Some patients with SIOD, however, do not harbour apparent PSVs in SMARCAL1. This might be due to PSVs located in deep intron regions of SMARCAL1 [12], the impact of epigenetic and environmental factors, and the possibility of the existence of other genes involved in the pathogenesis of SIOD (oligogenic inheritance) [13]. This evidence concerns the gene SMARCAL1 and Schimke immuno-osseous dysplasia.