Functional characterization of two novel germline mutations of the KCNJ5 gene in hypertensive patients without primary aldosteronism but with ACTH-dependent aldosterone hypersecretion.
BACKGROUND
Germline mutations of the KCNJ5 gene encoding Kir3·4, a member of the inwardly rectifying K+channel, have been identified in 'normal' adrenal glands, patients with familial hyperaldosteronism (FH) type III, aldosterone-producing adenomas (APAs) and sporadic cases of primary aldosteronism (PA).


OBJECTIVE
To present two novel KCNJ5 gene mutations in hypertensive patients without PA, but with Adrenocorticotropic hormone (ACTH)-dependent aldosterone hypersecretion.


METHODS
Two hypertensive patients without PA, who exhibited enhanced ACTH-dependent response of aldosterone secretion, underwent genetic testing for the presence of the CYP11B1/CYP11B2 chimeric gene and KCNJ5 gene mutations. Genomic DNA was isolated from peripheral white blood cells, and the exons of the entire coding regions of the above genes were amplified and sequenced. Electrophysiological studies were performed to determine the effect of identified mutation(s) on the membrane reversal potentials. Structural biology studies were also carried out.


RESULTS
Two novel germline heterozygous KCNJ5 mutations, p.V259M and p.Y348N, were detected in the two subjects. Electrophysiological studies showed that the Y348N mutation resulted in significantly less negative reversal potentials, suggesting loss of ion selectivity, while the V259M mutation did not affect the Kir3.4 current. In the mutated structural biology model, the N348 mutant resulted in significant loss of the ability for hydrogen bonding, while the M259 mutant was capable of establishing weaker interactions. The CYP11B1/CYP11B2 chimeric gene was not detected.


CONCLUSIONS
These findings expand on the clinical spectrum of phenotypes associated with KCNJ5 mutations and implicate these mutations in the pathogenesis of hypertension associated with increased aldosterone response to ACTH stimulation.
Division of Endocrinology, Metabolism and Diabetes, First Department of Pediatrics, National and Kapodistrian University of Athens Medical School, 'Aghia Sophia' Children's Hospital, Athens, Greece.
Amalia
A
Sertedaki
Department of Endocrinology and Diabetes Center, 'G. Gennimatas' General Hospital, Athens, Greece.
Athina
A
Markou
Bioinformatics & Medical Informatics Team, Biomedical Research Foundation of the Academy of Athens, Athens, Greece.
Dimitrios
D
Vlachakis
Bioinformatics & Medical Informatics Team, Biomedical Research Foundation of the Academy of Athens, Athens, Greece.
Sophia
S
Kossida
Molecular Neurophysiology and Biophysics Section, Program in Developmental Neuroscience, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA.
Emilie
E
Campanac
Molecular Neurophysiology and Biophysics Section, Program in Developmental Neuroscience, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA.
Dax A
DA
Hoffman
Program in Developmental Endocrinology and Genetics, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA.
Maria De La Luz
ML
Sierra
Program in Developmental Endocrinology and Genetics, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA.
Paraskevi
P
Xekouki
Program in Developmental Endocrinology and Genetics, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA.
Constantine A
CA
Stratakis
Department of Pathophysiology, National and Kapodistrian University of Athens Medical School, 'Laikon' Hospital, Athens, Greece.
Gregory
G
Kaltsas
Department of Endocrinology and Diabetes Center, 'G. Gennimatas' General Hospital, Athens, Greece.
George P
GP
Piaditis
Division of Endocrinology, Metabolism and Diabetes, First Department of Pediatrics, National and Kapodistrian University of Athens Medical School, 'Aghia Sophia' Children's Hospital, Athens, Greece.
George P
GP
Chrousos
Division of Endocrinology, Metabolism and Diabetes, First Department of Pediatrics, National and Kapodistrian University of Athens Medical School, 'Aghia Sophia' Children's Hospital, Athens, Greece.
Evangelia
E
Charmandari
D000324:Adrenocorticotropic Hormone / Q000494:pharmacology*; D000450:Aldosterone / Q000378:metabolism*; D019405:Cytochrome P-450 CYP11B2 / Q000235:genetics; D055724:Electrophysiological Phenomena; D005260:Female; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels / Q000235:genetics*; D056726:Genetic Association Studies; D018095:Germ-Line Mutation / Q000502:physiology*; D006801:Humans; D006929:Hyperaldosteronism; D006973:Hypertension / Q000209:etiology*; D008297:Male; D008875:Middle Aged; D013252:Steroid 11-beta-Hydroxylase / Q000235:genetics
D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; C484274:KCNJ5 protein, human; D000450:Aldosterone; D000324:Adrenocorticotropic Hormone; D019405:Cytochrome P-450 CYP11B2; D013252:Steroid 11-beta-Hydroxylase