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.

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 Biomarkers and Hearing Impairments in Patients with Neonatal Hypoxic-Ischemic Encephalopathy.

Identifying biomarkers for hearing impairments (HIs) in patients with neonatal hypoxic-ischemic encephalopathy (HIE), to initialize early hearing habilitation, is crucial. Seventy-eight neonates with HIE were divided into the following two groups: those with HIs and those without HIs. We compared those patients with 11,837 newborns without HIE, and analyzed the risk factors of HIs among neonatal HIE. Of the 78 patients, 11 were confirmed to have an HI, which is a substantially higher percentage than in the 11,837 newborns without HIE (14.1% vs. 0.87%; p < 0.001). More patients with moderate-to-severe HIE had confirmed HIs (p = 0.020; odds ratio, 8.61) than those with mild HIE. Clinical staging, and blood lactate and glucose levels could be predictive factors for HIs among patients with HIE. The patients who exhibited HIs had significantly higher lactate (104.8 ± 51.0 vs. 71.4 ± 48.4; U = 181, p = 0.032) and serum glucose (159.5 ± 86.1 vs. 112.1 ± 62.3; U = 166, p = 0.036) levels than those without HIs. A higher prevalence of HIs was noted in the patients with stage III HIE than those with stage II HIE (43.8% vs. 10%; p = 0.008). The degree of HI correlated with brain anomalies and neurodevelopmental outcomes at 1 year of age. Clinical staging, and blood lactate and glucose levels could be predictive factors for HIs among patients with HIE.

Troponin I Levels in Neonatal Hypoxic-Ischemic Encephalopathy Are Related to Cardiopulmonary Comorbidity and Neurodevelopmental Outcomes.

Troponin I is a biomarker for cardiac injury in children. The role of troponin I in neonatal Hypoxic-Ischemic encephalopathy (HIE) may have valuable clinical implications. Troponin I levels were measured within 6 h of birth to determine their relationship to HIE stage, short-term cardiac functional outcomes, and neurodevelopmental outcomes at 1 year. Seventy-three patients were divided into two groups: mild HIE and moderate to severe HIE. Troponin I levels within 6 h of birth were obtained in 61 patients, and were significantly higher in patients with moderate to severe HIE than in patients with mild HIE (Mann-Whitney U test, U = 146, p = 0.001). A troponin I cut-off level of ≥60 pg/mL predicted moderate to severe HIE with a specificity of 81.1% and a negative prediction rate of 76.9%. A troponin I cut-off level of ≥180 pg/mL was significantly (χ2 (1, n = 61) = 33.1, p = 0.001, odds ratio 96.8) related with hypotension during first admission and significantly (χ2 (1, n = 61) = 5.3, p = 0.021, odds ratio 4.53) related with abnormal neurodevelopmental outcomes at 1 year. Early troponin I level may be a useful biomarker for predicting moderate to severe HIE, and initialization of hypothermia therapy.

Identifying Early Diagnostic Biomarkers Associated with Neonatal Hypoxic-Ischemic Encephalopathy.

BACKGROUND: Identifying an effective method for the early diagnosis of neonatal hypoxic-ischemic encephalopathy (HIE) would be beneficial for effective therapies. METHODS: We studied blood biomarkers before 6 h after birth to correlate the degree of neonatal HIE. A total of 80 patients were divided into group 1 (mild HIE) and group 2 (moderate or severe HIE). Then, 42 patients from group 2 received hypothermia therapy and were further divided into group 3 (unremarkable or mild MRI results) and group 4 (severe MRI results). RESULTS: Between groups 1 and 2, lactate, creatinine, white blood cells, and lactate dehydrogenase (LDH) were significantly different. Between groups 3 and 4, lactate, prothrombin time, and albumin were significantly different. Sarnat staging was based on our observation that more than 45 mg/dL of lactate combined with more than 1000 U/L of LDH yielded the highest positive predictive value (PPV) (95.7%; odds ratio, 22.00), but a low negative predictive value (NPV) for moderate or severe HIE. Using more than 45 mg/dL of lactate yielded the highest NPV (71.4%) correlated with moderate or severe HIE. CONCLUSIONS: Lactate combined with LDH before 6 h after birth yielded a high PPV. Using combined biomarkers to exclude mild HIE, include moderate or severe HIE, and initialize hypothermia therapy is feasible.

Heteromeric Kv7.2 current changes caused by loss-of-function of KCNQ2 mutations are correlated with long-term neurodevelopmental outcomes.

Pediatric epilepsy caused by KCNQ2 mutations can manifest benign familial neonatal convulsions (BFNC) to neonatal-onset epileptic encephalopathy (EE). Patients might manifest mild to profound neurodevelopmental disabilities. We analysed c.853C > A (P285T) and three mutations that cause KCNQ2 protein changes in the 247 position: c.740C > T (S247L), c.740C > A (S247X), and c.740C > G (S247W). S247L, S247W, and P285T cause neonatal-onset EE and poor neurodevelopmental outcomes; S247X cause BFNC and normal outcome. We investigated the phenotypes correlated with human embryonic kidney 293 (HEK293) cell functional current changes. More cell-current changes and a worse conductance curve were present in the homomeric transfected S247X than in S247L, S247W, and P285T. But in the heteromeric channel, S247L, S247W and P285T had more current impairments than did S247X. The protein expressions of S247X were nonfunctional. The outcomes were most severe in S247L and S247W, and severity was correlated with heteromeric current. Current changes were more significant in cells with homomeric S247X, but currents were "rescued" after heteromeric transfection of KCNQ2 and KCNQ3. This was not the case in cells with S247L, S247W. Our findings support that homomeric current changes are common in KCNQ2 neonatal-onset EE and KCNQ2 BFNC; however, heteromeric functional current changes are correlated with long-term neurodevelopmental outcomes.

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.

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.

Characterization of genomic structures and expression profiles of three tandem repeats of a mouse double homeobox gene: Duxbl.

We identified and cloned a mouse double homeobox gene (Duxbl), which encodes two homeodomains. Duxbl gene, a tandem triplicate produces two major transcripts, Duxbl and Duxbl-s. The amino acid sequences of Duxbl homeodomains are most similar to those of human DUX4 protein, associated with facioscapulohumeral muscular dystrophy. In adult tissues, Duxbl is predominantly expressed in female reproductive organs and eyes, and slightly expressed in brain and testes. During gonad development, Duxbl is expressed from embryonic to adult stages and specifically expressed in oocytes and spermatogonia. During embryonic development, Duxbl is transcribed in limbs and tail. However, Duxbl proteins were only detected in trunk and limb muscles and in elongated myocytes and myotubes. In C2C12 muscle cell line, Duxbl expression pattern is similar to differentiated marker gene, Myogenin, increased in expression from 2 days onward in differentiating medium. We suggest that Duxbl proteins play regulatory roles during myogenesis and reproductive developments.