PAPSS2 and skeletal dysplasia: Other genes including PAPSS2 have involvement with abnormal skeletal growth and development in humans [76], and the clinical spectrum associated with PAPSS2 and SLC26A2 has further expanded to include knee osteoarthritis [81], suggesting that sulphation disorders are likely to be more prevalent than the estimated 2% of all skeletal dysplasias which is based on live births [82].