Early-onset Primary Aldosteronism Research Articles

S-13-5: UPDATES ON FAMILIAL HYPERALDSOTERONISM

The first reported (Sutherland et al. 1966) form of familial primary aldosteronism (PA) involved a father and son and was glucocorticoid-remediable (familial hyperaldosteronism type I, FH-I). In 1992, Lifton and colleagues elucidated its causation, a hybrid gene mutation composed of CYP11B1 (encoding 11beta-hydroxylase) regulatory sequences and CYP11B2 (aldosterone synthase) coding sequences causing ACTH-regulated aldosterone overproduction and hypertension, both readily controlled by low-dose glucocorticoid administration. Expression of aldosterone synthase activity within zona fasciculata (ZF) explained overproduction of hybrid steroids, 18-hydroxy- and 18-oxocortisol. Since 2011, PA-causing germline mutations in another four genes (three associated with FH) have been reported. While three encode cation channels (KCNJ5, CACNA1H and CACNA1D), one encodes an anion channel (CLCN2). FH-III is caused by inheritance of gain-of-function mutations in KCNJ5, encoding an inwardly rectifying potassium channel (GIRK-4). Depending on the exact mutation involved, phenotype varies from very severe (profound PA, hybrid steroid elevation and ZF hyperplasia and requiring bilateral adrenalectomy to control hypertension) to mild (absence of above with PA controllable with spironolactone). Most pedigrees demonstrate early-onset hypertension. Mutations reduce selectivity of GIRK-4 to potassium, permitting entry of sodium into the adrenal cortical cell, which results in cell depolarization and calcium influx, leading to increased expression of CYP11B2 and aldosterone synthesis. A gain-of-function mutation in CACNA1H, encoding a T-type voltage-gated calcium channel, was found in five of 40 subjects with early-onset PA and three relatives with early-onset hypertension (FH-IV). Adrenals appeared normal on imaging. The mutation shifts activation of zona glomerulosa (ZG) cells to a more hyperpolarized potential and slows inactivation, putatively resulting in increased calcium influx and aldosterone production. Germline mutations in CACNA1D, encoding an L-type voltage-gated calcium channel highly expressed in ZG, were identified in two of 100 individuals with early-onset PA. Both occurred de novo, and were associated with seizures and a variety of neurological abnormalities (PASNA). Both mutations cause channel activation at less depolarized membrane potentials, and one nearly abolished channel inactivation. In a large Australian family with FH-II, a mutation was found in CLCN2 encoding a chloride channel, ClC-2. CLCN2 mutations were found in another seven of 80 individuals with early-onset PA. A concurrent report found a CLCN2 mutation in one of 12 subjects with early-onset PA. PA due to CLCN2 mutations responds well to medical treatment. In the adrenal, ClC-2 localizes predominantly to ZG and mutations predispose cell depolarization, leading to calcium influx via activation of voltage-gated calcium channels and increased aldosterone production.

SAT-554 Genetic Profile of Early-Onset Aldosterone-Producing Adenomas

Background: Aldosterone-producing adenoma (APA) is a major subtype of primary aldosteronism (PA) which is the most common cause of endocrine-related hypertension. The Endocrine Society clinical practice guideline suggests that young patients (< 35 years old) with a CT-detected adrenocortical adenoma and typical phenotype of PA may not need adrenal venous sampling prior to adrenalectomy. In recent years, aldosterone-driver somatic mutations have been identified in APA, and prevalence studies suggest potential effects of patient age and sex. However, the rare nature of early-onset PA has prevented a detailed study of the histologic characteristics and aldosterone-driver somatic mutations in adrenal tumors from these patients. Objective: To determine histologic and somatic mutation profile in early-onset APA. Methods: Fifty-five formalin-fixed paraffin-embedded (FFPE) adrenals from patients at the age of 35 years old or younger who underwent adrenalectomy at the participating centers were studied (45 women, 9 men, and 1 unknown sex). CYP11B2 immunohistochemistry (IHC)-guided tumor capturing was used to selectively obtain DNA from APA. Mutation status was determined either by Sanger sequencing or targeted next-generation sequencing. Results: CYP11B2 IHC identified APAs in all adrenal specimens. Solitary APAs were found in 53 adrenals. One adrenal had multiple APAs and one had a dominant CYP11B2-negative tumor and a smaller APA. In total, DNA from 57 APAs were sequenced. Two APAs were excluded from the analysis due to low sample quality. In 52 of the 55 APAs, somatic mutations were identified in one of the aldosterone-driver genes or CTNNB1 gene, encoding β-catenin. The most common genetic alteration was seen in KCNJ5 (37/55, 67%), followed by CACNA1D (7/55, 13%), ATP1A1 (3/55, 5%), CTNNB1 (3/55, 5%), and ATP2B3 (2/55, 4%). No sex difference in the prevalence of KCNJ5 mutation was observed in this age group. Conclusion: The majority of adrenals from early-onset PA patients had a solitary APA. Regardless of sex, the most common genetic cause of early-onset APA was somatic mutations in KCNJ5.

SAT-549 Identification of Somatic Mutations in CLCN2 as a Cause of Aldosterone-Producing Adenomas

Background: Primary aldosteronism (PA) results from both unilateral and bilateral adrenal disease. Unilateral disease is most often caused by aldosterone-producing adenomas (APAs). We recently identified aldosterone-driver somatic mutations in approximately 90% of APAs using an aldosterone synthase (CYP11B2) immunohistochemistry (IHC)-guided DNA sequencing approach. In the present study, we analyzed DNA from APA samples found to be mutation negative. Methods: Formalin-fixed paraffin-embedded tissue samples from PA patients who underwent adrenalectomy were studied. Genomic DNA was isolated from 118 APAs (identified by CYP11B2 IHC). Next generation sequencing (NGS) was performed to identify known aldosterone-driver mutations in KCNJ5, ATP1A1, ATP2B3, and CACNA1D. APA DNA that was mutation negative and the adjacent normal adrenal tissue DNA were subjected to Whole Exome Sequencing (WES). Results: Targeted NGS and WES detected two variants in the voltage-gated chloride channel ClC-2 (encoded by CLCN2), which were confirmed by Sanger sequencing. One of the CLCN2 mutations (p.Gly24Asp) was identical to that previously found to cause germline early-onset PA. The second CLCN2 mutation, which would affect the same region of the protein, was an unreported PA mutation (p.Met22fs). The presence of these variants in two tumors suggests that CLCN2 mutations as a cause of APAs are rare with an approximate prevalence of 1.7% (2/118 APAs). Conclusion: In this study, we identified somatic mutations in CLCN2, in two of 118 APAs. Germline variants in this gene have previously been shown to cause of familial hyperaldosteronism type II and the current findings indicate that similar mutations cause a small proportion of APAs. These findings also indicate that WES of CYP11B2-guided mutation negative APAs can help determine rarer genetic causes of sporadic PA.

Pathogenesis of Familial Hyperaldosteronism Type II: New Concepts Involving Anion Channels.

The application of advanced genetic techniques has recently begun to unravel the genetic basis for familial primary aldosteronism type 2 (FH-II). Whole-exome sequencing in a large family with FH-II revealed a shared rare damaging heterozygous variant in CLCN2 (chr.3: g.184075850C>T, p.Arg172Gln) in three severely affected members. The gene encodes a chloride channel, ClC-2. A cohort of 80 unrelated individuals diagnosed with early-onset primary aldosteronism was also examined for CLCN2 mutations finding three further occurrences of p.Arg172Gln mutations and four single cases of other potentially damaging heterozygous mutations for an overall prevalence of 9.9%. A concurrent report also found a different CLCN2 mutation (p.Gly24Asp) in a single severely affected patient from a cohort of 12 with early-onset PA for a prevalence of 8.3%. Cases of primary aldosteronism associated with CLCN2 mutations appear to be bilateral and respond well to medical treatment. In the adrenal, ClC-2 has been demonstrated to localize predominantly to the zona glomerulosa (ZG), and functional analysis suggests that mutations in ClC-2 predispose ZG cells to depolarization, thus leading to calcium influx via activation of voltage-gated calcium channels and increased aldosterone production. Germline CLCN2 mutations appear to account for a substantial proportion of early-onset primary aldosteronism cases, and genetic testing for mutations in this gene should be considered in appropriate cases.

Somatic and inherited mutations in primary aldosteronism

Primary aldosteronism (PA), the most common form of secondary hypertension, is caused in the majority of cases by unilateral aldosterone-producing adenoma (APA) or bilateral adrenal hyperplasia. Over the past few years, somatic mutations in KCNJ5, CACNA1D, ATP1A1 and ATP2B3 have been proven to be associated with APA development, representing more than 50% of sporadic APA. The identification of these mutations has allowed the development of a model for APA involving modification on the intracellular ionic equilibrium and regulation of cell membrane potential, leading to autonomous aldosterone overproduction. Furthermore, somatic CTNNB1 mutations have also been identified in APA, but the link between these mutations and APA development remains unknown. The sequence of events responsible for APA formation is not completely understood, in particular, whether a single hit or a double hit is responsible for both aldosterone overproduction and cell proliferation. Germline mutations identified in patients with early-onset PA have expanded the classification of familial forms (FH) of PA. The description of germline KCNJ5 and CACNA1H mutations has identified FH-III and FH-IV based on genetic findings; germline CACNA1D mutations have been identified in patients with very early-onset PA and severe neurological abnormalities. This review summarizes current knowledge on the genetic basis of PA, the association of driver gene mutations and clinical findings and in the contribution to patient care, plus the current understanding on the mechanisms of APA development.

CACNA1H Mutations Are Associated With Different Forms of Primary Aldosteronism

Primary aldosteronism (PA) is the most common form of secondary hypertension. Mutations in KCNJ5, ATP1A1, ATP2B3 and CACNA1D are found in aldosterone producing adenoma (APA) and familial hyperaldosteronism (FH). A recurrent mutation in CACNA1H (coding for Cav3.2) was identified in a familial form of early onset PA. Here we performed whole exome sequencing (WES) in patients with different types of PA to identify new susceptibility genes.Four different heterozygous germline CACNA1H variants were identified. A de novo Cav3.2 p.Met1549Ile variant was found in early onset PA and multiplex developmental disorder. Cav3.2 p.Ser196Leu and p.Pro2083Leu were found in two patients with FH, and p.Val1951Glu was identified in one patient with APA. Electrophysiological analysis of mutant Cav3.2 channels revealed significant changes in the Ca2+ current properties for all mutants, suggesting a gain of function phenotype. Transfections of mutant Cav3.2 in H295R-S2 cells led to increased aldosterone production and/or expression of genes coding for steroidogenic enzymes after K+ stimulation. Identification of CACNA1H mutations associated with early onset PA, FH, and APA suggests that CACNA1H might be a susceptibility gene predisposing to PA with different phenotypic presentations, opening new perspectives for genetic diagnosis and management of patients with PA.

CACNA1H(M1549V) Mutant Calcium Channel Causes Autonomous Aldosterone Production in HAC15 Cells and Is Inhibited by Mibefradil.

We recently demonstrated that a recurrent gain-of-function mutation in a T-type calcium channel, CACNA1H(M1549V), causes a novel Mendelian disorder featuring early-onset primary aldosteronism and hypertension. This variant was found independently in five families. CACNA1H(M1549V) leads to impaired channel inactivation and activation at more hyperpolarized potentials, inferred to cause increased calcium entry. We here aimed to study the effect of this variant on aldosterone production. We heterologously expressed empty vector, CACNA1H(WT) and CACNA1H(M1549V) in the aldosterone-producing adrenocortical cancer cell line H295R and its subclone HAC15. Transfection rates, expression levels, and subcellular distribution of the channel were similar between CACNA1H(WT) and CACNA1H(M1549V). We measured aldosterone production by an ELISA and CYP11B2 (aldosterone synthase) expression by real-time PCR. In unstimulated cells, transfection of CACNA1H(WT) led to a 2-fold increase in aldosterone levels compared with vector-transfected cells. Expression of CACNA1H(M1549V) caused a 7-fold increase in aldosterone levels. Treatment with angiotensin II or increased extracellular potassium levels further stimulated aldosterone production in both CACNA1H(WT)- and CACNA1H(M1549V)-transfected cells. Similar results were obtained for CYP11B2 expression. Inhibition of CACNA1H channels with the T-type calcium channel blocker Mibefradil completely abrogated the effects of CACNA1H(WT) and CACNA1H(M1549V) on CYP11B2 expression. These results directly link CACNA1H(M1549V) to increased aldosterone production. They suggest that calcium channel blockers may be beneficial in the treatment of a subset of patients with primary aldosteronism. Such blockers could target CACNA1H or both CACNA1H and the L-type calcium channel CACNA1D that is also expressed in the adrenal gland and mutated in patients with primary aldosteronism.

An Update on Familial Hyperaldosteronism.

Familial forms of primary aldosteronism have been suggested to account for up to 6% of cases in referral centers. For many years, the genetics of familial hyperaldosteronism remained unknown, with the notable exception of glucocorticoid-remediable aldosteronism, due to unequal crossing over and formation of a chimeric 11β-hydroxylase/aldosterone synthase gene. Over the past 5 years, mutations in 3 additional genes have been shown to cause familial forms of primary aldosteronism. Gain-of-function heterozygous germline mutations in KCNJ5, which encodes an inward rectifier potassium channel, cause autosomal dominant syndromes of PA and hypertension with or without adrenal hyperplasia. Germline mutations in CACNA1D, which codes for an L-type calcium channel, have so far only been found in 2 cases with a syndrome of primary aldosteronism, seizures, and neurologic abnormalities. Both KCNJ5 and CACNA1D mutations in familial hyperaldosteronism were only discovered following identification of similar or identical somatic mutations in aldosterone-producing adenomas. In contrast, a recent exome sequencing study identified germline mutations in CACNA1H (a T-type calcium channel), previously undescribed in adenomas, in 5 unrelated families with early-onset primary aldosteronism and hypertension, without any additional shared symptoms. Future exome or genome sequencing studies are expected to shed light on the genetic basis of many cases of familial hyperaldosteronism that remain unexplained.

New insights into aldosterone-producing adenomas and hereditary aldosteronism

Primary aldosteronism is a major cause of secondary hypertension worldwide. This review describes the recent studies that have provided dramatic new insight into the pathogenesis of aldosterone-producing adenomas (APAs) and inherited primary aldosteronism, revealing the role of mutations in the potassium channel KCNJ5 in these disorders. Either of two somatic gain-of-function mutations in the inward rectifier potassium channel KCNJ5 (Kir3.4) are present in approximately 40% of APAs. These tumor-causing mutations are heterozygous and alter the channel's selectivity filter. Mutant channels gain permeability to sodium, resulting in cellular depolarization and activation of voltage-gated calcium channels. The resulting calcium influx is sufficient to produce aldosterone secretion and cell proliferation, accounting for APA development. Germline KCNJ5 mutations also result in either of two autosomal-dominant syndromes featuring early-onset primary aldosteronism. Mutations identical or similar to those found in APAs result in massive bilateral adrenal hyperplasia. A different mutation at the same position produces a less severe syndrome without adrenal hyperplasia because this mutation results in Na-dependent cell lethality caused by a drastic increase in Na conductance. These findings provide fundamental insight into the pathogenesis of APAs and primary aldosteronism, and have implications for new diagnostic and therapeutic strategies.