SPARC and idiopathic juvenile osteoporosis: The importance of Sox9 has been demonstrated in neurogenesis(116) and auditory hair cell development.(117)Sox9 is known to be a major fate determinant in MSCs that undergo chondrogenesis and osteoblastogenesis.(118) We verified its importance for the osteoblast‐secreted SPARC protein, which enhances bone formation.(110) In addition, mutations or polymorphisms in Sparc lead to idiopathic osteoporosis and osteogenesis imperfecta.(110, 119)