WT1 and renal hypoplasia: The synergistic interaction of Osr1 and Wt1 in the regulation of MM specification, together with the finding that about 6% of the Caucasian population carries the functionally impaired OSR1rs12329305(T) allele [31, 32], suggest that OSR1 has a significant contribution to renal hypoplasia and other renal conditions in humans.