Hypophosphatemic rickets is caused by low levels of phosphate. The bones become painfully soft and pliable. This is caused by a genetic dominant X-linked defect in the ability for the kidneys to control the amount of phosphate excreted in the urine. The individual affected is able to absorb phosphate and calcium, but the phosphate is lost in the urine. This is not caused by a vitamin D deficiency. Patients with hypophosphatemic rickets typically have obvious symptoms by 1 year of age. Treatment is generally through nutritional supplements of phosphate and calcitriol (the activated form of vitamin D).