BTNL2 and sarcoidosis: One of the most well-replicated genetic associations in adult sarcoidosis involves an exonic splice site variant in exon 5 of the BTNL2 (butyrophilin-like protein 2) gene, which results in loss of function due to truncation of the protein product,26,27 although the association may reflect linkage disequilibrium with the nearby HLA-DRB1.28 Butyrophilins are implicated in T-cell inhibition and the modulation of epithelial cell–T-cell interactions,29 and we have shown recently that a rare variant in BTNL2 is associated with inflammatory bowel disease.30