)). HLA-DRB1 had the strongest association with IA-2A (P = 1.94 × 10(-41)), with HLA-A*24 adding to the association, albeit negatively (P = 1.21 × 10(-10)). There was no evidence of association of either IA-2A or GADA with the highly type 1 diabetes predisposing genotype, HLA-DRB1*03/04.
  
  
  CONCLUSIONS
  Despite genetic association of type 1 diabetes and the islet autoantibodies localizing to the same HLA class II genes, HLA-DRB1 and HLA-DQB1, the effects of the class II alleles and genotypes involved are quite different. Therefore, the presence of autoantibodies is unlikely to be causal, and their role in pathogenesis remains to be established.
authors.affiliation: Juvenile Diabetes Research Foundation/Wellcome Trust Diabetesand Inflammation Laboratory, Cambridge Institute for Medical Research, Departmentof Medical Genetics, University of Cambridge, Cambridge, U.K. joanna.howson@cimr.cam.ac.uk
authors.forename: Joanna M M
authors.initials: JM
authors.lastname: Howson
authors.forename: Helen
authors.initials: H
authors.lastname: Stevens
authors.forename: Deborah J
authors.initials: DJ
authors.lastname: Smyth
authors.forename: Neil M
authors.initials: NM
authors.lastname: Walker
authors.forename: Kyla A
authors.initials: KA
authors.lastname: Chandler
authors.forename: Polly J
authors.initials: PJ
authors.lastname: Bingley
authors.forename: John A
authors.initials: JA
authors.lastname: Todd
mesh_terms: D000293:Adolescent; D001323:Autoantibodies / Q000235:genetics / Q000276:immunology*; D002648:Child; D003922:Diabetes Mellitus, Type 1 / Q000235:genetics*; D005260:Female; D005805:Genes, MHC Class I / Q000235:genetics*; D005802:Genes, MHC Class II / Q000235:genetics*; D020022:Genetic Predisposition to Disease; D005838:Genotype; D005968:Glutamate Decarboxylase / Q000276:immunology*; D006801:Humans; D008297:Male
chemical_list: D001323:Autoantibodies; C096322:ICA512 autoantibody; D005968:Glutamate Decarboxylase