Which of the following conditions is associated with hypophosphatemia?

Hypophosphatemia, defined as an abnormally low level of phosphate in the blood, can occur due to several conditions that impact phosphate metabolism or homeostasis. In the case of rickets, particularly the form known as nutritional rickets, there is a direct relationship with phosphate levels.

Rickets is primarily caused by a deficiency in vitamin D, which is crucial for the absorption of phosphate and calcium in the intestines. When vitamin D levels are inadequate, the absorption of phosphate can be reduced, leading to its depletion in the bloodstream, which characterizes hypophosphatemia. In children, this results in impaired mineralization of bones, causing the characteristic symptoms of rickets, such as bone pain and deformities.

Other conditions like multiple myeloma may affect phosphate levels but are more often associated with hypercalcemia rather than hypophosphatemia. Renal failure typically causes hyperphosphatemia due to the kidney's inability to excrete phosphate effectively, while hypervitaminosis D usually leads to increased levels of calcium and phosphate due to enhanced absorption, creating the opposite effect (hyperphosphatemia). Thus, rickets is the condition most clearly linked to hypophosphatemia.