Cystinuria caused by mutations in rBAT, a gene involved in the transport of cystine.

Cystinuria is a classic heritable aminoaciduria that involves the defective transepithelial transport of cystine and dibasic amino acids in the kidney and intestine. Six missense mutations in the human rBAT gene, which is involved in high-affinity transport of cystine and dibasic amino acids in kidney and intestine, segregate with cystinuria. These mutations account for 30% of the cystinuria chromosomes studied. Homozygosity for the most common mutation (M467T) was detected in three cystinuric siblings. Mutation M467T nearly abolished the amino acid transport activity induced by rBAT in Xenopus oocytes. These results establish rBAT as a cystinuria gene.

Non-type I cystinuria caused by mutations in SLC7A9, encoding a subunit (bo,+AT) of rBAT.

Cystinuria (MIM 220100) is a common recessive disorder of renal reabsorption of cystine and dibasic amino acids. Mutations in SLC3A1, encoding rBAT, cause cystinuria type I (ref. 1), but not other types of cystinuria (ref. 2). A gene whose mutation causes non-type I cystinuria has been mapped by linkage analysis to 19q12-13.1 (Refs 3,4). We have identified a new transcript, encoding a protein (bo, +AT, for bo,+ amino acid transporter) belonging to a family of light subunits of amino acid transporters, expressed in kidney, liver, small intestine and placenta, and localized its gene (SLC7A9) to the non-type I cystinuria 19q locus. Co-transfection of bo,+AT and rBAT brings the latter to the plasma membrane, and results in the uptake of L-arginine in COS cells. We have found SLC7A9 mutations in Libyan-Jews, North American, Italian and Spanish non-type I cystinuria patients. The Libyan Jewish patients are homozygous for a founder missense mutation (V170M) that abolishes b o,+AT amino-acid uptake activity when co-transfected with rBAT in COS cells. We identified four missense mutations (G105R, A182T, G195R and G295R) and two frameshift (520insT and 596delTG) mutations in other patients. Our data establish that mutations in SLC7A9 cause non-type I cystinuria, and suggest that bo,+AT is the light subunit of rBAT.

Entering into 2.0 cystinuric management with a medical digital tool to monitor urine pH: a prospective, randomized study.

BACKGROUND AND OBJECTIVES: Individuals with cystinuria can experiment recurrent lithiasis events due to the relative insolubility of cystine at physiological urine pH, resulting in renal function decline. The Lit-Control® pH Meter is a medical device that accurately allows urine pH self-monitoring. The main objective of this study was to compare the usability of the Lit-Control® pH Meter with the reactive strips for self-monitoring of urinary pH at home by patients with cystinuria, and their overall satisfaction with each tool. PATIENTS AND METHODS: We included 28 patients (9 females and 19 males, age 19-76 years), who were randomly assigned to monitor their urine pH with reactive strips (n = 17) or the Lit-Control® pH-meter (n = 11). RESULTS: After six months of use, the satisfaction with the two methods was similarly high, but the patients rated (0-10 scale) the pH meter better in terms of ease of learning (mean ±â€¯SD, 8.11 ±â€¯0.60 vs. 7.06 ±â€¯1.18; P = 0.038), ease to prepare (8.22 ±â€¯0.67 vs. 7.25 ±â€¯1.18; P = 0.034), and ease of use (8.22 ±â€¯0.67 vs. 7.25 ±â€¯1.39; P = 0.062). Overall, patients did not reach the alkalinization goals (pH between 7.0 and 8.0). CONCLUSIONS: The Lit-Control® pH Meter demonstrated to be an easy-to-use device that can facilitate urinary pH control by cystinuric patients. A prospective study is warranted to assess the correlation between urine pH monitoring, a treat to target approach, and the recurrence of cystine stones.

New insights into cystinuria: 40 new mutations, genotype-phenotype correlation, and digenic inheritance causing partial phenotype.

OBJECTIVE: To clarify the genotype-phenotype correlation and elucidate the role of digenic inheritance in cystinuria. METHODS: 164 probands from the International Cystinuria Consortium were screened for mutations in SLC3A1 (type A) and SLC7A9 (type B) and classified on the basis of urine excretion of cystine and dibasic amino acids by obligate heterozygotes into 37 type I (silent heterozygotes), 46 type non-I (hyperexcretor heterozygotes), 14 mixed, and 67 untyped probands. RESULTS: Mutations were identified in 97% of the probands, representing 282 alleles (86.8%). Forty new mutations were identified: 24 in SLC3A1 and 16 in SLC7A9. Type A heterozygotes showed phenotype I, but mutation DupE5-E9 showed phenotype non-I in some heterozygotes. Type B heterozygotes showed phenotype non-I, with the exception of 10 type B mutations which showed phenotype I in some heterozygotes. Thus most type I probands carried type A mutations and all type non-I probands carried type B mutations. Types B and A mutations contributed to mixed type, BB being the most representative genotype. Two mixed cystinuria families transmitted mutations in both genes: double compound heterozygotes (type AB) had greater aminoaciduria than single heterozygotes in their family. CONCLUSIONS: Digenic inheritance is an exception (two of 164 families), with a limited contribution to the aminoaciduria values (partial phenotype) in cystinuria. Further mutational analysis could focus on one of the two genes (SLC3A1 preferentially for type I and SLC7A9 for type non-I probands), while for mixed probands analysis of both genes might be required, with priority given to SLC7A9.

[Isotopic study with double phase 99mTc-sestamibi in the localization of parathyroid gland lesions]. / Exploración isotópica con 99mTc-sestamibi en doble fase en la localización de lesiones de las glándulas paratiroides.

BACKGROUND: The use of preoperative imaging in patients with hyperparathyroidism remains controversial. The aim of this study is to assess the usefulness of the double-phase 99mTc-sestamibi scintigraphy in the diagnosis of abnormal parathyroid glands in patients with primary hyperparathyroidism. PATIENTS AND METHODS: We studied 60 patients presenting with primary hyperparathyroidism who were referred to surgery; four of them had been unsuccessfully operated. 99mTc-sestamibi scintigraphy were performed in all patients previously to surgery. Scintigraphic technique: planar imaging of the neck and thorax was done in the anterior view at 15 and 150 min postinjection of 740 MBq (20 mCi) of 99mTc-sestamibi. RESULTS: Surgery found 57 adenomas (2.59 [SD, 5.84] g; range 0.160-40), 6 hyperplastic glands (0.34 [SD, 0.26] g) and one carcinoma 8.2 g. The 99mTc-sestamibi was able to localize correctly 60 out of 64 lesions (55/57 adenomas, 4/6 hyperplastic glands and 1/1 carcinoma) (global sensitivity of 94%, adenomas sensitivity of 96%, positive predictive value of 97% and specificity of 98%). Isotopic imaging detected the abnormal tissue in all patients who had undergone unsuccessful previous surgery. PTH (4 [SD, 1.51] pmol/l) and calcium postoperative serum levels (2.13 [SD, 0.22] mmol/l) showed curation of all patients. CONCLUSION: Double phase parathyroid scintigraphy with 99mTc-sestamibi is the method of choice to localize abnormal parathyroid glands.

[Advancements in the genetics of cystinuria]. / Progrès dans la génétique de la cystinurie.

Cystinuria is an amino acid disease due to a defect of intestinal and renal tubular transport of cystine and various basic amino acids (lysine, arginine and ornithine). The disease is transmitted horizontally according to an autosomal recessive pattern. The overall prevalence is one per 7,000 live births. It is the commonest hereditary disease affecting amino acid transport (MIM 220100). This disease is characterized by excessive urinary excretion of cystine and basic amino acids. From a clinical point of view, almost 50% of homozygotes will develop cystine renal stones with urinary tract infection, renal colic, partial or total obstruction of the urinary tract and possibly loss of renal function.

[A new approach to urinary stone analysis according to the combination of the components: experience with 7949 cases]. / Un nuevo enfoque en el análisis de la litiasis urinaria en función de la combinación de sus componentes: experiencia con 7.949 casos.

OBJECTIVE: To evaluate a new approach to urinary stone analysis according to the combination of the components. MATERIALS AND METHODS: A total of 7949 stones were analysed and their main components and combinations of components were classified according to gender and age. Statistical analysis was performed using the chi-square test. RESULTS: Calcium oxalate monohydrate (COM) was the most frequent component in both males (39%) and females (37.4%), followed by calcium oxalate dihydrate (COD) (28%) and uric acid (URI) (14.6%) in males and by phosphate (PHO) (22.2%) and COD (19.6%) in females (p=0.0001). In young people, COD and PHO were the most frequent components in males and females respectively (p=0.0001). In older patients, COM and URI (in that order) were the most frequent components in both genders (p=0.0001). COM is oxalate dependent and is related to diets with a high oxalate content and low water intake. The progressive increase in URI with age is related mainly to overweight and metabolic syndrome. Regarding the combinations of components, the most frequent were COM (26.3%), COD+Apatite (APA) (15.5%), URI (10%) and COM+COD (7.5%) (p=0.0001). CONCLUSIONS: This study reports not only the composition of stones but also the main combinations of components according to age and gender. The results prove that stone composition is related to the changes in dietary habits and life-style that occur over a lifetime, and the morphological structure of stones is indicative of the aetiopathogenic mechanisms.

[Cystinuria and cystine kidney lithiasis. Diagnosis and therapeutic approach]. / Cistinuria y litiasis renal de cistina. Estudio y enfoque terapéutico.

OBJECTIVE: Cystine renal stone is the only clinical consequence of cystinuria, an autosomal recessive hereditary disease that affects an average of 1 out of 7,000 newborns, and whose geographical distribution varies significantly. The diagnosis and treatment of this condition is reviewed in the light of the advances in genetics and molecular biology. METHODS: The evolution of current knowledge about this disease is reviewed. RESULTS/CONCLUSIONS: The advances over the last 8 years have led to the characterization, at the present time, of two genes responsible for this disease, which demonstrates its polygenic origin. By phenotype, cystinuria can be classified into two types: type 1 and non-type 1. Both types show genetic and biochemical, but not clinical differences. From the therapeutic viewpoint, the main objective is to eliminate existing calculi and, above all, prevent recurrence by acting on the pathophysiologic mechanisms of renal cystine. Experience shows that despite the correct use of our current therapeutic armamentarium and the application of the general guidelines discussed in this paper, some cystinuric patients still maintain an important stone-forming activity. Patient clinical evaluation and a genetic study of both patient and family will be decisive for phenotyping.

[Analysis and clinical course of residual lithiasis after shock wave renal treatment]. / Análisis y evolución de la litiasis residual tras la aplicación renal de ondas de choque.

OBJECTIVE: Although residual lithiasis after the application of shock waves is a situation that coexists with the procedure, in some cases it can be considered to be a failure of ESWL. The natural history and outcome of 244 cases of residual renal stone followed over a 5-year period are analyzed, and the approach based on a pre-established classification is discussed. METHODS: Of 1,407 patients treated by ESWL for renal lithiasis during 1995, 244 cases with a renal calculus larger than 3 mm were followed for a period of 5 years after treatment and evaluated by clinical, radiological, ultrasound and analytical methods. RESULTS: At 3 months post-ESWL, 1,013 cases (72%) were completely stone-free and 394 (28%) showed residual stone; of these, 244 (62%) had residual stone fragments greater than 3 mm. At 5 years, 190 (78%) remained stable and the remaining 54 (22%) showed stone regrowth that warranted additional treatments: 52 ESWL, 1 PNL and 1 partial nephrectomy. Despite the retreatments, only 42% became completely stone-free. CONCLUSIONS: A classification of residual renal stone can be established based on the data obtained to orient the approach in each case, although the frequency of residual stone can be reduced by the appropriate indication of ESWL. Once a renal stone has formed retreatments with ESWL cannot ensure complete elimination of the stone.

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.

Triglyceride-rich lipoprotein abnormalities in CAPD-treated patients.

In the present study intermediate-density lipoproteins (IDL) and very-low-density lipoproteins (VLDL) composition, structure, and mass were analysed in fasting uraemic patients on continuous ambulatory peritoneal dialysis (CAPD) (n = 12) and on haemodialysis (HD) (n = 15), and in 15 healthy volunteers. All the groups were matched for sex, age, and time on dialysis. Both groups of patients had elevated very-low-density lipoprotein levels, CAPD patients four and HD group three times that of control. We found a fourfold and a twofold increase in the concentration of IDL cholesterol in the CAPD and HD group respectively when they were compared with the control group. Both groups of patients present an increased VLDL mass. The CAPD group showed a four-fold increase in IDL mass compared with the control group, which indicated a preponderance of large size and suggested that defective IDL clearance was involved. The IDL composition of the CAPD patients was significantly different from that of the HD patients: a twofold increase in IDL mass was observed in the CAPD patients if compared with HD patients. We report new data concerning the metabolism of triglyceride-rich lipoproteins in CAPD treated patients, which confirm the adverse effect of CAPD on serum lipids.

Molecular genetics of cystinuria: identification of four new mutations and seven polymorphisms, and evidence for genetic heterogeneity.

A cystinuria disease gene (rBAT) has been recently identified, and some mutations causing the disease have been described. The frequency of these mutations has been investigated in a large sample of 51 Italian and Spanish cystinuric patients. In addition, to identify new mutated alleles, genomic DNA has been analyzed by an accurate and sensitive method able to detect nucleotide changes. Because of the lack of information available on the genomic structure of rBAT gene, the study was carried out using the sequence data so far obtained by us. More than 70% of the entire coding sequence and 8 intron-exon boundaries have been analyzed. Four new mutations and seven intragenic polymorphisms have been detected. All mutations so far identified in rBAT belong only to cystinuria type I alleles, accounting for approximately 44% of all type I cystinuric chromosomes. Mutation M467T is the most common mutated allele in the Italian and Spanish populations. After analysis of 70% of the rBAT coding region, we have detected normal sequences in cystinuria type II and type III chromosomes. The presence of rBAT mutated alleles only in type I chromosomes of homozygous (type I/I) and heterozygous (type I/III) patients provides evidence for genetic heterogeneity where rBAT would be responsible only for type I cystinuria and suggests a complementation mechanism to explain the intermediate type I/type III phenotype.

Cystinuria type I: identification of eight new mutations in SLC3A1.

BACKGROUND: Cystinuria is a heritable disorder of amino acid transport characterized by the defective transport of cystine and the dibasic amino acids through the brush border epithelial cells of the renal tubule and intestine tract. Three types of cystinuria (I, II, and III) have been described based on the urinary excretion of cystine and dibasic amino acids in obligate heterozygotes. The SLC3A1 gene coding for an amino acid transporter named rBAT is responsible for type I cystinuria, whereas the SLC7A9 gene coding for a subunit (b0,+AT) of rBAT is involved in determining non-type I (types II and III) cystinuria. METHODS: The SLC3A1 gene sequence was investigated in a sample of seven type I/type I, three type I/non-type I, six type I/untyped, and four untyped unrelated cystinuric patients by RNA single-strand conformation polymorphism (RNA-SSCP). RESULTS: Eight new point mutations (S168X, 765+1G>T, 766-2A>G, R452Q, Y461X, S547W, L564F, and C673W) and seven previously reported mutations were detected. These new mutations increase the number of mutated alleles so far characterized in SLC3A1 to 62. CONCLUSIONS: We have found SLC3A1 mutations in 0.739 of the type I chromosomes studied. The relatively high proportion of uncharacterized type I chromosomes suggests either that there may be mutations not yet found in SLC3A1 or that many of the assigned type I chromosomes in mixed type I/non-type I patients may have mutations in SLC7A9. If the hypothesis is excluded in the future, we believe that a third gene may be involved in cystinuria.