Cystinuria is a congenital renal anomaly that leads to a breakdown in protein metabolism. The illness can not be cured, but its manifestations can be prevented and consequences avoided. Cystinuria is a disease of the excretory system, which is hereditary. The cause of the disease is genetic factors. This excludes the possibility of a complete cure, but allows, if the appropriate diet and recommendations of specialists are met, to completely compensate its influence.
This ailment is one of the many possible disorders of protein metabolism, in which the walls of the small intestine and the renal tubules do not absorb dibasic amino acids - the products of the amino acid metabolism: cystine, lysine, arginine, ornithine. Accordingly, their level in the blood plasma drops noticeably, and in the urine increases.
However, all listed substances are poorly soluble, with urine being only partially withdrawn. The concentration of substances in the kidney and bladder leads to the formation of s
tones in the organs. With a timely examination, the disease can be detected already in the newborn, without waiting for the accumulation of the substance to lead to the formation of deposits. Most often, the disease is found in the 10-20 years of age, when it begins to progress and manifests itself in the form of urolithiasis.
Accordingly, amino acids are not absorbed by the kidneys or intestines. In the carrier of one gene, the cystine in the urine may exceed the norm, but its blood level remains normal, and does not affect the functionality of the kidney.
Pathogenesis and causes of
A provoking factor for the disease is a high concentration of cystine and other amino acids in the primary urine. Normally, up to 90% of the substances should be reabsorbed in the renal tubules and returned to the blood. However, in patients with this diagnosis, cystine is not absorbed, which leads to a decrease in its level in the blood plasma.
The gene in homozygous state is a complete recessive form, provides inaction of transport systems and, accordingly, absence of reabsorption. With urine, up to 250 mg per 1 liter is output, but this is not enough: the maximum concentration of the saturated solution of the substance is 400 mg / l, provided that the urine acidity is not lower than 7. Once the equilibrium is broken, and the accumulation of cystine is this factor, the substance drops outin the precipitate. The first "victims" are the kidneys and bladder.
Recent research shows that for cystine and other diaminomonocarboxylic amino acids there are separate transport systems - in the side membranes of the tubules, and one common - in the luminal membrane facing the lumen of the tubule. Accordingly, the development of an ailment is possible, in which only a special transport system is switched off-isolated cystinuria, in which only cystine is not absorbed, and an option is possible when the general system refuses. In this case, the cystine is excreted through the luminal membrane, creating the appearance of reabsorption. In this case, the clearance of the substance exceeds the parameters of glomerular filtration.
The specific "culprit" of the disease is the gene Slc3a1.The cause of the ailment is its mutation. It is impossible to prevent the appearance of cystinuria, but it is possible to prevent its manifestation.
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Types and their characteristics
Cystinuria is a common congenital disease associated with the formation of kidney stones. However, cystine stones account for only 1-2% of all possible formations in the bladder and kidneys. Such a small "contribution" to the background of the prevalence is explained by physiological features: at a maximum solubility of 400 ml / l, extraction 600-1800 mg / day is a hazard. However, with normal or alkaline urine reaction and diet compliance, no deposits occur.
A violation of cystine metabolism is possible in two forms - cystinuria and cystinosis:
- With cystinuria, the level of the substance in the urine increases sharply, and its excess is deposited in the kidneys, ureter, and bladder.
- In cystinosis, cystine accumulates in the skin, liver, spleen, bone marrow and lymph nodes, but, in the first place, the formation of stones also occurs in the kidneys.
Classify the disease by the degree of impaired absorption of amino acids by the intestine and the degree of excretion in the urine. The pattern of renal clearance is the same for all homozygotes.
There are 3 genotypic variants:
- 1 - there is no transport for both cystine and other diaminomonocarboxylic amino acids, both in the kidneys and in the intestine. At the carrier of one such gene the level of cystine in the urine is absolutely normal.
- 2 - Cystine is absorbed in the kidneys to 50%, but lysine, arginine, ornithine is not absorbed in either the kidneys or the intestine. This is the most frequent form of ailment.
- 3 - against a background of normal absorption in the intestines, transport in the kidneys of all substances is reduced. In heterozygotes 2 and 3, the concentration of cystine in the urine is increased, but not critical.
The presence of several forms of cystinuria is explained by the allelic mutations of the gene. Types of cystinuria
Symptoms of ailment can appear at any age, but most often for the first time it occurs in 10-20 years. The high concentration of cystine in the urine itself does not cause any changes in the state of health: the symptoms appear only when stones are deposited in the kidneys and ureter.
Symptoms are typical for any kidney stone disease:
- renal colic and quite often;
- pain often radiates to the abdomen, inguinal folds, genitalia;
- constant irritation by metabolic products leads to disturbance of urodynamics - frequent desires, painful urination, and later, to the appearance of inflammatory diseases - pyelonephritis, cystitis, gastritis;
- decrease in the functionality of the kidney naturally causes an increase in blood pressure.
The disease occurs with equal frequency in both men and women, but practice shows that women tolerate it more easily.
It is impossible to determine the form of the disease by external symptoms.
To establish the correct diagnosis, the following tests are prescribed:
- General urine analysis - with cystinuria in the urine, a large number of erythrocytes are found.
- Microscopic examination of urine - under the microscope it is easy to detect characteristic hexagonal crystals of cystine of yellow-brown color.
- Cyanide nitroprusside test, if positive, i.e., an excessive amount of the substance, the urine is colored in the characteristic color of the red wine.
- Yodasin test - in the absence of cystine, the complex of iodine and sodium azide decolorizes in 2-3 minutes. The test is considered positive if the brown color is retained for more than 5 minutes.
- When confirming the diagnosis, an additional study is carried out - paper chromatography or electrophoresis, where the excretion of lysine, cystine, arginine and ornithine is measured quantitatively and separately for each amino acid.
In addition to biochemical analyzes, a hardware examination is also performed to determine the degree of kidney damage.
- Ultrasound - provides complete information about the condition of the body, the presence of stones and sand, the state of the blood supply system.
- Urography on the background of an X-ray contrast substance injected into a vein. When you encounter an obstacle - a stone, the signal is lost. Thus, an accurate picture of the state of the kidney and urinary tract is obtained.
- Obstetric radiography of the abdominal cavity may be prescribed, especially if cystinosis is suspected.
The essence of the treatment consists of two purposes: to organize a diet in which the concentration of cystine does not exceed the norm, and the urine reaction becomes alkaline, and also transfer the cystine stones in the kidneys into a soluble form in order to remove the formed deposits.
This is an indispensable and indispensable element of therapy. Without compliance, treatment will be ineffective. This applies equally to adult patients and children.
The first condition is a large volume of urine. It is necessary to ensure that the excretion of cystine does not exceed 250-300 mg / l. To do this, the patient must consume at least 4 liters of clean, non-carbonated and non-mineral water per day. Ideally, this volume should reach 5-7 liters, but this condition against the already emerged chronic insufficiency is more difficult to perform.
The volume of water should be distributed for the entire waking time, with not less than 1/4 of the volume, and even 1/3 should be taken before bedtime. Water with cystinuria is the same medicine as special drugs. A large volume makes it possible to increase the pH of urine, and even at an index of 7.5, the solubility of cystine increases markedly. That is, with the help of abundant drink, you can achieve not only the excretion of small cystine stones, but also the dissolution of large ones.
- It is clear that the patient's diet should be aimed at the same goals: alkalinization of urine and reduction in the amount of protein products, which include methionine: fish, egg cottage cheese, cheese.
- During the actual treatment, that is, removing and dissolving the formed stones, the diet consists entirely of vegetable dishes. Fruit, some types of pastries and sweets are allowed. Proteins are excluded. You can not stick to such a diet for more than 1 month. Most often, it is based on potatoes in any form, except fried. Strong tea, coffee, alcohol, any other water-retention products, are excluded.
- At normal times, the diet is supplemented with protein products except for methionine-containing foods. Fats are consumed, but in small quantities and in the morning. Allowed protein foods also need to eat in the morning: cystine is faster accumulated in the second half of the day. Salt is limited. Coffee and tea are allowed, but not strong.
If the above measures are not enough, as often happens, prescribe additional drugs that promote alkalization of urine. These are diacarb, sodium hydrogencarbonate, hypothiazide, citrate mixtures.
As a rule, treatment is accompanied by the intake of vitamins A and B, as they have a beneficial effect on the operation of the renal tubules.
Another method is to administer penicillin at 1-2 grams per day. The substance reacts with cystine and effectively dissolves even large stones. However, this approach is not always possible, since penicillin often causes an allergic reaction. Additionally, pyridoxine is prescribed to prevent unwanted reactions with penicillin. Recently, instead, the drug began to use N-acetyl-D-penicillamine, as less dangerous.
For larger stones that exceed the diameter of the urinary tract, surgical intervention is necessary. The method is determined depending on the patient's condition.
Complications and consequences
Prognosis for cystinuria is favorable. It is impossible to heal a congenital anomaly, but it is quite possible to eliminate its consequences and prevent a relapse. However, in case of complications, the result of treatment will not be so stable and complete.
- The most frequent complication is inflammation and not only in the kidneys - cystitis, gastritis, pyelonephritis.
- Another severe complication, usually following inflammation is chronic renal failure. Treatment against its background is difficult.
Preventive measures prevent not the disease itself, but its manifestation. The activities are simple and accessible to everyone and are equally effective for both adult patients and small patients.
- Plentiful drink - a minimum of 2 liters per day, and preferably 3, remains the main requirement. And it means pure, non-mineral water, because the latter reaction is acidic. Acceptance of alkaline water, and even more so of catholyte should be done after consulting a doctor. With too zealous consumption of alkaline products, alkaline stones can be produced.
- Restrictions in the diet should also be observed consistently. Only the sulfur-containing proteins are excluded, and there are not many such proteins. However, it is important to comply with the norms of caloric intake: according to statistics, the risk of stone formation in people with excess weight is always much greater.
- Physical activity is an essential element of the regime. Available load improves blood circulation, which positively affects the work of the kidneys.
When diagnosing a disease, one of the parents or members of his family must undergo a medical genetic examination before conception of the child.
Cystinuria is a very common congenital anomaly, leading to a breakdown in protein metabolism and the formation of stones in the organs. The illness is incurable, but its manifestations can be prevented.