Human Molecular Genetics Advance Access originally published online on September 25, 2006
Human Molecular Genetics 2006 15(21):3195-3205; doi:10.1093/hmg/ddl395
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Evidence for unique association signals in SLE at the CD28–CTLA4–ICOS locus in a family-based study
1 Imperial College, Molecular Genetics and Rheumatology Section, Hammersmith Hospital, Du Cane Road, London W12 0NN, UK, 2 Royal National Hospital for Rheumatic Diseases, Bath BA1 1RL, UK and 3 Department of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, UK
* To whom correspondence should be addressed. Tel: +44 2083832339; Fax: +44 2087433109; Email: t.vyse{at}imperial.ac.uk
Received May 24, 2006; Accepted September 14, 2006
CD28, CTLA4 (cytotoxic T lymphocyte-associated protein 4) and ICOS (inducible T cell co-stimulator) are good candidate genes for systemic lupus erythematosus (SLE) because of their role in regulating T cell activation. CTLA4 inhibits CD28-mediated T cell activation. CTLA4 is expressed on CD4+ and CD8+ activated T cells, and also B cells, but CD28 and ICOS are largely restricted to T cells. An interval encompassing the CD28–CTLA4–ICOS locus on chromosome 2q33 was linked to lupus in two genome-wide linkage scans. This large family-based association study in 532 UK SLE families represents the first high-density genetic screen of 80 SNPs at this locus. There are seven haplotype blocks across the locus. In CTLA4, the strongest signal comes from two variants, located 2.1 kb downstream from the 3'-UTR. These polymorphisms, rs231726 (SNP 43) and rs231726 (SNP 44), are in complete linkage disequilibrium (LD) (r2=1) and are associated with SLE P=0.0008 (GH) and P=0.01 (family-based association test). There is also a signal in the distal 3' flanking region of CTLA4/ICOS promoter (P=0.003). There was no confirmation of published associations for SLE in the promoter or coding region of CTLA4. These SLE risk alleles are more distal than those identified in Graves' disease and are in LD with Graves' disease protective alleles identified in both of these regions of CTLA4 (Ueda et al. 2003). These factors suggest an SLE-specific pattern of association. The functional consequences of the associated polymorphisms are likely to influence CTLA4 expression, although it is possible that genetically modulated ICOS expression is involved in SLE susceptibility.
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