title: TNF-alpha gene polymorphisms in type 1 (insulin-dependent) diabetes mellitus.
abstract: Type 1 (insulin-dependent) diabetes mellitus, like some other autoimmune diseases, is linked to certain alleles coded by genes in the HLA-D region. Sequence analysis of DQ beta chains indicates that aspartic acid at codon 57 confers resistance to the development of Type 1 diabetes. However, a full explanation for the HLA-association of Type 1 diabetes, particularly the increased susceptibility of DR3/4 heterozygotes is still awaited. The localisation of tumour necrosis factor genes on the short arm of chromosome 6 between HLA-B and the complement genes (Class III) prompted us to investigate a possible polymorphism of TNF-alpha at the genomic level in relation to Type 1 diabetes susceptibility. A dialleleic TNF-alpha restriction fragment length polymorphism was found with Ncol and its segregation with HLA-haplotypes analysed in diabetic families. We describe here a strong linkage of TNF-alpha alleles with certain DR haplotypes. For example, the common extended haplotype HLA A1-B8-DR3 was almost exclusively associated with the 5.5 kb TNF-alpha allele whereas Bw62-DR4 with the 10.5 kb allele. Thus both alleles segregate to diabetic patients. DR matched haplotypes of affected family members differed significantly from those of the non-affected at the TNF alpha locus. All affected sibling pairs in 11 multiplex affected families were identical for TNF-alpha alleles, even if they were only haploidentical for HLA-B-DR haplotypes. In addition, heterozygosity for the TNF-alpha alleles was significantly more frequent in the patients. This tight linkage of TNF-alpha alleles with some extended haplotypes could help to explain the HLA-association of Type 1 diabetes as well as some other autoimmune diseases.
authors.affiliation: Department of Diabetes and Immunogenetics, St. Bartholomew's Hospital, West Smithfield, London, UK.
authors.forename: K
authors.initials: K
authors.lastname: Badenhoop
authors.forename: G
authors.initials: G
authors.lastname: Schwarz
authors.forename: J
authors.initials: J
authors.lastname: Trowsdale
authors.forename: V
authors.initials: V
authors.lastname: Lewis
authors.forename: K H
authors.initials: KH
authors.lastname: Usadel
authors.forename: E A
authors.initials: EA
authors.lastname: Gale
authors.forename: G F
authors.initials: GF
authors.lastname: Bottazzo
mesh_terms: D003920:Diabetes Mellitus / Q000209:etiology / Q000235:genetics*; D005260:Female; D006684:HLA-DR Antigens / Q000235:genetics; D006801:Humans; D008297:Male; D011110:Polymorphism, Genetic; D012150:Polymorphism, Restriction Fragment Length; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics*
chemical_list: D006684:HLA-DR Antigens; D014409:Tumor Necrosis Factor-alpha