A novel compound heterozygous KCNJ1 gene mutation presenting as late-onset Bartter syndrome: Case report

RATIONALE: Bartter syndrome is an autosomal-recessive inherited disease in which patients present with hypokalemia and metabolic alkalosis. We present 1 case with Bartter syndrome, due to a novel compound heterozygous mutation in the KCNJ1 gene encoding the ATP-sensitive inward rectifier potassium channel in the thick ascending limb of the loop of Henle. PATIENT CONCERNS: A patient was admitted to our hospital because of weakness, polyuria, and polydipsia. At presentation to our hospital, the female Chinese patient was 34 years old and her physical examination was normal. Laboratory studies revealed hypokalemia, metabolic alkalosis, hypercalciuria, hyperparathyroidemia, and hyper-reninemia. In addition, urinary potassium was obviously higher. Computer tomography scan confirmed the patient had the bilateral medullary nephrocalcinosis. DIAGNOSIS: Blood samples were received from the patient and her parents, and deoxyribonucleic acid was extracted. The genetic analysis of SLC12A1, SLC12A3, KCNJ1, CLCNKB, BSND, and CASR was performed. The compound heterozygous KCNJ1 gene mutation was validated using conventional Sanger sequencing methods. INTERVENTIONS: The patient was treated with potassium supplementation. Her blood and urine chemistries improved over the next week. Serum potassium normalized with improvement in polyuria and polydipsia over the next month. OUTCOMES: Our patient was compound heterozygous for Thr234Ile and Thr71Met in the KCNJ1 gene. The c.701C>T variant predicted a change from a threonine codon to an isoleucine codon (p.Thr234Ile). The c.212C>T variant predicted a change from a threonine codon to a methionine codon (p.Thr71Met). The unaffected mother was heterozygous for the Thr234Ile mutation, whereas unaffected father was heterozygous for the Thr71Met mutation. LESSONS: The phenotypes of the patient were similar to other patients with Bartter syndrome. The phenotypes of the patient could eventually be explained by the presence of the novel compound heterozygous p.Thr234Ile/p.Thr71Met variants in the KCNJ1 gene.