Polymorphism in the PBX1 gene is related to cystinuria in Brazilian families.

The aim of our study was to determine regions of loss of heterozygosity, copy number variation analysis, and single nucleotide polymorphisms (SNPs) in Brazilian patients with cystinuria. A linkage study was performed using DNA samples from six patients with cystinuria and six healthy individuals. Genotyping was done with the Genome-Wide Human SNP 6.0 arrays (Affymetrix, Inc., Santa Clara, CA, USA). For validation, SNPs were genotyped using a TaqMan® SNP Genotyping Assay Kit. The homozygote polymorphic genotype of SNP rs17383719 in the gene PBX1 was more frequent (P = 0.015) in cystinuric patients. The presence of the polymorphic allele for this SNP increased the chance of cystinuria by 3.0-fold (P = 0.036). Pre-B-cell leukaemia transcription factor 1 (PBX1) was overexpressed 3.3-fold in patients with cystinuria. However, when we compared the gene expression findings with the genotyping, patients with a polymorphic homozygote genotype had underexpression of PBX1, while patients with a heterozygote or wild-type homozygote genotype had overexpression of PBX1. There is a 3-fold increase in the risk of the development of cystinuria among individuals with this particular SNP in the PBX1 gene. We postulate that the presence of this SNP alters the expression of PBX1, thus affecting the renal absorption of cystine and other amino acids, predisposing to nephrolithiasis.

Feline cystinuria caused by a missense mutation in the SLC3A1 gene.

BACKGROUND: Cystinuria is an inherited metabolic disease that is relatively common in dogs, but rare in cats and is characterized by defective amino acid reabsorption, leading to cystine urolithiasis. OBJECTIVES: The aim of this study was to report on a mutation in a cystinuric cat. ANIMALS: A male domestic shorthair (DSH) cat with cystine calculi, 11 control cats from Wyoming, and 54 DSH and purebred control cats from elsewhere in the United States. METHODS: Exons of the SLC3A1 gene were sequenced from genomic DNA of the cystinuric cat and a healthy cat. Genetic screening for the discovered polymorphisms was conducted on all cats. RESULTS: A DSH cat showed stranguria beginning at 2 months of age, and cystine calculi were removed at 4 months of age. The cat was euthanized at 6 months of age because of neurological signs possibly related to arginine deficiency. Twenty-five SLC3A1 polymorphisms were observed in the sequenced cats when compared to the feline reference sequence. The cystinuric cat was homozygous for 5 exonic and 8 noncoding SLC3A1 polymorphisms, and 1 of them was a unique missense mutation (c.1342C>T). This mutation results in a deleterious amino acid substitution (p.Arg448Trp) of a highly conserved arginine residue in the rBAT protein encoded by the SLC3A1 gene. This mutation was found previously in cystinuric human patients, but was not seen in any other tested cats. CONCLUSIONS AND CLINICAL IMPORTANCE: This study is the first report of an SLC3A1 mutation causing cystinuria in a cat, and could be used to characterize other cystinuric cats at the molecular level.

SLC3A1 and SLC7A9 mutations in autosomal recessive or dominant canine cystinuria: a new classification system.

BACKGROUND: Cystinuria, one of the first recognized inborn errors of metabolism, has been reported in many dog breeds. HYPOTHESIS/OBJECTIVES: To determine urinary cystine concentrations, inheritance, and mutations in the SLC3A1 and SLC7A9 genes associated with cystinuria in 3 breeds. ANIMALS: Mixed and purebred Labrador Retrievers (n = 6), Australian Cattle Dogs (6), Miniature Pinschers (4), and 1 mixed breed dog with cystine urolithiasis, relatives and control dogs. METHODS: Urinary cystinuria and aminoaciduria was assessed and exons of the SLC3A1 and SLC7A9 genes were sequenced from genomic DNA. RESULTS: In each breed, male and female dogs, independent of neuter status, were found to form calculi. A frameshift mutation in SLC3A1 (c.350delG) resulting in a premature stop codon was identified in autosomal-recessive (AR) cystinuria in Labrador Retrievers and mixed breed dogs. A 6 bp deletion (c.1095_1100del) removing 2 threonines in SLC3A1 was found in autosomal-dominant (AD) cystinuria with a more severe phenotype in homozygous than in heterozygous Australian Cattle Dogs. A missense mutation in SLC7A9 (c.964G>A) was discovered in AD cystinuria in Miniature Pinschers with only heterozygous affected dogs observed to date. Breed-specific DNA tests were developed, but the prevalence of each mutation remains unknown. CONCLUSIONS AND CLINICAL IMPORTANCE: These studies describe the first AD inheritance and the first putative SLC7A9 mutation to cause cystinuria in dogs and expand our understanding of this phenotypically and genetically heterogeneous disease, leading to a new classification system for canine cystinuria and better therapeutic management and genetic control in these breeds.

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.

Frequency of cystinuria among stone-forming patients in region of Brazil.

Occasional urine samples from 200 stone-forming individuals were screened by the successive application of the cyanide-nitroprusside test, qualitative-semiquantitative thin-layer amino acid chromatography, and quantitative ion-exchange amino acid analysis to determine the frequency of cystinuria in this region of Brazil. Only 1 homozygous cystinuria patient was detected, a lower frequency than 1 to 6 per cent reported in other countries. The patient's family showed a I/I genotype. Since 6 heterozygotes for cystinuria +/II or +/III were also detected, the relative rarity of homozygotes in this sample supports the view of the relatively greater contribution of etiologic factors other than gene frequency to stone formation. The importance of diagnosis based on quantitative amino acid analysis is emphasized because of the different therapeutic and prognostic implications of the homozygote and heterozygote forms of the disease.

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.

[Cystinolysinuric lithiasis]. / Litiásis cistinolisinúrica.

Cystinuria is a disease characterized by the excessive elimination of cystine and of dibasic amino acids (lysine, arginine, and ornithine) through urine of homozygotes. This study included 6 children complaining of abdominal pain with or without hematuria. The existence of renal radio-opaque lithiasis was confirmed in 5 of them and in the sixth, it was vesical. The clinical and analytic data were practically normal with the exception of the qualitative test of the amino acid urinary excretion that showed increase in urinary excretion of cystine. Likewise, percentages of tubular reabsorption were pathological in all the patients showing values between 35.4% and 74%. The diagnosis of systini-lysinuric lithiasis was established through amino acid excretion study in the six patients which was below normal; it fluctuated between 36% and 74%. Lysine, together with cystine, was the most frequently affected.