Genotype and Phenotype Analysis in Pediatric Patients with Cystinuria

Cystinuria is an inherited disorder characterized by defective renal reabsorption of cystine and dibasic amino acids leading to nephrolithiasis. This study was conducted to analyze the genotypes and phenotypes of pediatric patients with cystinuria. Eight children from Seoul National University Hospital and Asan Medical Center presenting with cystinuria from January 2003 to June 2016 were retrospectively analyzed. Mutational studies were performed by direct sequencing. Two of the 8 were male and 6 were female. The median ages at onset and diagnosis were 1.5 (range, 0.3-13.6) and 2.6 (range, 0.7-16.7) years, respectively. The median followed up was 7.7 (range, 3.4-14.0) years. Mutational analyses were performed in 7 patients and revealed biallelic SLC3A1 mutations (AA genotype) in 4 patients, a single heterozygous SLC3A1 mutation (A- genotype) in 1 patient, biallelic SLC7A9 mutations (BB genotype) in 1 patient, and a single heterozygous SLC7A9 mutation (B- genotype) in 1 patient. Two of the mutations were novel. No genotype-phenotype correlations were observed, except for earlier onset age in patients with non-AA genotypes than in patients with the AA genotype. All patients suffered from recurrent attacks of symptomatic nephrolithiasis, which lead to urologic interventions. At the last follow-up, 3 patients had a mild-to-moderate degree of renal dysfunction. This is the first study of genotypic and phenotypic analyses of patients with cystinuria in Korea.