An 80% incidence of vitamin D deficiency in people with CKD has been reported based on measurement of calcidiol.196 Low concentrations of calcidiol in CKD may be the result of reduced megalin expression, which reduces calcidiol uptake into tubular cells and decreases its return to circulation (due to enhanced loss of the calcidiol–VDBP complex into urine). The gene discussed is GC; the disease is chronic kidney disease.