Copy Number Variation at the FCGR Locus Includes FCGR3A, FCGR2C and FCGR3B but Not FCGR2A and FCGR2B

Human Fcgamma receptors (FcgammaRs) are glycoproteins that bind the Fc region of IgG. The genes encoding the low-affinity FcgammaRs are located on chromosome 1q23-24. Beside single nucleotide polymorphisms (SNPs), gene copy number variation (CNV) is now being recognized as an important indicator for inter-individual differences. Recent studies on identifying CNV in the human genome suggest large areas at chromosome 1q23-24 to be involved, and CNV in this region has been associated with manifestations of systemic autoimmune disease. To study both SNPs and CNV of the low-affinity FcgammaRs in one assay, we have developed a Multiplex Ligation-dependent Probe Amplification (MLPA) assay. A novel CNV for FCGR3A was observed. Similar to FCGR3B and FCGR2C, a gene-dosage effect of FCGR3A was found, that seemed to correlate nicely with the FcgammaRIIIa expression on NK cells. Next, we delineated the approximate boundaries of CNV at the FCGR locus. Variation in co-segregation of neighboring FCGR genes was limited to four variants, with patterns of Mendelian inheritance. No CNV of the FCGR2A and FCGR2B genes was observed in over 600 individuals. In conclusion, we report a novel CNV of the FCGR3A gene that correlates with FcgammaRIIIa expression and function on NK cells. Only FCGR3A, FCGR2C and FCGR3B show CNV, in contrast to FCGR2A and FCGR2B.