Gardos channelopathies: novel insights into KCNN4 mutations and their clinical impact.

Gardos channelopathies are rare hereditary hemolytic anaemias caused by mutations in the KCNN4 gene, which encodes the calcium-activated potassium channel (KCa3.1) in red blood cells. In this study, we report three unrelated Indian patients with unexplained chronic hemolytic anaemia. Whole exome sequencing revealed distinct KCNN4 mutations: a homozygous c.5G > A mutation (p.Gly2Asp) in Case I, a compound heterozygous condition with the Hb Nottingham mutation (HBB: c.296T > G) and a splice-site mutation in KCNN4 (c.931-1G > C) in Case II, and homozygous c.541A > T mutation (p.Ser181Cys) in Case III. All three patients presented with chronic anaemia, indirect hyperbilirubinemia, reticulocytosis, and recurrent blood transfusions. Red cell enzyme studies (G6PD, PK, GPI) showed normal activities, and flow cytometry-based EMA binding was normal. Haemoglobin electrophoresis by HPLC was normal, except in Case II, and tested positive for unstable haemoglobin using a heat instability test. Flow cytometry revealed significantly elevated intracellular calcium levels and reactive oxygen species (ROS) in all cases, indicating oxidative stress under osmotic stress. In Case III, a Percoll density gradient assay demonstrated dehydrated erythrocytes, supporting the diagnosis. This study expands the mutation spectrum of Genetic diagnosis using NGS, which is essential for appropriate clinical management and genetic counselling in unexplained cases of hemolytic anaemia. Elevated intracellular calcium levels play a key role in hemolysis, suggesting that calcium-modulating therapies could aldehyleviate symptoms.