Mutations of WT1 gene cause Wilms' tumor (nephroblastoma), which is a cancer of kidney that manifests in the early childhood. It is a relatively rare condition (incidence: 8 in one million individuals). Many times it is combined with other congenital anomalies to constitute a variety of syndromes. The most common of these is WAGR syndrome, which is characterized by Wilms' tumor, Aniridia (bilateral absence of the iris), Genitourinary abnormalities, and mental Retardation.