A common functional variant of endoplasmic reticulum aminopeptidase 2 (ERAP2) that reduces major histocompatibility complex class I expression is not associated with ankylosing spondylitis

Abstract

Sir, The strong genetic association between AS and HLA-B27 has defied explanation for nearly 40 years. However, the additional discovery of a strong association between AS and ERAP1 (endoplasmic reticulum aminopeptidase 1), a gene that almost certainly operates in the trimming of peptides for optimal binding to MHC class I molecules, has rekindled hopes of rapid advances in this field [1]. It has been suggested that another aminopeptidase, endoplasmic reticulum aminopeptidase 2 (ERAP2), may act in concert with ERAP1, trimming residues inefficiently removed by ERAP1 [2]. The association described recently between ERAP2 and Crohn’s disease, which shares many clinical and genetic overlaps with AS [3], suggests that ERAP2 is worthy of further study in AS. An experiment of nature allows us to do this relatively simply.