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PubMed2002

Cystinuria in children: distribution and frequencies of mutations in the SLC3A1 and SLC7A9 genes.

BACKGROUND: Cystinuria is a common inherited disorder of defective renal reabsorption of cystine, ornithine, lysine and arginine leading to nephrolithiasis. Two responsible genes have been identified so far: Mutations in the SLC3A1 gene encoding the heavy chain rbAT of the renal cystine transport system rbAT/b(0,+)AT cause cystinuria type I, while variants in SLC7A9, the gene of its light chain b(0,+)AT, have been demonstrated in non-type I cystinuria. In this study, we searched for mutations in both genes in a cohort of children with cystinuria. METHODS: Twenty-one cystinuric children from 16 families were analyzed by mutational analysis of the genes SLC3A1 and the SLC7A9. The patients were classified by the urinary amino acid excretion profile of their parents. Additionally, 10 unclassified patients were screened for genomic variants. The screening techniques included single strand conformation polymorphism analysis, restriction assays and direct sequencing. RESULTS: Two novel mutations were identified in SLC3A1 and three in SLC7A9; three were missense mutations and two frameshift mutations. In the pediatric patients, mutations were found in 54% of type I (SLC3A1) and in 25% of non-type I (SLC7A9) chromosomes. For this group of patients a total detection rate of 46.6% for mutations in both genes was delineated. In the cohort of unclassified 10 patients, 70% of mutations were determined. M467T and G105R were the preponderant mutations in SLC3A1 and SLC7A9, respectively; T216M was the major mutation in Turkey and Greece. CONCLUSIONS: The detection rate for mutations in SLC3A1 and SLC7A9 in children was 54% in the SLC3A1 gene for type I chromosomes and 25% in the SLC7A9 gene for non-type I chromosomes. It was lower than that in 10 further patients with an unclassified cystinuria, although the clinical characterization in the first group was more stringent; additionally, different spectrums of mutations were observed. The lack of detectable mutations in many patients indicates the possibility of other yet unidentified genes involved in cystinuria. We could not correlate the severity of the disease to the type of cystinuria in the pediatric patients.

Adolescent↗
PubMed2000

Advances in genetic aspects of cystinuria.

Cystinuria has been clinically classified into three subtypes (I, II, and III) by Rosenberg and associates. In 1994, the SLC3A1 (rBAT) genes which is one of the genes responsible for cystinuria, was located on chromosome 2(2p21). However, it was demonstrated that rBAT is responsible only for Type I cystinuria. At present, 43 mutations, including 5 discovered in our laboratory, have been reported in the rBAT gene of patients with cystinuria. Recent studies suggest that the rBAT-encoded protein was not a transporter itself; rather, the protein represented a specific "guidance molecule" for a selected amino acid transporter. In 1999, the SLC7A9 (BAT1) gene was located on chromosome 19(19q13) by us and by a European group. It seemed that the BAT1 gene is responsible for non-Type I cystinuria and that its protein was a subunit linked to the rBAT protein via a disulfide bond. Mutational, structural, and functional analyses of the gene have been performed by several groups, including our laboratory. It is expected that the roles of these genes in cystinuria will be clarified further, and genetic diagnosis and therapy of patients with cystinuria may be facilitated in the future.

Amino Acid Transport Systems, Basic↗
PubMed2001

Functional analysis of mutations in SLC7A9, and genotype-phenotype correlation in non-Type I cystinuria.

Cystinuria (OMIM 220100) is a common recessive disorder of renal reabsorption of cystine and dibasic amino acids that results in nephrolithiasis of cystine. Mutations in SLC3A1, which encodes rBAT, cause Type I cystinuria, and mutations in SLC7A9, which encodes a putative subunit of rBAT (b(o,+)AT), cause non-Type I cystinuria. Here we describe the genomic structure of SLC7A9 (13 exons) and 28 new mutations in this gene that, together with the seven previously reported, explain 79% of the alleles in 61 non-Type I cystinuria patients. These data demonstrate that SLC7A9 is the main non-Type I cystinuria gene. Mutations G105R, V170M, A182T and R333W are the most frequent SLC7A9 missense mutations found. Among heterozygotes carrying these mutations, A182T heterozygotes showed the lowest urinary excretion values of cystine and dibasic amino acids. Functional analysis of mutation A182T after co-expression with rBAT in HeLa cells revealed significant residual transport activity. In contrast, mutations G105R, V170M and R333W are associated to a complete or almost complete loss of transport activity, leading to a more severe urinary phenotype in heterozygotes. SLC7A9 mutations located in the putative transmembrane domains of b(o,+)AT and affecting conserved amino acid residues with a small side chain generate a severe phenotype, while mutations in non-conserved residues give rise to a mild phenotype. These data provide the first genotype-phenotype correlation in non-Type I cystinuria, and show that a mild urinary phenotype in heterozygotes may associate with mutations with significant residual transport activity.

Amino Acid Sequence↗
PubMed2001

Is the SLC7A10 gene on chromosome 19 a candidate locus for cystinuria?

One of the genes (SLC7A9) that causes cystinuria, an inborn error of amino acid transport, is localized to 19q13. Close examination of human genomic DNA sequences has identified a similar gene (SLC7A10) that also maps to the 19q13.1 region and is highly expressed in kidney. The homologies between SLC7A9 and SLC7A10 are likely the result of gene duplication. SLC7A10 is known to encode a protein with a function similar to that of the SLC7A9 gene product. To determine if mutations in the SLC7A10 gene could also cause cystinuria, we characterized the primary genomic structure and sequenced the 11 exons and surrounding sequences from 10 unrelated patients with cystinuria. We identified one missense mutation which may account for cystinuria in one family. We also observed one intronic change, as well as one silent mutation, that were seen only in cystinuria patients. We therefore suggest that the SLC7A10 gene warrants further investigation as another candidate gene for cystinuria.

Amino Acid Sequence↗
PubMed2006

SLC7A9 cDNA cloning and mutational analysis of SLC3A1 and SLC7A9 in canine cystinuria.

Cystinuria is a genetic disorder in the domestic dog that leads to recurrent urolith formation. The genetic basis of the disorder is best characterized in humans and is caused by mutations in one of the amino acid transporter genes SLC3A1 or SLC7A9, which results in hyperexcretion of cystine and the dibasic amino acids in the urine and subsequent precipitation of cystine due to its low solubility in urine. In this study we describe the cloning of the canine SLC7A9 cDNA and present a thorough mutation analysis of the coding SLC3A1 and SLC7A9 regions in cystinuric dogs of different breeds. Mutation analysis of the two cystinuria disease genes revealed one SLC7A9 mutation (A217T) and two SLC3A1 mutations (I192V and S698G) in French and English Bulldogs that affect nonconserved amino acid residues, arguing against functional impact on the proteins. The absence of deleterious mutations linked to cystinuria in the remainder of our panel of cystinuric dogs is surprising because SLC3A1 or SLC7A9 mutations explain approximately 70% of all human cystinuria cases studied. The present study, along with previous investigations of canine and human cystinuria, implies that regulatory parts of the SLC3A1 and SLC7A9 genes as well as other unknown genes may harbor mutations causing cystinuria.

Amino Acid Transport Systems, Basic↗
PubMed1993

Prospective analysis and classification of patients with cystinuria identified in a newborn screening program.

Patients who inherit mutant cystinuria genes excrete high concentrations of cystine, ornithine, arginine, and lysine in the urine. At least three variants of cystinuria can be distinguished in heterozygotes. To determine whether certain combinations of mutant genes are more disadvantageous than others, we analyzed amino acid excretion in families of 17 probands with cystinuria identified by the Quebec neonatal screening program. Parents of the probands were classified into the three known phenotypes by calculating the sum of cystine, ornithine, arginine, and lysine excretion. Although parents of type I/I homozygotes excreted amounts of cystine in the normal range, their offspring excreted significantly greater amounts of urinary cystine than did children who have type I/III genetic compounds. This observation suggests that types I and III cystinuria mutations might involve two distinct genetic loci. Children with type I/I homozygous cystinuria often excrete cystine at levels greater than the theoretic solubility limit and may be at greatest risk for nephrolithiasis. We outline an approach to monitoring children with cystinuria who come to medical attention before formation of cystine stones.

Arginine↗
PubMed1985

Ontogeny modifies manifestations of cystinuria genes: implications for counseling.

Among 339,868 newborn infants screened at 3 weeks of age (91% compliance rate), 730 had elevated rates of excretion of cystine and the dibasic amino acids lysine, ornithine, and arginine; 191 infants had persistent "infantile cystinuria" on follow-up screening (100% compliance). Apparent incidence of the phenotype was 562 per million infants; this rate is seven times higher than for classic cystinuria in the adult segment of the Quebec population. We studied longitudinally 26 probands 2 to 4 months of age. Initially, each excreted cystine and dibasic amino acids at much higher levels than did normal infants or either parent. From parental phenotypes (heterozygous or homozygous normal) and urine amino acid excretion values at 6 months of age in probands, the infants were classified as either heterozygous for the various classic cystinuria genotypes--type I ("silent"), eight infants; type II (high excretor), three; type III (moderate excretor), nine--or homozygous (and genetic compound), six. Urine amino acid excretion diminished steadily with age, to reach the variant parental value in heterozygous infants but not in homozygotes. Cystinuria heterozygotes, with the possible exception of some type I individuals, could not be distinguished reliably from homozygotes in early infancy, although homozygotes had significantly higher excretion values as a group. We deduce that renal ontogeny amplifies phenotypic expression of cystinuria alleles, thus influencing correct classification of genotype (heterozygote vs homozygote, and type of allele). These findings have implications for counseling and the need for follow-up of infantile cystinuria.

Aging↗
PubMed2006

A novel missense mutation of SLC7A9 frequent in Japanese cystinuria cases affecting the C-terminus of the transporter.

Cystinuria is caused by the inherited defect of apical membrane transport systems for cystine and dibasic amino acids in renal proximal tubules. Mutations in either SLC7A9 or SLC3A1 gene result in cystinuria. The mutations of SLC7A9 gene have been identified mainly from Italian, Libyan Jewish, North American, and Spanish patients. In the present study, we have analyzed cystinuria cases from oriental population (mostly Japanese). Mutation analyses of SLC7A9 and SLC3A1 genes were performed on 41 cystinuria patients. The uptake of 14C-labeled cystine in COS-7 cells was measured to determine the functional properties of mutants. The protein expression and localization were examined by Western blot and confocal laser-scanning microscopy. Among 41 patients analyzed, 35 were found to possess mutations in SLC7A9. The most frequent one was a novel missense mutation P482L that affects a residue near the C-terminus end of the protein and causes severe loss of function. In MDCK II and HEK293 cells, we found that P482L protein was expressed and sorted to the plasma membrane as well as wild type. The alteration of Pro482 with amino acids with bulky side chains reduced the transport function of b(0,+)AT/BAT1. Interestingly, the mutations of SLC7A9 for Japanese cystinuria patients are different from those reported for European and American population. The results of the present study contribute toward understanding the distribution and frequency of cystinuria-related mutations of SLC7A9.

Amino Acid Substitution↗
PubMed1998

Cystinuria subtype and the risk of nephrolithiasis.

BACKGROUND: Cystinuria patients may be classified into several subgroups based on the urinary phenotype of heterozygotes. However, the relative risk for nephrolithiasis and the prevalence of SLC3A1 mutations in these subgroups are unknown. METHODS: Urinary cystine excretion, age at onset of nephrolithiasis and nature of SLC3A1 mutations were assessed prospectively in 23 cystinuria patients identified primarily through the Quebec Newborn Screening Program. Probands were classified as to cystinuria subtype on the basis of parental urinary cystine excretion. RESULTS: For classical Type I/I cystinuria, both parents excrete cystine in the normal range and probands carry two mutations of the SLC3A1 gene in nearly every case. Between ages 1 to 7 years, mean cystine excretion was high (4566 +/- 480 microns cystine/g creatinine) and exceeded the theoretic threshold for solubility on 70% of visits. Four of eight Type I/I patients began forming stones in the first decade. Type I/III patients (N = 12) excreted less cystine (1544 +/- 163 mumol cystine/g creatinine), exceeded the threshold of urinary cystine solubility less frequently (22% of visits) and had no nephrolithiasis in the first decade; one formed a stone at age 16 years. Only one SLC3A1 mutation was identified in this group. Two Type II/N cystinuria children were identified. In these families, the same level of relatively high excretion (> 600 mumol cystine/g creatinine) was noted in two or three generations, but no SLC3A1 mutations were identified. CONCLUSIONS: Classical recessive Type I/I cystinuria is genetically and phenotypically distinct from the other subtypes (Type I/III and Type II/N) identified in our population.

Adolescent↗
PubMed2000

Identification of five novel SLC3A1 (rBAT) gene mutations in Japanese cystinuria.

UNLABELLED: Identification of five novel SLC3A1 (rBAT) gene mutations in Japanese cystinuria. BACKGROUND: Cystinuria is an inheritable amino aciduria and has been classified into three subtypes: I, II, and III. One of the genes responsible for cystinuria has recently been identified as SLC3A1 or rBAT, but only type I cystinuria seems to be caused by genetic alterations in rBAT. To our knowledge, thus far 38 mutations in rBAT gene have been described. In this study, we investigated rBAT mutations in Japanese patients and compared the results with the previously reported mutations in other races. METHODS: We investigated 36 Japanese cystinuria patients by mutational analysis of rBAT gene. To identify newly mutated alleles, genomic DNA was analyzed by polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP). When an abnormal migration was observed on SSCP, a nucleotide sequence determination was performed. RESULTS: Five novel mutations were identified in five patients, three with missense mutations (L346P, I445T, C673R), one with a 1 bp deletion (1820delT), and one with a 2 bp insertion (1898insTA), and we detected three previously reported polymorphisms. Three of the mutations were homozygous, in whom parents had intermarried, and two were heterozygous for each mutations. Analysis of rBAT in family of the 1898insTA patient revealed that the patient had inherited the mutated allele from his parents. CONCLUSION: Five novel mutations in the rBAT gene have been identified in Japanese patients with cystinuria. A racial difference was not apparent in the position and frequency of the mutations.

Amino Acid Transport Systems, Basic↗
PubMed2003

Mutation analysis of SLC7A9 in cystinuria patients in Sweden.

Cystinuria is an autosomal recessive disorder characterized by increased urinary excretion of cystine and dibasic amino acids, which cause recurrent stone formation in affected individuals. Three subtypes of cystinuria have been described (type I, II, and III): type I is caused by mutations in the SLC3A1 gene, whereas nontype I (II and III) has been associated with SLC7A9 mutations. Of the 53 patients reported in our previous work, patients that showed SLC7A9 mutations in single-strand conformation polymorphism (SSCP) screening and/or either lacked or showed heterozygosity for SLC3A1 mutations were included in the present study. The entire coding region and the exon/intron boundaries of the SLC7A9 gene were analyzed by means of both SSCP and DNA sequencing in 16 patients, all but one of which were clinically diagnosed as homozygous cystinurics. Three novel SLC7A9 mutations were identified in the patient group: two missense mutations (P261L and V330M), and one single base-pair deletion (1009 delA). We also detected the previously reported A182T and nine novel polymorphisms in the patients. Mutations V330M and 1009delA occurred on different alleles in one individual, and we suggest that these mutations cause cystinuria in this patient. One patient that was homozygously mutated in the SLC3A1 gene carried the third novel mutation (P261L). We conclude that SLC3A1 is still the major disease gene among Swedish cystinuria patients, with only a minor contribution of SLC7A9 mutations as the genetic basis of cystinuria. The absence of SLC3A1 and SLC7A9 mutations in a substantial proportion of the patients implies that mutations in parts of the genes that were not analyzed may be present, as well as large deletions that escape detection by the methods used. However, our results raise the question of whether other, as yet unknown genes, may also be involved in cystinuria.

Adult↗
PubMed2003

Slc7a9-deficient mice develop cystinuria non-I and cystine urolithiasis.

Cystinuria is a common recessive disorder of renal reabsorption of cystine and dibasic amino acids that results in urolithiasis of cystine. Cystinuria is caused by defects in the amino acid transport system b0,+ (i.e. the rBAT/b0,+AT heteromeric complex). Mutations in SLC3A1, encoding rBAT, cause cystinuria type A, characterized by a silent phenotype in heterozygotes (phenotype I). Mutations in SLC7A9, encoding b0,+AT, cause cystinuria type B, in which heterozygotes in most cases hyperexcrete cystine and dibasic amino acids (phenotype non-I). To facilitate in vivo investigation of b0,+AT in cystinuria, Slc7a9 knockout mice have been generated. Expression of b0,+AT protein is completely abolished in the kidney of Slc7a9-/- mice ('Stones'). In contrast, Stones expressed significant amounts of rBAT protein, which is covalently linked to unidentified light subunit(s). Stones mice present a dramatic hyperexcretion of cystine and dibasic amino acids, while Slc7a9+/- mice show moderate but significant hyperexcretion of these amino acids (phenotype non-I). Forty-two per cent of Stones mice develop cystine calculi in the urinary system. Calculi develop during the first month of life and grow throughout the life span of the animals. Histopathology in kidney reveals typical changes for urolithiasis (tubular and pelvic dilatation, tubular necrosis, tubular hyaline droplets and chronic interstitial nephritis). The fact that some Stones mice, generated in a mixed genetic background, develop cystine calculi from an early age, while others do not develop them in their first year of life, suggests the involvement of modifier genes in the lithiasis phenotype. Thus, Stones provide a valid model of cystinuria which can be used in the study of genetic, pharmacological and environmental factors involved in cystine urolithiasis.

Amino Acid Transport Systems, Basic↗
PubMed2006

Cystinuria.

UNLABELLED: Cystinuria is an autosomal recessive disorder characterized by impaired transport of cystine, lysine, ornithine and arginine in the proximal renal tubule and in the epithelial cells of the gastrointestinal tract. Following recent progress in the genetic understanding of the disease, the traditional classification, based on the excretion of cystine and dibasic amino acids in obligate heterozygotes, may no longer be considered valid. A new classification is therefore needed: type A due to two mutations of SLC3A1 on chromosome 2, and type B due to two mutations of SLC7A9 on chromosome 19. The possibility of a third type, AB, with one mutation on each of the above-mentioned genes, is left open, but is unlikely. Clinical data show that cystinuria is more severe in males than in females in terms of stone production and early age of onset. The two types of cystinuria (A and B) have a similar outcome. A mild renal failure is present in 17% of patients. Medical treatment of this disorder is possible, but requires a composite approach: urine dilution and alkalization, and the use of drugs to form chemical bonds with the sulphydryl domains of the cystine molecule, which lower the amount of free cystine in the urine. CONCLUSION: Following new achievements in the genetics of cystinuria, a new classification has been proposed. Cystinuria is more severe in males than in females, but only rarely leads to renal insufficiency. The two types of cystinuria have a similar clinical outcome. A combined medical treatment may be effective in reducing renal stone incidence.

Comorbidity↗
PubMed1987

Cystine fluxes across the isolated jejunal epithelium in cystinuria: increased efflux permeability at the luminal membrane.

In cystinuria, renal clearance of cystine frequently exceeds creatinine clearance, suggesting net cystine secretion; and absorption of the (di)basic amino acid is impaired at the luminal membrane of the jejunal and probably also renal tubular epithelium. We studied cystine transport in vitro in jejunal biopsy specimens of eight subjects with homozygous cystinuria and in 12 controls. Cellular/medium cystine distribution ratio was reduced in cystinuria (1.36 +/- 0.36 versus 5.36 +/- 0.61, p less than 0.001). Cystine influx across the luminal membrane was normal (221 +/- 48 versus 261 +/- 79 pmol X h-1 cm-2). Measurement of transepithelial cystine fluxes showed net absorption in controls but secretion in cystinuria. Apparent permeability coefficients were close to normal in cystinuria except that the efflux permeability at the luminal membrane was significantly increased (0.839 +/- 0.22 versus 0.186 +/- 0.12 X h-1 cm-2), and, accordingly, at the luminal membrane, the influx over efflux permeability ratio was small (1.01 +/- 0.50 versus 4.95 +/- 0.80, p less than 0.001). The defect in cystine transport in cystinuria is apparently not caused by decreased influx but increased efflux of cystine (or cystine) from the cell to the lumen across the luminal membrane.

Adult↗
PubMed1975

Subacute combined degeneration of the spinal cord with cystinuria.

An 18-year-old man had noticed increasing difficulty in walking for 4 years. Examination disclosed spastic paraparesis and posterior column signs suggestive of subacute combined degeneration of the spinal cord. Urinalysis, urinary thin-layer chromatography, and intestinal biopsy disclosed typical cystinuria. Pernicious anemia and other known enteropathies were excluded. Although this could be a chance association of cystinuria and subacute combined degeneration, one other paper has reported a cystinuria patient with similar neurologic findings. A chance association between cystinuria and nonpernicious anemia subacute combined degeneration of the spinal cord should occur only once in 120 million individuals. Thus, identification of only a few more cases would suggest a pathogenetic link between the two disorders. These observations emphasize the need to search for neurologic signs in patients with cystinuria and to screen the urine of patients with spinal cord signs of obscure origin for cystinuria.

Adolescent↗
PubMed2006

Functional characterization of SLC7A9 polymorphisms assumed to influence the cystinuria phenotype.

Cystinuria is a hereditary disorder of cystine and dibasic amino acid transport across the luminal membrane of renal tubules and intestine, resulting in recurrent nephrolithiasis. While mutations in the SLC3-A1 gene cause type I cystinuria, patients with non-type I cystinuria mostly carry mutations in the SLC7A9 gene. However, there is evidence that further genetic factors cause and influence the cystinuria phenotype. We recently demonstrated that specific polymorphisms in Exons 3, 4, 5 and 6 of the SLC7A9 gene show a significant different allelic distribution between cystinuria patients and controls. To determine the role of the variants in these exons we transfected COS7 cells with expression constructs containing different haplotypes. Sequencing of cDNAs derived from the resulting SLC7A9 mRNAs did not reveal any differences in expression between the minigenes of the specific haplotypes. Our findings suggest that the variants in SLC7A9 do not influence splicing behavior. Thus, the reasons for the different allelic distribution between cystinuria patients and controls remain unclear. It is conceivable that this distribution is caused by the association of certain alleles with so far undetected mutations in the gene.

Amino Acid Transport Systems, Basic↗
PubMed1999

Linkage of type II and type III cystinuria to 19q13.1: codominant inheritance of two cystinuric alleles at 19q13.1 produces an extreme stone-forming phenotype.

Cystinuria, a renal tubule disease affecting urinary cystine excretion with or without kidney stone formation, previously was mapped to chromosome region 2p.21. Mutations in the gene SLC3A1 or NBAT, the reported candidate gene for cystinuria at 2p.21, have been demonstrated in individuals with the autosomal recessive Type I cystinuria phenotype. Recently, the Type III cystinuria phenotype was mapped to chromosome region 19q13.1. Here we report a kindred of 39 persons in two families of cystinurics, Types II and III, that support linkage to 19q13.1 and exclude 2p.21. Based on a dominant model of inheritance, two-point analysis of the entire pedigree produced a maximum lod score (Z(max)) of 3.82 at marker D19S425. Multipoint analysis yielded a lod score of 4.96 at this marker, and a resultant lod score of 5.90 using a codominant model of inheritance. Furthermore, a candidate gene interval of 8.9 cM, flanked by markers D19S225 and D19S223, was obtained using multipoint and haplotype analyses. Thus, this kindred demonstrates the linkage of Type II cystinuria to 19q13.1 and confirms the linkage of Type III cystinuria at 19q13.1 while excluding the marker D19S225 that was previously included in the critical interval.

Adolescent↗
PubMed1991

Diagnostic and genetic studies in 43 patients with classic cystinuria.

We present results for laboratory screening and diagnostic tests--cyanide-nitroprusside test, semi-quantitative thin-layer chromatography, and quantitative amino acid column chromatography--of 43 patients with classic cystinuria. We report the efficaciousness of the cyanide-nitroprusside test and of thin-layer chromatography, as compared with quantitative amino acid chromatography, for detecting heterozygotes for type II or III cystinuria. The quantitative results for aminoaciduria in 57 blood relatives in 23 families were used to categorize the index patients with classic cystinuria. By column chromatography the ranges of excretion rates (mumol/24 h per 1.73 m2 body surface area) of diagnostic amino acids in the index patients were as follows: cystine 556-54044 (normal 20-128), arginine 131-11543 (10-80), lysine 768-21848 (51-514), ornithine 185-5685 (0-80). Also by column chromatography the median values for arginine and ornithine excretion in cystine-lysinuric heterozygotes (among the 57 blood relatives) were significantly higher (P less than 0.01) than in controls but never approached the values for homozygotes. The cyanide-nitroprusside test results were positive in urine samples of 41 of 43 index patients and in 16 (51.6%) of the urine samples of 31 obligate heterozygotes with column chromatographically proven cystine-lysinuria. Thin-layer chromatography detected all of the homozygotes, all the compound heterozygotes, and 54.8% of the carriers. According to the type of aminoaciduria in their relatives, 11 patients with classic cystinuria could be classified as having classic cystinuria type I, 11 as having type II or III, and three as being compound heterozygotes. We discuss the implications of these results for correct diagnoses and for genetic studies in classic cystinuria.

Amino Acids↗