Bartter syndrome representing digenic-based salt-losing tubulopathies presumably accelerated by renal insufficiency

Bartter syndrome and Gitelman syndrome (GS) are autosomal recessive disorders usually caused by homozygous or compound heterozygous mutations in causative genes. In some patients, these two syndromes cannot be discriminated based on clinical features or mutation type; thus, a single disease concept, salt-losing tubulopathies (SLTs), has been used instead. Despite the existence of several SLT causative genes, cases of digenic heterozygous mutations in two different genes are extremely rare. Here, we report the case of a 36-year-old woman with renal insufficiency and hypokalemia caused by an SLT. To evaluate the SLT phenotype, we performed next-generation sequencing (NGS) with a gene panel including SLC12A3, SLC12A1, CLCNKB, and CLCNKA as well as laboratory examinations and diuretic loading tests. The results of the diuretic loading tests were consistent with a GS phenotype, while the NGS results showed that the patient had heterozygous mutations in SLC12A1 and CLCNKB. Both genes have been associated with BS, suggesting that the SLT was caused by digenic heterozygous mutations in two different genes. To date, only a few SLT cases caused by digenic heterozygous mutations in two different genes have been reported. The digenic SLT phenotype in the patient was presumably accelerated by moderate renal insufficiency.