Cystinuria-lysinuria

Cystinuria-lysinuria is a rare, inherited metabolic disorder characterized by the abnormal transport and increased excretion of certain amino acids, including cystine and lysine, in the urine. This condition is a result of a defect in the renal tubular reabsorption of these dibasic amino acids, leading to their accumulation in the urine. Cystinuria-lysinuria falls under the broader category of aminoacidurias, which are disorders affecting the metabolism of amino acids.

Causes and Genetics

Cystinuria-lysinuria is caused by mutations in specific genes responsible for the transport of cystine and lysine in the kidney. These mutations lead to defective amino acid transporters in the renal tubular cells, preventing the reabsorption of cystine and lysine back into the bloodstream. As a result, these amino acids are excreted in high concentrations in the urine. The condition is inherited in an autosomal recessive manner, meaning that an individual must inherit two copies of the mutated gene, one from each parent, to be affected.

Symptoms

The primary symptom of cystinuria-lysinuria is the formation of kidney stones, which occur due to the accumulation and crystallization of cystine in the kidneys and urinary tract. Kidney stones can lead to various complications, including pain, urinary tract infections, and kidney damage. The increased excretion of lysine does not typically result in symptoms, as lysine does not form crystals like cystine.

Diagnosis

Diagnosis of cystinuria-lysinuria involves a combination of urine tests, genetic testing, and sometimes imaging studies. Urine tests can detect the elevated levels of cystine and lysine, while genetic testing can identify mutations in the genes associated with the condition. Imaging studies, such as ultrasound or CT scans, may be used to identify the presence of kidney stones.

Treatment

Treatment for cystinuria-lysinuria focuses on preventing the formation of cystine stones and managing symptoms. Strategies include increasing fluid intake to dilute the concentration of cystine in the urine, dietary modifications to reduce cystine excretion, and medications that can help dissolve cystine stones or prevent their formation. In some cases, surgical intervention may be necessary to remove large kidney stones.

Prognosis

With appropriate management, individuals with cystinuria-lysinuria can lead relatively normal lives. However, they may require ongoing treatment to prevent the formation of kidney stones and to manage any complications that arise from stone formation.

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