title: Identification of compound heterozygous KCNJ1 mutations (encoding ROMK) in a kindred with Bartter's syndrome and a functional analysis of their pathogenicity.
abstract: A multiplex family was identified with biochemical and clinical features suggestive of Bartter's syndrome (BS). The eldest sibling presented with developmental delay and rickets at 4 years of age with evidence of hypercalciuria and hypokalemia. The second sibling presented at 1 year of age with urinary tract infections, polyuria, and polydipsia. The third child was born after a premature delivery with a history of polyhydramnios and neonatal hypocalcemia. Following corrective treatment she also developed hypercalciuria and a hypokalemic metabolic alkalosis. There was evidence of secondary hyperreninemia and hyperaldosteronism in all three siblings consistent with BS. Known BS genes were screened and functional assays of ROMK (alias KCNJ1, Kir1.1) were carried out in Xenopus oocytes. We detected compound heterozygous missense changes in KCNJ1, encoding the potassium channel ROMK. The S219R/L220F mutation was segregated from father and mother, respectively. In silico modeling of the missense mutations suggested deleterious changes. Studies in Xenopus oocytes revealed that both S219R and L220F had a deleterious effect on ROMK-mediated potassium currents. Coinjection to mimic the compound heterozygosity produced a synergistic decrease in channel function and revealed a loss of PKA-dependent stabilization of PIP2 binding. In conclusion, in a multiplex family with BS, we identified compound heterozygous mutations in KCNJ1. Functional studies of ROMK confirmed the pathogenicity of these mutations and defined the mechanism of channel dysfunction.
authors.affiliation: Institute of Genetic Medicine, Newcastle University Central Parkway, Newcastle upon Tyne, NE1 3BZ, U.K. ; Newcastle Hospitals NHS Foundation Trust Newcastle upon Tyne, NE7 7DN, U.K.
authors.forename: Shalabh
authors.initials: S
authors.lastname: Srivastava
authors.affiliation: Department of Physiology, University of Maryland Medical School 655 W Baltimore Street, Baltimore, 21201, Maryland.
authors.forename: Dimin
authors.initials: D
authors.lastname: Li
authors.affiliation: Institute of Genetic Medicine, Newcastle University Central Parkway, Newcastle upon Tyne, NE1 3BZ, U.K.
authors.forename: Noel
authors.initials: N
authors.lastname: Edwards
authors.affiliation: Institute of Genetic Medicine, Newcastle University Central Parkway, Newcastle upon Tyne, NE1 3BZ, U.K.
authors.forename: Ann-M
authors.initials: AM
authors.lastname: Hynes
authors.affiliation: Newcastle Hospitals NHS Foundation Trust Newcastle upon Tyne, NE7 7DN, U.K.
authors.forename: Katrina
authors.initials: K
authors.lastname: Wood
authors.affiliation: Institute of Genetic Medicine, Newcastle University Central Parkway, Newcastle upon Tyne, NE1 3BZ, U.K. ; Department of Genetics, King Faisal Specialist Hospital and Research Centre Riyadh, Saudi Arabia.
authors.forename: Mohamed
authors.initials: M
authors.lastname: Al-Hamed
authors.affiliation: South Tees NHS Foundation Trust Middlesbrough, TS4 3BW, U.K.
authors.forename: Anna C
authors.initials: AC
authors.lastname: Wroe
authors.affiliation: South Tees NHS Foundation Trust Middlesbrough, TS4 3BW, U.K.
authors.forename: David
authors.initials: D
authors.lastname: Reaich
authors.affiliation: UCL Centre for Nephrology, Royal Free Hospital Pond Street, London, NW3 2QG, U.K.
authors.forename: Shabbir H
authors.initials: SH
authors.lastname: Moochhala
authors.affiliation: Department of Physiology, University of Maryland Medical School 655 W Baltimore Street, Baltimore, 21201, Maryland.
authors.forename: Paul A
authors.initials: PA
authors.lastname: Welling
authors.affiliation: Institute of Genetic Medicine, Newcastle University Central Parkway, Newcastle upon Tyne, NE1 3BZ, U.K. ; Newcastle Hospitals NHS Foundation Trust Newcastle upon Tyne, NE7 7DN, U.K.
authors.forename: John A
authors.initials: JA
authors.lastname: Sayer
keywords: Hypercalciuria; KCNJ1; Kir1.1; ROMK; hypokalemia; missense mutation; potassium; salt wasting