Genetic variation of the Fc gamma receptor 3B gene and association with rheumatoid arthritis.
BACKGROUND
Fc gamma receptors (FcγRs) play a crucial role in immunity by linking IgG antibody-mediated responses with cellular effector and regulatory functions. Genetic variants in these receptors have been previously identified as risk factors for several chronic inflammatory conditions. The present study aimed to investigate the presence of copy number variations (CNVs) in the FCGR3B gene and its potential association with the autoimmune disease rheumatoid arthritis (RA).


RESULTS
CNV of the FCGR3B gene was studied using Multiplex Ligation Dependent Probe Amplification (MLPA) in 518 Dutch RA patients and 304 healthy controls. Surprisingly, three independent MLPA probes targeting the FCGR3B promoter measured different CNV frequencies, with probe#1 and #2 measuring 0 to 5 gene copies and probe#3 showing little evidence of CNV. Quantitative-PCR correlated with the copy number results from MLPA probe#2, which detected low copy number (1 copy) in 6.7% and high copy number (≥3 copies) in 9.4% of the control population. No significant difference was observed between RA patients and the healthy controls, neither in the low copy nor the high copy number groups (p-values = 0.36 and 0.71, respectively). Sequencing of the FCGR3B promoter region revealed an insertion/deletion (indel) that explained the disparate CNV results of MLPA probe#1. Finally, a non-significant trend was found between the novel -256A>TG indel and RA (40.7% in healthy controls versus 35.9% in RA patients; P = 0.08).


CONCLUSIONS
The current study highlights the complexity and poor characterization of the FCGR3B gene sequence, indicating that the design and interpretation of genotyping assays based on specific probe sequences must be performed with caution. Nonetheless, we confirmed the presence of CNV and identified novel polymorphisms in the FCGR3B gene in the Dutch population. Although no association was found between RA and FCGR3B CNV, the possible protective effect of the -256A>TG indel polymorphism must be addressed in larger studies.
Marques
Rute B
RB
Department of Rheumatology, Leiden University Medical Center, Leiden, The Netherlands. r.b.marques@lumc.nl
Thabet
Mohamed M
MM
White
Stefan J
SJ
Houwing-Duistermaat
Jeanine J
JJ
Bakker
Aleida M
AM
Hendriks
Gert-Jan
GJ
Zhernakova
Alexandra
A
Huizinga
Tom W
TW
van der Helm-van Mil
Annette H
AH
Toes
Rene E
RE
D001172:Arthritis, Rheumatoid / Q000235:genetics*; D001483:Base Sequence; D016022:Case-Control Studies; D002878:Chromosomes, Human, Pair 1; D017931:DNA Primers; D018628:Gene Dosage; D014644:Genetic Variation; D006801:Humans; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D017452:Receptors, IgG / Q000235:genetics*; D012689:Sequence Homology, Nucleic Acid
D017931:DNA Primers; D017452:Receptors, IgG