dRTA – distal Renal Tubular Acidosis

Distal renal tubular acidosis (dRTA) was first described by Lightwood and Butler in the 1930s. It is a rare disease that may have genetic origin (due to genetic mutations, hence called hereditary ATRd) or acquired, as a result of autoimmune diseases such as systemic lupus erythematosus or Sjogren’s syndrome.

If literature is minimal and prevalence rates are poorly known, it is estimated that about 30,000 patients in Europe and about 20,000 patients in the United States suffer from dRTA.

dRTA affects the distal part of the renal tubule, causing an alteration of acid ions excretion (H +) in the urine. This alteration results in an imbalance of blood pH, causing many complications:

Clinically and biologically, the major sign that leads to the diagnosis of the disease is a blood acidosis with hypokalemia and hyperchloremia, which is revealed by a severe fall in the blood alkali reserve, a severe decrease of bicarbonatemia, associated with an inability to acidify the urine.

Clinically, the consequences of dRTA are combining :

  1. Stunting, as the most visible symptom of dRTA in children and often leads to biologic exploration that leads to the diagnostic. Stunting follows long-term acidosis, which causes a reduction in the peak secretion of growth hormone, inducing a significant decrease in growth.
  2. Hypokalemia (potassium deficiency in the blood), which impairs the function of several organs and in particular affects the cardiovascular system, which can lead to arrhythmia and be a cause of hospitalization for patients.
  3. Rickets or bones decalcification. Indeed, to compensate for the imbalance of blood pH, the body uses phosphate (especially originating from bones where it is combined with calcium) to buffer the blood pH. Hence, rickets or osteomalacia is often observed (rickets is a disease affecting the development of bones in children; osteomalacia : a weakening of the bones). This reduction of calcium scaffold within the bones can lead to fractures and pain that significantly and negatively impact quality of life on a daily basis.
  4. Kidney stones and Nephrocalcinosis. Calcium associated with phosphate forms the scaffold of the bones. As phosphate is used to buffer blood pH, calcium is reabsorbed and excreted in the urine, leading to hypercalciuria. Hypercalciuria then leads to calcium crystallization within soft organs, than may cause kidney dysfunction and may ultimately lead to kidney failure.

In addition, patients experiment significant digestive disorders. The most commonly encountered digestive disorders are anorexia, vomiting, diarrhea and constipation. They are due to metabolic acidosis and also to hypokalemia which causes a decrease in gastrointestinal motility.

The clinical consequences of the complete form of dRTA are stunting, hyperchloremic blood pH acidosis, hypokalemia, hypercalciuria with nephrocalcinosis and hypocitraturia. Deafness may occur.

These consequences are particularly devastating in children and infants.