To date, two genes have been reported to be associated with PHO: hydroxyprostaglandin dehydrogenase (HPGD; MIM 601688), which encodes 15-hydroxyprostaglandin dehydrogenase (15-PGDH), and solute carrier organic anion transporter family, member 2A1 (SLCO2A1; MIM 601460), which encodes a prostaglandin transporter (1, 5). Here, HPGD is linked to primary hypertrophic osteoarthropathy.