However, when we crossed Nes-Cre; Tfap2bflox/+ mice with Tfap2bflox/flox mice to obtain the cKD mice, only 19 out of 176 pups were cKD, which is lower than the expected ratio of 1/4, implying that some of the cKD mice died either prenatally or immediately after birth. This evidence concerns the gene NES and chronic kidney disease.