A combined approach to the molecular analysis of cystinuria: from urinalysis to sequencing via genotyping

BACKGROUND

Cystinuria is an autosomal recessive disease that is manifested by kidney stones and is caused by mutations in two genes: SLC3AI on chromosome 2p and SLC7A9 on chromosome 19q. Urinary cystine levels in obligate carriers are often, but not always, helpful in identifying the causative gene.

OBJECTIVES

To characterize the clinical features and analyze the genetic basis of cystinuria in an inbred Moslem Arab Israeli family.

METHODS

Family members were evaluated for urinary cystine and amino acid levels. DNA was initially analyzed with polymorphic markers close to the two genes and SLC7A9 was fully sequenced.

RESULTS

Full segregation was found with the marker close to SLC7A9. Sequencing of this gene revealed a missense mutation, P482L, in the homozygous state in all three affected sibs.

CONCLUSIONS

A combination of urinary cystine levels in obligate carriers, segregation analysis with polymorphic markers, and sequencing can save time and resources in the search for cystinuria mutations.

Hazards associated with pregnancies and deliveries in lysinuric protein intolerance

Lysinuric protein intolerance (LPI) is an autosomal recessive transport disorder of the dibasic amino acids. The defect leads to deficiency of lysine, arginine, and ornithine and, secondarily, to a functional disorder of the urea cycle. Transient postprandial hyperammonemia and subsequent persistent protein aversion, linked with several other biochemical and clinical characteristics of the disease, suggest an increased risk for maternal and fetal complications during pregnancy and delivery. Our unique material on the outcomes of 18 pregnancies of 9 Finnish mothers with LPI and the follow-up of their 19 children shows that maternal LPI is truly associated with increased risk of anemia, toxemia, and intrauterine growth retardation during pregnancy and bleeding complications during delivery. Successful pregnancies and deliveries can still be achieved with careful follow-up of blood pressure and laboratory values. The children of the mothers with LPI generally develop normally. Special care of maternal protein nutrition and control of ammonemia, anemia, and toxemia during pregnancy are essential. We propose centralization of deliveries to obstetric units with capability to deal with bleeding complications and rare inborn errors of metabolism.

Metabolism of dietary ODAP in humans may be responsible for the low incidence of neurolathyrism

OBJECTIVES

The reasons for the very low incidence of the disease neurolathyrism in humans even after excessive consumption of the pulse, Lathyrus sativus, under severe drought and famine conditions, and its continued consumption by large populations during normal periods without any deleterious effects have been examined in the context of a possible metabolism or detoxification of beta-N-oxalyl-L-alpha, beta-diaminopropionic acid (ODAP), the major neurotoxic amino acid of L. sativus.

DESIGN AND METHODS

ODAP in urine samples from 54 subjects habitually consuming the pulse and in three volunteers on an L. sativus diet was determined by the OPT method following clean up of the samples on an alumina column. Urinary oxalate was also determined in these individuals.

RESULTS

Twenty-five subjects showed no excretion of ODAP and it was only less than 0.7% of the dietary intake in the remaining 29 subjects. Urinary excretion of ODAP in three volunteers was also less than 1% with a peak excretion in the 4-h sample. The 4-h blood sample from one volunteer had a maximum ODAP concentration of 177 microM. The urinary oxalate content in the volunteers was nearly 3-fold higher compared to controls.

CONCLUSIONS

The low excretion of dietary ingested ODAP in humans is in sharp contrast to that seen in animals and indicates a metabolism or detoxification of ODAP which may be unique to humans and may explain the low incidence of neurolathyrism.

Urinary excretion of total cystine and the dibasic amino acids arginine, lysine and ornithine in relation to genetic findings in patients with cystinuria treated with sulfhydryl compounds

Advances in molecular genetics have brought a deeper understanding of cystinuria. This autosomal recessive disease, which is caused by a defective tubular reabsorption of cystine and the three dibasic amino acids arginine, lysine and ornithine, results in a lifelong risk of renal stone formation because of the low solubility of cystine in urine. Mutations detected within the two genes known to be associated with cystinuria, SLC3A1 (related to type I) and SLC7A9 (related to non-type I), cannot, however, in all cases explain the disease. Inasmuch as a high urinary concentration of cystine is the basis of stone formation in these patients, our aim was to measure urinary total cystine, arginine, lysine and ornithine, in patients currently lacking a full genetic explanation for their disease. Thirty-three patients with cystinuria who were on long-term treatment with tiopronin or D-penicillamine were divided into two groups. Group 1 comprised eight patients who carried mutation in one of the SLC3A1 alleles and two patients who completely lacked mutations both in the SLC3A1 and the SLC7A9 genes, that is genetic findings discordant with the increased urinary excretion of cystine and the dibasic amino acids in these patients. Group 2 comprised 23 patients homozygous for mutations within SLC3A1, that is genetic findings in accordance with the excretion pattern of classic type I cystinuria. When the two groups were compared, Group 1 had a significantly higher total urinary excretion of cystine ( p<0.01) as well as of arginine, lysine and ornithine ( p<0.05) than Group 2. Also, when the two patients without mutations were excluded from the calculations, there still was a significant difference in the urinary excretion of total cystine ( p<0.05). This suggests that the two patients without any detected mutations in the two known cystine transport genes also contributed to the difference. These unexpected findings indicate that an additional gene or genes participate in the urinary cystine reabsorption in the cystinuric patients who currently are without a full genetic explanation for their disease.

Reference values of urinary excretion of cystine and dibasic aminoacids: classification of patients with cystinuria in the Valencian Community, Spain

OBJECTIVE

Cystinuria is an autosomal-recessive disorder of the kidneys and small intestine affecting a luminal transport mechanism shared by cystine, ornithine, arginine, and lysine. Three different types of cystinuria can be distinguished according to the excretion of these amino acids in urine samples. We propose cutoff values from our population as references and we present a classification of cystinuric patients using quantitative amino acid chromatography in first morning urine samples.

DESIGN AND METHODS

A random sample of forty healthy subjects belonging to general population of the Valencian Community were selected as control subjects. Cystine, lysine, arginine, and ornithine were quantified by reverse-phase HPLC. Seventy-two subjects, diagnosed previously as cystinuric by the cyanide-nitroprusside test were classified. Probands excreting more than 113.12 micromol cystine per mmol of creatinine (i.e., 1,000 micromol cystine per gram of creatinine) were classified as homozygotes. Parents of homozygotes in whom excretion of amino acids were normal were classified as heterozygotes type I. Those probands showing the excretion of at least one amino acid and the sum of urinary cystine plus the basic amino acids higher than the corresponding references ranges in our population were classified as heterozygotes type II or type III (heterozygotes non-type 1).

RESULTS

We identified 24 homozygotes, 39 non-type I heterozygotes and 3 type I heterozygotes. The remaining 6 probands could not be classified. Means for cystine, lysine, arginine ornithine and their sum in homozygotes and heterozygotes non-type I were significantly (p < 0.001) in excess of the respective reference ranges. Moreover, means values in homozygotes were statistically different (p < 0.001) from heterozygotes non-type I.

CONCLUSION

Urinary excretion of cystine per mmol creatinine allow us to distinguish heterozygotes from homozygotes. However, the best discriminator to distinguish non-type I heterozygotes from normal population might be the excretion of lysine per mmol creatinine. Additional studies including characterization of appropriate haplotypes should be carried out for a more precise identification of types of cystinuria.

Molecular analysis of the cystinuria disease gene: identification of four new mutations, one large deletion, and one polymorphism

A cystinuria disease gene (rBAT) has recently been identified, but evidence strongly suggests that only Type-I cystinuria is due to mutations in this gene. Sixteen point mutations and a large deletion causing the disease have so far been described in the rBAT gene sequence. To identify new mutated alleles, genomic DNA was analyzed, after the determination of the entire genomic structure of the rBAT gene, by RNA-single strand conformation polymorphism analysis, an accurate and sensitive method able to detect nucleotide changes. Four new point mutations, a large deletion, and a common intragenic polymorphism were detected. These new mutations increase to 22 the number of mutated alleles so far characterized in rBAT. In addition, the frequency of 21 mutations was assessed in a sample of accurately defined Type-I cystinuria chromosomes. They account for about 58% of all Type-I chromosomes, mutation M467T being the most common (0.26).

Genetic heterogeneity in cystinuria: the SLC3A1 gene is linked to type I but not to type III cystinuria

Cystinuria is an autosomal recessive amino-aciduria where three urinary phenotypes have been described (I, II, and III). An amino acid transporter gene, SLC3A1 (formerly rBAT), was found to be responsible for this disorder. To assess whether mutations in SLC3A1 are involved in different cystinuria phenotypes, linkage with this gene and its nearest marker (D2S119) was analyzed in 22 families with type I and/or type III cystinuria. Linkage with heterogeneity was proved (alpha = 0.45; P < 0.008). Type I/I families showed homogeneous linkage to SLC3A1 (Zmax > 3.0 at theta = 0.00; alpha = 1), whereas types I/III and III/III were not linked. Our data suggest that type I cystinuria is due to mutations in the SLC3A1 gene, whereas another locus is responsible for type III. This result establishes genetic heterogeneity for cystinuria, classically considered as a multiallelic monogenic disease.

A study on the metabolism of spermidine in mammals: purification and identification of a newly identified metabolite, 2-oxo-1-pyrrolidinepropionic acid, in rat urine

In order to study the metabolism of spermidine in mammals, radioactive spermidine was injected intraperitoneally into a rat and urine was collected for analysis. Incorporation of radioactivity into putreanine, isoputreanine, spermidic acid, and N-aminopropylpyrrolidin-2-one was confirmed by ion-exchange chromatography, thin layer chromatography, and paper electrophoresis, the highest radioactivity being observed in the non-polar and acidic fraction of the collected urine. A radioactive compound was purified from the non-polar and acidic fraction, and identified as 2-oxo-1-pyrrolidinepropionic acid by comparison of its behavior on ion-exchange chromatography and thin layer chromatography with that of authentic 2-oxo-1-pyrrolidinepropionic acid, and recrystallization with the authentic compound. Acid hydrolysis of the radioactive compound produced radioactive spermidic acid, confirming the identification. To examine the interconversion between isoputreanine and N-aminopropylpyrrolidin-2-one, these compounds were deuterated and then intraperitoneally injected into a rat. Analysis of 24-h urine by gas-chromatography-mass-spectrometry indicated no interconversion between the two metabolites of spermidine under these conditions. An intracerebroventricular injection of radioactive spermidine into a rat showed that radioactivity was also incorporated into the metabolites of spermidine in the brain, and oxidative deamination of the aminopropyl moiety of spermidine was thought to be dominant in the central nervous system and vice versa in peripheral organs.

[An enteral modular formula in dibasic amino aciduria]

Lysinuric protein intolerance (LPI) or dibasic amino acid aminoaciduria is an unusual metabolic illness which, in countries where it is most common, affects one individual for every 60,000-80,000 births, and which is characterised by the inability to transport dibasic amino acids to the interior of the different cells of the organism. This paper sets out the design for an enteral modular formula for a pediatric patient very probably suffering from LPI. The formula has a very limited protein content, and incorporates L-citruline, a non-proteinogenic amino acid which intervenes in the urea cycle.

2-Amino-3-(methylamino)propanoic acid (BMAA) bioavailability in the primate

2-Amino-3-(methylamino)-propanoic acid (BMAA) is a low potency excitatory amino acid present in the cycad plant that has been proposed as a factor in the high incidence of amyotrophic lateral sclerosis-parkinsonism dementia (ALS-PD) in the western Pacific region. We employed stable isotopic forms of BMAA to assess the oral bioavailability of this compound in cynomolgous monkeys (n = 3). The stable isotope labeled BMAA ([15N]-BMAA) was injected i.v. at the same time that the unlabeled compound was administered orally. Both forms of BMAA were then quantified in a 48h urine sample by gas chromatography-mass spectrometry (GC/MS). Following oral dosing, 80% of the administered BMAA was absorbed into the systemic circulation; thus, oral bioavailability was high and other routes of administration could not result in significantly higher circulating levels of BMAA for a given administered dose.

[Laboratory diagnosis of cystinuria]

Delayed diagnosis, apparently due to insufficient knowledge of partly simple methods of cystine determination and their practical application, is often a particular problem in the treatment of cystine lithiasis. The present paper gives a survey of a variety of laboratory methods to determine cystine in the urine both qualitatively and quantitatively. Their applicability in various diagnostic situations is discussed. In clinico-chemical routine, colorimetric cystine determinations using Brands test, but partibularly the nickel/dithionite reagent, is an established and reliable laboratory method. Possibilities of its use as quick screening assays are described.

Urinary polyamine and metabolite excretion by children with Zellweger's syndrome

In order to investigate whether, due to a lack of peroxisomes, polyamine degradation is altered in patients with the cerebro-hepato-renal syndrome of Zellweger, we determined total, free and acetylated polyamines and some of their catabolites in urines of six patients and age-matched healthy children. The normal polyamine excretion patterns of the patients, compared to the control group, suggest that either the intracellular localisation of the polyamine degrading enzyme, polyamine oxidase, is not exclusively limited to peroxisomes or that the enzyme is located in the peroxisomal matrix.

Two-dimensional gas chromatography with electron-capture detection used in the determination of specific peptidoglycan and lipopolysaccharide constituents of gram-negative bacteria in infected human urine

Gas chromatography with electron-capture detection was used in the determination of diaminopimelic acid (as the N-heptafluorobutyryl isobutyl derivative) and 3-hydroxymyristic acid (as the O-pentafluorobenzoyl methyl derivative) in Gram-negative bacterial cells in infected human urine. Use of the column-switching (two-dimensional gas chromatography) technique greatly enhanced the selectivity of the detection and simplified the processing of samples. The system described should prove useful for trace detection of specific bacterial constituents in complex environments.

Total polyamines and their non-alpha-amino acid metabolites simultaneously determined in urine by capillary gas chromatography, with nitrogen-phosphorus detector; and some clinical applications

A capillary gas-chromatographic method with nitrogen-phosphorus detection is used here to simultaneously determine 1,3-diaminopropane, putrescine, cadaverine, spermidine, spermine, isoputreanine , putreanine , and N-(3-aminopropyl)-N'-(2-carboxyethyl)-1,4- diaminobutane in urine. After acid hydrolysis the compounds are isolated by adsorption onto silica gel and converted into their methyl-heptafluorobutyryl derivatives. We give quality-control data and age-dependent values for urinary excretion of these analytes by 76 apparently healthy controls. Circadian rhythmicity in the excretion of spermidine and (especially) isoputreanine was established and is discussed in the light of its implications for monitoring therapy of cancer. Investigation of menstrual-cycle-dependent diurnal variation in one normal woman showed no distinct, consistent fluctuations. We applied the method to monitor (by use of 24-h urine specimens) an uncomplicated, normally progressing pregnancy, a patient with metastatic melanoma being treated with cytostatic drugs, and (in more detail) the treatment of a patient with high-grade non-Hodgkin lymphoma.

Growth hormone studies in lysinuric protein intolerance

Our two patients with lysinuric protein intolerance, a 14-year-old boy and his 12-year-old sister, showed growth retardation and their bone ages were retarded. Growth hormone secretion responded to glucagon-propranolol and showed a good response to arginine. However, growth hormone showed little response to insulin. After the oral administration of arginine hydrochloride, growth hormone showed a good response to insulin and glucagon-propranolol, and gain in height and weight accelerated. This result may suggest that an adequate supply of arginine is effective in improving the growth retardation in lysinuric protein intolerance.

Oral administration of arginine and citrulline in the treatment of lysinuric protein intolerance

In two sibling patients with lysinuric protein intolerance (LPI), the therapeutic effect of oral supplement of arginine and citrulline on postprandial hyperammonemia was investigated. Intravenous load of L-alanine (6.6 mmol/kg of body weight), and oral load of L-arginine (0.8 mmol/kg of body weight) or of L-citrulline (1.0 mmol/kg of body weight) during intravenous load of L-alanine were performed to study the preventive effect of arginine or citrulline supplement on hyperammonemia induced by intravenous amino nitrogen load. In the older sibling, the hyperammonemia induced by the intravenous amino nitrogen load was completely prevented by the oral supplement of citrulline, but not completely prevented in the younger sibling. On the other hand, the hyperammonemia was prevented by the oral supplement of arginine only in the younger sibling, but not in the older sibling. In the light of these results, the younger patient received an oral administration of L-arginine and the older patient L-citrulline for the treatment of postprandial hyperammonemia. Two-year observation of each patient revealed that postprandial hyperammonemia and aversion to protein-rich food completely disappeared and that a marked increase of body weight and height was obtained. Furthermore, there was no side effect with these amino acids supplements. The present study suggests that an oral supplement of arginine or citrulline is effective for preventing postprandial hyperammonemia in this disorder.

Combined iminoglycinuria and cystine- and dibasic aminoaciduria in patients with propionic acidaemia and 3-methylcrotonylglycinuria

Urinary amino acids have been determined in six patients with propionic acidaemia, one of whom also showed 3-methylcrotonylglycinuria. Two patients, including the subject with 3-methylcrotonylglycinuria, showed a gross aminoaciduria with features of both cystinuria and iminoglycinuria. We suggest a defect in certain amino acid transport systems in some patients with these disorders.

Automated analysis of common basic amino acids, mono-, di-, and polyamines, phenolicamines, and indoleamines in crude biological samples

A fully automated, fast, and sensitive method for the separation of common basic amino acids and mono-, di-, and polyamines as well as phenolic- and indoleamines is described. Picomole level determination of hydroxytryptophan, tryptophan, histidine, lysine, ethanol amine, arginine, noradrenaline, diaminopropane, putrescine, histamine, cadaverine, dopamine, hexamethylenediamine, agmatine, tyramine, phenethylamine, serotonin, 5,6-dihydroxytryptamine, 5-methoxytryptamine, tryptamine, spermidine, and spermine is carried out by ion-exchange column chromatography on a single sample in 170 min of total analysis. This method is well suited for crude extracts without preliminary purification, thus reducing preparative losses. The reproducibility of the method has been studied and the percentage recovery of the different compounds after column chromatography is reported. Its application to crude samples from different biological sources such as microorganisms, vegetables, platelets, and urine is presented. This method could serve as a powerful tool for the analysis of these amino compounds in which there is currently a considerable interest.

Urinary excretion of amino acids in patients receiving intravenous hyperalimentation

Urinary outputs of amino acids in nine patients receiving intravenous hyperalimentation were estimated for evaluating adequacy of dosage and composition of the infusage for the maintenance of normal metabolism of tissue proteins in the subjects. The daily outputs of the methylated amino acids (3-methylhistidine, epsilon-N-methylated lysines and guanidino-N-methylated arginines), which are thought to be derived from tissue proteins, remained in the normal ranges, suggesting that the normal metabolism of tissue proteins was sustained during intravenous hyperalimentation. Relatively large urinary excretion of threonine, serine and glycine might reflect the large dosage of glucose in the infusate and disuse of these amino acids during the treatment, especially in the patients with hepatic dysfunction. Diurnal rhythms in urinary outputs of amino acids in patients receiving intravenous hyperalimentation were not observed, except for the outputs of threonine, serine and glycine, which were large during the 3.00-9.00 h and 15.00-21.00 h periods. The absence of daily fluctuations of the methylated amino acids in urine suggested that there were no diurnal rhythms in the metabolism of tissue proteins in the subjects.

Hyperdibasicaminoaciduria and hyperammonemia in familial protein intolerance

A 3-year-old boy with hyperdibasicaminoaciduria and hyperammonemia showed characteristics of familial protein intolerance (FPI). Oral loading tests of lysine and arginine disclosed a remarkably reduced capability for intestinal absorption of these amino acids. Because urinary excretion and renal clearance of dibasic amino acids were only moderately elevated in the patient, the conspicuously decreased serum concentration of lysine, arginine, and ornithine was attributed to the defect in internal absorption. A possible explanation for elevated blood ammonia levels in FPI is that it is due to a deficiency of arginine and ornithine in the urea cycle that in turn results from a severe impairment in absorption of the amino acids by the gut mucosa.

Renal handling of diamino acids in lysinuric protein intolerance

Lysinuric protein intolerance (LPI) is a rare recessively inherited disease in which one of the fundamental physiological defects is in the mechanism by which diamino acids are transported by the kidney. The purpose of the present studies was to examine that mechanism in four controls and seven patients with LPI. Two types of studies were conducted. In the first set, the renal handling of l-arginine and l-ornithine was evaluated by gradually increasing the plasma concentration of each of these amino acids by constant infusion techniques. In the second set of studies, the possible existence of competitive inhibition between l-arginine, l-ornithine, and l-lysine was examined. In the control subjects, there was almost complete reabsorption of arginine and ornithine, with increases in their filtered loads to 50-100 times normal. With further increases in the filtered loads of these amino acids, there was a gradual decrease in their fractional reabsorption. Mutual competitive inhibition was suggested by the observation that an increase in the filtered load of one diamino acid was associated with a decrease in the reabsorption of the other two. In LPI, the fasting plasma diamino acid concentrations were significantly lower than in the controls. With low filtered loads, the fractional reabsorption of the diamino acids was clearly below normal. This defect diminished with higher loads. A stepwise increase in the plasma concentration of one diamino acid resulted in a biphasic response. Initially, net tubular secretion of the other diamino acids was noted, but later was followed by return to net absorption. When two diamino acids were infused simultaneously, net absorption of both took place, though less efficiently than in the controls. We conclude that the renal reabsorption mechanism is defective in patients with LPI. With low normal filtered loads, there is increased fractional excretion of all three diamino acids resulting in low serum concentrations of these compounds. However, at higher artificially elevated concentrations of diamino acids, the capacity of the renal transport system in these patients appears normal.

Homoarginine in cystinuria

1. By using ion-exchange columns coupled to a sensitive automated Sakaguchi reaction, in addition to the normal ninhydrin reaction for amino acids, homoarginine, a guanidino homologue of arginine, was found in the plasma and urine of both normal and cystinuric individuals.

2. In all seven cystinuric subjects studied, urinary excretion of homoarginine was approximately ten times that found in normal subjects; the plasma levels of this amino acid were considerably reduced relative to normal individuals.

3. Homoarginine in the plasma can be derived either metabolically from lysine or from dietary sources.

4. In normal subjects homoarginine was cleared at a higher rate than arginine. On the other hand, the clearance of arginine exceeded that for homoarginine in the majority of cystinuric subjects although the values obtained for homoarginine indicate that the defect in amino acid transport also affects this amino acid.

5. The defect in the proximal tubular reabsorption of homoarginine is less severe than that for arginine, suggesting that the reabsorptive site for homoarginine may not be the same as that for arginine.

6. In the design of models for the tubular reabsorption of amino acids in health and disease, the presence of homoarginine and its excessive loss in cystinuria must be accounted for.