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CHLORIDE CHANNEL 2; CLCN2

CHLORIDE CHANNEL 2; CLCN2

Alternative titles; symbolsCLC2HGNC Approved Gene Symbol: CLCN2Cytogenetic location: 3q27.1 Genomic coordinates (GRCh38): 3:184,346,184-184,361,604 (from NCB...

Alternative titles; symbols

  • CLC2

HGNC Approved Gene Symbol: CLCN2

Cytogenetic location: 3q27.1 Genomic coordinates (GRCh38): 3:184,346,184-184,361,604 (from NCBI)

▼ Description
The CLCN2 gene encodes a voltage-gated chloride channel with high expression in the adrenal glomerulosa. Channel opening depolarizes glomerulosa cells and induces expression of aldosterone synthase (CYP11B2; 124080) (summary by Scholl et al., 2018).

▼ Cloning and Expression
Cid et al. (1995) cloned a human homolog of the rat voltage-gated chloride channel CLC2 from a T84 epithelial cell cDNA library. The predicted 898-amino acid protein is over 93% identical to the rat sequence.

Scholl et al. (2018) found expression of the CLCN2 gene predominantly in the zona glomerulosa in the human adrenal cortex.

In mice, Fernandes-Rosa et al. (2018) found expression of the Clcn2 gene in adrenal gland and brain.

▼ Mapping
By PCR of somatic cell hybrid DNAs, Cid et al. (1995) mapped the CLCN2 gene to 3q26-qter.

Stumpf (2019) mapped the CLCN2 gene to chromosome 3q27.1 based on an alignment of the CLCN2 sequence (GenBank BC072004.1) with the genomic sequence (GRCh38).

▼ Gene Function
Schwiebert et al. (1998) found that CLC2 chloride channels are expressed in epithelia affected by cystic fibrosis (CF; 219700) and raised the possibility that these might represent an alternative target for pharmacotherapy of CF. The explore this possibility, they manipulated genetically the expression levels of CLC2 channels in airway epithelial cells derived from cystic fibrosis patients. Whole-cell patch-clamp analysis of cells overexpressing CLC2 identified hyperpolarization-activated chloride ion currents (HACCs) that displayed time- and voltage-dependent activation and an inwardly rectifying steady-state current voltage relationship. Reduction of extracellular pH to 5.0 caused significant increases in HACCs in overexpressing cells and the appearance of robust currents in parental cells from the cystic fibrosis patient. CF cells stably transfected with the antisense CLC2 cDNA showed reduced expression of CLC2 compared with parental cells by Western blotting, and a significant reduction in the magnitude of pH-dependent HACCs. To determine whether changes in the extracellular pH alone could initiate chloride transport via CLC2 channels, they performed chloride-36 efflux studies on overexpressing cells and cells with endogenous expression of CLC2. Acidic extracellular pH increased chloride-36 efflux rates in both cell types, although the CLC2-overexpressing cells had significantly greater chloride conduction and a longer duration of efflux than the parental cells. Compounds that exploit the pH mechanism of activating endogenous CLC2 channels may provide a pharmacologic option for increasing chloride conductance in airways of CF patients.

The chloride homeostasis of neurons and nonneuronal cells is maintained in part by chloride conductance through the CLCN2 channel. By immunostaining, Sik et al. (2000) showed that CLCN2 channels were localized in the plasma membranes of dendrites, axons, and somata of pyramidal and nonpyramidal cells of the hippocampus. In addition, the end feet of astrocytes in the neuropil and around small blood vessels were strongly immunoreactive. Localization was within or adjacent to active zones of symmetrical, presumed GABAergic, synapses, and the authors concluded that CLCN2 is involved in transmembrane chloride movements associated with GABAergic synaptic transmission. Haug et al. (2003) noted that CLCN2 channels act as a chloride-efflux pathway which establishes and maintains a high transmembrane chloride gradient necessary for an inhibitory GABA response.

Using immunohistochemistry of healthy human brain tissue, Depienne et al. (2013) found expression of the CLCN2 gene on the surface of cell bodies and processes of virtually all GFAP (137780)-positive fibrous astrocytes in the posterior limb of the internal capsule. CLCN2 showed a fine punctate quality, consistent with a membrane protein. CLCN2 was enriched in perivascular astrocytes with GlialCAM (611642) and MLC1 (605908). CLCN2 expression was also seen along axons, in oligodendrocytes, and in the ependymal lining. CLCN2 was not detected in neuronal perikarya. Electron microscopy confirmed that CLCN2 was present in white matter astrocytes and enriched in cell processes with astrocyte-astrocyte and astrocyte-abaxonal myelin contacts. Immunoreactivity was also visible in astrocytic endfeet around blood vessels.

▼ Molecular Genetics
Controversial Role of CLCN2 Mutations in Epilepsy

In a genomewide linkage study of 130 families with idiopathic generalized epilepsy (see IGE; 600669), Sander et al. (2000) identified a susceptibility locus on chromosome 3q26.1 (EIG11; 607628). In 3 of 46 unrelated families with IGE localized to 3q26 (including some of the families reported by Sander et al. (2000)), Haug et al. (2003) identified 3 mutations in the CLCN2 gene (600570.0001-600570.0003). In a reevaluation of 2 of the families reported by Haug et al. (2003), Kleefuss-Lie et al. (2009) found discrepancies in the family structure, phenotype, and genetic analysis. On this basis, all but one of the original authors retracted the paper.

Stogmann et al. (2006) did not identify pathogenic mutations in the CLCN2 gene in 61 patients with IGE or 35 patients with temporal lobe epilepsy, suggesting that CLCN2 gene mutations are not a common cause of these disorders.

By sequencing of a large collection of human DNA followed by electrophysiologic analysis, Blanz et al. (2007) concluded that several CLCN2 sequence abnormalities previously found in patients with epilepsy most likely represented innocuous polymorphisms.

Saint-Martin et al. (2009) identified 2 different heterozygous mutations in the CLCN2 gene (600570.0004; 600570.0005) in affected members of 2 unrelated families with juvenile myoclonic epilepsy (EJM8) and idiopathic generalized epilepsy (EIG11), respectively (see 607628). In both families, the unaffected father also had the mutation, suggesting either reduced penetrance or additional unidentified factors necessary for full phenotypic expression.

Niemeyer et al. (2010) disagreed with the conclusion by Kleefuss-Lie et al. (2009) that some of the work by Haug et al. (2003) had merit. Based on lack of functional consequences of the variants reported by Haug et al. (2003) (600570.0001-600570.0003), Niemeyer et al. (2010) asserted that there is no evidence for a role of CLCN2 variants in idiopathic generalized epilepsy.

Leukoencephalopathy with Ataxia

In 6 unrelated patients with leukoencephalopathy with ataxia (LKPAT; 615651), Depienne et al. (2013) identified homozygous or compound heterozygous mutations in the CLCN2 gene (see, e.g., 600570.0006-600570.0009). The initial mutations were found using a combination of homozygosity mapping and whole-exome sequencing, and all mutations were shown to cause a loss of function. Affected individuals had prominent signal abnormalities and decreased apparent diffusion coefficient (ADC) values in the posterior limbs of the internal capsules, middle cerebral peduncles, pyramidal tracts in the pons, and middle cerebellar peduncles. The findings suggested myelin microvacuolation restricted to certain brain regions. Clinical features included ataxia and unstable gait; some patients had additional features of visual field defects, headaches, and learning disabilities. None of the patients had seizures. The clinical findings were similar to those observed in Clcn2-deficient mice (see ANIMAL MODEL).

Familial Hyperaldosteronism Type 2

In affected members of 8 unrelated families with familial hyperaldosteronism type 2 (HALD2; 605635), Scholl et al. (2018) identified 5 different heterozygous missense mutations in the CLCN2 gene (600570.0010-600570.0014). The mutation in the first family (family 3, originally reported by Stowasser et al., 1992) was found by exome sequencing and confirmed by Sanger sequencing. The variant segregated with the disorder in the family, although there was evidence of incomplete penetrance and variable disease expressivity. Subsequent CLCN2 mutations in the other families were found by screening the CLCN2 gene in 80 patients with a similar phenotype. In 2 patients, the CLCN2 mutation occurred de novo. One mutation (R172Q; 600570.0010) was found in 4 unrelated families, and haplotype analysis suggested independent occurrence of the mutation. In vitro functional expression studies in human HEK293 and H295R human adrenocortical cancer cells showed that all mutants shifted the activation curve of the channel to more positive voltages with higher open probabilities at the glomerulosa resting potential. All except 1 variant (S865R; 600570.0012) modified the common gate by increasing the minimum open probability and accelerating activation, resulting in significantly larger chloride efflux compared to wildtype. The S865R variant, which likely has a regulatory function, slowed down deactivation of the gates, with a similar overall effect of increasing chloride flux. The mutations increased expression of CYP11B2 (124080) and its upstream regulator NR4A2 (601828), which increased aldosterone production. Current clamp recordings showed that the R172Q significantly amplified the depolarization of H295R-derived cells compared to wildtype. The findings demonstrated a role of anion channels in glomerulosa membrane potential determination and aldosterone production, and further showed that CLCN2 mutations can increase excitatory anion efflux by modifying the voltage dependence of channel opening, resulting in a gain of function.

In a girl with HALD2, Fernandes-Rosa et al. (2018) identified a de novo heterozygous missense mutation in the CLCN2 gene (G24D; 600570.0015). The mutation was found by whole-exome sequencing and confirmed by Sanger sequencing. The patient was 1 of 12 patients with early-onset hypertension and hyperaldosteronism who underwent whole-exome sequencing. Expression of the mutant protein in Xenopus oocytes dramatically increased current amplitudes compared to wildtype due to a change in the voltage-dependent gating of CLCN2. Expression of the mutation into human adrenocortical cells resulted in increased expression of aldosterone synthase (CYP11B2; 124080) and increased aldosterone production, as well as robust chloride currents that lacked strong voltage dependence. Cells expressing the mutation also had increased aldosterone production after stimulation with angiotensin II compared to cells with wildtype CLCN2. Knockdown of CLCN2 in human adrenocortical cells using shRNA abolished chloride currents and decreased aldosterone production. Sequencing of exon 2 of the CLCN2 gene in 100 patients with bilateral adrenal hyperplasia identified 2 rare heterozygous variants (R66Q and P48R) in 2 patients diagnosed with hypertension at 29 and 19 years, respectively, during pregnancy. However, both variants failed to significantly change CLCN2 currents in Xenopus oocytes. The findings suggested that gain-of-function CLCN2 mutations increase chloride conductance in zona glomerulosa cells, resulting in depolarization and a subsequent increase in opening of voltage-gated calcium channels that trigger autonomous aldosterone production by increasing intracellular calcium concentrations.

▼ Animal Model
Bosl et al. (2001) found that Clcn2-null mice developed severe degeneration of the retina and the testes, which led to selective male infertility. Seminiferous tubules did not develop lumina, and germ cells failed to complete meiosis. Beginning around puberty there was a massive death of primary spermatocytes and later also of spermatogonia. Tubules were filled with abnormal Sertoli cells, which normally express Clcn2 in patches adjacent to germ cells. In the retina, photoreceptors lacked normal outer segments and degenerated between days P10 and P30. The current across the retinal pigment epithelium was severely reduced at P36. Thus, Clcn2 disruption resulted in the death of 2 cell types that depend on supporting cells that form the blood-testes and blood-retina barriers.

Blanz et al. (2007) found that Clcn2-null mice were blind and developed progressive widespread spongiform vacuolation of white matter in the brain and spinal cord. Fluid-filled spaces appeared between myelin sheaths of the central but not the peripheral nervous system. However, neuronal morphology appeared normal, and neurologic deficits were mild, mainly including decreased conduction velocity in neurons of the central auditory pathway. The phenotype resembled a leukodystrophy; however, no CLCN2 mutations were found in 150 human leukodystrophy patients. Heterozygous loss of Clcn2 had no detectable functional or morphologic consequences. Neither heterozygous nor homozygous Clcn2 knockout mice had lowered seizure thresholds. Blanz et al. (2007) postulated a role for CLCN2 in glial function and ionic homeostasis in the central nervous system.

▼ ALLELIC VARIANTS ( 15 Selected Examples):

.0001 RECLASSIFIED - VARIANT OF UNKNOWN SIGNIFICANCE
CLCN2, 1-BP INS, 597G
This variant, formerly titled SUSCEPTIBILITY TO JUVENILE MYOCLONIC EPILEPSY 8 based on the report by Haug et al. (2003), has been reclassified based on the findings of Niemeyer et al. (2004) and Kleefuss-Lie et al. (2009).

Haug et al. (2003) identified a heterozygous 1-bp insertion (597insG) in the CLCN2 gene in a family in which 4 members had juvenile myoclonic epilepsy (EJM8; see 607628) and 1 member had epilepsy with grand mal seizures on awakening (EMGA). The insertion mutation resulted in a premature stop codon and a truncated protein lacking major sequence determinants of the ionic pore. Functional studies showed that mutant channels did not yield detectable chloride currents, and the authors suggested that resultant intracellular chloride accumulation would reduce an inhibitory GABA response, resulting in neuronal hyperexcitability and epileptic seizures.

In a reevaluation of the family reported by Haug et al. (2003), Kleefuss-Lie et al. (2009) found that only the proband had JME; no other family members had seizures. In addition, the pedigree structure was different from that previously described, and resequencing of the CLCN2 gene in new blood samples showed that 3 of the original DNA samples were contaminated. On this basis, all but one of the original authors offered a retraction of the paper. However, Kleefuss-Lie et al. (2009) noted that the mutation was not observed in 4,700 German control individuals and may act as a susceptibility factor in the development of epilepsy.

The 597insG mutation results in a truncated CLCN2 protein lacking 13 of 18 membrane helices including most putative pore-forming regions, resulting in a loss of function. Niemeyer et al. (2004) showed that coexpression of wildtype and 597insG CLCN2 produced currents with voltage dependence similar to wildtype, but with nonsignificant lower maximal conductance. The authors also showed that the mutant protein did not reach the plasma membrane. The results were not consistent with a dominant-negative effect, and the authors questioned the findings of Haug et al. (2003) and the role of CLCN2 mutations in epilepsy.

Blanz et al. (2007) found that the 597insG mutant protein lacked dominant-negative effects when coexpressed in Xenopus cells with wildtype CLCN2, suggesting that it has no influence of channel function in the heterozygous state.

.0002 RECLASSIFIED - VARIANT OF UNKNOWN SIGNIFICANCE
CLCN2, IVS2, 11-BP DEL
This variant, formerly titled EPILEPSY WITH GRAND MAL SEIZURES ON AWAKENING and CHILDHOOD ABSENCE EPILEPSY based on the report by Haug et al. (2003), has been reclassified based on the findings of Niemeyer et al. (2004) and Kleefuss-Lie et al. (2009).

Haug et al. (2003) identified a heterozygous 11-bp deletion in intron 2 of the CLCN2 gene close to the splice acceptor site in a family in which several members had epilepsy with grand mal seizures on awakening (EGMA) and 1 member had childhood absence epilepsy (CAE). Of note, the patients who reportedly had EGMA became seizure-free without medication. The mutation resulted in an in-frame deletion of 44 amino acids, predicting the deletion of helix B of the protein. Studies showed that the mutation rendered a nonfunctional chloride channel.

In vitro studies by Niemeyer et al. (2004) showed that coexpression of wildtype and IVS2del11 CLCN2 did not change the characteristics of the wildtype channel. There was also no difference in the proportion of exon-skipped to normally spliced mRNA, predicting no alteration in channel expression in individuals with this variant. The authors also showed that the mutant protein did not reach the plasma membrane. The results were not consistent with a dominant-negative effect, and the authors questioned the findings of Haug et al. (2003) and the role of CLCN2 mutations in epilepsy.

In a reevaluation of the family reported by Haug et al. (2003), Kleefuss-Lie et al. (2009) found that only the index case was affected with idiopathic generalized epilepsy (607628). This patient's deceased great-grandfather was reportedly affected with epilepsy. Molecular fingerprinting of the original DNA samples showed a discrepancy in the number of individuals from whom a sample was obtained, rendering the results inconclusive. On this basis, all but one of the original authors retracted the paper (Haug et al., 2003). Kleefuss-Lie et al. (2009) noted, however, that the mutation was not observed in 4,700 German control individuals and may act as a susceptibility factor in the development of epilepsy.

.0003 RECLASSIFIED - VARIANT OF UNKNOWN SIGNIFICANCE
CLCN2, GLY715GLU
This variant, formerly titled SUSCEPTIBILITY TO JUVENILE ABSENCE EPILEPSY 2 based on the report by Haug et al. (2003), has been reclassified based on the findings of Niemeyer et al. (2004) and Kleefuss-Lie et al. (2009).

In 2 sibs with juvenile absence epilepsy (EJA2; see 607628), Haug et al. (2003) identified a heterozygous 2144G-A mutation, resulting in a gly715-to-glu (G715E) substitution. Another sib with generalized spike-wave discharges on EEG also carried the mutation. The father, who also carried the mutation, reportedly had unclassified seizures in childhood, but his severe alcoholism as an adult rendered his disease status uncertain. Functional studies of the mutant channel showed normal current amplitudes, but altered voltage-dependent gating, potentially leading to hyperexcitability. The family structure, diagnosis, and mutation status were confirmed by Kleefuss-Lie et al. (2009). The mutation was not observed in 4,700 German control individuals.

Niemeyer et al. (2004) stated that the G715E substitution occurs in the long intracellular C terminus of the channel between the 2 CBS domains. In vitro functional studies showed no differences regarding voltage dependence of gating and kinetic parameters between wildtype and G715E channels. The G715E mutant had diminished opening and closing response to ATP, but the effect was not significant when coexpressed with wildtype CLCN2. Although Niemeyer et al. (2004) suggested that the effect may become pathologic in conditions of cellular ATP depletion, the observed effect was 'far from being deleterious,' raising doubt about its pathogenicity.

.0004 EPILEPSY, JUVENILE MYOCLONIC, SUSCEPTIBILITY TO, 8
CLCN2, ARG235GLN
In 2 sibs of Tunisian origin with juvenile myoclonic epilepsy (see 607628), Saint-Martin et al. (2009) identified a heterozygous 704G-A transition in the CLCN2 gene, resulting in an arg235-to-gln (R235Q) substitution in a short loop between the fourth and fifth putative transmembrane domains. In vitro functional expression studies showed that the mutant channel had accelerated deactivation rates compared to wildtype, but normal activation and peak current. The mutation was not observed in 263 control individuals from North Africa or 183 French controls. The unaffected father also had the mutation, suggesting either reduced penetrance or that additional unidentified factors are necessary for full phenotypic expression. Another sib with JME was not available for genetic analysis.

.0005 EPILEPSY, IDIOPATHIC GENERALIZED, SUSCEPTIBILITY TO, 11
CLCN2, ARG577GLN
In 2 German sibs with idiopathic generalized epilepsy (EIG11; 607628), Saint-Martin et al. (2009) identified a heterozygous 1730G-A transition in the CLCN2 gene, resulting in an arg577-to-gln (R577Q) substitution close to the first CBS domain. In vitro functional expression studies showed that the mutant channel had accelerated deactivation rates compared to wildtype, but normal activation and peak current. The mutation was not observed in 203 German controls or 183 French controls. The unaffected father also had the mutation, suggesting either reduced penetrance or that additional unidentified factors are necessary for full phenotypic expression.

.0006 LEUKOENCEPHALOPATHY WITH ATAXIA
CLCN2, TRP570TER
In 2 unrelated patients from North Africa with adult-onset leukoencephalopathy with ataxia (LKPAT; 615651) Depienne et al. (2013) identified a homozygous c.1709G-A transition in exon 15 of the CLCN2 gene, resulting in a trp570-to-ter (W570X) substitution. The mutation, which was found by whole-exome sequencing and confirmed by Sanger sequencing, was not present in the HapMap Project or 1000 Genomes Project databases or in controls. Patient fibroblasts showed decreased mutant mRNA, consistent with nonsense-mediated mRNA decay and suggesting a loss of function.

.0007 LEUKOENCEPHALOPATHY WITH ATAXIA
CLCN2, 6-BP DEL, NT430
In a woman from North Africa, born of consanguineous parents, with adult-onset leukoencephalopathy with ataxia (LKPAT; 615651), Depienne et al. (2013) identified a homozygous 6-bp in-frame deletion (c.430_435del) in exon 4 of the CLCN2 gene, resulting in the deletion of 2 highly conserved hydrophobic residues, Leu144 and Ile145, in a transmembrane domain. The mutation, which was found using a combination of homozygosity mapping and whole-exome sequencing, was confirmed by Sanger sequencing and was not present in the HapMap Project or 1000 Genomes Project databases or in healthy controls. In vitro functional expression assays in COS-7 cells showed that the mutant protein was restricted to the endoplasmic reticulum and hardly reached the plasma membrane. There were also lower amounts of the mutant protein compared to wildtype. These findings were consistent with a loss of function.

.0008 LEUKOENCEPHALOPATHY WITH ATAXIA
CLCN2, ALA500VAL
In a boy with childhood-onset leukoencephalopathy with ataxia (LKPAT; 615651), Depienne et al. (2013) identified a homozygous c.1499C-T transition in exon 14 of the CLCN2 gene, resulting in an ala500-to-val (A500V) substitution at a highly conserved hydrophobic residue in a transmembrane domain. The unaffected parents were heterozygous for the mutation, which was not found in the HapMap Project or 1000 Genomes Project databases or in healthy controls. In vitro functional expression assays in COS-7 cells showed that the mutant protein was restricted to the endoplasmic reticulum and hardly reached the plasma membrane. There were also lower amounts of the mutant protein compared to wildtype. These findings were consistent with a loss of function.

.0009 LEUKOENCEPHALOPATHY WITH ATAXIA
CLCN2, 1-BP DUP, 828G
In a girl, born of consanguineous parents, with childhood-onset leukoencephalopathy with ataxia (LKPAT; 615651), Depienne et al. (2013) identified a homozygous 1-bp duplication (c.828dupG) in exon 8 of the CLCN2 gene, resulting in a frameshift and premature termination (Arg277AlafsTer23). The unaffected parents were heterozygous for the mutation, which was not found in the HapMap Project or 1000 Genomes Project databases or in healthy controls.

.0010 HYPERALDOSTERONISM, FAMILIAL, TYPE II
CLCN2, ARG172GLN
In affected members of 4 unrelated families (families 3, 1786, 318, and 537) with familial hyperaldosteronism type 2 (HALD2; 605635), Scholl et al. (2018) identified a heterozygous mutation (chr3.184,075,850C-T, GRCh37) in the CLCN2 gene, resulting in a arg172-to-gln (R172Q) substitution at a highly conserved residue. The mutation in family 3 was found by exome sequencing and confirmed by Sanger sequencing; mutations in subsequent families were found by analysis of CLCN2 in exome data or by direct sequencing of CLCN2 in additional patients with a similar phenotype. The mutation segregated with the phenotype in 2 of the families; it occurred de novo in family 318 and was found in only 1 patient in family 537. The mutation was not found in the ExAC or gnomAD databases. Family 3 was originally reported by Stowasser et al. (1992). Haplotype analysis suggested independent occurrence of the mutation in the families. In vitro functional expression studies in human HEK293 and H295R human adrenocortical cancer cells showed that the R172Q mutation shifted the activation curve of the channel to more positive voltages, which increased the minimum open probability and accelerated activation, resulting in significantly larger chloride efflux compared to wildtype. There was increased expression of CYP11B2 (124080) and its upstream regulator NR4A2 (601828), which also increased aldosterone production. Current clamp recordings showed that the R172Q significantly amplified the depolarization of H295R-derived cells compared to wildtype. The findings were consistent with a gain of function.

.0011 HYPERALDOSTERONISM, FAMILIAL, TYPE II
CLCN2, MET22LYS
In a 1-year-old girl (family 1281) with familial hyperaldosteronism type 2 (HALD2; 605635), Scholl et al. (2018) identified a de novo heterozygous mutation (chr3.184,076,918, GRCh37) in the CLCN2 gene, resulting in a met22-to-lys (M22K) substitution at a conserved residue. The mutation was not found in the ExAC or gnomAD databases.

.0012 HYPERALDOSTERONISM, FAMILIAL, TYPE II
CLCN2, SER865ARG
In a 20-year-old man (family 840) with familial hyperaldosteronism type 2 (HALD2; 605635), Scholl et al. (2018) identified a heterozygous mutation (chr3.184,064,498T-G, GRCh37) in the CLCN2 gene, resulting in a ser865-to-arg (S865R) substitution at a moderately conserved residue. Parental DNA was not available for segregation analysis, but the parents were reportedly unaffected. The mutation was not found in the ExAC or gnomAD databases. The S865 residue is phosphorylated, suggesting a regulatory function. In vitro cellular functional expression studies showed that the S865R mutation slowed down deactivation of the channel pore gate, resulting in increased pore open probability.

.0013 HYPERALDOSTERONISM, FAMILIAL, TYPE II
CLCN2, TYR26ASN
In a 20-year-old woman (family 531) with familial hyperaldosteronism type 2 (HALD2; 605635), Scholl et al. (2018) identified a heterozygous mutation (chr3.184,076,907A-T, GRCh37) in the CLCN2 gene, resulting in a tyr26-to-asn (Y26N) substitution at a highly conserved residue. The patient presented with hypertension at age 6 years. Her deceased mother was affected, but DNA was not available for segregation analysis. The mutation was not found in the ExAC or gnomAD databases.

.0014 HYPERALDOSTERONISM, FAMILIAL, TYPE II
CLCN2, LYS362DEL
In a male infant (family 1492) with familial hyperaldosteronism type 2 (HALD2; 605635), Scholl et al. (2018) identified a heterozygous mutation (chr3.184,074,782T-A, GRCh37) in the CLCN2 gene, predicted to create a new splice donor site at the end of exon 10. A splicing assay in HEK cells showed that the mutation resulted in an in-frame deletion of codon 362. The patient's mother was affected, but DNA was not available for segregation studies. The mutation was not found in the ExAC or gnomAD databases.

.0015 HYPERALDOSTERONISM, FAMILIAL, TYPE II
CLCN2, GLY24ASP
In a girl with familial hyperaldosteronism type 2 (HALD2; 605635), Fernandes-Rosa et al. (2018) identified a de novo heterozygous c.71G-A transition (c.71G-A, NM_004366) in the CLCN2 gene, resulting in a gly24-to-asp (G24D) substitution at a highly conserved residue in the N-terminal cytoplasmic inactivation domain. The mutation, which was found by whole-exome sequencing and confirmed by Sanger sequencing, was not found in the ExAC database or in an in-house database. Expression of the mutant protein in Xenopus oocytes dramatically increased current amplitudes compared to wildtype due to a change in the voltage-dependent gating of Clcn2. Expression of the mutation into human adrenocortical cells resulted in increased expression of aldosterone synthase (CYP11B2; 124080) and increased aldosterone production, as well as robust chloride currents that lacked strong voltage dependence. Cells expressing the mutation also had increased aldosterone production after stimulation with angiotensin II compared to cells with wildtype CLCN2. The data suggested that a gain-of-function CLCN2 mutation may depolarize the cell, activate the steroidogenic pathway, and increase aldosterone production.

Tags: 3q27.1