Distal renal tubular acidosis

Distal renal tubular acidosis (dRTA) is the classical form of RTA, being the first described. Distal RTA is characterized by a failure of acid secretion by the alpha intercalated cells of the distal tubule and cortical collecting duct of the distal nephron. This failure of acid secretion may be due to a number of causes. It leads to relatively alkaline urine, due to the kidney's inability to acidify the urine to a pH of less than 5.3.

Symptoms and signs

Because renal excretion is the primary means of eliminating acid from the body, there is consequently a tendency towards acidemia.

This leads to the clinical features of dRTA:

Normal anion gap metabolic acidosis/acidemia

Hypokalemia

Urinary stone formation (related to alkaline urine, hypercalciuria, and low urinary citrate).

Nephrocalcinosis (deposition of calcium in the substance of the kidney)

Bone demineralisation (causing rickets in children and osteomalacia in adults)

The symptoms and sequelae of dRTA are variable and range from being completely asymptomatic, to loin pain and hematuria from kidney stones, to failure to thrive and severe rickets in childhood forms as well as possible renal failure and even death.

dRTA commonly leads to sodium loss and volume contraction, which causes a compensatory increase in blood levels of aldosterone. Aldosterone causes increased resorption of sodium and loss of potassium in the collecting duct of the kidney, so these increased aldosterone levels cause the hypokalemia which is a common symptom of dRTA.

Causes

Hereditary causes include mutations of Band 3 the basolateral bicarbonate transporter of the intercalated cell, which may be transmitted in an autosomal dominant fashion in western European cases, or in an autosomal recessive fashion in South East Asian cases. The South East Asian cases are associated with more severe hypokalemia.