MTNR1B and Horseshoe kidney: This study aimed to characterize the developmental and spatial expression patterns of melatonin receptors MTNR1A and MTNR1B in normal human fetal kidneys and in CAKUT phenotypes.<h4>Methods</h4>This study analyzed 40 human fetal kidney specimens, including healthy controls and CAKUT cases (horseshoe kidneys, duplex kidneys, and dysplastic kidneys), obtained from spontaneous abortions and pregnancy terminations.