A Case of Cystinuria With Compound Heterozygous Mutations Both in <i>SLC3A1</i> and <i>SLC7A9</i> Genes

Cystinuria is an autosomal recessively inherited genetic disorder, and is typically classified into type A, caused by mutations in <i>SLC3A1</i>, or type B, caused by mutations in <i>SLC7A9</i>. While the predominance of the genotypes varies among countries, due to lack of a large scale cohort, the characterization of mutations in <i>SLC3A1</i> or <i>SLC7A9</i> is still limited in East Asia. A 61-year-old male patient admitted to the department of nephrology, with a chief complaint of fever, chillness and left flank pain for a week. The patient had a past history of recurrent urolithiasis, with a frequency of at least 1 to 2 times a year. Computed tomography visualized 1 cm-sized stone at distal ureter, which was removed by retrograde ureteroscopy. The stone analysis documented 100% of cystine, indicating an underlying genetic disorder, cystinuria. Whole genome sequencing from peripheral blood unveiled 3 heterozygous missense mutations in coding exons of <i>SLC3A1</i> gene, and 2 heterozygous missense mutations in coding exons of <i>SLC7A9</i> gene. We here report a case of cystinuria with compound heterozygous mutations both in <i>SLC3A1</i> and <i>SLC7A9</i> genes, with a total of 5 mutant alleles in a patient.