To define the onset and progression of kidney developmental defects in the Osr1+/-Wt1+/- mice, we compared the formation of MM and UB in the Osr1+/-Wt1+/- embryos with that of the Osr1+/- and Wt1+/- littermates at E10.5 and E11.5, respectively. The gene discussed is OSR1; the disease is Miyoshi myopathy.