Tubulopathies directly affect various renal functions and cause many disorders depending upon the affected renal function.
As an example, nephrogenic diabetes insipidus is typified by the kidney losing its concentration ability due to an anomaly in the reabsorption of water in the renal tubule. This disease, which affects a child from a very young age, can result in severe dehydration which may cause significant neurological complications.
Most of these are hereditary; some are acquired secondary to another disease or following treatments.
The consequence of other tubulopathies may be an abnormal loss of salts (Na, K, Ca). Amongst the most well-known are the following syndromes:
- Congenital pseudo-hypoadrenocorticism
- Gitelman syndrome
- Bartter syndrome
- Dent’s disease (causing hypercalciuria)
- Chronic familial hypokaliaemia (loss of potassium).
Some mutations may modify renal transport and the reabsorption of certain amino-acids, and cause an aminoaciduria such as cystinuria, glycinuria, xanthinuria. Tubular disorders may also concern the elimination of H+ ions, causing chronic idiopathic distal tubular acidosis (e.g. Albright Syndrome). When all the reabsorption functions are affected, causing a global loss of bicarbonate, potassium, sodium, calcium, phosphorus, glucose, amino-acids and proteins, this is known as “Fanconi syndrome”. The origin of this may be genetic or acquired. The most frequent genetic cause of Fanconi syndrome is cystinosis, for which the tubulopathy is linked to an innate metabolic disorder. Generally the consequences of tubular impairment are variable depending on the location within the tubule and the existence, or not, of compensatory pathways. The most usual clinical symptoms are the following:
- Loss in the urine of minerals, salts, vitamins, etc.
- Internal environment imbalance (Water balance, acid-base balance disorders for example)
- Delayed or defective growth (rickets, osteomalacia).
Current treatments are based on the correction of disorders, following tubular impairment, by various adapted supplementations.
These supplementations are either combined with restrictive dietary measures, or with therapeutics making it possible to correct one of the symptoms induced by the tubular impairment.