Cystinuria

Cystinuria is a hereditary defect of the renal tubules, in which the resorption of the amino acid of cystine is disturbed, its excretion in the urine is increased, cystine stones are formed in the urinary ways. Symptoms include the development of renal colic in connection with stone formation and, probably, infection of the urinary system or manifestations of renal failure. The diagnosis is based on the definition of excretion of cystine with urine. Treatment of cystinuria includes an increase in the daily volume of fluid and alkalinization of urine.

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Causes of cystinuria

Cystinuria is inherited by autosomal recessive type. In heterozygous carriage, there may be increased excretion of cystine with urine, but rarely sufficient to form stones.

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Pathophysiology of cystinuria

The primary defect is the restriction of tubular reabsorption of cystine in the kidneys, which increases its concentration in the urine. Cystine is poorly soluble in acidic urine, so if its concentration in the urine exceeds its solubility, urinary cystine crystals are formed in the urine, which subsequently form cystine stones.

Reabsorption of two basic amino acids (lysine, ornithine, arginine) is also disrupted, which does not cause significant problems, since these amino acids have an alternative transport system independent of the cystine transport system. Moreover, these amino acids are more soluble in urine than cystine, and their increased excretion does not lead to crystal precipitation and stone formation. Their absorption in the small intestine (and cystine absorption) is also reduced.

Symptoms of cystinuria

Symptoms of cystinuria, most often renal colic, usually appear between the ages of 10 and 30 years. IC can develop and kidney failure due to obstructive uropathy.

Radiopaque cystine stones form in the renal pelvis or bladder. Coral concretions are often noted. Cystine can be present in the urine in the form of yellow-brown hexagonal crystals. An excessive amount of cystine in the urine can be detected using a cyanide nitroprusside test. The diagnosis confirms the detection of daily excretion of cystine over 400 mg / day (normally less than 30 mg / day).

Treatment of cystinuria

Eventually, terminal renal failure usually develops. Reducing the concentration of cystine in the urine reduces damage to the kidneys. This is achieved by increasing the volume of urine. The fluid intake should be sufficient to provide a diuresis of about 3-4 liters per day. Hydration is especially important at night, when urine pH decreases. Urine alkalinisation to pH more than 7.4 with sodium bicarbonate or potassium 1 mEq / kg orally 2 times a day and acetazolamide 5 mg / kg (up to 250 mg) orally at night significantly increases the solubility of cystine. If high fluid intake and alkalinization of urine does not reduce the formation of stone, you can try to use other drugs. Penicillamine (7.5 mg / kg 4 times a day and 250-1000 mg orally 4 times a day in older children) is effective, but the toxic effects limit its use. Approximately 1/2 patients develop intoxication, such as a rise in body temperature, rash, arthralgia or less often nephrotic syndrome, pancytopenia or SLE-like reactions. Cystinuria can be treated with captopril (0.3 mg / kg orally 3 times a day), but it is not as effective as penicillamine, but it is much less toxic.