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At a glance

Genetic disorder with increased renal clearance of cystine, lysine, arginine, and ornithine caused by a dysfunction of the reabsorptive capacity of the renal tubules. In addition, defective intestinal absorption results in increased degradation of these amino acids by bacteria in the intestine.

Synonyms

Cystine-Lysinuria; Cystinuria.

Incidence

The exact incidence remains unknown. Fewer than five patients reported in the literature.

Genetic inheritance

Genetic inheritance is unknown.

Pathophysiology

Increased renal clearance of cystine and the dibasic amino acids lysine, arginine, and ornithine, in the presence of normal or low plasma levels of these compounds, is secondary to dysfunction of the reabsorptive capacity of the renal tubule. Defective intestinal absorption of cystine, lysine, arginine, and ornithine results in increased degradation of these amino acids by bacteria in the intestinal tract. Alternate intestinal transport routes may protect cystinuric patients from amino acid malnutrition because they respond to a large oral dose of lysine with a normal increase of its plasma concentration. Although cystinuria may be associated with central nervous system (CNS) abnormalities, the precise mechanism of action remains to be determined. In cystine-lysinuria, production of cadaverine (1,5-diaminopentane) and putrescine by bacterial conversion of lysine and ornithine may play a role in the pathophysiology.

Diagnosis

Diagnosis made by the clinical course, microscopic examination of the urinary sediment (cystine crystals), screening for crystalluria by cyanide-nitroprusside urine test, urinary amino acids measurements by ion exchange chromatography, or liquid chromatography mass spectrometry. Cystine-lysinuria also can be diagnosed by an oral lysine loading test: urinary excretion of cystine and lysine is increased and, in case of associated neurologic abnormalities, the EEG reveals mild background slowing following lysine loading.

Clinical aspects

Peak times for clinical expression of cystinuria are usually during the second and third decades of life (the disease may appear as early as in the first year or as late as in the ninth decade of life). Renal colics with hematuria as a consequence of nephrolithiasis, urinary tract infections, and obstructive uropathies are common manifestations. Hypertension and renal failure occur occasionally. The onset of neurologic symptoms, such as progressive loss of motor and cognitive milestones, seizures, spasticity, and ataxia, has been reported to occur in early childhood. Further deterioration of neurologic status often coincides with urinary tract infections. Alteration of intestinal flora by neomycin and Lactobacillus acidophilus may lessen the neurologic injury. Maintaining good hydration can help reduce the risk of nephrolithiasis.

Precautions before anesthesia

Assess renal function. If serum creatinine levels are increased, obtain a creatinine clearance test and request, if necessary, urology/nephrology consultation. Check serum electrolytes, hemoglobin, and blood cell counts (frequent urinary tract infections and hematuria). Leukopenia, agranulocytosis, or even aplastic anemia are possible adverse effects ...

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