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1.
Mutations in KCNK4 that Affect Gating Cause a Recognizable Neurodevelopmental Syndrome.
Bauer, CK, Calligari, P, Radio, FC, Caputo, V, Dentici, ML, Falah, N, High, F, Pantaleoni, F, Barresi, S, Ciolfi, A, et al
American journal of human genetics. 2018;(4):621-630
Abstract
Aberrant activation or inhibition of potassium (K+) currents across the plasma membrane of cells has been causally linked to altered neurotransmission, cardiac arrhythmias, endocrine dysfunction, and (more rarely) perturbed developmental processes. The K+ channel subfamily K member 4 (KCNK4), also known as TRAAK (TWIK-related arachidonic acid-stimulated K+ channel), belongs to the mechano-gated ion channels of the TRAAK/TREK subfamily of two-pore-domain (K2P) K+ channels. While K2P channels are well known to contribute to the resting membrane potential and cellular excitability, their involvement in pathophysiological processes remains largely uncharacterized. We report that de novo missense mutations in KCNK4 cause a recognizable syndrome with a distinctive facial gestalt, for which we propose the acronym FHEIG (facial dysmorphism, hypertrichosis, epilepsy, intellectual disability/developmental delay, and gingival overgrowth). Patch-clamp analyses documented a significant gain of function of the identified KCNK4 channel mutants basally and impaired sensitivity to mechanical stimulation and arachidonic acid. Co-expression experiments indicated a dominant behavior of the disease-causing mutations. Molecular dynamics simulations consistently indicated that mutations favor sealing of the lateral intramembrane fenestration that has been proposed to negatively control K+ flow by allowing lipid access to the central cavity of the channel. Overall, our findings illustrate the pleiotropic effect of dysregulated KCNK4 function and provide support to the hypothesis of a gating mechanism based on the lateral fenestrations of K2P channels.
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2.
Epilepsy in hemiplegic migraine: Genetic mutations and clinical implications.
Prontera, P, Sarchielli, P, Caproni, S, Bedetti, C, Cupini, LM, Calabresi, P, Costa, C
Cephalalgia : an international journal of headache. 2018;(2):361-373
Abstract
Objective We performed a systematic review on the comorbidities of familial/sporadic hemiplegic migraine (F/SHM) with seizure/epilepsy in patients with CACNA1A, ATP1A2 or SCN1A mutations, to identify the genotypes associated and investigate for the presence of mutational hot spots. Methods We performed a search in MEDLINE and in the Human Gene Mutation and Leiden Open Variation Databases for mutations in the CACNA1A, ATP1A2 and SCN1A genes. After having examined the clinical characteristics of the patients, we selected those having HM and seizures, febrile seizures or epilepsy. For each gene, we determined both the frequency and the positions at protein levels of these mutations, as well as the penetrance of epilepsy within families. Results Concerning F/SHM-Epilepsy1 (F/SHME1) and F/SHME2 endophenotypes, we observed a prevalent involvement of the transmembrane domains, and a strong correlation in F/SHME1 when the positively charged amino acids were involved. The penetrance of epilepsy within the families was highest for patients carrying mutation in the CACNA1A gene (60%), and lower in those having SCN1A (33.3%) and ATP1A2 (30.9%) mutations. Conclusion Among the HM cases with seizure/epilepsy, we observed mutational hot spots in the transmembrane domains of CACNA1A and ATP1A2 proteins. These findings could lead to a better understanding of the pathological mechanisms underlying migraine and epilepsy, therein guaranteeing the most appropriate therapeutic approach.
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The analysis of myotonia congenita mutations discloses functional clusters of amino acids within the CBS2 domain and the C-terminal peptide of the ClC-1 channel.
Altamura, C, Lucchiari, S, Sahbani, D, Ulzi, G, Comi, GP, D'Ambrosio, P, Petillo, R, Politano, L, Vercelli, L, Mongini, T, et al
Human mutation. 2018;(9):1273-1283
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Abstract
Myotonia congenita (MC) is a skeletal-muscle hyperexcitability disorder caused by loss-of-function mutations in the ClC-1 chloride channel. Mutations are scattered over the entire sequence of the channel protein, with more than 30 mutations located in the poorly characterized cytosolic C-terminal domain. In this study, we characterized, through patch clamp, seven ClC-1 mutations identified in patients affected by MC of various severities and located in the C-terminal region. The p.Val829Met, p.Thr832Ile, p.Val851Met, p.Gly859Val, and p.Leu861Pro mutations reside in the CBS2 domain, while p.Pro883Thr and p.Val947Glu are in the C-terminal peptide. We showed that the functional properties of mutant channels correlated with the clinical phenotypes of affected individuals. In addition, we defined clusters of ClC-1 mutations within CBS2 and C-terminal peptide subdomains that share the same functional defect: mutations between 829 and 835 residues and in residue 883 induced an alteration of voltage dependence, mutations between 851 and 859 residues, and in residue 947 induced a reduction of chloride currents, whereas mutations on 861 residue showed no obvious change in ClC-1 function. This study improves our understanding of the mechanisms underlying MC, sheds light on the role of the C-terminal region in ClC-1 function, and provides information to develop new antimyotonic drugs.
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Impact of HBV genotype and mutations on HBV DNA and qHBsAg levels in patients with HBeAg-negative chronic HBV infection.
Kuhnhenn, L, Jiang, B, Kubesch, A, Vermehren, J, Knop, V, Susser, S, Dietz, J, Carra, G, Finkelmeier, F, Grammatikos, G, et al
Alimentary pharmacology & therapeutics. 2018;(11):1523-1535
Abstract
BACKGROUND HBV DNA and quantitative (q)HBsAg levels as prognostic markers for HBV-related disease are mostly validated in Asia and their significance in Western populations is uncertain. AIM: To analyse the impact of the HBV genotype and frequent mutations in precore (PC), basal core promoter (BCP) and preS on HBV DNA and qHBsAg levels. METHODS HBV DNA and qHBsAg serum levels of 465 patients with HBeAg-negative chronic HBV infection were correlated with the HBV genotype and mutations in PC, BCP and preS. For a detailed analysis of the molecular virology, genotype A2 genomes harbouring these mutations were analysed for replication efficacy and HBsAg release in cell culture. RESULTS While no impact of the HBV genotype on HBV DNA levels was observed, qHBsAg levels differed up to 1.4 log among the genotypes (P < 0.001), reflected by large differences regarding the 1000 IU/mL HBsAg cut-off. While PC mutations were associated with higher (P < 0.001), BCP mutations were associated with lower HBV DNA levels (P < 0.001). Higher qHBsAg levels were associated with preS and lower levels with PC mutations (P < 0.001 and P = 0.001, respectively). The cell culture experiments revealed a higher HBsAg release and shorter filaments in case of a HBV genome harbouring a preS deletion. In contrast, a perinuclear HBsAg accumulation was detected for the PC and BCP-variants, reflecting an impaired HBsAg release. CONCLUSIONS qHBsAg serum levels depend on the HBV genotype and together with HBV DNA levels on frequent mutations in PC, BCP and preS in HBeAg-negative patients. qHBsAg cut-offs when used as prognostic markers require genotype-dependent validation.
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5.
Episodic ataxias.
Jen, JC, Wan, J
Handbook of clinical neurology. 2018;:205-215
Abstract
Primary episodic ataxias (EAs) are a group of dominantly inherited disorders characterized by transient recurrent incoordination and truncal instability, often triggered by physical exertion and emotional stress, variably associated with progressive baseline ataxia. There are now eight designated subtypes based largely on genetic loci. Mutations have been identified in multiple individuals and families with EA1, EA2, and EA6, mostly with onset before adulthood. EA1 and EA2 are prototypical neurologic channelopathies. EA1 is caused by heterozygous mutations in KCNA1, which encodes the α1 subunit of a neuronal voltage-gated potassium channel, Kv1.1. EA2, the most common and best characterized, is caused by heterozygous mutations in CACNA1A, which encodes the α1A subunit of a neuronal voltage-gated calcium channel, Cav2.1. EA6 is caused by heterozygous mutations in SLC1A3, which encodes a subunit of a glial excitatory amino acid transporter, EAAT1. The other EA subtypes were defined in single families awaiting gene identification and further confirmation. This chapter focuses on the best-characterized EA syndromes, the clinical assessment and genetic diagnosis of EA, and the management of EA, as well as newly recognized allelic disorders that have greatly expanded the clinical spectrum of EA2. Illustrative cases are discussed, with a focus on sporadic patients with congenital features without episodic ataxia who present diagnostic and therapeutic challenges.
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Complicated Gitelman syndrome and autoimmune thyroid disease: a case report with a new homozygous mutation in the SLC12A3 gene and literature review.
Zhou, H, Liang, X, Qing, Y, Meng, B, Zhou, J, Huang, S, Lu, S, Huang, Z, Yang, H, Ma, Y, et al
BMC endocrine disorders. 2018;(1):82
Abstract
BACKGROUND Gitelman syndrome (GS) is an inherited autosomal recessive renal tubular disorder characterized by low levels of potassium and magnesium in the blood, decreased excretion of calcium in the urine, and elevated blood pH. GS is caused by an inactivating mutation in the SLC12A3 gene, which is located on the long arm of chromosome 16 (16q13) and encodes a thiazide-sensitive sodium chloride cotransporter (NCCT). CASE PRESENTATION A 45-year-old man with Graves' disease complicated by paroxysmal limb paralysis had a diagnosis of thyrotoxic periodic paralysis for 12 years. However, his serum potassium level remained low despite sufficiently large doses of potassium supplementation. Finally, gene analysis revealed a homozygous mutation in the SLC12A3 gene. After his thyroid function gradually returned to normal, his serum potassium level remained low, but his paroxysmal limb paralysis resolved. CONCLUSIONS GS combined with hyperthyroidism can manifest as frequent episodes of periodic paralysis; to date, this comorbidity has been reported only in eastern Asian populations. This case prompted us to more seriously consider the possibility of GS associated with thyroid dysfunction.
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Involvement of the def-1 Mutation in the Response of Tomato Plants to Arbuscular Mycorrhizal Symbiosis Under Well-Watered and Drought Conditions.
Sánchez-Romera, B, Calvo-Polanco, M, Ruiz-Lozano, JM, Zamarreño, ÁM, Arbona, V, García-Mina, JM, Gómez-Cadenas, A, Aroca, R
Plant & cell physiology. 2018;(2):248-261
Abstract
Jasmonic acid (JA) and arbuscular mycorrhizal (AM) symbioses are known to protect plants against abiotic and biotic stresses, but are also involved in the regulation of root hydraulic conductance (L). The objective of this experiment was to elucidate the role of JA in the water relations and hormonal regulation of AM plants under drought by using tomato plants defective in the synthesis of JA (def-1). Our results showed that JA is involved in the uptake and transport of water through its effect on both physiological parameters (stomatal conductance and L) and molecular parameters, mainly by controlling the expression and abundance of aquaporins. We observed that def-1 plants increased the expression of seven plant aquaporin genes under well-watered conditions in the absence of AM fungus, which partly explain the increment of L by this mutation under well-watered conditions. In addition, the effects of the AM symbiosis on plants were modified by the def-1 mutation, with the expression of some aquaporins and plant hormone concentration being disturbed. On the other hand, methyl salicylate (MeSA) content was increased in non-mycorrhizal def-1 plants, suggesting that MeSA and JA can act together in the regulation of L. In a complementary experiment, it was found that exogenous MeSA increased L, confirming our hypothesis. Likewise, we confirmed that JA, ABA and SA are hormones involved in plant mechanisms to cope with stressful situations, their concentrations being controlled by the AM symbiosis. In conclusion, under well-watered conditions, the def-1 mutation mimics the effects of AM symbiosis, but under drought conditions the def-1 mutation changed the effects of the AM symbiosis on plants.
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8.
Diagnosis and Management of Genetic Iron Overload Disorders.
Palmer, WC, Vishnu, P, Sanchez, W, Aqel, B, Riegert-Johnson, D, Seaman, LAK, Bowman, AW, Rivera, CE
Journal of general internal medicine. 2018;(12):2230-2236
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Abstract
Iron overload disorders lead to excess iron deposition in the body, which can occur as a result of genetic or secondary causes. Genetic iron overload, referred to as hereditary hemochromatosis, may present as a common autosomal recessive mutation or as one of several uncommon mutations. Secondary iron overload may result from frequent blood transfusions, exogenous iron intake, or certain hematological diseases such as dyserythropoietic syndrome or chronic hemolytic anemia. Iron overload may be asymptomatic, or may present with significant diseases of the liver, heart, endocrine glands, joints, or other organs. If treated appropriately prior to end-organ damage, life expectancy has been shown to be similar compared to matched populations. Alongside clinical assessment, diagnostic studies involve blood tests, imaging, and in some cases liver biopsy. The mainstay of therapy is periodic phlebotomy, although oral chelation is an option for selected patients.
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Case of hypomagnesemia with secondary hypocalcemia with a novel TRPM6 mutation.
Lal, N, Bhardwaj, S, Lalgudi Ganesan, S, Sharma, R, Jain, P
Neurology India. 2018;(6):1795-1800
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10.
Genetics of Atrial Fibrillation.
Feghaly, J, Zakka, P, London, B, MacRae, CA, Refaat, MM
Journal of the American Heart Association. 2018;(20):e009884
Abstract
Background Atrial fibrillation ( AF ) is a common arrhythmia seen in clinical practice. Occasionally, no common risk factors are present in patients with this arrhythmia. This suggests the potential underlying role of genetic factors associated with predisposition to developing AF . Methods and Results We conducted a comprehensive review of the literature through large online libraries, including PubMed. Many different potassium and sodium channel mutations have been discussed in their relation to AF . There have also been non-ion channel mutations that have been linked to AF . Genome-wide association studies have helped in identifying potential links between single-nucleotide polymorphisms and AF . Ancestry studies have also highlighted a role of genetics in AF . Blacks with a higher percentage of European ancestry are at higher risk of developing AF . The emerging field of ablatogenomics involves the use of genetic profiles in their relation to recurrence of AF after catheter ablation. Conclusions The evidence for the underlying role of genetics in AF continues to expand. Ultimately, the role of genetics in risk stratification of AF and its recurrence is of significant interest. No established risk scores that are useful in clinical practice are present to date.