When compared with unilateral WT, BWT is more frequent in patients with structural birth defects and known predisposition for WT, including WT1 disorder (congenital/infantile or childhood onset of steroid-resistant nephrotic syndrome, genitourinary anomalies, predisposition for WT) and WAGR (Wilms tumor, aniridia, genitourinary anomalies, range of developmental delays)5–10. Here, WT1 is linked to isolated aniridia.