Cystinuria and its relationship to mental retardation

Bardet-Biedl syndrome and cystinuria

An unusual association of Bardet-Biedl syndrome with cystinuria was described in one patient. A 21-year-old male was admitted to hospital because of renal failure, severe deterioration of visual acuity, polydactyly, brachydactyly, and mental retardation. Laboratory investigations revealed a serum creatinine of 292 mumol/L (3.3 mg/dL) and a GFR of 25 mL/min per 1.73 m2. Quantitative ion exchange chromatography demonstrated an increased urinary excretion rate of cystine, lysine, arginine, and ornithine. The ophthalmologic examination showed a severe atypical retinal dystrophy. Visual acuity was severely deteriorated and the patient could only count the examining physician's fingers. The patient had been previously evaluated at the age of 7 years for polyuria, polydipsia, and growth failure. His workup at that time demonstrated nephrogenic diabetes insipidus, normal GFR, and a urinary amino acid pattern consistent with the cystinuric phenotype. There was mental retardation notwithstanding the normal ophthalmologic examination. Intravenous pyelography showed calyceal clubbing, calyceal cysts, and lobulated renal outlines of the fetal type. The patient was evaluated again at the age of 13 years for deterioration of visual acuity and the ophthalmologic examination showed an atypical retinal dystrophy, with sparse pigmentation, central and peripheral atrophy, attenuated vessels, and marked optic disk pallor. To our knowledge the association of Bardet-Biedl syndrome with cystinuria has never been reported. It is unlikely that cystinuria may have contributed to the kidney damage. The possibility that mental retardation has been induced or aggravated by cystinuria cannot be excluded.

Sulfur amino acid metabolism in cystinuria: a biochemical and clinical study of patients

Sulfur amino acid metabolism was studied in 26 homozygotic cystinuric patients, some of whom received D-penicillamine, 2-mercaptopropionylglycine or N-acetylcysteine treatments in order to evaluate signs of cyst(e)ine deficiency. Decreased leukocyte glutathione and taurine levels, plasma cyst(e)ine and taurine concentrations and urinary inorganic sulfate, taurine, mercaptolactate and thiosulfate outputs were found in cystinuric patients, probably reflecting intracellular cyst(e)ine deficiency. An increased mercaptoacetate-cysteine mixed disulfide output was found, probably as result of a poor tubular reabsorption of this compound, as well as for cystine. Normal retinal function was recorded in all patients. During drug treatments, the excretion of most of the sulfur compounds in cystinurics was as those found in controls, probably reflecting an increased mobilization of cysteine. N-acetylcysteine treatment increased the excretion of cyst(e)ine and can thus not be recommended as stone preventive therapy in cystinuria.

Urinary screening for abnormalities of amino acid or mucopolysaccharide metabolism in patients in a hospital for the mentally handicapped in Wessex

Urine from 348 patients of a hospital for the mentally handicapped in Wessex was screened for abnormalities of aminoacid and mucopolysaccharide excretion. Persistent aminoacid abnormalities were found in 16 patients: two had phenylketonuria and one a severe variant form of hyperphenylalaninaemia (dihydropteridine reductase deficiency). In at least nine of the other patients, the observed abnormality was probably a secondary phenomenon. Two patients excreted excessive amounts of a glycosaminoglycan identified tentatively as hyaluronic acid. The study also uncovered one undiagnosed diabetic and three patients with urinary tract infection.

Uptake of L-[35S]cystine by isolated rat brain capillaries

Adult rat brain capillaries were isolated by a simplified procedure and showed an enrichment of the marker enzyme, gamma-glutamyltranspeptidase. The uptake of [35S]cystine at 37 degrees C by this preparation can be divided into two components, a sodium- and energy-dependent transport process for the free amino acid pool, with an apparent Km of 36 microM, and a binding process, with an apparent Km of 1.13 mM. Chemical analysis of the amino acid pool indicates that cystine is the major from of intracapillary 35S. Cystine transport was not inhibited by lysine, but glycine, alpha-methylaminoisobutyric acid and beta-2-aminobicyclo-[2,2,1]-heptane-2-carboxylic acid were inhibitory to a small extent.

Developmental and other characteristics of lysine uptake by rat brain synaptosomes

Synaptosomes isolated from adult or newborn rat cerebrum take up L-lysine by two saturable systems, one with a high affinity low capacity and the other with a low affinity high capacity. Initial rate of uptake for low lysine concentrations is mort tissue. Analysis of kinetic data indicates that synaptosomes of the newborn have a higher Vmax than those of the adult for high affinity system but adult for high affinity system but adult synaptosomes have a higher Vmax than newborn for low affinity system. At a physiological lysine concentration of 0.5 mM, the calculated contributions of two systems indicate that the adult uptake occurs for about 71% by low affinity system but the newborn utilizes both systems to the same extent. The uptake is sodium independent but pH dependent. Lysine uptake is inhibited by other dibasic amino acids, arginine and ornithine but not cystine. Kinetic analysis indicates that arginine specifically inhibits the high affinity, low Km system for lysine uptake.