More than 50 different SLCO2A1 mutations have been identified in patients with PHO (33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45), which are located in different exons or at splicing sites, led to changes to different functional domains or truncation of the protein. This evidence concerns the gene SLCO2A1 and primary hypertrophic osteoarthropathy.