RICKETS AND OSTEOMALACIA
Definition.
Rickets/ OSTEOMALACIA is a diseases which is characterized by an inadequate bone mineralization resulting in a deficient amount of the mineral phase of the bone and an excess of unmineralized osteoid.The osteoid excess is caused by a failure of the process of mineralization to keep up with the formation of osteoid during bone formation and remodeling. Rickets occurs in children while osteomalacia occurs in Adults.
Etiology and Pathogenesis.
Rickets (in children, 6-30months) and osteomalacia (adults) may be caused by either of the following:
- A deficiency of vitamin D.
- Abnormal metabolism of vitamin D.
- Deficiency of inorganic phosphate (Pi).
- Abnormal utilization/excretion of inorganic phosphate i.e. reduced excretion of Pi.
Deficiencies may be due to:
- Reduced dietary intake of vitamin D and Pi.
- Insufficient UV light exposure.
- Malabsorptions that interfere with the intestinal absorption of the vitamin. Some of conditions that interfere with absorption of vitamins in the intestine include intestinal diseases.
Abnormal metabolism of vitamin occurs as follows:
Before we can tell the aspect of abnormal metabolism it is worth important to review the normal metabolism of vitamin D in the body. Mechanism of vitamin D metabolism can be outlined as follows:
- The vitamin is taken in food or synthesized through UV light exposure.
- The inactive vitamin binds to the globulin and is transported to the liver.
- In the liver the vitamin is converted to 25-hydroxycholecalciferol via a series of hydroxylation reaction at carbon number 25.
- The formed 25-hydroxycholecalciferol is then transported to the Kidney.
- In the kidney, 25-hydroxycholecalciferol is converted to 1, 25-dihydroxycholecalciferol after a hydroxylation reaction at carbon number 1.
- This final product (1, 25-dihydroxycholecalciferol) is a biological active and functional form of vitamin D.
It is obvious that if metabolism of vitamin D is not proper, the active form of the vitamin will not be produced and hence will be lacking in the body. In this case any thing that will interfere with metabolism in the liver or kidney will result in abnormal vitamin D. Some of the things that can interfere with Vitamin D metabolism include:
- Drugs such as Phenytoin interfere with metabolism in the liver.
- Chronic liver diseases such as biliary cirrhosis, alcoholism liver disease and biliary tract obstruction.
- Chronic renal (kidney) disease.
- Chronic pancreatitis.
The main function of vitamin D is to maintain a normal serum (blood) balance of calcium and inorganic phosphate through the action of target organs: Intestine, Bone, and Parathyroid gland:
- Absorption of Calcium from the intestine; where it activates the synthesis of calcium transport proteins.
- Absorption of Pi from the intestine secondarily to calcium transport.
- Excretion of Pi in the Kidney.
- Inhibits Parathyroid hormones synthesis from Parathyroid gland.
Pathogenesis of Rickets/Osteomalcia.
Low intake of vitamin D or abnormally metabolized vitamin will ultimately results into a low level of functional vitamin D in the body. Low functional vitamin D will result in reduced absorption of calcium and Pi in the intestine and subsequently low
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