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.jpg): Failed to open stream: No such file or directory in C:\Inetpub\vhosts\kidney.de\httpdocs\pget.php on line 117 Arthritis+Res+Ther
2014 ; 16
(3
): R114
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Resequencing the susceptibility gene, ITGAM, identifies two functionally
deleterious rare variants in systemic lupus erythematosus cases
#MMPMID24886912
Roberts AL
; Thomas ER
; Bhosle S
; Game L
; Obraztsova O
; Aitman TJ
; Vyse TJ
; Rhodes B
Arthritis Res Ther
2014[May]; 16
(3
): R114
PMID24886912
show ga
INTRODUCTION: The majority of the genetic variance of systemic lupus
erythematosus (SLE) remains unexplained by the common disease-common variant
hypothesis. Rare variants, which are not detectable by genome-wide association
studies because of their low frequencies, are predicted to explain part of this
"missing heritability." However, recent studies identifying rare variants within
known disease-susceptibility loci have failed to show genetic associations
because of their extremely low frequencies, leading to the questioning of the
contribution of rare variants to disease susceptibility. A common (minor allele
frequency = 17.4% in cases) nonsynonymous coding variant rs1143679 (R77H) in
ITGAM (CD11b), which forms half of the heterodimeric integrin receptor,
complement receptor 3 (CR3), is robustly associated with SLE and has been shown
to impair CR3-mediated phagocytosis. METHODS: We resequenced ITGAM in 73 SLE
cases and identified two previously unidentified, case-specific nonsynonymous
variants, F941V and G1145S. Both variants were genotyped in 2,107 and 949
additional SLE cases, respectively, to estimate their frequencies in a disease
population. An in vitro model was used to assess the impact of F941V and G1145S,
together with two nonsynonymous ITGAM polymorphisms, A858V (rs1143683) and M441T
(rs11861251), on CR3-mediated phagocytosis. A paired two-tailed t test was used
to compare the phagocytic capabilities of each variant with that of wild-type
CR3. RESULTS: Both rare variants, F941V and G1145S, significantly impair
CR3-mediated phagocytosis in an in vitro model (61% reduction, P = 0.006; 26%
reduction, P = 0.0232). However, neither of the common variants, M441T and A858V,
had an effect on phagocytosis. Neither rare variant was observed again in the
genotyping of additional SLE cases, suggesting that their frequencies are
extremely low. CONCLUSIONS: Our results add further evidence to the functional
importance of ITGAM in SLE pathogenesis through impaired phagocytosis.
Additionally, this study provides a new example of the identification of rare
variants in common-allele-associated loci, which, because of their extremely low
frequencies, are not statistically associated. However, the demonstration of
their functional effects adds support to their contribution to disease risk, and
questions the current notion of dismissing the contribution of very rare variants
on purely statistical analyses.
|Animals
[MESH]
|Base Sequence
[MESH]
|CD11b Antigen/*genetics/immunology
[MESH]
|COS Cells
[MESH]
|Chlorocebus aethiops
[MESH]
|Flow Cytometry
[MESH]
|Gene Frequency
[MESH]
|Genetic Predisposition to Disease/*genetics
[MESH]