PBX1 and Horseshoe kidney: PBX1 haploinsufficiency, caused either by microdeletion encompassing the entire gene or by splice-site, frameshift, and nonsense variants that lead to premature termination of protein synthesis, results in structural renal abnormalities, most commonly manifested as bilateral renal hypoplasia, dysplasia, ectopia, or horseshoe kidneys (2–6).