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.
Botzenhart
Elke
E
Institute of Human Genetics, Technical University of Aachen, Pauwelsstrasse 30, D-52074 Aachen, Germany.
Vester
Udo
U
Schmidt
Christa
C
Hesse
Albrecht
A
Halber
Marc
M
Wagner
Carsten
C
Lang
Florian
F
Hoyer
Peter
P
Zerres
Klaus
K
Eggermann
Thomas
T
D000293:Adolescent; D000328:Adult; D026923:Amino Acid Transport Systems, Basic; D002352:Carrier Proteins / Q000235:genetics*; D002648:Child; D003555:Cystinuria / Q000235:genetics*; D004252:DNA Mutational Analysis; D016368:Frameshift Mutation; D005838:Genotype; D006801:Humans; D008562:Membrane Glycoproteins / Q000235:genetics*; D008875:Middle Aged; D020125:Mutation, Missense; D010641:Phenotype
D026923:Amino Acid Transport Systems, Basic; D002352:Carrier Proteins; D008562:Membrane Glycoproteins; C499489:SLC7A9 protein, human