Autori: Paola Imbrici (1), Dalila Sahbani (2), Elena Conte (3), Silvana Tedeschi (4), Bice Strumbo (5), Elisa Benetti (6), Giovanni Montini (7), Diana Conte (8), Antonella Liantonio (9)
Affiliazioni: (1) Department of Pharmacy-Drug Sciences, University of Bari “Aldo Moro”, Bari, Italy (2) Department of Pharmacy-Drug Sciences, University of Bari “Aldo Moro”, Bari, Italy (3) Department of Pharmacy-Drug Sciences, University of Bari “Aldo Moro”, Bari, Italy (4) Laboratory of Medical Genetics, Fondazione IRCCS Ca’ Granda Ospedale Maggiore Policlinico, Milan, Italy (5) Laboratory of Medical Genetics, Fondazione IRCCS Ca’ Granda Ospedale Maggiore Policlinico, Milan, Italy (6) Nephrology, Dialysis and Transplant Unit, Department of Women’s and Children’s Health, University-Hospital of Padova, Padova, Italy (7) Pediatric Nephrology, Dialysis, and Transplant Unit, Fondazione IRCCS Ca’ Granda Ospedale Maggiore Policlinico, Milan, and Department of Clinical Sciences and Community Health, University of Milan, Milan, Italy (8) Department of Pharmacy-Drug Sciences, University of Bari “Aldo Moro”, Bari, Italy (9) Department of Pharmacy-Drug Sciences, University of Bari “Aldo Moro”, Bari, Italy
Type III and IV BS Bartter syndromes (BS) are rare diseases characterized by massive salt and fluid loss, increased levels of renin and aldosterone, caused by loss-of-function mutations in the CLCNKB and BSND genes coding for ClC-Kb chloride channels and accessory subunit barttin (Simon et al., 1997; Birkenhäger et al., 2001). ClC-K channels are expressed in the Henle’s loop, distal convoluted tubule and cortical collecting ducts of the kidney and contribute to chloride absorption and urine concentration (Fahlke and Fischer, 2010). In collaboration with nephrology and genetics laboratory in Milano and Padova, we identified two new mutations in CLCNKB in two children affected by BS. The homozygous G289R mutation is associated with growth delay, polydipsia and polyuria. The mutation G167V is compound heterozygous with the deletion of CLCNKB and presents with more severe phenotype. In order to define the role of G167V and G289R in determining BS, WT and mutant channels were co-expressed with barttin in HEK293 cells and chloride currents were recorded by patch-clamp. G167V channels show a drastic current reduction compared to ClC-Kb WT (0.14 nA vs 1.09 nA at +60mV), while G289R channels show a little current decrease compared to WT (0.8 nA vs 1.09 nA). These results suggest that the degree of chloride current reduction correlates with the severity of BS phenotype, confirming a genotype-phenotype correlation.