SMARCAL1 and Schimke immuno-osseous dysplasia: By contrast, mutations that similarly affect SMARCAL1 ATPase activity give raise to both severe and mild SIOD, arguing for the existence of genetic factors that can modulate disease phenotypes or of additional ATPase-independent SMARCAL1 functions that are affected by missense mutations (Baradaran-Heravi et al., 2012; Elizondo et al., 2006, 2009).