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

Human Fc gamma receptors (Fc gamma Rs) are glycoproteins that bind the Fc region of IgG. The genes encoding the low-affinity Fc gamma Rs 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 Fc gamma Rs 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 Fc gamma RIIIa 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 Fc gamma RIIIa expression and function on NK cells. Only FCGR3A, FCGR2C and FCGR3B show CNV, in contrast to FCGR2A and FCGR2B. (C) 2009 Wiley-Liss, Inc