SLCO2A1 and primary hypertrophic osteoarthropathy: Subsequently, in 2012 and 2021, our team found that SLCO2A1 gene deficiency is responsible for both PHO autosomal recessive type 2 (PHOAR2, OMIM 614441) and PHO autosomal dominant (PHOAD, OMIM 167100) 6, 7.