Administration of high doses of 25(OH)D3 to Vdr(R270L) rats ameliorated rickets symptoms associated with decreased plasma 1,25(OH)2D3 to the normal level and increased plasma 25(OH)D3, strongly suggesting that the therapeutic effect of 25(OH)D3 is due to the direct binding of 25(OH)D3 to Vdr(R270L)11. The gene discussed is VDR; the disease is rickets.