Mixed renal tubular acidosis is characterized by the simultaneous presence of both type I (distal) and type II (proximal) RTA. This results in significant hyperchloremic metabolic acidosis, with both excessive urinary loss of bicarbonate (HCO3-) and reduced excretion of ammonia (NH3). Symptoms tend to be more severe.
It can be caused by mutations in carbonic anhydrase II, which is inherited in an autosomal recessive manner. In addition to type III RTA, affected individuals may also present with brain calcification, intellectual developmental delay, and osteoporosis.
Treatment is primarily symptomatic and follows the management approaches for type I and type II RTA.