Coeliac disease: investigation of proposed causal variants in the CTLA4 gene region

Abstract

Coeliac disease (CD) is an immune-mediated enteropathy triggered by gluten in genetically predisposed individuals. Patients with CD have an increased prevalence of other autoimmune disorders, including type 1 diabetes (T1D) and Graves' disease (GD). CD shares with these conditions certain HLA susceptibility alleles. A number of studies have also shown association of autoimmune diseases, including CD, with the CD28-cytotoxic T lymphocyte antigen 4 (CTLA4)-inducible costimulator (ICOS) region of chromosome 2q33, but until recently the precise causal variant has remained unknown. Recently, it was shown that, in GD, CT60 (+6230G>A), a single nucleotide polymorphism (SNP) at the end of the CTLA4 transcript, is associated with an alteration in the ratio of splice forms of the CTLA4 gene and that this ratio affects disease susceptibility. A similar but weaker association was found with T1D. There is also an independent association of GD and T1D with the SNP MH30 (-23 327G>C), which possibly affects promoter region function. Hypothesizing that CT60 and MH30 may be causal variants in other autoimmune disorders, we investigated these SNPs in CD using 149 family trios and 100 unrelated/unaffected controls. No association was detected with either SNP using both the transmission disequilibrium test (TDT) and case-control methods. Our study appears to have good power to detect moderate genetic effects, but possibly these SNPs exert too weak an effect on risk of CD to have been detected in our sample. Alternatively, the previously noted association of CD with the CTLA4 gene region may be due to different causal variants. Unlike T1D and GD, CD is not a true autoimmune disease, and CD has different associations at the CTLA4 exon 1 SNP +49G>A from all other autoimmune disorders. MH30, CT60, and other SNPs in the region may still warrant further investigation in other CD samples.