Human Molecular Genetics Advance Access published online on September 30, 2004
Human Molecular Genetics, doi:10.1093/hmg/ddh318
© 2004 by Oxford University Press
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1 Department of Human Genetics, Graduate School of Medicine, The University of Tokyo, Tokyo 113-0033, Japan
* To whom correspondence should be addressed. E-mail: tsuchiya-tky{at}umin.ac.jp.
We previously reported association of FCGR2B-Ile232Thr with systemic lupus erythematosus (SLE) in three Asian populations. Because polymorphism of CD72, another inhibitory receptor of B cells, was associated with murine SLE, we identified human CD72 polymorphisms, tested their association with SLE, and examined genetic interaction with FCGR2B in the Japanese (160 SLE, 277 controls), the Thais (87 SLE, 187 controls) and the Caucasians (94 families containing SLE members). Four polymorphisms and 6 rare variations were detected. The former constituted 2 major haplotypes that contained 1 or 2 repeat of 13 nucleotides in intron 8 (designated as *1 and *2). Although association with susceptibility to SLE was not detected, *1 allele was significantly associated with nephritis among the Japanese patients (P=0.024). RT-PCR identified a novel alternatively spliced (AS) transcript that was expressed at the protein level in COS-7 transfectants. The ratio of AS/common isoforms was strikingly increased in individuals with *2/*2 genotype as compared with *1/*1 (P=0.000038) or *1/*2 (P=0.0085). Using the two Asian cohorts, significant association of FCGR2B-232Thr/Thr with SLE was observed only in the presence of CD72-*1/*1 genotype (OR 4.63, 95%CI 1.47-14.6, P=0.009 vs FCGR2B-232Ile/Ile plus CD72-*2/*2). Minigene assays demonstrated that the 13-nucleotide repeat and 4 bp deletion within the same haplotype of the intron 8 could regulate alternative splicing. The AS isoform lacks exon 8, and is deduced to contain 49 amino acid changes in the membrane-distal portion of the extracellular domain, where considerable amino acid changes are known in CD72c allele associated with murine SLE. These results indicated that presence of CD72-*2 allele decreases risk for human SLE conferred by FCGR2B-232Thr, possibly by increasing the AS isoform of CD72.
Article
CD72 polymorphisms associated with alternative splicing modify susceptibility to human systemic lupus erythematosus through epistatic interaction with FCGR2B
2 Department of Human Genetics, Graduate School of Medicine, The University of Tokyo, Tokyo 113-0033, Japan; Department of Medicine, University of Minnesota School of Medicine, Minneapolis, MN 55455, U.S.A
3 Department of Allergy and Rheumatology, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan
4 Department of Rheumatology and Internal Medicine, Juntendo University, Tokyo, Japan
5 Department of Transfusion Medicine, Faculty of Medicine, Siriraj Hospital, Mahidol University, Bangkok, Thailand
6 Department of Dermatology, Faculty of Medicine, Siriraj Hospital, Mahidol University, Bangkok, Thailand
7 Department of Medicine, UCLA School of Medicine, Los Angeles, CA 90095-1670, U.S.A.
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