Sindrome de Bartter: uma série de casos e revisão de literatura

Abstract

Bartter Syndrome (BS) is a rare hereditary renal tubulopathy with an autosomal recessive inheritance pattern, characterized by loss-of-function genetic variants in transporter proteins in the epithelial cells of the thick ascending limb of the loop of Henle. Clinical manifestations due to increased natriuresis, hypokalemia, and metabolic alkalosis generally appear during childhood; however, few studies describe the follow-up of these patients in adulthood. This study aimed to describe the epidemiological, clinical, laboratory, and therapeutic characteristics in a case series of adult patients with BS. We included patients over 18 years of age diagnosed with BS since childhood, undergoing outpatient nephrology treatment through the Brazilian Unified Health System (SUS). We analyzed epidemiological and clinical data, serum laboratory tests (eGFR by CKD-EPI, Na, K, Ca, P, Mg, Cl, HCO₃, 25OH-vitamin D), urinary parameters (specific gravity and protein-to-creatinine ratio - PCR), as well as therapeutic regimens. Based on established criteria, we selected 6 patients with a diagnosis of BS (66% male, mean age 25.2±10.0 years, 100% non-white, BMI 22.0±3.6 kg/m², 16% with higher education, eGFR 107±39 mL/min/1.73 m²). The main clinical manifestations were: arterial hypotension in 100%, polyuria in 66%, growth and cognitive disorders in 50%, neuromuscular abnormalities in 33%, medullary nephrocalcinosis in 33%, and deafness and history of polyhydramnios in 16%. Regarding laboratory abnormalities, all patients presented with metabolic alkalosis (HCO₃ 36.1±2.8 mmol/L), hypokalemia (3.1±0.5 mmol/L), and hypochloremia (93.7±2.2 mmol/L). Hypomagnesemia was observed in 33%, and interestingly, 66% had hypophosphatemia (3.3±0.4 mg/dL), along with mild vitamin D deficiency (25OH-vitamin D 26±12.5 ng/mL). Urine specific gravity was low (1.007±0.004), and only one patient had an eGFR <60 mL/min/1.73 m² and a PCR >0.2. All patients were on potassium chloride and magnesium supplementation; 66% were using potassium-sparing diuretics, and 66% were on non-steroidal anti-inflammatory drugs (NSAIDs). In summary, our patients with BS showed metabolic alkalosis, mild hypokalemia, and decreased urinary concentrating ability. Most were treated with NSAIDs and had preserved renal function. We highlight the presence of hypophosphatemia, which is uncommon in BS and possibly related to vitamin D deficiency. Despite the limited availability of genotypic diagnosis for BS in Brazil's public health system (SUS), clinical management based on phenotype showed a favorable prognosis regarding renal function in adulthood.