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Open Access Research article

Identification of low-frequency TRAF3IP2 coding variants in psoriatic arthritis patients and functional characterization

Beate Böhm1, Harald Burkhardt1, Steffen Uebe2, Maria Apel2, Frank Behrens1, André Reis2 and Ulrike Hüffmeier2*

Author Affiliations

1 Divisions of Rheumatology, Department of Internal Medicine II, Johann Wolfgang Goethe University, Theodor-Stern-Kai 7, 60590 Frankfurt am Main, Germany

2 Institute of Human Genetics, University of Erlangen-Nuremberg, Schwabachanlage 10, 91054 Erlangen, Germany

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Arthritis Research & Therapy 2012, 14:R84  doi:10.1186/ar3807

Published: 18 April 2012

Abstract

Introduction

In recent genome-wide association studies for psoriatic arthritis (PsA) and psoriasis vulgaris, common coding variants in the TRAF3IP2 gene were identified to contribute to susceptibility to both disease entities. The risk allele of p.Asp10Asn (rs33980500) proved to be most significantly associated and to encode a mutant protein with an almost completely disrupted binding property to TRAF6, supporting its impact as a main disease-causing variant and modulator of IL-17 signaling.

Methods

To identify further variants, exons 2-4 encoding both known TNF-receptor-associated factor (TRAF) binding domains were sequenced in 871 PsA patients. Seven missense variants and one three-base-pair insertion were identified in 0.06% to 1.02% of alleles. Five of these variants were also present in 931 control individuals at comparable frequency. Constructs containing full-length wild-type or mutant TRAF3IP2 were generated and used to analyze functionally all variants for TRAF6-binding in a mammalian two-hybrid assay.

Results

None of the newly found alleles, though, encoded proteins with different binding properties to TRAF6, or to the cytoplasmic tail of the IL-17-receptor α-chain, suggesting that they do not contribute to susceptibility.

Conclusions

Thus, the TRAF3IP2-variant p.Asp10Asn is the only susceptibility allele with functional impact on TRAF6 binding, at least in the German population.