Q. My son aged 4 years has knock-knees. He has been treated for rickets to no avail. What should be done now?
A. If your 4-year-old son has knock-knees, for diagnosis of rickets, his blood should be checked for serum calcium, phosphorus and alkaline phosphatase and X-ray should be taken of knees and wrists to diagnose rickets. If both the tests suggest rickets and since the commonest cause of rickets in children in our country is Vit D deficiency, 600,000 units of oral or intramuscular Vit D should be given to the child and after 3-4 weeks, X rays and blood tests should be repeated to assess improvement. If there is no improvement in the x-rays and blood test, such a case is labeled as Vit D resistant rickets. Renal tubular acidosis (RTA) is one of the commonest causes of Vit D resistant rickets.

Q. What is renal tubular acidosis?
A.RTA is a group of disorders in which there is metabolic acidosis due to defect in renal tubular acidification mechanism to maintain normal plasma bicarbonate and blood pH. In normal healthy children, daily 2-3 meq / kg of H+ ion (acid) is generated from protein, carbohydrate and fat metabolism. Kidneys play an important role in eliminating the acids by

1. Reabsorption of sodium bicarbonate (alkali) by proximal renal tubules.
2. Regeneration of bicarbonate (HCO₃) and production of ammonia (NH₃) by distal tubules which secrete H+ ion and maintain a gradient of H+ ion between cell and lumen.

Renal acidification mechanism keeps the blood pH within a narrow range of 7.35 – 7.45 which is vital for normal functioning of cellular and tissue metabolism. This mechanism is slow but sustained and is mainly by elimination of nonvolatile acids in urine unlike lungs which washout CO₂ very fast to maintain PCO₂, PO₂, and blood pH via respiratory mechanism.

Q. What are the various types of RTA?
A. There are 4 types of RTA.

• Type I or classical RTA or distal RTA: It is due to inability of distal tubules to maintain H+ion gradient between lumen and cell.
• Type II or Proximal tubular acidosis: It is due to excessive loss of sodium bicarbonate (alkali) in urine with low renal threshold for bicarbonate.
• Type III or distal RTA with excessive bicarbonate loss in urine, which occurs in infancy.
• Type IV or Hyperkalemic RTA due to obstructive uropathy or chronic tubulointerstitial disease.
  RTA can be primary/ idiopathic or secondary.

Last updated on 14-03-2001