cystinuria

What is Cystinuria

Cystinuria is an autosomal recessive genetic disorder that affects one person every 600 to 10, 000 individuals;

it manifests itself with the presence of amino acids (endogenous and alimentary) in the urine and represents a disorder in its own right; therefore, its presence does NOT correlate in any way with CISTINOSI or Fanconi Lignac syndrome.

Aminacids involved

From the anatomical and functional point of view, cystinuria is a congenital tubular defect that causes insufficient renal reabsorption of cystine, lysine, arginine and ornithine.

Cystine: is a sulfur amino acid obtained by the oxidative reaction of two cysteine molecules. It is present in many proteins, of which it influences the tertiary structure, and is also involved in the formation of gluten. Cystinuria is easily recognizable thanks to the excretion levels of cystine, which in the healthy subject reach about 80mg / day, while in cystinuremic they undergo an almost exponential increase. However, cystine is not an essential nutrient or the recommended intake rations should be monitored; it is in fact synthesized ex novo by two cysteine molecules, an amino acid deriving from L-methionine.
Lysine: it is an essential amino acid. His biological roles are many: synthesis of L-carnitine, synthesis of collagen, precursor of niacin (vit. PP) ...
Arginine: is an essential amino acid in children . Its functions are creatine precursor, hepatic detoxification of nitrogenous groups, nitric oxide precursor ...
Ornithine: derives from arginine and is a fundamental product of the urea cycle in which it allows the elimination of excess nitrogen; it is also involved in protein synthesis.

NB. Some experimental studies have shown that in cystinuria, in addition to a renal loss, an alteration in the absorption capacity of these amino acids coexists in the intestine.

Complications

To learn more: Symptoms Cystinuria

Considering that cystine and cysteine are NOT particularly difficult to introduce amino acids, and that they are simple enough to synthesize, the amino acid urine loss would be more serious if it concerned lysine and possibly arginine; nevertheless, the plasma depletion of amino acids caused by the tubular defect of the kidney is NOT the most relevant aspect in cystinuria.

Observing the chemical nature of the amino acids involved emerges that, while lysine, arginine and ornithine prove to be SOLUBLE in the acidic fluid of the urinary tract, cystine is NOT, consequently it tends to CRYSTALLIZE.

NB. The cystine crystals present in the severe cystinuria can also be scrutinized in the fresh urine not treated in the laboratory, while for the less important forms qualitative (nitroprussite) and quantitative investigations are necessary (by chromatography on paper or on column).

Cystine calculations

In the case of cystinuria, the cystine crystals can precipitate and give rise to kidney stones which, in the most problematic cases, evolve into VISIBLE RADIO MOLD CALCULATIONS and can be scrutinized by white radiograph of the abdomen. Recall that kidney stones often cause OBSTRUCTION and urinary tract INFECTION but, although cystinuria represents only 1% of all clinical manifestations of kidney stones, it becomes more important in the onset of the child's stones.

Treatment of stones in cystinuria

In cystinuria with related kidney stones, the most successful preventive treatment applied consists of hyperhydration and alkalinization of the urine, while as regards drug therapy the most recently studied molecule is D-penicillamine. In the most serious cases it is advisable to associate the alkalinization of the urine and the hyperhydration to the pharmacological therapy, also undertaking a restrictive dietary therapy towards the amino acids METHIONINE AND CISTEIN.

Hyperhydration : periperhydration means (improperly!) The increase of dietary salt and water with the aim of more dilute the plasma, favoring diuresis. With this arrangement it is possible to reduce the crystallization of cystine and the formation of crystals. See: Hydropinic cure

Alkalinization: alkalinizing urine is a process of voluntary modification of the pH of the renal filtrate, and therefore of the blood. Pharmacological research has experimented with various active ingredients that allow for variations in the filtrate ranging from 5 to 8.5 (where the neutral is 7); among these molecules, the most used are undoubtedly carbonic anhydrase inhibitors, citrates and bicarbonates. It is also essential to keep in mind some dietary rules useful in the alkalization process:

Water supply of at least 1ml / kcal of introduced energy
Supply of mineral salts and alkalizing trace elements
Limitation of protein excess
Acidosis induced by ketogenic diets
Limitation of alcohol and coffee

Restrictive methionine and cysteine dietary therapy: in which it is important to limit or eliminate foods that contain exceptional quantities of methionine and / or cysteine; among these: spirulina algae, soy protein powder, egg powder, parmesan, walnuts, tuna, chicken breast ...? and all other highly protein foods.

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