Renal tubular acidosis, distal. Distal primary acidosis, familial.
Incidence
Autosomal dominant form, multiple dominant and a recessive form(s). The disorder is often sporadic but several siblings in the same family may be affected. This is most likely due to autosomal recessive transmission of the trait.
Clinical Characteristics
Renal tubular acidosis (RTA) is a disease that occurs when the kidneys fail to excrete acids into the urine, which causes a person's blood to remain too acidic. Without proper treatment, chronic acidity of the blood leads to growth retardation, kidney stones, bone disease, and progressive renal failure. This disorder may be inherited as a primary disorder or may be one symptom of a disease that affects many parts of the body. Researchers have now discovered the abnormal gene responsible for the inherited form. More often, however, classic distal RTA is a complication of diseases that affect many organ systems (systemic diseases), like the autoimmune disorders Sjögren's syndrome and lupus. Other diseases and conditions associated with distal RTA include hyperparathyroidism, a hereditary form of deafness, analgesic nephropathy, rejection of a transplanted kidney, renal medullary cystic disease, obstructive uropathy, and chronic urinary tract infections. A major consequence of classic distal RTA is low blood-potassium. The level drops if the kidneys excrete potassium into urine instead of returning it to the blood supply. Since potassium helps regulate nerve and muscle health and heart rate, low levels can cause extreme weakness, cardiac arrhythmias, paralysis, and even death. Untreated distal RTA causes growth retardation in children and progressive renal and bone disease in adults. Restoring normal growth and preventing kidney stones, another common problem in this disorder, are the major goals of therapy. If acidosis is corrected with sodium bicarbonate or sodium citrate, then low blood-potassium, salt depletion, and calcium leakage into urine will be corrected. Alkali therapy also helps decrease the development of kidney stones. Potassium supplements are rarely needed except in infants, since alkali therapy prevents the kidney from excreting potassium into the urine.
Precipitants
Dehydration may trigger an attack of muscle weakness.
Provocation Tests
None
Diagnostic Procedures
Formal diagnosis is made by a urine acidifying test: it is impossible to bring the pH lower than 6, although bicarbonatemia is lower than 18 mmol/L, while bicarbonaturia remains low.