Cystinuria. Cystinuria-lysinuria
Incidence
It is an autosomal recessive disorder. The estimated prevalence of cystinuria ranges from 1:2,500 in the Libyan Jewish population to 1:100,000 in some reports.
Clinical Characteristics
Cystinuria is an autosomal recessive disorder characterized by an impaired transport of cystine, lysine, ornithine and arginine in the proximal renal tubule and in the epithelial cells of the gastrointestinal tract. An elevated cystine concentration in the urinary tract is responsible for the formation of renal stones. Symptoms are those related to renal stone disease: renal colic is often the first symptom, but renal stones may also be detected following a urinary tract infection or unexpectedly found in patients undergoing an abdominal X-ray or ultrasound scan for other reasons. The estimated prevalence of cystinuria ranges from 1:2,500 in the Libyan Jewish population to 1:100,000 in some reports. Treatment requires several different approaches: increased urine pH with alkali to improve cystine solubility, administration to a large amounts of fluids to reduce urine osmolality, using molecules (like alpha-mercaptopropionylglycine and D-Penicillamine) forming chemical bonds with the sulfhydryl domains of the cystine, as they lower the amount of free cystine in the urine. Four subtypes of Cystinuria are recognized. In Type I Cystinuria, there is a defect in the active transport of cystine and the amino acids (dibasic) lysine, arginine, and ornithine in the kidneys and small intestine. People who are carriers of the gene for this type of the disorder generally have no symptoms. In Type II Cystinuria, cystine and lysine transport is severely impaired in the kidneys and only somewhat impaired in the intestines. In Type III Cystinuria, kidney transport of cystine and lysine is defective; intestinal transport is normal. People who are carriers of the gene for this variety of the disease typically have slightly elevated levels of cystine and lysine in the urine. In Hypercystinuria, there is generally a moderate elevation of cystine in the urine; intestinal absorption of cystine and the dibasic amino acids is normal.
Precipitants
Probably dehydration.
Provocation Tests
None
Diagnostic Procedures
An elevated cystine concentration in the urinary tract is responsible for the formation of renal stones. There is increased urinary levels of cystine, lysine, ornithine and arginine.