Defining a genetic background for bamboo spine and axial spondyloarthritis

Bamboo spine is the most severe complication of axial spondyloarthritis (AxSpA). This study aims to address whether haplotypes of endoplasmic reticulum aminopeptidase (ERAP)1 and ERAP2 single nucleotide polymorphisms (SNPs), previously associated with AxSpA, are associated with the development of bamboo spine in an AxSpA cohort.

The study included 192 patients with AxSpA followed in MARS (MARmara Spondyloarthritis) clinic and fulfilling the modified New York criteria. ERAP1 and ERAP2 polymorphisms were determined by real-time PCR on genomic DNA using the TaqMan SNP Genotyping Assay for SNPs rs72773968, rs3734016, rs26653, rs26618, rs27895, rs2287987, rs30187, rs10050860, rs17482078, rs27044, rs2549782, rs2248374. The HLA-B genotypes were assessed using the LABTypeTM SSO method.

Male gender (P<0.001) and HLA-B27 positivity (P<0.05) were associated with an increased risk of developing a bamboo spine, and peripheral arthritis was significantly less prevalent in AxSpA patients with a bamboo spine (P<0.05). Of the ten ERAP1 haplotypes, haplotype 3 was significantly more prevalent in AxSpA patients with bamboo spine adjusted for HLA-B27 status (P<0.05). Haplotype 3 and -6 were significantly more prevalent exclusively in HLA-B27 (+) patients (P<0.05). Allele frequencies and genotype distributions of single ERAP1 SNPs alone were not significantly different between AxSpA patients with and without bamboo spines. There was no association between bamboo spine development and ERAP2 SNPs.

Our results indicate that HLA-B27 positivity, ERAP1 haplotype 3 and -6, and being male confer a significant risk for developing bamboo spine. Whether the association of haplotype 3 and -6 with bamboo spine is confined only to our Turkish patient cohort may deserve attention in other ethnicities.