Histological examination of a renal leiomyoma reveals fusiform to spindle shaped cells with positive immunohistochemical staining for smooth muscle markers (desmin, caldesmon, and SMA) and negative staining for HMB-45 and cathepsin K. It should not reveal atypical nuclei, mitotic figures, or microscopic necrosis [13]. The gene discussed is SMN1; the disease is renal leiomyoma.