title: MHC susceptibility genes to IgA deficiency are located in different regions on different HLA haplotypes.
abstract: Familial predisposition to IgA deficiency (IgAD) suggests that genetic factors influence susceptibility. Most studies support a polygenic inheritance with a susceptibility locus (designated IGAD1) in the MHC, but its exact location is still controversial. This study aimed to map the predisposing IGAD1 locus (or loci) within the MHC by investigating the pattern of association of the disease with several markers in the region. DNA-based techniques were used to type individual alleles of four polymorphic HLA genes (HLA-DR, -DQA1, -DQB1, and HLA-B), six microsatellites (all located between HLA-DR and HLA-B), and three single nucleotide polymorphisms on the TNF gene. The frequencies of these alleles were compared among ethnically matched populations comprising 182 patients and 343 controls. Additionally, we investigated parents and siblings of 100 of these patients. All four parental haplotypes were established in each family (n = 400), and transmission disequilibrium tests were performed. Surprisingly, our results did not support the hypothesis of a unique susceptibility gene being shared by all MHC susceptibility haplotypes. On HLA-DR1 and -DR7-positive haplotypes IGAD1 mapped to the class II region, whereas on haplotypes carrying HLA-DR3 the susceptibility locus mapped to the telomeric end of the class III region, as reported previously. Our results show how, in complex diseases, individuals may be affected for different genetic reasons and a single linkage signal to a region of a chromosome may actually be the result of disease-predisposing alleles in different linked genes in different pedigrees.
authors.affiliation: Department of Immunology, Hospital Clinico San Carlos, La Paz Hospital, 28040 Madrid, Spain. egomezdela@hcsc.insalud.es
authors.forename: Emilio G
authors.initials: EG
authors.lastname: De la Concha
authors.forename: Miguel
authors.initials: M
authors.lastname: Fernandez-Arquero
authors.forename: Lorena
authors.initials: L
authors.lastname: Gual
authors.forename: Patricia
authors.initials: P
authors.lastname: Vigil
authors.forename: Alfonso
authors.initials: A
authors.lastname: Martinez
authors.forename: Elena
authors.initials: E
authors.lastname: Urcelay
authors.forename: Antonio
authors.initials: A
authors.lastname: Ferreira
authors.forename: Maria C
authors.initials: MC
authors.lastname: Garcia-Rodriguez
authors.forename: Gumersindo
authors.initials: G
authors.lastname: Fontan
mesh_terms: D000483:Alleles; D005260:Female; D005787:Gene Frequency / Q000276:immunology; D005805:Genes, MHC Class I; D005802:Genes, MHC Class II; D005819:Genetic Markers / Q000276:immunology; D020022:Genetic Predisposition to Disease / Q000235:genetics*; D006680:HLA Antigens / Q000032:analysis / Q000235:genetics*; D006684:HLA-DR Antigens / Q000032:analysis / Q000235:genetics; D015803:HLA-DR3 Antigen / Q000032:analysis / Q000235:genetics; D015809:HLA-DR7 Antigen / Q000032:analysis / Q000235:genetics; D059811:HLA-DRB1 Chains; D006239:Haplotypes / Q000276:immunology*; D006650:Histocompatibility Testing / Q000379:methods; D006801:Humans; D017098:IgA Deficiency / Q000235:genetics* / Q000276:immunology*; D008297:Male; D016133:Polymerase Chain Reaction / Q000379:methods
chemical_list: D005819:Genetic Markers; D006680:HLA Antigens; D006684:HLA-DR Antigens; D015803:HLA-DR3 Antigen; D015809:HLA-DR7 Antigen; D059811:HLA-DRB1 Chains