CLCN2 chloride channel mutations in familial hyperaldosteronism type II

Report on three cases of familial primary aldosteronism type IV

Primary aldosteronism is the most common cause of secondary hypertension, which is caused by increased aldosterone secretion in the adrenal cortex and contains many subtypes, among which familial hyperaldosteronism is relatively rare. Familial hyperaldosteronism can be divided into four subtypes based on its clinical manifestations and mutated genes: FH-I , FH-II , FH-III , and FH-IV . This article reports on three patients with FH-IV: a mother and her two sons. They were diagnosed with hypertension in other hospitals, and hypokalemia was found during hospitalization in our department. Diltiazem and terazosin were used for elution for 1 month. Renin and aldosterone levels in standing or supine positions improved, and the aldosterone-to-renin ratio was positive. Primary aldosteronism was diagnosed based on improved saline and captopril inhibition tests. As the three patients were blood-related immediate family members, gene screening was performed, diagnosing them with FH-IV . This article reports the clinical characteristics of the three cases in combination with related literature to improve the understanding of FH-IV .

Insights into CLC-0's Slow-Gating from Intracellular Proton Inhibition

The opening of the Torpedo CLC-0 chloride (Cl-) channel is known to be regulated by two gating mechanisms: fast gating and slow (common) gating. The structural basis underlying the fast-gating mechanism is better understood than that of the slow-gating mechanism, which is still largely a mystery. Our previous study on the intracellular proton (H+i)-induced inhibition of the CLC-0 anionic current led to the conclusion that the inhibition results from the slow-gate closure (also called inactivation). The conclusion was made based on substantial evidence such as a large temperature dependence of the H+i inhibition similar to that of the channel inactivation, a resistance to the H+i inhibition in the inactivation-suppressed C212S mutant, and a similar voltage dependence between the current recovery from the H+i inhibition and the recovery from the channel inactivation. In this work, we further examine the mechanism of the H+i inhibition of wild-type CLC-0 and several mutants. We observe that an anion efflux through the pore of CLC-0 accelerates the recovery from the H+i-induced inhibition, a process corresponding to the slow-gate opening. Furthermore, various inactivation-suppressed mutants exhibit different current recovery kinetics, suggesting the existence of multiple inactivated states (namely, slow-gate closed states). We speculate that protonation of the pore of CLC-0 increases the binding affinity of permeant anions in the pore, thereby generating a pore blockage of ion flow as the first step of inactivation. Subsequent complex protein conformational changes further transition the CLC-0 channel to deeper inactivated states.

Diagnosis and management of resistant hypertension

Resistant hypertension is defined as blood pressure that remains above the therapeutic goal despite concurrent use of at least three antihypertensive agents of different classes, including a diuretic, with all agents administered at maximum or maximally tolerated doses. Resistant hypertension is also diagnosed if blood pressure control requires four or more antihypertensive drugs. Assessment requires the exclusion of apparent treatment resistant hypertension, which is most often the result of non-adherence to treatment. Resistant hypertension is associated with major cardiovascular events in the short and long term, including heart failure, ischemic heart disease, stroke, and renal failure. Guidelines from several professional organizations recommend lifestyle modification and antihypertensive drugs. Medications typically include an angiotensin converting enzyme inhibitor or angiotensin receptor blocker, a calcium channel blocker, and a long acting thiazide-type/like diuretic; if a fourth drug is needed, evidence supports addition of a mineralocorticoid receptor antagonist. After a long pause since 2007 when the last antihypertensive class was approved, several novel agents are now under active development. Some of these may provide potent blood pressure lowering in broad groups of patients, such as aldosterone synthase inhibitors and dual endothelin receptor antagonists, whereas others may provide benefit by allowing treatment of resistant hypertension in special populations, such as non-steroidal mineralocorticoid receptor antagonists in patients with chronic kidney disease. Several device based approaches have been tested, with renal denervation being the best supported and only approved interventional device treatment for resistant hypertension.

Renal Hypokalemia: An Endocrine Perspective

The majority of disorders that cause renal potassium wasting present with abnormalities in adrenal hormone secretion. While these findings frequently lead patients to seek endocrine evaluation, clinicians often struggle to accurately diagnose these conditions, delaying treatment and adversely impacting patient care. At the same time, growing insight into the genetic and molecular basis of these disorders continues to improve their diagnosis and management. In this review, we outline a practical integrated approach to the evaluation of renal hypokalemia syndromes that are seen in endocrine practice while highlighting recent advances in understanding of the genetics and pathophysiology behind them.

Update in genetic and epigenetic causes of hypertension

Hypertension is a heritable disease that affects one-fourth of the population and accounts for about 50% of cardiovascular deaths. The genetic basis of hypertension is multifaceted, involving both monogenic and most commonly complex polygenic forms. With the advent of the human genome project, genome-wide association studies (GWAS) have identified a plethora of loci linked to hypertension by examining common genetic variations. It's notable, however, that the majority of these genetic variants do not affect the protein-coding sequences, posing a considerable obstacle in pinpointing the actual genes responsible for hypertension. Despite these challenges, precise mapping of GWAS-identified loci is emerging as a promising strategy to reveal novel genes and potential targets for the pharmacological management of blood pressure. This review provides insight into the monogenic and polygenic causes of hypertension. Special attention is given to PRDM6, among the earliest functionally characterized GWAS-identified genes. Moreover, this review delves into the roles of genes contributing to renal and vascular forms of hypertension, offering insights into their genetic and epigenetic mechanisms of action.

Familial hyperaldosteronism: an European Reference Network on Rare Endocrine Conditions clinical practice guideline

We describe herein the European Reference Network on Rare Endocrine Conditions clinical practice guideline on diagnosis and management of familial forms of hyperaldosteronism. The guideline panel consisted of 10 experts in primary aldosteronism, endocrine hypertension, paediatric endocrinology, and cardiology as well as a methodologist. A systematic literature search was conducted, and because of the rarity of the condition, most recommendations were based on expert opinion and small patient series. The guideline includes a brief description of the genetics and molecular pathophysiology associated with each condition, the patients to be screened, and how to screen. Diagnostic and treatment approaches for patients with genetically determined diagnosis are presented. The recommendations apply to patients with genetically proven familial hyperaldosteronism and not to families with more than one case of primary aldosteronism without demonstration of a responsible pathogenic variant.

Double somatic mutations in CTNNB1 and GNA11 in an aldosterone-producing adenoma

Double somatic mutations in CTNNB1 and GNA11/Q have recently been identified in a small subset of aldosterone-producing adenomas (APAs). As a possible pathogenesis of APA due to these mutations, an association with pregnancy, menopause, or puberty has been proposed. However, because of its rarity, characteristics of APA with these mutations have not been well characterized. A 46-year-old Japanese woman presented with hypertension and hypokalemia. She had two pregnancies in the past but had no history of pregnancy-induced hypertension. She had regular menstrual cycle at presentation and was diagnosed as having primary aldosteronism after endocrinologic examinations. Computed tomography revealed a 2 cm right adrenal mass. Adrenal venous sampling demonstrated excess aldosterone production from the right adrenal gland. She underwent right laparoscopic adrenalectomy. The resected right adrenal tumor was histologically diagnosed as adrenocortical adenoma and subsequent immunohistochemistry (IHC) revealed diffuse immunoreactivity of aldosterone synthase (CYP11B2) and visinin like 1, a marker of the zona glomerulosa (ZG), whereas 11β-hydroxylase, a steroidogenic enzyme for cortisol biosynthesis, was mostly negative. CYP11B2 IHC-guided targeted next-generation sequencing identified somatic CTNNB1 (p.D32Y) and GNA11 (p.Q209H) mutations. Immunofluorescence staining of the tumor also revealed the presence of activated β-catenin, consistent with features of the normal ZG. The expression patterns of steroidogenic enzymes and related proteins indicated ZG features of the tumor cells. PA was clinically and biochemically cured after surgery. In conclusion, our study indicated that CTNNB1 and GNA11-mutated APA has characteristics of the ZG. The disease could occur in adults with no clear association with pregnancy or menopause.

Differences in the clinical and hormonal presentation of patients with familial and sporadic primary aldosteronism

Purpose

To compare the clinical and hormonal characteristics of patients with familial hyperaldosteronism (FH) and sporadic primary aldosteronism (PA).

Methods

A systematic review of the literature was performed for the identification of FH patients. The SPAIN-ALDO registry cohort of patients with no suspicion of FH was chosen as the comparator group (sporadic group).

Results

A total of 360 FH (246 FH type I, 73 type II, 29 type III, and 12 type IV) cases and 830 sporadic PA patients were included. Patients with FH-I were younger than sporadic cases, and women were more commonly affected (P = 0.003). In addition, the plasma aldosterone concentration (PAC) was lower, plasma renin activity (PRA) higher, and hypokalemia (P < 0.001) less frequent than in sporadic cases. Except for a younger age (P < 0.001) and higher diastolic blood pressure (P = 0.006), the clinical and hormonal profiles of FH-II and sporadic cases were similar. FH-III had a distinct phenotype, with higher PAC and higher frequency of hypokalemia (P < 0.001), and presented 45 years before sporadic cases. Nevertheless, the clinical and hormonal phenotypes of FH-IV and sporadic cases were similar, with the former being younger and having lower serum potassium levels.

Conclusion

In addition to being younger and having a family history of PA, FH-I and III share other typical characteristics. In this regard, FH-I is characterized by a low prevalence of hypokalemia and FH-III by a severe aldosterone excess causing hypokalemia in more than 85% of patients. The clinical and hormonal phenotype of type II and IV is similar to the sporadic cases.

Who needs to be screened for primary aldosteronism?

The prevalence of patients with primary aldosteronism (PA) is about 5%-15% in hypertensive patients, and it is common cause of secondary hypertension in clinical practice. Two major causes of PA are noted, namely bilateral adrenal hyperplasia and aldosterone-producing adenoma, and the general diagnosis is based on three steps: (1) screening, (2) confirmatory testing, and (3) subtype differentiation (Figure 1). The recommendation for screening patients is at an increased risk of PA, here we focus on which patients should be screened for PA, not only according to well-established guidelines but for potential patients with PA. We recommend screening for 1) patients with resistant or persistent hypertension, 2) hypertensive patients with hypokalemia (spontaneous or drug-induced), 3) young hypertensive patients (age <40 years), and 4) all hypertensive patients with a history of PA in first-degree relatives. Moreover, we suggest screening for 1) hypertensive patients themselves or first-degree relatives with early target organ damage, such as stroke and other diseases, 2) all hypertensive patients with a concurrent adrenal incidentaloma, 3) hypertensive patients with obstructive sleep apnea, 4) hypertensive patients with atrial fibrillation unexplained by structural heart defects and/or other conditions resulting in the arrhythmia, 5) hypertensive patients with anxiety and other psychosomatic symptoms, and 6) hypertensive patients without other comorbidities to maintain cost-effectiveness.

Urine steroid metabolomics as a diagnostic tool in primary aldosteronism

Primary aldosteronism (PA) causes 5-10% of hypertension cases, but only a minority of patients are currently diagnosed and treated because of a complex, stepwise, and partly invasive workup. We tested the performance of urine steroid metabolomics, the computational analysis of 24-hour urine steroid metabolome data by machine learning, for the identification and subtyping of PA. Mass spectrometry-based multi-steroid profiling was used to quantify the excretion of 34 steroid metabolites in 24-hour urine samples from 158 adults with PA (88 with unilateral PA [UPA] due to aldosterone-producing adenomas [APAs]; 70 with bilateral PA [BPA]) and 65 sex- and age-matched healthy controls. All APAs were resected and underwent targeted gene sequencing to detect somatic mutations associated with UPA. Patients with PA had increased urinary metabolite excretion of mineralocorticoids, glucocorticoids, and glucocorticoid precursors. Urine steroid metabolomics identified patients with PA with high accuracy, both when applied to all 34 or only the three most discriminative steroid metabolites (average areas under the receiver-operating characteristics curve [AUCs-ROC] 0.95-0.97). Whilst machine learning was suboptimal in differentiating UPA from BPA (average AUCs-ROC 0.65-0.73), it readily identified APA cases harbouring somatic KCNJ5 mutations (average AUCs-ROC 0.79-85). These patients showed a distinctly increased urine excretion of the hybrid steroid 18-hydroxycortisol and its metabolite 18-oxo-tetrahydrocortisol, the latter identified by machine learning as by far the most discriminative steroid. In conclusion, urine steroid metabolomics is a non-invasive candidate test for the accurate identification of PA cases and KCNJ5-mutated APAs.

CryoEM structures of the human CLC-2 voltage-gated chloride channel reveal a ball-and-chain gating mechanism

CLC-2 is a voltage-gated chloride channel that contributes to electrical excitability and ion homeostasis in many different tissues. Among the nine mammalian CLC homologs, CLC-2 is uniquely activated by hyperpolarization, rather than depolarization, of the plasma membrane. The molecular basis for the divergence in polarity of voltage gating among closely related homologs has been a long-standing mystery, in part because few CLC channel structures are available. Here, we report cryoEM structures of human CLC-2 at 2.46 - 2.76 Å, in the presence and absence of the selective inhibitor AK-42. AK-42 binds within the extracellular entryway of the Cl--permeation pathway, occupying a pocket previously proposed through computational docking studies. In the apo structure, we observed two distinct conformations involving rotation of one of the cytoplasmic C-terminal domains (CTDs). In the absence of CTD rotation, an intracellular N-terminal 15-residue hairpin peptide nestles against the TM domain to physically occlude the Cl--permeation pathway. This peptide is highly conserved among species variants of CLC-2 but is not present in other CLC homologs. Previous studies suggested that the N-terminal domain of CLC-2 influences channel properties via a "ball-and-chain" gating mechanism, but conflicting data cast doubt on such a mechanism, and thus the structure of the N-terminal domain and its interaction with the channel has been uncertain. Through electrophysiological studies of an N-terminal deletion mutant lacking the 15-residue hairpin peptide, we support a model in which the N-terminal hairpin of CLC-2 stabilizes a closed state of the channel by blocking the cytoplasmic Cl--permeation pathway.

Molecular pathology of endocrine gland tumors: genetic alterations and clinicopathologic relevance

Tumors of the endocrine glands are common. Knowledge of their molecular pathology has greatly advanced in the recent past. This review covers the main molecular alterations of tumors of the anterior pituitary, thyroid and parathyroid glands, adrenal cortex, and adrenal medulla and paraganglia. All endocrine gland tumors enjoy a robust correlation between genotype and phenotype. High-throughput molecular analysis demonstrates that endocrine gland tumors can be grouped into molecular groups that are relevant from both pathologic and clinical point of views. In this review, genetic alterations have been discussed and tabulated with respect to their molecular pathogenetic role and clinicopathologic implications, addressing the use of molecular biomarkers for the purpose of diagnosis and prognosis and predicting response to molecular therapy. Hereditary conditions that play a key role in determining predisposition to many types of endocrine tumors are also discussed.

What We Know about and What Is New in Primary Aldosteronism

Primary aldosteronism (PA), a significant and curable cause of secondary hypertension, is seen in 5-10% of hypertensive patients, with its prevalence contingent upon the severity of the hypertension. The principal aetiologies of PA include bilateral idiopathic hypertrophy (BIH) and aldosterone-producing adenomas (APAs), while the less frequent causes include unilateral hyperplasia, familial hyperaldosteronism (FH) types I-IV, aldosterone-producing carcinoma, and ectopic aldosterone synthesis. This condition, characterised by excessive aldosterone secretion, leads to augmented sodium and water reabsorption alongside potassium loss, culminating in distinct clinical hallmarks: elevated aldosterone levels, suppressed renin levels, and hypertension. Notably, hypokalaemia is present in only 28% of patients with PA and is not a primary indicator. The association of PA with an escalated cardiovascular risk profile, independent of blood pressure levels, is notable. Patients with PA exhibit a heightened incidence of cardiovascular events compared to counterparts with essential hypertension, matched for age, sex, and blood pressure levels. Despite its prevalence, PA remains frequently undiagnosed, underscoring the imperative for enhanced screening protocols. The diagnostic process for PA entails a tripartite assessment: the aldosterone/renin ratio (ARR) as the initial screening tool, followed by confirmatory and subtyping tests. A positive ARR necessitates confirmatory testing to rule out false positives. Subtyping, achieved through computed tomography and adrenal vein sampling, aims to distinguish between unilateral and bilateral PA forms, guiding targeted therapeutic strategies. New radionuclide imaging may facilitate and accelerate such subtyping and localisation. For unilateral adrenal adenoma or hyperplasia, surgical intervention is optimal, whereas bilateral idiopathic hyperplasia warrants treatment with mineralocorticoid antagonists (MRAs). This review amalgamates established and emerging insights into the management of primary aldosteronism.

Treating Primary Aldosteronism-Induced Hypertension: Novel Approaches and Future Outlooks

Primary aldosteronism (PA) is the most common cause of secondary hypertension and is associated with increased morbidity and mortality when compared with blood pressure-matched cases of primary hypertension. Current limitations in patient care stem from delayed recognition of the condition, limited access to key diagnostic procedures, and lack of a definitive therapy option for nonsurgical candidates. However, several recent advances have the potential to address these barriers to optimal care. From a diagnostic perspective, machine-learning algorithms have shown promise in the prediction of PA subtypes, while the development of noninvasive alternatives to adrenal vein sampling (including molecular positron emission tomography imaging) has made accurate localization of functioning adrenal nodules possible. In parallel, more selective approaches to targeting the causative aldosterone-producing adrenal adenoma/nodule (APA/APN) have emerged with the advent of partial adrenalectomy or precision ablation. Additionally, the development of novel pharmacological agents may help to mitigate off-target effects of aldosterone and improve clinical efficacy and outcomes. Here, we consider how each of these innovations might change our approach to the patient with PA, to allow more tailored investigation and treatment plans, with corresponding improvement in clinical outcomes and resource utilization, for this highly prevalent disorder.

Developing the novel diagnostic model and potential drugs by integrating bioinformatics and machine learning for aldosterone-producing adenomas

Background: Aldosterone-producing adenomas (APA) are a common cause of primary aldosteronism (PA), a clinical syndrome characterized by hypertension and electrolyte disturbances. If untreated, it may lead to serious cardiovascular complications. Therefore, there is an urgent need for potential biomarkers and targeted drugs for the diagnosis and treatment of aldosteronism. Methods: We downloaded two datasets (GSE156931 and GSE60042) from the GEO database and merged them by de-batch effect, then screened the top50 of differential genes using PPI and enriched them, followed by screening the Aldosterone adenoma-related genes (ARGs) in the top50 using three machine learning algorithms. We performed GSEA analysis on the ARGs separately and constructed artificial neural networks based on the ARGs. Finally, the Enrich platform was utilized to identify drugs with potential therapeutic effects on APA by tARGseting the ARGs. Results: We identified 190 differential genes by differential analysis, and then identified the top50 genes by PPI, and the enrichment analysis showed that they were mainly enriched in amino acid metabolic pathways. Then three machine learning algorithms identified five ARGs, namely, SST, RAB3C, PPY, CYP3A4, CDH10, and the ANN constructed on the basis of these five ARGs had better diagnostic effect on APA, in which the AUC of the training set is 1 and the AUC of the validation set is 0.755. And then the Enrich platform identified drugs tARGseting the ARGs with potential therapeutic effects on APA. Conclusion: We identified five ARGs for APA through bioinformatic analysis and constructed Artificial neural network (ANN) based on them with better diagnostic effects, and identified drugs with potential therapeutic effects on APA by tARGseting these ARGs. Our study provides more options for the diagnosis and treatment of APA.

Genetic Variants Associated with Hypertension Risk: Progress and Implications

Background

Genetic variants causing diseases with hypertension as a secondary feature have previously been identified. Studies focussing on primary hypertension have utilised common and latterly rare genetic variants in attempts to elucidate the genetic contribution to the risk of primary hypertension.

Summary

Using genome-wide association studies (GWASs), associations of hypertension with hundreds of common genetic variants have been reported, implicating thousands of genes. Individual variants have small effect sizes and cumulatively account for around 6% of genetic risk. The common variant signal is enriched for relevant tissues and physiological processes, while some variants are associated with traits expected to have secondary impacts on hypertension risk, such as fruit intake, BMI, or time watching television. Studies using rare variants obtained from exome sequence data have implicated a small number of genes for which impaired function has moderate effects on blood pressure and/or hypertension risk. Notably, genetic variants which impair elements of guanylate cyclase activation, stimulated by either natriuretic hormones or nitric oxide, increase hypertension risk. Conversely, variants impairing dopamine beta-hydroxylase or renin production are associated with lower blood pressure. Variants for which a definite effect can be designated remain cumulatively extremely rare and again make only a small contribution to overall genetic risk. Although these results are of interest, it is not clear that they provide radical new insights or identify drug targets which were not previously known. Nor does it seem that genetic testing could be useful in terms of quantifying disease risk or guiding treatment.

Key Messages

Research has increased our knowledge about the relationship between naturally occurring genetic variation and risk of hypertension. Although some results serve to confirm our understanding of underlying physiology, their value in terms of potentially leading to practical advances in the management of hypertension appears questionable.

Adrenal Anion Channels: New Roles in Zona Glomerulosa Physiology and in the Pathophysiology of Primary Aldosteronism

The mineralocorticoid aldosterone is produced in the zona glomerulosa of the adrenal cortex. Its synthesis is regulated by the serum concentrations of the peptide hormone angiotensin II and potassium. The primary role of aldosterone is to control blood volume and electrolytes. The autonomous production of aldosterone (primary aldosteronism, PA) is considered the most frequent cause of secondary hypertension. Aldosterone-producing adenomas and (micro-)nodules are frequent causes of PA and often carry somatic mutations in ion channels and transporters. Rare familial forms of PA are due to germline mutations. Both somatic and germline mutations in the chloride channel gene CLCN2, encoding ClC-2, have been identified in PA. Clinical findings and results from cell culture and animal models have advanced our knowledge about the role of anions in PA. The zona glomerulosa of the adrenal gland has now been firmly established as a tissue in which anions play a significant role for signaling. In this overview, we aim to summarize the current knowledge and highlight novel concepts as well as open questions.

Biophysical and Pharmacological Insights to CLC Chloride Channels

The CLC family encompasses two functional categories of transmembrane proteins: chloride conducting channels and proton-chloride antiporters. All members in this chloride channel/transporter family consist of two identical protein subunits, and each subunit forms an independent ion-transport pathway, a structural architecture known as "double barrel." These CLC proteins serve biological functions ranging from membrane excitability and cell volume regulation to acidification of endosomes. Despite their ubiquitous expression, physiological significance, and resolved molecular structures of some of the family members, the mechanisms governing these molecules' biophysical functions are still not completely settled. However, a series of functional and structural studies have brought insights into interesting questions related to these proteins. This chapter explores the functional peculiarities underlying CLC channels aided by information observed from the chloride-proton antiporters in the CLC family. The overall structural features of these CLC proteins will be presented, and the biophysical functions will be addressed. Finally, the mechanism of pharmacological agents that interact with CLC channels will also be discussed.

Monogenic Etiology of Hypertension

Monogenic hypertension encompasses a group of conditions wherein single gene mutations result in increased renal sodium reabsorption manifesting as low renin hypertension. As these diseases are rare, their contribution to hypertension in children and adolescents is often overlooked. Precise diagnosis is essential in those who have not been found to have more common identifiable causes of hypertension in adolescents, since treatment strategies for these rare conditions are specific and different from antihypertensive regimens for the other more common causes of hypertension in this age group. The objective of this review is to provide insight to the rare, monogenic forms of hypertension.

Primary aldosteronism: molecular medicine meets public health

Primary aldosteronism is the most common single cause of hypertension and is potentially curable when only one adrenal gland is the culprit. The importance of primary aldosteronism to public health derives from its high prevalence but huge under-diagnosis (estimated to be <1% of all affected individuals), despite the consequences of poor blood pressure control by conventional therapy and enhanced cardiovascular risk. This state of affairs is attributable to the fact that the tools used for diagnosis or treatment are still those that originated in the 1970-1990s. Conversely, molecular discoveries have transformed our understanding of adrenal physiology and pathology. Many molecules and processes associated with constant adrenocortical renewal and interzonal metamorphosis also feature in aldosterone-producing adenomas and aldosterone-producing micronodules. The adrenal gland has one of the most significant rates of non-silent somatic mutations, with frequent selection of those driving autonomous aldosterone production, and distinct clinical presentations and outcomes for most genotypes. The disappearance of aldosterone synthesis and cells from most of the adult human zona glomerulosa is the likely driver of the mutational success that causes aldosterone-producing adenomas, but insights into the pathways that lead to constitutive aldosterone production and cell survival may open up opportunities for novel therapies.

2023 Korean Endocrine Society Consensus Guidelines for the Diagnosis and Management of Primary Aldosteronism

Primary aldosteronism (PA) is a common, yet underdiagnosed cause of secondary hypertension. It is characterized by an overproduction of aldosterone, leading to hypertension and/or hypokalemia. Despite affecting between 5.9% and 34% of patients with hypertension, PA is frequently missed due to a lack of clinical awareness and systematic screening, which can result in significant cardiovascular complications. To address this, medical societies have developed clinical practice guidelines to improve the management of hypertension and PA. The Korean Endocrine Society, drawing on a wealth of research, has formulated new guidelines for PA. A task force has been established to prepare PA guidelines, which encompass epidemiology, pathophysiology, clinical presentation, diagnosis, treatment, and follow-up care. The Korean clinical guidelines for PA aim to deliver an evidence-based protocol for PA diagnosis, treatment, and patient monitoring. These guidelines are anticipated to ease the burden of this potentially curable condition.

CryoEM structures of the human CLC-2 voltage gated chloride channel reveal a ball and chain gating mechanism

CLC-2 is a voltage-gated chloride channel that contributes to electrical excitability and ion homeostasis in many different mammalian tissues and cell types. Among the nine mammalian CLC homologs, CLC-2 is uniquely activated by hyperpolarization, rather than depolarization, of the plasma membrane. The molecular basis for the divergence in polarity of voltage gating mechanisms among closely related CLC homologs has been a long-standing mystery, in part because few CLC channel structures are available, and those that exist exhibit high conformational similarity. Here, we report cryoEM structures of human CLC-2 at 2.46 - 2.76 Å, in the presence and absence of the potent and selective inhibitor AK-42. AK-42 binds within the extracellular entryway of the Cl--permeation pathway, occupying a pocket previously proposed through computational docking studies. In the apo structure, we observed two distinct apo conformations of CLC-2 involving rotation of one of the cytoplasmic C-terminal domains (CTDs). In the absence of CTD rotation, an intracellular N-terminal 15-residue hairpin peptide nestles against the TM domain to physically occlude the Cl--permeation pathway from the intracellular side. This peptide is highly conserved among species variants of CLC-2 but is not present in any other CLC homologs. Previous studies suggested that the N-terminal domain of CLC-2 influences channel properties via a "ball-and-chain" gating mechanism, but conflicting data cast doubt on such a mechanism, and thus the structure of the N-terminal domain and its interaction with the channel has been uncertain. Through electrophysiological studies of an N-terminal deletion mutant lacking the 15-residue hairpin peptide, we show that loss of this short sequence increases the magnitude and decreases the rectification of CLC-2 currents expressed in mammalian cells. Furthermore, we show that with repetitive hyperpolarization WT CLC-2 currents increase in resemblance to the hairpin-deleted CLC-2 currents. These functional results combined with our structural data support a model in which the N-terminal hairpin of CLC-2 stabilizes a closed state of the channel by blocking the cytoplasmic Cl--permeation pathway.

Therapeutic management of congenital forms of endocrine hypertension

Congenital forms of endocrine hypertension are rare and potentially life-threatening disorders, primarily caused by genetic defects affecting adrenal steroid synthesis and activation pathways. These conditions exhibit diverse clinical manifestations, which can be distinguished by their unique molecular mechanisms and steroid profiles. Timely diagnosis and customized management approach are crucial to mitigate unfavorable outcomes associated with uncontrolled hypertension and other related conditions. Treatment options for these disorders depend on the distinct underlying pathophysiology, which involves specific pharmacological therapies or surgical adrenalectomy in some instances. This review article summarizes the current state of knowledge on the therapeutic management of congenital forms of endocrine hypertension, focusing on familial hyperaldosteronism (FH), congenital adrenal hyperplasia, apparent mineralocorticoid excess, and Liddle syndrome. We provide an overview of the genetic and molecular pathogenesis underlying each disorder, describe the clinical features, and discuss the various therapeutic approaches available and their risk of adverse effects, aiming to improve outcomes in patients with these rare and complex conditions.

Englerin A Inhibits T-Type Voltage-Gated Calcium Channels at Low Micromolar Concentrations

Englerin A (EA) is a potent agonist of tetrameric transient receptor potential canonical (TRPC) ion channels containing TRPC4 and TRPC5 subunits. TRPC proteins form cation channels that are activated by plasma membrane receptors. They convert extracellular signals such as angiotensin II into cellular responses, whereupon Na+ and Ca2+ influx and depolarization of the plasma membrane occur. Via depolarization, voltage-gated Ca2+ (CaV) channels can be activated, further increasing Ca2+ influx. We investigated the extent to which EA also affects the functions of CaV channels using the high-voltage-activated L-type Ca2+ channel CaV1.2 and the low-voltage-activated T-type Ca2+ channels CaV3.1, CaV3.2, and CaV3.3. After expression of cDNAs in human embryonic kidney (HEK293) cells, EA inhibited currents through all T-type channels at half-maximal inhibitory concentrations (IC50) of 7.5 to 10.3 μM. In zona glomerulosa cells of the adrenal gland, angiotensin II-induced elevation of cytoplasmic Ca2+ concentration leads to aldosterone release. We identified transcripts of low- and high-voltage-activated CaV channels and of TRPC1 and TRPC5 in the human adrenocortical (HAC15) zona glomerulosa cell line. Although no EA-induced TRPC activity was measurable, Ca2+ channel blockers distinguished T- and L-type Ca2+ currents. EA blocked 60% of the CaV current in HAC15 cells and T- and L-type channels analyzed at -30 mV and 10 mV were inhibited with IC50 values of 2.3 and 2.6 μM, respectively. Although the T-type blocker Z944 reduced basal and angiotensin II-induced 24-hour aldosterone release, EA was not effective. In summary, we show here that EA blocks CaV1.2 and T-type CaV channels at low-micromolar concentrations. SIGNIFICANCE STATEMENT: In this study we showed that englerin A (EA), a potent agonist of tetrameric transient receptor potential canonical (TRPC)4- or TRPC5-containing channels and currently under investigation to treat certain types of cancer, also inhibits the L-type voltage-gated Ca2+ (CaV) channel CaV1.2 and the T-type CaV channels CaV3.1, CaV3.2, and CaV3.3 channels at low micromolar concentrations.

Identification of a novel competing endogenous RNA network and candidate drugs associated with ferroptosis in aldosterone-producing adenomas

Aldosterone-producing adenoma (APA), characterized by unilaterally excessive aldosterone production, is a common cause of primary aldosteronism. Ferroptosis, a recently raised iron-dependent mode of programmed cell death, has been involved in the development and therapy of various diseases. This study obtained datasets of the mRNA and lncRNA expression profiles for APA and adjacent adrenal gland (AAG) from the Gene Expression Omnibus (GEO) database. Differentially expressed genes (DEGs) and lncRNAs (DE lncRNAs) associated with ferroptosis were identified. Enrichment analyses indicated 89 ferroptosis-related DEGs were primarily enriched in ROS related processes and ferroptosis. Two physical cores, and one combined core were identified in the protein-protein interaction (PPI). DEGs and clinical traits were used in conjunction to screen eight hub genes from two hub modules and 89 DEGs. A competitive endogenous RNA (ceRNA) network was constructed via co-express analysis. Thereafter, molecular docking was used to identify potential targets. Two active compounds, QL-X-138 and MK-1775, bound to AURKA and DUOX1, respectively, with the lowest binding energies. Molecular dynamics simulation verified the stability of the two complexes. In summary, our studies identified eight hub genes and a novel ceRNA regulatory network associated with ferroptosis, wherein QL-X-138 and MK-1775 were considered to be potential drugs for treating APA.

Primary Aldosteronism and Drug Resistant Hypertension: A "Chicken-Egg" Story

Drug-resistant arterial hypertension (RH) is a major risk factor for cardiovascular disease, often due to overlooked underlying causes. Identification of such causes poses significant clinical challenges. In this setting, primary aldosteronism (PA) is a frequent cause of RH and its prevalence in RH patients is likely higher than 20%.The pathophysiological link between PA and the development and maintenance of RH involves target organ damage and the cellular and extracellular effects of aldosterone excess that promote pro-inflammatory and pro-fibrotic changes in the kidney and vasculature.The feasibility of adrenal vein sampling in PA patients with RH, and the clinical benefit achieved by adrenalectomy, further emphasize the need to implement systematic screening for this common form of secondary hypertension in the management of a high-risk population as RH patients.: We herein review the current knowledge of the factors that contribute to the RH phenotype with a focus on PA and discuss the issues regarding the screening for PA in this setting and the therapeutic approaches (surgical and medical) aimed at resolving RH caused by PA.

Apo state pore opening as functional basis of increased EAAT anion channel activity in episodic ataxia 6

SLC1A2 and SLC1A3 encode the glial glutamate transporters EAAT2 and EAAT1, which are not only the predominant glutamate uptake carriers in our brain, but also function as anion channels. Two homologous mutations, which predict substitutions of prolines in the center of the fifth transmembrane helix by arginine (P289R EAAT2, P290R EAAT1), have been identified in patients with epileptic encephalopathy (SLC1A2) or with episodic ataxia type 6 (SLC1A3). Both mutations have been shown to impair glutamate uptake and to increase anion conduction. The molecular processes that link the disease-causing mutations to two major alterations of glutamate transporter function remain insufficiently understood. The mutated proline is conserved in every EAAT. Since the pathogenic changes mainly affect the anion channel function, we here study the functional consequences of the homologous P312R mutation in the neuronal glutamate transporter EAAT4, a low capacity glutamate transporter with predominant anion channel function. To assess the impact of charge and structure of the inserted amino acid for the observed functional changes, we generated and functionally evaluated not only P312R, but also substitutions of P312 with all other amino acids. However, only exchange of proline by arginine, lysine, histidine and asparagine were functionally tolerated. We compared WT, P312R and P312N EAAT4 using a combination of cellular electrophysiology, fast substrate application and kinetic modelling. We found that WT and mutant EAAT4 anion currents can be described with a 11-state model of the transport cycle, in which several states are connected to branching anion channel states to account for the EAAT anion channel function. Substitutions of P312 modify various transitions describing substrate binding/unbinding, translocation or anion channel opening. Most importantly, P312R generates a new anion conducting state that is accessible in the outward facing apo state and that is the main determinant of the increased anion conduction of EAAT transporters carrying this mutation. Our work provides a quantitative description how a naturally occurring mutation changes glutamate uptake and anion currents in two genetic diseases.

Chloride intracellular channel gene knockdown induces insect cell lines death and level increases of intracellular calcium ions

Chloride intracellular channel (CLIC) is a member of the chloride channel protein family for which growing evidence supports a pivotal role in fundamental cellular events. However, the physiological function of CLIC in insects is still rarely uncovered. The ovary-derived High Five (Hi-5) cell line isolated from the cabbage looper (Trichoplusia ni) is widely used in laboratories. Here, we studied both characteristics and functions of CLIC in Hi-5 cells (TnCLIC). We identified the TnCLIC gene in Hi-5 cells and annotated highly conserved CLIC proteins in most insect species. After RNA interference of TnCLIC, the phenomenon of significantly increased cell death suggests that the TnCLIC protein is essential for the survival of Hi-5 cells. The same lethal effect was also observed in Spodoptera frugiperda 9 and Drosophila melanogaster Schneider 2 cells after CLIC knockdown. Furthermore, we found that this kind of cell death was accompanied by increases in intracellular calcium ions after TnCLIC knockdown with the transcriptomic analyses and the detection of calcium levels. Our results provide insights into insect CLIC as a key factor for cell survival and lay the foundation for the cell death mechanism.

CaV3.2 (CACNA1H) in Primary Aldosteronism

Aldosterone is a steroid hormone produced in the zona glomerulosa (ZG) of the adrenal cortex. The most prominent function of aldosterone is the control of electrolyte homeostasis and blood pressure via the kidneys. The primary factors regulating aldosterone synthesis are the serum concentrations of angiotensin II and potassium. The T-type voltage-gated calcium channel Ca_V3.2 (encoded by CACNA1H) is an important component of electrical as well as intracellular calcium oscillations, which govern aldosterone production in the ZG. Excessive aldosterone production that is (partially) uncoupled from physiological stimuli leads to primary aldosteronism, the most common cause of secondary hypertension. Germline gain-of-function mutations in CACNA1H were identified in familial hyperaldosteronism, whereas somatic mutations are a rare cause of aldosterone-producing adenomas. In this review, we summarize these findings, put them in perspective, and highlight missing knowledge.

Cryo-EM structures of ClC-2 chloride channel reveal the blocking mechanism of its specific inhibitor AK-42

ClC-2 transports chloride ions across plasma membranes and plays critical roles in cellular homeostasis. Its dysfunction is involved in diseases including leukodystrophy and primary aldosteronism. AK-42 was recently reported as a specific inhibitor of ClC-2. However, experimental structures are still missing to decipher its inhibition mechanism. Here, we present cryo-EM structures of apo ClC-2 and its complex with AK-42, both at 3.5 Å resolution. Residues S162, E205 and Y553 are involved in chloride binding and contribute to the ion selectivity. The side-chain of the gating glutamate E205 occupies the putative central chloride-binding site, indicating that our structure represents a closed state. Structural analysis, molecular dynamics and electrophysiological recordings identify key residues to interact with AK-42. Several AK-42 interacting residues are present in ClC-2 but not in other ClCs, providing a possible explanation for AK-42 specificity. Taken together, our results experimentally reveal the potential inhibition mechanism of ClC-2 inhibitor AK-42.

Mineralocorticoid Receptor Antagonists for Preventing Chronic Kidney Disease Progression: Current Evidence and Future Challenges

Regulation and action of the mineralocorticoid receptor (MR) have been the focus of intensive research over the past 80 years. Genetic and physiological/biochemical analysis revealed how MR and the steroid hormone aldosterone integrate the responses of distinct tubular cells in the face of environmental perturbations and how their dysregulation compromises fluid homeostasis. In addition to these roles, the accumulation of data also provided unequivocal evidence that MR is involved in the pathophysiology of kidney diseases. Experimental studies delineated the diverse pathological consequences of MR overactivity and uncovered the multiple mechanisms that result in enhanced MR signaling. In parallel, clinical studies consistently demonstrated that MR blockade reduces albuminuria in patients with chronic kidney disease. Moreover, recent large-scale clinical studies using finerenone have provided evidence that the non-steroidal MR antagonist can retard the kidney disease progression in diabetic patients. In this article, we review experimental data demonstrating the critical importance of MR in mediating renal injury as well as clinical studies providing evidence on the renoprotective effects of MR blockade. We also discuss areas of future investigation, which include the benefit of non-steroidal MR antagonists in non-diabetic kidney disease patients, the identification of surrogate markers for MR signaling in the kidney, and the search for key downstream mediators whereby MR blockade confers renoprotection. Insights into these questions would help maximize the benefit of MR blockade in subjects with kidney diseases.

Aldosterone: Renal Action and Physiological Effects

Aldosterone exerts profound effects on renal and cardiovascular physiology. In the kidney, aldosterone acts to preserve electrolyte and acid-base balance in response to changes in dietary sodium (Na+ ) or potassium (K+ ) intake. These physiological actions, principally through activation of mineralocorticoid receptors (MRs), have important effects particularly in patients with renal and cardiovascular disease as demonstrated by multiple clinical trials. Multiple factors, be they genetic, humoral, dietary, or otherwise, can play a role in influencing the rate of aldosterone synthesis and secretion from the adrenal cortex. Normally, aldosterone secretion and action respond to dietary Na+ intake. In the kidney, the distal nephron and collecting duct are the main targets of aldosterone and MR action, which stimulates Na+ absorption in part via the epithelial Na+ channel (ENaC), the principal channel responsible for the fine-tuning of Na+ balance. Our understanding of the regulatory factors that allow aldosterone, via multiple signaling pathways, to function properly clearly implicates this hormone as central to many pathophysiological effects that become dysfunctional in disease states. Numerous pathologies that affect blood pressure (BP), electrolyte balance, and overall cardiovascular health are due to abnormal secretion of aldosterone, mutations in MR, ENaC, or effectors and modulators of their action. Study of the mechanisms of these pathologies has allowed researchers and clinicians to create novel dietary and pharmacological targets to improve human health. This article covers the regulation of aldosterone synthesis and secretion, receptors, effector molecules, and signaling pathways that modulate its action in the kidney. We also consider the role of aldosterone in disease and the benefit of mineralocorticoid antagonists. © 2023 American Physiological Society. Compr Physiol 13:4409-4491, 2023.

Biallelic CLCN2 mutations cause retinal degeneration by impairing retinal pigment epithelium phagocytosis and chloride channel function

CLCN2 encodes a two-pore homodimeric chloride channel protein (CLC-2) that is widely expressed in human tissues. The association between Clcn2 and the retina is well-established in mice, as loss-of-function of CLC-2 can cause retinopathy in mice; however, the ocular phenotypes caused by CLCN2 mutations in humans and the underlying mechanisms remain unclear. The present study aimed to define the ocular features and reveal the pathogenic mechanisms of CLCN2 variants associated with retinal degeneration in humans using an in vitro overexpression system, as well as patient-induced pluripotent stem cell (iPSC)-derived retinal pigment epithelium (RPE) cells and retinal organoids (ROs). A patient carrying the homozygous c.2257C > T (p.R753X) nonsense CLCN2 mutation was followed up for > 6 years. Ocular features were comprehensively characterized with multimodality imaging and functional examination. The patient presented with severe bilateral retinal degeneration with loss of photoreceptor and RPE. In vitro, mutant CLC-2 maintained the correct subcellular localization, but with reduced channel function compared to wild-type CLC-2 in HEK293T cells. Additionally, patient iPSC-derived RPE cells carrying the CLCN2 mutation exhibited dysfunctional ClC-2 chloride channels and outer segment phagocytosis. Notably, these functions were rescued following the repair of the CLCN2 mutation using the CRISPR-Cas9 system. However, this variant did not cause significant photoreceptor degeneration in patient-derived ROs, indicating that dysfunctional RPE is likely the primary cause of biallelic CLCN2 variant-mediated retinopathy. This study is the first to establish the confirmatory ocular features of human CLCN2-related retinal degeneration, and reveal a pathogenic mechanism associated with biallelic CLCN2 variants, providing new insights into the cause of inherited retinal dystrophies.

New advances in endocrine hypertension: from genes to biomarkers

Hypertension (HT) is a major cardiovascular risk factor that affects 10% to 40% of the general population in an age-dependent manner. Detection of secondary forms of HT is particularly important because it allows the targeted management of the underlying disease. Among hypertensive patients, the prevalence of endocrine HT reaches up to 10%. Adrenal diseases are the most frequent cause of endocrine HT and are associated with excess production of mineralocorticoids (mainly primary aldosteronism), glucocorticoids (Cushing syndrome), and catecholamines (pheochromocytoma). In addition, a few rare diseases directly affecting the action of mineralocorticoids and glucocorticoids in the kidney also lead to endocrine HT. Over the past years, genomic and genetic studies have allowed improving our knowledge on the molecular mechanisms of endocrine HT. Those discoveries have opened new opportunities to transfer knowledge to clinical practice for better diagnosis and specific treatment of affected subjects. In this review, we describe the physiology of adrenal hormone biosynthesis and action, the clinical and biochemical characteristics of different forms of endocrine HT, and their underlying genetic defects. We discuss the impact of these discoveries on diagnosis and management of patients, as well as new perspectives related to the use of new biomarkers for improved patient care.

Diagnosis and Treatment of Monogenic Hypertension in Children

Although the majority of individuals with hypertension (HTN) have primary and polygenic HTN, monogenic HTN is a secondary type that is widely thought to play a key role in pediatric HTN, which has the characteristics of early onset, refractory HTN with a positive family history, and electrolyte disorders. Monogenic HTN results from single genetic mutations that contribute to the dysregulation of blood pressure (BP) in the kidneys and adrenal glands. It is pathophysiologically associated with increased sodium reabsorption in the distal tubule, intravascular volume expansion, and HTN, as well as low renin and varying aldosterone levels. Simultaneously increased or decreased potassium levels also provide clues for the diagnosis of monogenic HTN. Discovering the genetic factors that cause an increase in BP has been shown to be related to the choice of and responses to antihypertensive medications. Therefore, early and precise diagnosis with genetic sequencing and effective treatment with accurate antihypertensive agents are critical in the management of monogenic HTN. In addition, understanding the genetic architecture of BP, causative molecular pathways perturbing BP regulation, and pharmacogenomics can help with the selection of precision and personalized medicine, as well as improve morbidity and mortality in adulthood.

[11C]metomidate PET-CT versus adrenal vein sampling for diagnosing surgically curable primary aldosteronism: a prospective, within-patient trial

Primary aldosteronism (PA) due to a unilateral aldosterone-producing adenoma is a common cause of hypertension. This can be cured, or greatly improved, by adrenal surgery. However, the invasive nature of the standard pre-surgical investigation contributes to fewer than 1% of patients with PA being offered the chance of a cure. The primary objective of our prospective study of 143 patients with PA ( NCT02945904 ) was to compare the accuracy of a non-invasive test, [11C]metomidate positron emission tomography computed tomography (MTO) scanning, with adrenal vein sampling (AVS) in predicting the biochemical remission of PA and the resolution of hypertension after surgery. A total of 128 patients reached 6- to 9-month follow-up, with 78 (61%) treated surgically and 50 (39%) managed medically. Of the 78 patients receiving surgery, 77 achieved one or more PA surgical outcome criterion for success. The accuracies of MTO at predicting biochemical and clinical success following adrenalectomy were, respectively, 72.7 and 65.4%. For AVS, the accuracies were 63.6 and 61.5%. MTO was not significantly superior, but the differences of 9.1% (95% confidence interval = -6.5 to 24.1%) and 3.8% (95% confidence interval = -11.9 to 9.4) lay within the pre-specified -17% margin for non-inferiority (P = 0.00055 and P = 0.0077, respectively). Of 24 serious adverse events, none was considered related to either investigation and 22 were fully resolved. MTO enables non-invasive diagnosis of unilateral PA.

Primary Aldosteronism: State-of-the-Art Review

We are witnessing a revolution in our understanding of primary aldosteronism (PA). In the past 2 decades, we have learned that PA is a highly prevalent syndrome that is largely attributable to pathogenic somatic mutations, that contributes to cardiovascular, metabolic, and kidney disease, and that when recognized, can be adequately treated with widely available mineralocorticoid receptor antagonists and/or surgical adrenalectomy. Unfortunately, PA is rarely diagnosed, or adequately treated, mainly because of a lack of awareness and education. Most clinicians still possess an outdated understanding of PA; from primary care physicians to hypertension specialists, there is an urgent need to redefine and reintroduce PA to clinicians with a modern and practical approach. In this state-of-the-art review, we provide readers with the most updated knowledge on the pathogenesis, prevalence, diagnosis, and treatment of PA. In particular, we underscore the public health importance of promptly recognizing and treating PA and provide pragmatic solutions to modify clinical practices to achieve this.

Genetic screening of hypertensive patients with aldosterone hypersecretion under conditions of stress

PURPOSE

Although ACTH is considered a secondary regulator of aldosterone production, patients with apparent essential hypertension have been treated with mineralocorticoid receptor antagonists (MRAs). In this study, we aimed to identify potentially damaging variants that might be implicated in the phenotype of a well-characterized cohort of 21 hypertensive patients without PA but with stress-induced aldosterone hypersecretion. The patients' blood pressure was normalized though MRA administration.

METHODS

Genetic screening was performed through whole-exome sequencing (WES), and variants in PA-associated or in ion-channels of aldosterone-regulating genes were prioritized. Variants with population frequency < 0.01, predicted to alter protein structure and classified as likely pathogenic by in silico tools, were retained.

RESULTS

Qualifying variants were identified in nine of the 21 patients screened. Seven patients were carriers of six potentially damaging variants in six genes associated with PA (KCNK9, KCNK5, ATP13A3, SLC26A2, CACNA1H, and CACNA1D). A novel variant in the KCNK9 gene (p.V221M) is reported. Our analysis revealed two variants in two novel susceptibility genes for aldosterone hypersecretion, namely, KCNK16 (p.P255H) and CACNA2D3 (p.V557I).

CONCLUSION

WES revealed potentially damaging germline variants in genes participating in aldosterone synthesis/regulating pathways in 9/21 patients of our cohort. The variants identified might play a role in aldosterone hypersecretion under conditions of stress. The potential pathogenicity of these variants should be examined in future functional studies.

Identification of risk loci for primary aldosteronism in genome-wide association studies

Primary aldosteronism affects up to 10% of hypertensive patients and is responsible for treatment resistance and increased cardiovascular risk. Here we perform a genome-wide association study in a discovery cohort of 562 cases and 950 controls and identify three main loci on chromosomes 1, 13 and X; associations on chromosome 1 and 13 are replicated in a second cohort and confirmed by a meta-analysis involving 1162 cases and 3296 controls. The association on chromosome 13 is specific to men and stronger in bilateral adrenal hyperplasia than aldosterone producing adenoma. Candidate genes located within the two loci, CASZ1 and RXFP2, are expressed in human and mouse adrenals in different cell clusters. Their overexpression in adrenocortical cells suppresses mineralocorticoid output under basal and stimulated conditions, without affecting cortisol biosynthesis. Our study identifies the first risk loci for primary aldosteronism and highlights new mechanisms for the development of aldosterone excess.

Who should be screened for primary aldosteronism? A comprehensive review of current evidence

Arterial hypertension is a major risk factor for cardiovascular disease. The prevalence of primary aldosteronism (PA) ranges from 5% to 10% in the general hypertensive population and is regarded as one of the most common causes of secondary hypertension. There are two major causes of PA: bilateral adrenal hyperplasia and aldosterone-producing adenoma. The diagnosis of PA comprises screening, confirmatory testing, and subtype differentiation. The Endocrine Society Practice Guidelines for the diagnosis and treatment of PA recommends screening of patients at an increased risk of PA. These categories include patients with stage 2 and 3 hypertension, drug-resistant hypertension, hypertensive with spontaneous or diuretic-induced hypokalemia, hypertension with adrenal incidentaloma, hypertensive with a family history of early onset hypertension or cerebrovascular accident at a young age, and all hypertensive first-degree relatives of patients with PA. Recently, several studies have linked PA with obstructive sleep apnea and atrial fibrillation unexplained by structural heart defects and/or other conditions known to cause the arrhythmia, which may be partly responsible for the higher rates of cardiovascular and cerebrovascular accidents in patients with PA. The aim of this review is to discuss which patients should be screened for PA, focusing not only on well-established guidelines but also on additional groups of patients with a potentially higher prevalence of PA, as has been reported in recent research.

Update on the Genetics of Primary Aldosteronism and Aldosterone-Producing Adenomas

PURPOSE OF THE REVIEW

Primary aldosteronism (PA) is the leading cause of secondary hypertension, accounting for over 10% of patients with high blood pressure. It is characterized by autonomous production of aldosterone from the adrenal glands leading to low-renin levels. The two most common forms arise from bilateral adrenocortical hyperplasia (BAH) and aldosterone-producing adenoma (APA). We discuss recent discoveries in the genetics of PA.

RECENT FINDINGS

Most APAs harbor variants in the KCNJ5, CACNA1D, ATP1A1, ATP2B3, and CTNNB1 genes. With the exception of β-catenin (CTNNB1), all other causative genes encode ion channels; pathogenic variants found in PA lead to altered ion transportation, cell membrane depolarization, and consequently aldosterone overproduction. Some of these genes are found mutated in the germline state (CYP11B2, CLCN2, KCNJ5, CACNA1H, and CACNA1D), leading then to familial hyperaldosteronism, and often BAH rather than single APAs. Several genetic defects in the germline or somatic state have been identified in PA. Understanding how these molecular abnormalities lead to excess aldosterone contributes significantly to the elucidation of the pathophysiology of low-renin hypertension. It may also lead to new and more effective therapies for this disease acting at the molecular level.

Focus on adrenal and related causes of hypertension in childhood and adolescence: Rare or rarely recognized?

High blood pressure (BP) is not restricted to adults; children and adolescents may also be affected, albeit less frequently. Aside from unfavorable environmental factors, such as obesity and sedentary life leading to early-onset essential hypertension (HT), several secondary causes must be investigated in the occasional hypertensive child/adolescent. Endocrine causes are relevant and multiple, related to the pituitary, thyroid, parathyroid, gonads, insulin, and others, but generally are associated with adrenal disease. This common scenario has several vital components, such as aldosterone, deoxycorticosterone (DOC), cortisol, or catecholamines, but there are also monogenic disorders involving the kidney tubule that cause inappropriate salt retention and HT that simulate adrenal disease. Finally, a blood vessel disease was recently described that may also participate in this vast spectrum of pediatric hypertensive disease. This review will shed some light on the diagnosis and management of conditions, focusing on the most prevalent adrenal (or adrenal-like) disturbances causing HT.

Monogenic forms of low-renin hypertension: clinical and molecular insights

Monogenic disorders of hypertension are a distinct group of diseases causing dysregulation of the renin-angiotensin-aldosterone system and are characterized by low plasma renin activity. These can chiefly be classified as causing (i) excessive aldosterone synthesis (familial hyperaldosteronism), (ii) dysregulated adrenal steroid metabolism and action (apparent mineralocorticoid excess, congenital adrenal hyperplasia, activating mineralocorticoid receptor mutation, primary glucocorticoid resistance), and (iii) hyperactivity of sodium and chloride transporters in the distal tubule (Liddle syndrome and pseudohypoaldosteronism type 2). The final common pathway is plasma volume expansion and catecholamine/sympathetic excess that causes urinary potassium wasting; hypokalemia and early-onset refractory hypertension are characteristic. However, several single gene defects may show phenotypic heterogeneity, presenting with mild hypertension with normal electrolytes. Evaluation is based on careful attention to family history, physical examination, and measurement of blood levels of potassium, renin, and aldosterone. Genetic sequencing is essential for precise diagnosis and individualized therapy. Early recognition and specific management improves prognosis and prevents long-term sequelae of severe hypertension.

Pathophysiology of bilateral hyperaldosteronism

PURPOSE OF REVIEW

Renin-independent aldosterone production from one or both affected adrenal(s), a condition known as primary aldosteronism (PA), is a common cause of secondary hypertension. In this review, we aimed to summarize recent findings regarding pathophysiology of bilateral forms of PA, including sporadic bilateral hyperaldosteronism (BHA) and rare familial hyperaldosteronism.

RECENT FINDINGS

The presence of subcapsular aldosterone synthase (CYP11B2)-expressing aldosterone-producing micronodules, also called aldosterone-producing cell clusters, appears to be a common histologic feature of adrenals with sporadic BHA. Aldosterone-producing micronodules frequently harbor aldosterone-driver somatic mutations. Other potential factors leading to sporadic BHA include rare disease-predisposing germline variants, circulating angiotensin II type 1 receptor autoantibodies, and paracrine activation of aldosterone production by adrenal mast cells. The application of whole exome sequencing has also identified new genes that cause inherited familial forms of PA.

SUMMARY

Research over the past 10 years has significantly improved our understanding of the molecular pathogenesis of bilateral PA. Based on the improved understanding of BHA, future studies should have the ability to develop more personalized treatment options and advanced diagnostic tools for patients with PA.

A narrative review of Hyporeninemic hypertension-an indicator for monogenic forms of hypertension

BACKGROUND AND OBJECTIVE

While the role of the renin-angiotensin-aldosterone system (RAAS) in the development of hypertension is well known, the significance and contribution of low renin hypertension is often overlooked. RAAS stimulation results in more tubular absorption of sodium and water along the nephron, contributing to a higher circulating vascular volume. In addition, members of the RAAS system, such as angiotensin II, have direct effects on vascular vasoconstriction, the heart, aldosterone synthesis in the adrenal glands, the sympathetic nervous system, and the central nervous system. This has resulted in a line of antihypertensive therapeutics targeting RAAS with angiotensin converting enzyme (ACE) inhibitors, angiotensin receptor blockers (ARBs), and renin inhibitors, which prevent conversion of angiotensinogen to angiotensin. While general practitioners and nephrologists are well aware of the causes and the long-term consequences of elevated renin and aldosterone levels, the opposite situation with low renin and/or low aldosterone levels is frequently underappreciated. The objective of this review is to provide insight to the less common forms of hyporeninemic hypertension.

METHODS

We searched the PubMed online library for keywords related to hyporeninemic hypertension and focused on the pediatric population. For pathophysiology we focused on literature of the last 5 years.

KEY CONTENT AND FINDINGS

The low renin and aldosterone levels may be indicators of inherited (especially when associated with hypokalemia), monogenic forms of hypertension stimulating excessive tubular sodium and water absorption which subsequently results in plasma volume expansion and hypertension. These forms of hypertension require frequently specific forms of therapy. This underlines the importance of the practitioner to be familiar with these rare diseases.

CONCLUSIONS

In this review article, we outline the different forms of hypertension characterized by low renin/low aldosterone and low renin/high aldosterone levels, how to diagnose these forms of hypertension, and how to treat them.

Genetic Alterations in Benign Adrenal Tumors

The genetic basis of most types of adrenal adenomas has been elucidated over the past decade, leading to the association of adrenal gland pathologies with specific molecular defects. Various genetic studies have established links between variants affecting the protein kinase A (PKA) signaling pathway and benign cortisol-producing adrenal lesions. Specifically, genetic alterations in GNAS, PRKAR1A, PRKACA, PRKACB, PDE11A, and PDE8B have been identified. The PKA signaling pathway was initially implicated in the pathogenesis of Cushing syndrome in studies aiming to understand the underlying genetic defects of the rare tumor predisposition syndromes, Carney complex, and McCune-Albright syndrome, both affected by the same pathway. In addition, germline variants in ARMC5 have been identified as a cause of primary bilateral macronodular adrenal hyperplasia. On the other hand, primary aldosteronism can be subclassified into aldosterone-producing adenomas and bilateral idiopathic hyperaldosteronism. Various genes have been reported as causative for benign aldosterone-producing adrenal lesions, including KCNJ5, CACNA1D, CACNA1H, CLCN2, ATP1A1, and ATP2B3. The majority of them encode ion channels or pumps, and genetic alterations lead to ion transport impairment and cell membrane depolarization which further increase aldosterone synthase transcription and aldosterone overproduction though activation of voltage-gated calcium channels and intracellular calcium signaling. In this work, we provide an overview of the genetic causes of benign adrenal tumors.

Overview of the 2022 WHO Classification of Adrenal Cortical Tumors

The new WHO classification of adrenal cortical proliferations reflects translational advances in the fields of endocrine pathology, oncology and molecular biology. By adopting a question-answer framework, this review highlights advances in knowledge of histological features, ancillary studies, and associated genetic findings that increase the understanding of the adrenal cortex pathologies that are now reflected in the 2022 WHO classification. The pathological correlates of adrenal cortical proliferations include diffuse adrenal cortical hyperplasia, adrenal cortical nodular disease, adrenal cortical adenomas and adrenal cortical carcinomas. Understanding germline susceptibility and the clonal-neoplastic nature of individual adrenal cortical nodules in primary bilateral macronodular adrenal cortical disease, and recognition of the clonal-neoplastic nature of incidentally discovered non-functional subcentimeter benign adrenal cortical nodules has led to redefining the spectrum of adrenal cortical nodular disease. As a consequence, the most significant nomenclature change in the field of adrenal cortical pathology involves the refined classification of adrenal cortical nodular disease which now includes (a) sporadic nodular adrenocortical disease, (b) bilateral micronodular adrenal cortical disease, and (c) bilateral macronodular adrenal cortical disease (formerly known primary bilateral macronodular adrenal cortical hyperplasia). This group of clinicopathological entities are reflected in functional adrenal cortical pathologies. Aldosterone producing cortical lesions can be unifocal or multifocal, and may be bilateral with no imaging-detected nodule(s). Furthermore, not all grossly or radiologically identified adrenal cortical lesions may be the source of aldosterone excess. For this reason, the new WHO classification endorses the nomenclature of the HISTALDO classification which uses CYP11B2 immunohistochemistry to identify functional sites of aldosterone production to help predict the risk of bilateral disease in primary aldosteronism. Adrenal cortical carcinomas are subtyped based on their morphological features to include conventional, oncocytic, myxoid, and sarcomatoid subtypes. Although the classic histopathologic criteria for diagnosing adrenal cortical carcinomas have not changed, the 2022 WHO classification underscores the diagnostic and prognostic impact of angioinvasion (vascular invasion) in these tumors. Microscopic angioinvasion is defined as tumor cells invading through a vessel wall and forming a thrombus/fibrin-tumor complex or intravascular tumor cells admixed with platelet thrombus/fibrin. In addition to well-established Weiss and modified Weiss scoring systems, the new WHO classification also expands on the use of other multiparameter diagnostic algorithms (reticulin algorithm, Lin-Weiss-Bisceglia system, and Helsinki scoring system) to assist the workup of adrenal cortical neoplasms in adults. Accordingly, conventional carcinomas can be assessed using all multiparameter diagnostic schemes, whereas oncocytic neoplasms can be assessed using the Lin-Weiss-Bisceglia system, reticulin algorithm and Helsinki scoring system. Pediatric adrenal cortical neoplasms are assessed using the Wieneke system. Most adult adrenal cortical carcinomas show > 5 mitoses per 10 mm² and > 5% Ki67. The 2022 WHO classification places an emphasis on an accurate assessment of tumor proliferation rate using both the mitotic count (mitoses per 10 mm²) and Ki67 labeling index which play an essential role in the dynamic risk stratification of affected patients. Low grade carcinomas have mitotic rate of ≤ 20 mitoses per 10 mm², whereas high-grade carcinomas show > 20 mitoses per 10 mm². Ki67-based tumor grading has not been endorsed in the new WHO classification, since the proliferation indices are continuous variables rather than being static thresholds in tumor biology. This new WHO classification emphasizes the role of diagnostic and predictive biomarkers in the workup of adrenal cortical neoplasms. Confirmation of the adrenal cortical origin of a tumor remains a critical requirement when dealing with non-functional lesions in the adrenal gland which may be mistaken for a primary adrenal cortical neoplasm. While SF1 is the most reliable biomarker in the confirmation of adrenal cortical origin, paranuclear IGF2 expression is a useful biomarker in the distinction of malignancy in adrenal cortical neoplasms. In addition to adrenal myelolipoma, the new classification of adrenal cortical tumors has introduced new sections including adrenal ectopia, based on the potential role of such ectopic tissue as a possible source of neoplastic proliferations as well as a potential mimicker of metastatic disease. Adrenal cysts are also discussed in the new classification as they may simulate primary cystic adrenal neoplasms or even adrenal cortical carcinomas in the setting of an adrenal pseudocyst.