KCNQ2 mutations cause unique neonatal behavior arrests without motor seizures: Functional characterization.

OBJECTIVE: KCNQ2 gene mutation usually manifests as neonatal seizures in the first week of life. Nonsense mutations cause a unique self-limited familial neonatal epilepsy (SLFNE), which is radically different from developmental epileptic encephalopathy (DEE). However, the exact underlying mechanisms remain unclear. METHODS: The proband, along with their mother and grandmother, carried the c.1342C > T (p.Arg448Ter) mutation in the KCNQ2 gene. The clinical phenotypes, electroencephalography (EEG) findings, and neurodevelopmental outcomes were comprehensively surveyed. The mutant variants were transfected into HEK293 cells to investigate functional changes. RESULTS: The proband exhibited behavior arrests, autonomic and non-motor neonatal seizures with changes in heart rate and respiration. EEG exhibited focal sharp waves. Seizures were remitted after three months of age. The neurodevelopmental outcomes at three years of age were unremarkable. A functional study demonstrated that the currents of p.Arg448Ter were non-functional in homomeric p.Arg448Ter compared with that of the KCNQ2 wild type. However, the current density and V1/2 exhibited significant improvement and close to that of the wild-type after transfection with heteromeric KCNQ2 + p.Arg448Ter and KCNQ2 + KCNQ3 + p.Arg448Ter respectively. Channel expression on the cell membrane was not visible after homomeric transfection, but not after heteromeric transfection. Retigabine did not affect homomeric p.Arg448Ter but improved heteromeric p. Arg448Ter + KCNQ2 and heteromeric KCNQ2 + Arg448Ter + KCNQ3. CONCLUSIONS: The newborn carrying the p. Arg448Ter mutation presented frequent behavioral arrests, autonomic, and non-motor neonatal seizures. This unique pattern differs from KCNQ2 seizures, which typically manifest as motor seizures. Although p.Arg448Ter is a non-sense decay, the functional study demonstrated an almost-full compensation mechanism after transfection of heteromeric KCNQ2 and KCNQ3.

Vascular endothelial dysfunction induced by 3-bromofluoranthene via MAPK-mediated-NFκB pro-inflammatory pathway and intracellular ROS generation.

3-Bromofluoranthene (3-BrFlu) is the secondary metabolite of fluoranthene, which is classified as a polycyclic aromatic hydrocarbon, through bromination and exists in the fine particulate matter of air pollutants. Endothelial dysfunction plays a critical role in the pathogenesis of cardiovascular and vascular diseases. Little is known about the molecular mechanism of 3-BrFlu on endothelial dysfunction in vivo and in vitro assay. In the present study, 3-BrFlu included concentration-dependent changes in ectopic angiogenesis of the sub-intestinal vein and dilation of the dorsal aorta in zebrafish. Disruption of vascular endothelial integrity and up-regulation of vascular endothelial permeability were also induced by 3-BrFlu in a concentration-dependent manner through pro-inflammatory responses in vascular endothelial cells, namely, SVEC4-10 cells. Generation of pro-inflammatory mediator PGE2 was induced by 3-BrFlu through COX2 expression. Expression of COX2 and generation of pro-inflammatory cytokines, including TNFα and IL-6, were induced by 3-BrFlu through phosphorylation of NF-κB p65, which was mediated by phosphorylation of MAPK, including p38 MAPK, ERK and JNK. Furthermore, generation of intracellular ROS was induced by 3-BrFlu, which is associated with the down-regulated activities of the antioxidant enzyme (AOE), including SOD and catalase. We also found that 3-BrFlu up-regulated expression of the AOE and HO-1 induced by 3-BrFlu through Nrf-2 expression. However, the 3-BrFlu-induced upregulation of AOE and HO-1 expression could not be revised the responses of vascular endothelial dysfunction. In conclusion, 3-BrFlu is a hazardous substance that results in vascular endothelial dysfunction through the MAPK-mediated-NFκB pro-inflammatory pathway and intracellular ROS generation.

Ototoxicity among cisplatin, carboplatin, and oxaliplatin in zebrafish model.

Platinum-based antineoplastic drugs, including cisplatin, carboplatin, and oxaliplatin, are widely used in the treatment of various cancers. Ototoxicity is a common adverse effect of platinum-based drugs. Ototoxicity leads to irreversible hearing impairment. We hypothesize that different platinum-based drugs exhibit varying ototoxic concentrations, time effects, and ototoxic mechanisms. We tested this hypothesis by using a zebrafish model (pvalb3b: TagGFP) to assess the viability of hair cells collected from zebrafish larvae. Cisplatin, carboplatin, and oxaliplatin were administered at dosages of 100, 200, or 400 µM, and the ototoxic effects of these drugs were assessed 1, 2, or 3 h after administration. Fm4-64 and a TUNEL assay were used to label the membranes of living hair cells and to detect cell apoptosis, respectively. We observed that >50% of hair cells were damaged at 1 h after cisplatin (100 µM) exposure, and this ototoxic effect increased at higher dosages and over time. Owing to the smaller ototoxic effects of carboplatin and oxaliplatin, we conducted higher-strength and longer-duration experiments with these drugs. Neither carboplatin nor oxaliplatin was obviously ototoxic, even at 1600 µM and after 6 h. Moreover, only cisplatin damaged the membranes of the hair cells. Cell apoptosis and significantly increased antioxidant gene expression were observed in only the cisplatin group. In conclusion, cisplatin significantly damages sensory hair cells and has notable dosage and time effects. Carboplatin and oxaliplatin are less ototoxic than cisplatin, likely due to having different ototoxic mechanisms than cisplatin.

Protective mechanism of ferulic acid against neomycin-induced ototoxicity in zebrafish.

Ototoxicity refers to damage of sensory hair cells and functional hearing impairment following aminoglycosides exposure. Previously, we have determined that ferulic acid (FA) protected hair cells against serial concentrations of neomycin-induced ototoxic damage. The aim of the present study is to assess the mechanism and effects of FA on neomycin-induced hair cells loss and impact on mechanosensory-mediated behaviors alteration using transgenic zebrafish (pvalb3b: TagGFP). We first identified the optimal protective condition as pre/co-treatment method in early fish development. Pretreatment of the larvae with FA significantly protected against neomycin-induced hair cells loss through preventing neomycin passed through the cytoplasm of hair cells, and subsequently decreased reactive oxygen species production and TUNEL signals in 4 day post-fertilization (dpf) transgenic zebrafish larvae. Moreover, preservation of functional hair cells correlated directly with rescue of the altered swimming behavior, indicates FA pretreatment protects against neomycin ototoxic damage in 7-dpf transgenic zebrafish larvae. Together, our findings unravel the otoprotective role of FA as an effective agent against neomycin-induced ototoxic effects and offering the theoretical foundation for discovering novel candidates for hearing protection.

Cichoric Acid May Play a Role in Protecting Hair Cells from Ototoxic Drugs.

Ototoxic hearing loss due to antibiotic medication including aminoglycosides and excess free radical production causes irreversible hair cell injury. Cichoric acid, a naturally occurring phenolic acid, has recently been found to exert anti-oxidative and anti-inflammatory properties through its free radical scavenging capacity. The present study aimed to investigate the protective effects of cichoric acid against neomycin-induced ototoxicity using transgenic zebrafish (pvalb3b: TagGFP). Our results indicated that cichoric acid in concentrations up to 5 µM did not affect zebrafish viability during the 2 h treatment period. Therefore, the otoprotective concentration of cichoric acid was identified as 5 µM under 2 h treatment by counting viable hair cells within the neuromasts of the anterior- and posterior-lateral lines in the study. Pretreatment of transgenic zebrafish with 5 µM of cichoric acid for 2 h significantly protected against neomycin-induced hair cell death. Protection mediated by cichoric acid was, however, lost over time. A terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) assay and FM4-64 staining, respectively, provided in situ evidence that cichoric acid ameliorated apoptotic signals and mechanotransduction machinery impairment caused by neomycin. A fish locomotor test (distance move, velocity, and rotation frequency) assessing behavioral alteration after ototoxic damage revealed rescue due to cichoric acid pretreatment before neomycin exposure. These findings suggest that cichoric acid in 5 µM under 2 h treatment has antioxidant effects and can attenuate neomycin-induced hair cell death in neuromasts. Although cichoric acid offered otoprotection, there is only a small difference between pharmacological and toxic concentrations, and hence cichoric acid can be considered a rather prototypical compound for the development of safer otoprotective compounds.

3-Bromofluoranthene-induced cardiotoxicity of zebrafish and apoptosis in the vascular endothelial cells via intrinsic and extrinsic caspase-dependent pathways.

Fluoranthene, a high-molecular-weight polycyclic aromatic hydrocarbon (PAH), is widely present in air pollutants, including fine inhalable particulate matter. 3-Bromofluoranthene (3-BrFlu), which is a brominated fluoranthene and halogenated PAH, is generated from waste combustion, metallurgical processes, cement production, e-waste dismantling, and photoreaction. Vascular endothelial cells have key functions in the homeostasis and the development of the cardiovascular system. The zebrafish model has been widely employed to study cardiotoxicity and embryotoxicity. However, no evidence has indicated that 3-BrFlu induces cytotoxicity in vascular endothelial cells, or cardiotoxicity and embryotoxicity in zebrafish. In this study, 3-BrFlu induced concentration-dependent changes in embryo- and cardiotoxicity. Cytotoxicity was also induced by 3-BrFlu in a concentration-dependent manner through apoptosis and necrosis in vascular endothelial cells, SVEC4-10 cells. The activities of caspase-3, -8, and -9 were induced by 3-BrFlu via an intrinsic pathway constituting Bcl-2 downregulation, Bad upregulation, and mitochondrial dysfunction; the extrinsic pathway included the expression of death receptors, including tumour necrosis factor α and Fas receptors. These results indicated that 3-BrFlu caused cardio- and embryotoxicity in zebrafish through vascular endothelial cells cytotoxicity resulting from caspase-dependent apoptosis through intrinsic and extrinsic pathways.

Novel Mutations in the TMPRSS3 Gene may Contribute to Taiwanese Patients with Nonsyndromic Hearing Loss.

A previous study indicated that mutations in the transmembrane protease serine 3 (TMPRSS3) gene, which encodes a transmembrane serine protease, cause nonsyndromic hearing loss (NSHL). This was the first description of a serine protease involved in hearing loss (HL). In Taiwan, however, data on the TMPRSS3 gene's association with NSHL is still insufficient. In this study, we described 10 mutations of TMPRSS3 genes found in 14 patients after screening 230 children with NSHL. The prevalence of the TMPRSS3 mutation appeared to be 6.09% (14/230). Of the 10 mutations, three were missense mutations: c.239G>A (p.R80H), c.551T>C (p.L184S), and 1253C>T (p.A418V); three were silent mutations, and four were mutations in introns. To determine the functional importance of TMPRSS3 mutations, we constructed plasmids carrying TMPRSS3 mutations of p.R80H, p.L184S, and p.A418V. TMPRSS3 function can be examined by secretory genetic assay for site-specific proteolysis (sGASP) and Xenopus oocyte expression system. Our results showed that p.R80H, p.L184S, and p.A418V TMPRSS3 mutations gave ratios of 19.4%, 13.2%, and 27.6%, respectively, via the sGASP system. Moreover, these three TMPRSS3 mutations failed to activate the epithelial sodium channel (ENaC) in the Xenopus oocyte expression system. These results indicate that the p.R80H, p.L184S, and p.A418V missense mutations of TMPRSS3 resulted in greatly diminishing the proteolytic activity of TMPRSS3. Our study provides information for understanding the importance of TMPRSS3 in the NSHL of Taiwanese children and provides a novel molecular explanation for the role of TMPRSS3 in HL.

An Application of NGS for WDR36 Gene in Taiwanese Patients with Juvenile-Onset Open-Angle Glaucoma.

Primary open-angle glaucoma (POAG) is one of the most important disease in ophthalmology with high prevalence and risk of irreversible blindness. If diagnosed before the age of 35, it is usually categorized as juvenile open-angle glaucoma (JOAG). The WDR36 gene is reckoned as one of the major causative genes of POAG, and had been studied to be related to the pathogenesis of POAG in the literature. We have selected 61 JOAG patients and 61 JOAG-free individuals, and by next-generation sequencing method, the WDR36 gene of the subjects were analyzed. We identified 26 variations exclusively in JOAG group. Among these 26 variations, there were 3 noteworthy variations. First, a novel variation c.460-650A>G was found in our study which might cause premature termination of splicing of the conserved domain in WDR36; second, c.1494+1111G>T (rs13178997) had significantly different frequency in our JOAG patients compared to the reference frequency on NCBI; third, a variation c.710+30C>T (rs10038177) was found in our study, which had already been reported to be related to high-pressure glaucoma. We offer the profile of WDR36 in JOAG in Taiwan population, and we suggest that WDR36 gene is involved in the pathogenesis of JOAG as a subordinate modifier gene.

Functional analysis of a nonsyndromic hearing loss-associated mutation in the transmembrane II domain of the GJC3 gene.

In a previous study, we identified a novel missense mutation, p.W77S, in the GJC3 gene encoding connexin30.2/connexin31.3 (CX30.2/CX31.3) from patients with hearing loss. The functional alteration of CX30.2/CX31.3 caused by the p.W77S mutant of GJC3 gene, however, remains unclear. In the current study, our result indicated that the p.W77 is localized at the second membrane-spanning segments (TM2) and near border of the E1 domain of the CX30.2/CX31.3 protein and highly conserved (Conseq score = 8~9) in all species. The p.W77S missense mutation proteins in the intracellular distribution are different CX30.2/CX31.3WT and an accumulation of the mutant protein in the endoplasmic reticulum (ER) of the HeLa cell. Furthermore, co-expression of WT and p.W77S mutant chimerae proteins showed that the heteromeric connexon accumulated in the cytoplasm, thereby impairing the WT proteins' expression in the cell membranes. In addition, we found that CX30.2/CX31.3W77S missense mutant proteins were degraded by lysosomes and proteosomes in the transfected HeLa cell. Based on these findings, we suggest that p.W77S mutant has a dominant negative effect on the formation and function of the gap junction. These results give a novel molecular elucidation for the mutation of GJC3 in the development of hearing loss.

A KCNQ2 E515D mutation associated with benign familial neonatal seizures and continuous spike and waves during slow-wave sleep syndrome in Taiwan.

BACKGROUND/PURPOSE: Pediatric epilepsy caused by a KCNQ2 gene mutation usually manifests as benign familial neonatal seizures (BFNS) during the 1st week of life. However, the exact mechanism, phenotype, and genotype of the KCNQ2 mutation are unclear. METHODS: We studied the KCNQ2 genotype from 75 nonconsanguineous patients with childhood epilepsy without an identified cause (age range: from 2 days to 18 years) and from 55 healthy adult controls without epilepsy. KCNQ2 mutation variants were transfected into HEK293 cells to investigate what functional changes they induced. RESULTS: Four (5%) of the patients had the E515D KCNQ2 mutation, which the computer-based PolyPhen algorithm predicted to be deleterious. Their seizure outcomes were favorable, but three had an intellectual disability. Two patients with E515D presented with continuous spikes and waves during slow-wave sleep (CSWS), and the other two presented with BFNS. We also analyzed 10 affected family members with the same KCNQ2 mutation: all had epilepsy (8 had BFNS and 2 had CSWS). A functional analysis showed that the recordings of the E515D currents were significantly different (p<0.05), which suggested that channels with KCNQ2 E515D variants are less sensitive to voltage and require stronger depolarization to reach opening probabilities than those with the wild type or N780T (a benign polymorphism). CONCLUSION: KCNQ2 mutations can cause various phenotypes in children: they lead to BFNS and CSWS. We hypothesize that patients with the KCNQ2 E515D mutation are susceptible to seizures.

Mechanism of a novel missense mutation, p.V174M, of the human connexin31 (GJB3) in causing nonsyndromic hearing loss.

Hearing loss is the most common sensory disorder, worldwide. In a recent study, we have identified a missense mutation, p.V174M, in the connexin 31 encoded by the GJB3 gene, in a patient with nonsyndromic hearing loss. However, the functional change in the CX31V174M mutant remains unknown. This study compared the intracellular distribution and assembly of the mutant CX31V174M with that of the wild-type (WT) CX31 in HeLa cells, and it examined the effect that the mutant protein had on those cells. A fluorescent localization assay of WT CX31 showed the typical punctuate pattern of a gap junction channel between the neighboring expression cells. Conversely, the p.V174M missense mutation resulted in the accumulation of the mutant protein in the lysosomes rather than in the cytoplasmic membrane. Moreover, dye transfer experiments have also demonstrated that the CX31V174M mutant did not form functional gap junction channels, probably due to the incorrect assembly or the altered properties of the CX31 channels. In addition, we found that CX31V174M-transfection can cause cell death by MTT assay. CX31V174M co-expressed with either CX31WT or CX26WT studies, suggested the impairment of the ability of CX26WT proteins to intracellular trafficking and targeting to the plasma membrane, but did not influence the trafficking of CX31WT. Based on these findings, we suggest that the CX31V174M mutant may have an effect on the formation and function of the gap junction, and CX31V174M has a trans-dominant negative effect on the function of wild types CX26. These results provide a novel molecular explanation for the role that GJB3 plays in hearing loss.

Parapyruvate Induces Neurodegeneration in C57BL/6JNarl Mice via Inhibition of the α-Ketoglutarate Dehydrogenase Complex.

Parapyruvate is a substance commonly found in commercial dietary supplements of calcium pyruvate (DSCP) that inhibits the α-ketoglutarate dehydrogenase complex (KGDHC) and has been shown to induce senescence in human Hs68 cells. However, it is unknown whether parapyruvate can induce neurodegeneration. In this study, the parapyruvate content in DSCP was converted to an equivalent dose for mice and administered to the C57BL/6JNarl mice at doses around the equivalent dose for 69 days, including 5, 50, and 500 mg/kg/day. The Morris water maze (MWM) task and the active avoidance test were conducted to assess the learning and memory ability in mice, and then brain tissues were collected for biochemical analyses. The results demonstrated that parapyruvate significantly impaired the learning and memory ability, decreased the KGDHC activity, and promoted the oxidative stress and acetylcholinesterase (AChE) activity in mice in a dose-dependent manner. Additionally, parapyruvate induced Tau and phosphorylated Tau (p-Tau) aggregation at dosages ≥5 mg/kg/day and increased the myelin basic protein (MBP) expression at a dosage of 500 mg/kg/day. These results suggest that the equivalent dose of parapyruvate can induce neurodegeneration in the C57BL/6JNarl mice.

KCNQ2 Selectivity Filter Mutations Cause Kv7.2 M-Current Dysfunction and Configuration Changes Manifesting as Epileptic Encephalopathies and Autistic Spectrum Disorders.

KCNQ2 mutations can cause benign familial neonatal convulsions (BFNCs), epileptic encephalopathy (EE), and mild-to-profound neurodevelopmental disabilities. Mutations in the KCNQ2 selectivity filter (SF) are critical to neurodevelopmental outcomes. Three patients with neonatal EE carry de novo heterozygous KCNQ2 p.Thr287Ile, p.Gly281Glu and p.Pro285Thr, and all are followed-up in our clinics. Whole-cell patch-clamp analysis with transfected mutations was performed. The Kv7.2 in three mutations demonstrated significant current changes in the homomeric-transfected cells. The conduction curves for V1/2, the K slope, and currents in 3 mutations were lower than those for the wild type (WT). The p.Gly281Glu had a worse conductance than the p.Thr287Ile and p.Pro285Thr, the patient compatible with p.Gly281Glu had a worse clinical outcome than patients with p.Thr287Ile and p.Pro285Thr. The p.Gly281Glu had more amino acid weight changes than the p.Gly281Glu and p.Pro285Thr. Among 5 BFNCs and 23 EE from mutations in the SF, the greater weight of the mutated protein compared with that of the WT was presumed to cause an obstacle to pore size, which is one of the most important factors in the phenotype and outcome. For the 35 mutations in the SF domain, using changes in amino acid weight between the WT and the KCNQ2 mutations to predict EE resulted in 80.0% sensitivity and 80% specificity, a positive prediction rate of 96.0%, and a negative prediction rate of 40.0% (p = 0.006, χ2 (1, n = 35) = 7.56; odds ratio 16.0, 95% confidence interval, 1.50 to 170.63). The findings suggest that p.Thr287Ile, p.Gly281Glu and p.Pro285Thr are pathogenic to KCNQ2 EE. In mutations in SF, a mutated protein heavier than the WT is a factor in the Kv7.2 current and outcome.

Early Blood Glucose Level Post-Admission Correlates with the Outcomes and Oxidative Stress in Neonatal Hypoxic-Ischemic Encephalopathy.

The antioxidant defense system is involved in the pathogenesis of neonatal hypoxic-ischemic encephalopathy (HIE). To analyze the relationship between first serum blood glucose levels and outcomes in neonatal HIE, seventy-four patients were divided, based on the first glucose level, into group 1 (>0 mg/dL and <60 mg/dL, n =11), group 2 (≥60 mg/dL and <150 mg/dL, n = 49), and group 3 (≥150 mg/dL, n = 14). Abnormal glucose levels had poor outcomes among three groups in terms of the clinical stage (p = 0.001), brain parenchymal lesion (p = 0.004), and neurodevelopmental outcomes (p = 0.029). Hearing impairment was more common in group 3 than in group 1 (p = 0.062) and group 2 (p = 0.010). The MRI findings of group 3 exhibited more thalamus and basal ganglion lesions than those of group 1 (p = 0.012). The glucose level was significantly correlated with clinical staging (p< 0.001), parenchymal brain lesions (p = 0.044), hearing impairment (p = 0.003), and neurodevelopmental outcomes (p = 0.005) by Pearson's test. The first blood glucose level in neonatal HIE is an important biomarker for clinical staging, MRI findings, as well as hearing and neurodevelopment outcomes. Hyperglycemic patients had a higher odds ratio for thalamus, basal ganglia, and brain stem lesions than hypoglycemic patients with white matter and focal ischemic injury. Hyperglycemia can be due to prolonged or intermittent hypoxia and can be associated with poor outcomes.

Aflatoxin B1 interferes with embryonic liver development: Involvement of p53 signaling and apoptosis in zebrafish.

Aflatoxin B1 (AFB1), a naturally occurring mycotoxin, is present in human placenta and cord blood. AFB1 at concentrations found in contaminated food commodities (0.25 and 0.5 µM) did not alter the spontaneous movement, heart rate, hatchability, or morphology of embryonic zebrafish. However, around 86 % of 0.25 µM AFB1-treated embryos had livers of reduced size, and AFB1 disrupted the hepatocyte structures, according to histological analysis. Additionally, AFB1 treatment that begins at any stage before 72 h post-fertilization (hpf) effectively reduced the size of embryonic livers. In hepatic areas, AFB1 suppressed the expression of Hhex and Prox1, which are two critical transcriptional factors for initiating hepatoblast specification. KEGG analysis based on transcriptome profiling indicated that p53 signaling and apoptosis are the only observed pathways in AFB1-treated embryos. AFB1 at 0.5 µM significantly activated the expression of tp53, mdm2, puma, noxa, pidd1, and gadd45aa genes that are related to the p53 pathway and also that of baxa, casp 8 and casp 3a in the apoptotic process. TUNEL staining demonstrated that AFB1 triggered the apoptosis of embryonic hepatocytes in a dose-dependent manner. These results indicate that the deficiency of both hhex and prox1 as well as hepatocyte apoptosis via the p53-Puma/Noxa-Bax axis may contribute to the embryonic liver shrinkage that is caused by AFB1.

Novel mutations in the connexin43 (GJA1) and GJA1 pseudogene may contribute to nonsyndromic hearing loss.

Connexins (CXs), a large family of membrane proteins, are key components of gap junction channels. Among a cohort of patients with nonsyndromic hearing loss, we have recently identified three novel missense mutations in the GJA1 gene and GJA1 pseudogene (rhoGJA1) as likely being causally related to hearing loss. However, the functional alteration of CX43 caused by the mutations of GJA1 and rhoGJA1 gene remains unclear. This study compares the intracellular distribution and assembly of three CX43 mutants expressed in HeLa cells with their wild-type (WT) counterparts and the effects of the mutant proteins on those cells. Localization assay of WT CX43 reveals a typical punctuate fluorescence pattern of a gap junction channel between neighboring expression cells. Additionally, immunoblotting analysis of the transfectants confirms the production of mutant proteins, in which their distributions along appositional membranes are determined using immunofluorescent staining procedures. Furthermore, dye transfer assay results demonstrate that gap junctional intercellular communication is less in HeLa cells carrying mutant GJA1 or rhoGJA1 gene than in WT-expressing cells. The results of this study suggest that the three mutations in GJA1 or rhoGJA1 that we previously reported result in at least partial loss of normal functions carried out by CX43, which may form a basis for the mechanism contributing to hearing loss in patients.

A novel mutation in the connexin 29 gene may contribute to nonsyndromic hearing loss.

Connexins (Cxs) are homologous four-transmembrane domain proteins and constitute the major components of gap junctions. Among a cohort of patients with nonsyndromic hearing loss, we recently identified a novel missense mutation, E269D, in the GJC3 gene encoding connexin 29 (Cx29), as being causally related to hearing loss. The functional alteration of Cx29 caused by the mutant GJC3 gene, however, remains unknown. This study compared the intracellular distribution and assembly of mutant Cx29 (Cx29E269D) with that of the wild-type Cx29 (Cx29WT) in HeLa cells and the effect the mutant protein had on those cells. Cx29TW showed continuous staining along apposed cell membranes in the fluorescent localization assay. In contrast, the p.E269D missense mutation resulted in accumulation of the Cx29 mutant protein in the endoplasmic reticulum (ER) rather than in the cytoplasmic membrane. Co-expression of Cx29WT and Cx29E269D proteins by a bi-directional tet-on expression system demonstrated that the heteromeric connexon accumulated in the cytoplasm, thereby impairing the formation of the gap junction. Based on these findings, we suggest that Cx29E269D has a dominant negative effect on the formation and function of the gap junction. These results provide a novel molecular explanation for the role Cx29 plays in the development of hearing loss.

Prospective variants screening of connexin genes in children with hearing impairment: genotype/phenotype correlation.

The crucial role of gap junctions, which are composed of connexin (CX) protein, in auditory functions has been confirmed by numerous studies. In this study, we investigate the prevalence and phenotype/genotype correlation of connexin (CX) gene family variants in a cohort of children with nonsyndromic hearing loss (HL). A total of 253 unrelated children with nonsyndromic HL were screened for the presence of variants in 6 genes of the CX gene family. The prevalence of CX gene variants in 253 patients was 19.7% (50/253). We found the frequency of a sloping audiometric configuration was significantly higher for children with GJB2 and GJB3 variants than for those with GJB4 and GJC3 variants (Adjusted OR = 4.89, p < 0.001). Conversely, the frequency of a flat audiometric configuration was significantly higher for children with GJB4 and GJC3 variants than for those with GJB2 and GJB3 variants (adjusted OR = 7.76, p < 0.001). The relative frequencies of multiplex families was significantly higher for children with GJB3 variants than for those with GJB2, GJB4, and GJC3 variants (Adjusted OR = 11.33, p = 0.003). Our results suggest the variants of GJC3, GJB4, and GJB3 may be the common genetic risk factor, after variants of GJB2, for the development of nonsyndromic HL in Taiwan. These data can be effectively applied to direct the clinical evaluation of children with CX gene variants.

Identification of novel variants in the Cx29 gene of nonsyndromic hearing loss patients using buccal cells and restriction fragment length polymorphism method.

The crucial role of gap junctions, which are composed of connexin (Cx) protein, in auditory functions has been confirmed by numerous studies. Cx29 is a relatively new member of the Cx protein family. In this article, we report variants of the Cx29 gene in 253 unrelated Taiwanese patients with nonsyndromic hearing loss. Thirteen (5.14%) of the 253 patients had variants of Cx29. Five sequence changes (c.43C-->G, c.230G-->C, c.525T-->G, c.781 + 62G-->A and c.*2T-->G) in the Cx29 gene were detected in the study, of which 3 (c.43C-->G, c.230G-->C and c.525T-->G) were novel variants. One novel compound heterozygote missense variant, c.[43C-->G(+) 230G-->C], was identified in the Cx29 gene carried by 1 patient, and this variant appears to have been inherited from the mother's chromosome. In addition, for diagnostic purposes, we developed a restriction fragment length polymorphism method using NaeI and StyI to identify c.43C-->G and c.525T-->G specific variants of the Cx29 gene, respectively. On the basis of the above results, we suggest that the c.[43C-->G(+)230G-->C] compound heterozygous variant of Cx29 may be a risk factor for the development of hearing loss in Taiwanese and that the restriction fragment length polymorphism method developed will be clinically useful in identifying variants of the Cx29 gene in patients with hearing loss.

A Wide Spectrum of Genetic Disorders Causing Severe Childhood Epilepsy in Taiwan: A Case Series of Ultrarare Genetic Cause and Novel Mutation Analysis in a Pilot Study.

BACKGROUND: Pediatric epileptic encephalopathy and severe neurological disorders comprise a group of heterogenous diseases. We used whole-exome sequencing (WES) to identify genetic defects in pediatric patients. METHODS: Patients with refractory seizures using ≥2 antiepileptic drugs (AEDs) receiving one AED and having neurodevelopmental regression or having severe neurological or neuromuscular disorders with unidentified causes were enrolled, of which 54 patients fulfilled the inclusion criteria, were enrolled, and underwent WES. RESULTS: Genetic diagnoses were confirmed in 24 patients. In the seizure group, KCNQ2, SCN1A, TBCID 24, GRIN1, IRF2BPL, MECP2, OSGEP, PACS1, PIGA, PPP1CB, SMARCA4, SUOX, SZT2, UBE3A, 16p13.11 microdeletion, [4p16.3p16.1(68,345-7,739,782)X1, 17q25.1q25.3(73,608,322-81,041,938)X3], and LAMA2 were identified. In the nonseizure group, SCN2A, SPTBN2, DMD, and FBN1 were identified. Ten novel mutations were identified. The recurrent genes included SCN1A, KCNQ2, and TBCID24. Male pediatric patients had a significantly higher (57% vs. 29%; p < 0.05, odds ratio = 3.18) yield than their female counterparts. Seventeen genes were identified from the seizure groups, of which 82% were rare genetic etiologies for childhood seizure and did not appear recurrently in the case series. CONCLUSIONS: Wide genetic variation was identified for severe childhood seizures by WES. WES had a high yield, particularly in male infantile patients.