SLCO2A1 and primary hypertrophic osteoarthropathy: However, unlike SHO, which is secondary to severe cardiopulmonary diseases or malignancies [4], PHO is a rare genetic disorder caused by mutations in the hydroxyprostaglandin dehydrogenase (HPGD) gene or the solute carrier organic anion transporter family member 2A1 (SLCO2A1) gene [5, 6].