SLCO2A1 and cranio-osteoarthropathy: Mutations in HPGD gene are responsible for autosomal recessive primary hypertrophic osteoarthropathy 1 (PHOAR1) (8) and mutations in SLCO2A1 gene are responsible for autosomal recessive primary hypertrophic osteoarthropathy 2 (PHOAR2) (4).