Related articles: Cystinuria
Definition
Cystinuria is a disease characterized by an inherited defect of the renal tubules, which reduces or prevents the reabsorption of cystine. This results in the increased urinary excretion of this amino acid. Cystine is poorly soluble in acid urine, so when the concentration in the urine exceeds its solubility, the crystals precipitate, leading to the formation of kidney stones.
In most cases, at the base of the disease there is a mutation against the genes responsible for cystine transport expressed in the kidneys (proximal renal tubules) and in the intestinal tract. Cystinuria is transmitted as an autosomal recessive trait; this means that for the disease to develop it is necessary for both parents to be healthy carriers of the mutated gene (each of their children has a 25% chance of inheriting two altered genes, one from each parent).
Cystinuria should not be confused with cystinosis (a metabolic disease characterized by cystine accumulation in the body due to a defect in the transport of the amino acid cystine outside the lysosomes).
Most common symptoms and signs *
- Kidney stones
- Colic
- Dysuria
- Pain in a hip
- Abdominal pain
- Abdominal pain on palpation
- Nausea
- nocturia
- Pancytopenia
- pollakiuria
- Blood in the urine
- Foam in urine
- Strangury
- Dark urine
- Cloudy urine
- He retched
Further indications
Cystinuria generally remains asymptomatic for a long time, up to progression into stones. The reduced renal tubular reabsorption of cystine increases, in fact, its concentration in the urine, from which follows the recurrent formation of radiopaque calculi in the renal pelvis or in the bladder.
The symptoms of cystinuria usually occur between the ages of 10 and 30 and most commonly include renal colic, nausea, vomiting and sometimes hematuria. Some patients may experience chronic pain localized to one or both kidneys.
Cystinuria increases the risk of chronic kidney disease. Furthermore, recurrent urinary tract infections, hydronephrosis and, rarely, renal failure due to obstruction may occur.
The diagnosis is based on the finding of excess cystine in the urine, found with the sodium nitroprusside test. In particular, the presence of cystinuria is confirmed showing cystine excretion> 400 mg / day (normally, it should be <30 mg / day). Upon observation with an optical microscope, cystine in the urine can present itself as hexagonal crystals of a brownish-yellow color.
The therapy consists of a greater water intake (increasing urinary volume, reducing the urinary concentration of cystine, thus decreasing renal toxicity) and in the alkalinization of urine at a pH> 7.0 (to increase the solubility of cystine). When the increase in fluid intake and alkalinization are unable to reduce the formation of stones, other drugs can be used, such as penicillamine, thiopronin and captopril.
