Distal renal tubular acidosis

Distal renal tubular acidosis (dRTA), also known as Type 1 renal tubular acidosis or classic renal tubular acidosis, is a rare disorder in which the kidneys are unable to properly acidify the urine. Specifically, the alpha-intercalated cells of the distal tubule and collecting duct of the kidney fail to adequately secrete hydrogen ions into the urine, leading to a buildup of acid in the blood (metabolic acidosis) with an inappropriately high urine pH (typically above 5.5). This chronic acid-base imbalance affects multiple body systems over time, including the skeletal system, urinary tract, and inner ear in some genetic forms. Key clinical features include failure to thrive and growth retardation in children, recurrent kidney stones (nephrolithiasis), calcium deposits in the kidneys (nephrocalcinosis), muscle weakness due to low potassium levels (hypokalemia), bone disease including rickets in children and osteomalacia in adults, and polyuria with polydipsia. Some hereditary forms, particularly those caused by mutations in the ATP6V0A4 or ATP6V1B1 genes, are associated with sensorineural hearing loss, which may be progressive or present from early childhood. If left untreated, chronic acidosis and nephrocalcinosis can lead to progressive kidney damage and chronic kidney disease. Distal RTA can be inherited or acquired. Hereditary forms may follow autosomal recessive inheritance (caused by mutations in ATP6V1B1, ATP6V0A4, or FOXI1 genes) or autosomal dominant inheritance (caused by mutations in the SLC4A1 gene encoding the anion exchanger AE1). Acquired forms can occur secondary to autoimmune diseases such as Sjögren syndrome, systemic lupus erythematosus, or from certain medications and toxins. Treatment centers on correcting the metabolic acidosis with oral alkali supplementation, typically sodium bicarbonate or potassium citrate. Potassium citrate is often preferred as it simultaneously addresses hypokalemia and helps reduce the risk of kidney stone formation. Early and consistent treatment can prevent nephrocalcinosis progression, normalize growth in children, and significantly improve long-term outcomes. Hearing aids or cochlear implants may be necessary for patients with associated sensorineural hearing loss.

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