title: Genotype effects and epistasis in type 1 diabetes and HLA-DQ trans dimer associations with disease.
abstract: Alleles of HLA class II genes DQB1, DQA1, and DRB1 in the MHC region are major determinants of genetic predisposition to type 1 diabetes (T1D). Several alleles of each of these three loci are associated with susceptibility or protection from disease. In addition, relative risks for some DR-DQ genotypes are not simply the sum or product of the single haplotype relative risks. For example, the risk of the DRB1*03-DQB1*02/DRB1*0401-DQB1*0302 genotype is often found to be higher than for the individual DRB1*03-DQB1*02 and DRB1*0401-DQB1*0302 homozygous genotypes. It has been hypothesized that this synergy or epistasis occurs through formation of highly susceptible trans-encoded HLA-DQ(alpha 1, beta 1) heterodimers. Here, we evaluated this hypothesis by estimating the disease associations of the range of DR-DQ genotypes and their inferred dimers in a large collection of nuclear families. We determined whether the risk of haplotypes in DRB1*0401-DQB1*0302-positive genotypes relative to the DRB1*03-DQB1*02-positive genotypes is different from that of DRB1*01-DQB1*0501, which we used as a baseline reference. Several haplotypes showed a different risk compared to DRB1*01-DQB1*0501, which correlated with their ability to form certain trans-encoded DQ dimers. This result provides new evidence for the potential importance of trans-encoded HLA DQ molecules in the determination of HLA-associated risk in T1D.
authors.affiliation: Department of ImmunoHaematology and Blood Transfusion, Leiden University Medical Center, The Netherlands. b.p.c.koeleman@med.uu.nl
authors.forename: B P C
authors.initials: BP
authors.lastname: Koeleman
authors.forename: B A
authors.initials: BA
authors.lastname: Lie
authors.forename: D E
authors.initials: DE
authors.lastname: Undlien
authors.forename: F
authors.initials: F
authors.lastname: Dudbridge
authors.forename: E
authors.initials: E
authors.lastname: Thorsby
authors.forename: R R P
authors.initials: RR
authors.lastname: de Vries
authors.forename: F
authors.initials: F
authors.lastname: Cucca
authors.forename: B O
authors.initials: BO
authors.lastname: Roep
authors.forename: M J
authors.initials: MJ
authors.lastname: Giphart
authors.forename: J A
authors.initials: JA
authors.lastname: Todd
mesh_terms: D016022:Case-Control Studies; D003922:Diabetes Mellitus, Type 1 / Q000208:ethnology / Q000235:genetics*; D019281:Dimerization; D004843:Epistasis, Genetic; D005260:Female; D005787:Gene Frequency / Q000235:genetics; D020022:Genetic Predisposition to Disease / Q000235:genetics; D005838:Genotype; D006683:HLA-DQ Antigens / Q000235:genetics* / Q000378:metabolism; D059866:HLA-DQ beta-Chains; D006684:HLA-DR Antigens / Q000235:genetics* / Q000378:metabolism; D059811:HLA-DRB1 Chains; D006239:Haplotypes / Q000235:genetics; D006801:Humans; D008297:Male; D012306:Risk; D044465:White People / Q000235:genetics
chemical_list: D006683:HLA-DQ Antigens; D059866:HLA-DQ beta-Chains; C069051:HLA-DQB1 antigen; D006684:HLA-DR Antigens; D059811:HLA-DRB1 Chains; C553505:HLA-DRB1*04:01 antigen