Aims - To replicate and refine previously reported genetic associations of the genes ANTXR2 (otherwise known as CMG2 - capillary morphogenesis factor) and TNFRSF1A (encoding the type 1 TNF receptor) with ankylosing spondylitis (AS).

Hypothesis

1) Variants of ANTXR2 have previously been associated with AS in 2 previous genome-wide association studies (GWAS) (Australo-Anglo-American Spondyloarthritis Consortium - TASC 2010, rs4333130, p=9.3 x 10^-8; Wellcome Trust Case Control Consortium - WTCCC2-TASC meta-analysis, rs4389526, p=9.4 x 10^-8). However, the replication set in the latter study only examined the single top SNP and did not conduct a systematic study of ANTXR2 variants. The discovery set in this study consisted of ~2,000 caucasian AS cases and the majority of significant "hits" were followed up in a large number of cases both of caucasian and other ethnicities using the customised "Immunochip" targeting 200k SNPs of largely immunologic or inflammatory function. Unfortunatley, the Immunochip contained no SNPs covering the ANTXR2 locus. We therefore hypothesise that there should be detectable associations at this locus in an independent set of patients and controls. We have therefore already formally genotyped 9 tagging SNPs across the ANTXR2 gene in a further 3,000 UK cases with AS and now wish to confirm association in an independent set of controls - the ALSPAC cohort. From these data, we shall also be able to impute associations with rare alleles and to refine the likely primary associations of AS with variants at ANTXR2.

2) Variants in LTBR-TNFRSF1A region have already been associated with AS in GWAS (TASC 2010, rs1800693, p=6.9 x 10^-5, WTCCC2-TASC meta-analysis, rs11616188, p=4.1 x 10^-12). Furthermore, variants in TNFRSF1A have also been associated with multiple sclerosis (MS) (Gregory et al., 2012). However, the variant rs1800693 has opposite effects in AS and MS. The G allele of this SNP leads to a splice variant that appears to have an anti-TNF effect. This allele (G) of rs1800693 is therefore, unsurprisingly, protective in AS, whereas it is predisposing in MS (a condition that can be provoked by anti-TNF therapy). It is important to confirm the association of this SNP with AS and analyse its effects further, particularly with respect to responses of AS to anti-TNF therapy and effects on disease severity.

Exposure variable

We have already typed about greater than 5000 cases for SNP across ANTXR2 and have undertaken scrupulous quality checks on the data. We will compare the allele and genotype frequencies in this case dataset to those in the 8365 controls obtained from the ALSPAC cohort. Genotypes of SNPs in regions containing genes ANTXR2 and TNFRSF1A will be used to do statistical tests to detect/confirm possible associations with AS. The precise regions for which data are required for us to be able to undertake this analysis are listed below:

ANTXR2 region (chr4) - 80,000,000 - 88,700,000 (Genome build 37)

LTBR-TNFRSF1A region (chr12) - 6,000,000 - 7,000,000 (Genome build 37)