ESRP2 and renal agenesis: However, we did not note a further apparent reduction in E18.5 kidney size when comparing Esrp1‐/‐;Esrp2+/+ mice to Esrp1‐/‐ mice that had a heterozygous or null allele for Esrp2. Interestingly, as we generated large numbers of mutants, we noted that a significant number of mice with Esrp1‐/‐ genotypes had unilateral renal aplasia, whereas all mice with at least one wild‐type (WT) Esrp1 allele had two kidneys, independent of the Esrp2 allele (Table 1).