To gain insights into the etiology and pathogenesis of SCOS, we referred to mouse models with Sertoli cell-only (SCO) phenotype; for instance, Prdm14−/−, Tcfap2c flox/flox:Sox2-cre, Fancb−/−, Id4−/−, Zfp145−/−, and Wt1−/flox; Cre-ERTM mice have the testicular phenotype similar to that of human SCOS [6–11]. The gene discussed is ID4; the disease is small cell osteogenic sarcoma.