Functional heterogeneity of ROMK mutations linked to hyperprostaglandin E syndrome

• Published in: Kidney international Vol. 59; no. 5; pp. 1803 - 1811
• Main Authors: Jeck, Nikola, Derst, Christian, Wischmeyer, Erhard, Ott, Henning, Weber, Stefanie, Rudin, Christoph, Seyberth, Hannsjörg W., Daut, Jürgen, Karschin, Andreas, Konrad, Martin
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01-05-2001; Elsevier Limited
• Subjects: Animals; antenatal Bartter syndrome; Bartter Syndrome - genetics; Bartter Syndrome - metabolism; Base Sequence; channelopathy; Child, Preschool; Codon, Nonsense; DNA Primers - genetics; Exons; Female; Genetic Linkage; Humans; In Vitro Techniques; Infant; K+ channel; KCNJ1 gene; Male; Mutation; Mutation, Missense; Oocytes - metabolism; Pedigree; Potassium Channels - chemistry; Potassium Channels - genetics; Potassium Channels - metabolism; Potassium Channels, Inwardly Rectifying; Prostaglandins E - metabolism; renal fluid wasting; salt reabsorption; Sequence Deletion; Syndrome; Transfection; Xenopus; K+ channel; salt reabsorption; renal fluid wasting; antenatal Bartter syndrome; channelopathy; KCNJ1 gene
• ISSN: 0085-2538; 1523-1755
• DOI: 10.1046/j.1523-1755.2001.0590051803.x

Functional heterogeneity of ROMK mutations linked to hyperprostaglandin E syndrome.
The renal K+ channel ROMK (Kir1.1) controls salt reabsorption in the kidney. Loss-of-function mutations in this channel cause hyperprostaglandin E syndrome/antenatal Bartter syndrome (HPS/aBS), which is characterized by severe renal salt and fluid wasting.
We investigated 10 HPS/aBS patients for mutations in the ROMK gene by single-strand conformation polymorphism analysis (SSCA) and direct sequencing. To assess the functional consequences, Ba2+-sensitive K+ currents were measured in five mutants of the core region as well as one mutant with truncated C-terminus, using the two-electrode voltage-clamp technique after an injection of mutant cRNA into Xenopus oocytes.
Three novel ROMK mutations were identified together with six mutations described previously. The mutations were categorized into three groups: (1) amino acid exchanges in the core region (M1-H5-M2), (2) truncation at the cytosolic C-terminus, and (3) deletions of putative promoter elements. While the core mutations W99C, N124K, and I142T led to significantly reduced macroscopic K+ currents (1 to 8% of wild-type currents), the A103V and P110L variants retained substantial K+ conductivity (23 and 35% of wild-type currents, respectively). Coexpression of A103V and P110L, resembling the compound heterozygous state of the affected individual, further reduced macroscopic currents to 9% of the wild-type currents. All mutants in the core region exerted a dominant-negative effect on wild-type ROMK1. The C-terminal frameshift (fs) mutation (H354fs) did not change current amplitudes compared with ROMK1 wild type, suggesting that a mechanism other than alteration of the electrophysiological properties may responsible for loss of channel activity.
Analysis of ROMK mutants linked to HPS/aBS revealed a spectrum of mechanisms accounting for loss of channel function. Further characterization of the molecular defects might be helpful for the development of new therapeutic approaches.