Bone is basically made up of two substances: the organic collagen portion and the inorganic mineral portion. The inorganic portion of bone is made up of both calcium and phosphate. Osteomalcia is a term used to describe bone that has poor mineral quality, and rickets refers to poor mineral quality of bone in childhood. While rickets actually looks the same on x-rays, there are many different types. These types depend on which actual mineral is deficient – either calcium, phosphorus, or the enzyme that helps create the mineral portion of bone, like alkaline phosphatase.
Opposite to common belief, the most common reason to have a calcium deficiency in bone is a lack of Vitamin D, not due to lack of calcium in the diet. Vitamin D is a hormone that allows the body to take in calcium. So if you don’t have enough vitamin D, then the body cannot take in calcium. If the body does not have enough calcium in the blood, then it will take the calcium out of bone instead. If this cycle continues, the bone becomes more and more deficient in calcium; it becomes weaker. Then a child can develop physical and laboratory signs of rickets.
The most common reason for a phosphorus deficiency in bone is due to an inherited disorder known as X-linked hypophosphatemic rickets. This is the most commonly inherited rickets in the United States with a prevalence of 1 out of every 20,000 births. Women are twice as likely as men to have this disorder.
The defect is in a gene, known as the PHEX gene, which regulates the movement of phosphate compounds from the kidney. Phosphates support normal body physiologic reactions. Normally, the kidney sends phosphates to the bone through the blood. The defect causes the kidney to get rid of the phosphate instead of sending it through the blood, leading to an overall phosphorus shortage in the blood.
Similar to low calcium in the blood, when the body recognizes that there is not enough phosphorus in the blood, it will remove it from the bone instead. Most of the body’s phosphorus is stored in bone. It is also believed that the genetic defect also prevents the kidneys from making the mature forms of Vitamin D, which are necessary for the body to absorb calcium.
When there is less calcium and/or phosphorus in bone, the bone and the growth plate of bone become weaker. This weakening of bone can lead to growth retardation since the bones cannot grow normally. In more severe cases, children can actually end up in the emergency room having to seizures from calcium deficiencies or fractures from weakened bone.
Treatment depends on which mineral is deficient. This may require the assistance of an endocrinologist. Once the deficiency is known, treatment involves replacing the mineral – whether it be calcium, vitamin D, phosphorus or a combination of these. In many cases, the bone changes that occur are reversible, while in more severe cases, children may continue to have growth retardation and bones that are somewhat crooked. Occasionally, bones become so crooked that they may require surgery for correction.