Association study of copy number variants in FCGR3A and FCGR3B gene with risk of ankylosing spondylitis in a Chinese population

Ankylosing spondylitis (AS) is a common inherited autoimmune disease. Copy number variation (CNV) of DNA segments has been found to be an important part of genetic variation, and the FCGR3A and FCGR3B gene CNVs have been associated with various autoimmune disorders. The aim of the study was to determine whether CNVs of FCGR3A and FCGR3B were also associated with the susceptibility of AS. A total of 801 individuals including 402 AS patients and 399 healthy controls were enrolled in this study. The copy numbers of FCGR3 gene (two fragments, included FCGR3A and FCGR3B) were measured by AccuCopy™ methods. Chi-square test and logistic regression model were used to evaluate association between FCGR3 gene CNVs and AS susceptibility. P values, odds ratio, and 95 % confidence intervals (CIs) were used to estimate the effects of risk. Significantly, difference in the frequencies of FCGR3A and FCGR3B gene CNVs was founded between the patients with AS and controls. For the FCGR3A gene, a low (≤3) copy number was significantly associated with AS [for ≤3 copies versus 4 copies, (OR 2.17, 95 % CI (1.41, 3.34), P < 0.001, adjusted OR 2.22, 95 % CI (1.44, 3.43), P < 0.001)]. A low FCGR3B copy number was also significantly associated with increasing risk of AS [for ≤3 copies versus 4 copies, (OR 1.87, 95 % CI (1.25, 2.79), P = 0.002, adjusted OR 1.94, 95 % CI (1.29, 2.91), P = 0.001)]; however, both the high FCGR3A and FCGR3B copy numbers (≥5) were not significantly associated with the risk of AS (≥5 copies versus 4 copies). The lower copy numbers (≤3) of FCGR3A and FCGR3B genes confer a risk factor for AS susceptibility.