SER252PHE and 776INS3 mutations in the CHRNA4 gene are rare in the Italian ADNFLE population

Nicotinic acetylcholine receptors in neurological and psychiatric diseases

Neuronal nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels that are widely distributed both pre- and post-synaptically in the mammalian brain. By modulating cation flux across cell membranes, neuronal nAChRs regulate neuronal excitability and the release of a variety of neurotransmitters to influence multiple physiologic and behavioral processes including synaptic plasticity, motor function, attention, learning and memory. Abnormalities of neuronal nAChRs have been implicated in the pathophysiology of neurologic disorders including Alzheimer's disease, Parkinson's disease, epilepsy, and Tourette´s syndrome, as well as psychiatric disorders including schizophrenia, depression, and anxiety. The potential role of nAChRs in a particular illness may be indicated by alterations in the expression of nAChRs in relevant brain regions, genetic variability in the genes encoding for nAChR subunit proteins, and/or clinical or preclinical observations where specific ligands showed a therapeutic effect. Over the past 25 years, extensive preclinical and some early clinical evidence suggested that ligands at nAChRs might have therapeutic potential for neurologic and psychiatric disorders. However, to date the only approved indications for nAChR ligands are smoking cessation and the treatment of dry eye disease. It has been argued that progress in nAChR drug discovery has been limited by translational gaps between the preclinical models and the human disease as well as unresolved questions regarding the pharmacological goal (i.e., agonism, antagonism or receptor desensitization) depending on the disease.

Paroxysmal hypnogenic dyskinesia is associated with mutations in the PRRT2 gene

Objective:

To explore the potential causative genes of paroxysmal hypnogenic dyskinesia (PHD), which was initially considered a subtype of paroxysmal dyskinesia and has been recently considered a form of nocturnal frontal lobe epilepsy (NFLE).

Methods:

Eleven patients with PHD were recruited. Mutations in proline-rich region transmembrane protein-2 (PRRT2), myofibrillogenesis regulator 1 (MR-1), solute carrier family 2, member 1 (SLC2A1), calcium-activated potassium channel alpha subunit (KCNMA1), cholinergic receptor, nicotinic, alpha 4 (CHRNA4), cholinergic receptor, nicotinic, beta 2 (CHRNB2), cholinergic receptor, nicotinic, alpha 2 (CHRNA2), and potassium channel subfamily T member 1 (KCNT1) were screened by direct sequencing.

Results:

Two PRRT2 mutations were identified in patients with typical PHD. A mutation of c.649dupC (p.Arg217ProfsX8) was identified in a patient with PHD and his father who was diagnosed with paroxysmal kinesigenic dyskinesia. An additional mutation of c.640G>C (p.Ala214Pro) was identified in a sporadic patient and his asymptomatic mother. No mutations were found in the other screened genes.

Conclusions:

The present study identified PRRT2 mutations in PHD, extending the phenotypic spectrum of PRRT2 and supporting the classification of PHD as a subtype of paroxysmal dyskinesia but not NFLE. Based on the results of this study, screening for the PRRT2 mutation is recommended in patients with PHD.

Neuronal nicotinic receptors in sleep-related epilepsy: studies in integrative biology

Although Mendelian diseases are rare, when considered one by one, overall they constitute a significant social burden. Besides the medical aspects, they propose us one of the most general biological problems. Given the simplest physiological perturbation of an organism, that is, a single gene mutation, how do its effects percolate through the hierarchical biological levels to determine the pathogenesis? And how robust is the physiological system to this perturbation? To solve these problems, the study of genetic epilepsies caused by mutant ion channels presents special advantages, as it can exploit the full range of modern experimental methods. These allow to extend the functional analysis from single channels to whole brains. An instructive example is autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE), which can be caused by mutations in neuronal nicotinic acetylcholine receptors. In vitro, such mutations often produce hyperfunctional receptors, at least in heterozygous condition. However, understanding how this leads to sleep-related frontal epilepsy is all but straightforward. Several available animal models are helping us to determine the effects of ADNFLE mutations on the mammalian brain. Because of the complexity of the cholinergic regulation in both developing and mature brains, several pathogenic mechanisms are possible, which also present different therapeutic implications.

The genetics of monogenic idiopathic epilepsies and epileptic encephalopathies

The group of idiopathic epilepsies encompasses numerous syndromes without known organic substrate. Genetic anomalies are thought to be responsible for pathogenesis, with a monogenic or polygenic model of inheritance. Over the last two decades, a number of genetic anomalies and encoded proteins have been related to particular idiopathic epilepsies and epileptic encephalopathies. Most of these mutations involve subunits of neuronal ion channels (e.g. potassium, sodium, and chloride channels), and may result in abnormal neuronal hyperexcitability manifesting with seizures. However non-ion channel proteins may also be affected. Correlations between genotype and phenotype are not easy to establish, since genetic and non-genetic factors are likely to play a role in determining the severity of clinical features. The growing number of discoveries on this topic are improving classification, prognosis and counseling of patients and families with these forms of epilepsy, and may lead to targeted therapeutic approaches in the near future. In this article the authors have reviewed the main genetic discoveries in the field of the monogenic idiopathic epilepsies and epileptic encephalopathies, in order to provide epileptologists with a concise and comprehensive summary of clinical and genetic features of these seizure disorders.

Tobacco habits modulate autosomal dominant nocturnal frontal lobe epilepsy

Mutations in neuronal nicotinic acetylcholine receptors have been demonstrated in autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE). The beneficial effect of nicotine administration was previously reported in one single case. We investigated the influence of the tobacco habits of 22 subjects from two pedigrees with alpha4 mutations (776ins3 and S248F). Subjects were interviewed with respect to pattern of nicotine intake and seizures. Seizure freedom was significantly associated with tobacco use (P=0.024). All seven nonsmokers with manifest ADNFLE had persistent seizures. Seizure fluctuations, including long remissions, corresponded to changes in tobacco habits in several patients. One patient who recently had begun treatment with transdermal nicotine experienced improvement. We conclude that tobacco appears to be an environmental factor that influences seizure susceptibility in ADNFLE. Inactivation by desensitization of the mutant receptors by nicotine may explain the beneficial effect. The efficacy and safety of transdermal nicotine in ADNFLE should be further explored.

A new paradigm of channelopathy in epilepsy syndromes: Intracellular trafficking abnormality of channel molecules

Mutations in genes encoding ion channels in brain neurons have been identified in various epilepsy syndromes. In neuronal networks, "gain-of-function" of channels in excitatory neurotransmission could lead to hyper-excitation while "loss-of-function" in inhibitory transmission impairs neuronal inhibitory system, both of which can result in epilepsy. A working hypothesis to view epilepsy as a disorder of channel or "channelopathy" seems rational to explore the pathogenesis of epilepsy. However, the imbalance resulting from channel dysfunction is not sufficient to delineate the pathogenesis of all epilepsy syndromes of which the underlying channel abnormalities have been verified. Mutations identified in epilepsy, mainly in genes encoding subunits of GABA(A) receptors, undermine intracellular trafficking, thus leading to retention of channel molecules in the endoplasmic reticulum (ER). This process may cause ER stress followed by apoptosis, which is a known pathomechanism of certain neurodegenerative disorders. Thus, the pathomechanism of "channel trafficking abnormality" may provide a new paradigm to channelopathy to unsolved questions underlying epilepsy, such as differences between generalized epilepsy with febrile seizures plus and severe myoclonic epilepsy in infancy, which share the causative genetic abnormalities in the same genes and hence are so far considered to be within the spectrum of one disease entity or allelic variants.

Two new putative susceptibility loci for ADNFLE

Autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE) has been up to now considered a simple Mendelian trait caused by mutations in neuronal nicotinic acetylcholine receptor (nAChR) subunit genes. We previously demonstrated that in a three-generation Italian family the disease was unlinked to all known ADNFLE loci as well as to all known brain-expressed nAChR subunits. The genome-wide linkage analysis here presented performed on this family points to the existence of two new putative ADNFLE loci on chromosomes 3p22-p24 and 8q11.2-q21.1. These findings, together with several ADNFLE characteristics, suggest that this epilepsy could be, at least in the above family, a complex disorder. In particular, we propose and discuss the hypothesis of a digenic transmission of the disease.

Evidence for a fourth locus for autosomal dominant nocturnal frontal lobe epilepsy

Mutations responsible for autosomal dominant nocturnal frontal lobe epilepsy have been identified in two members of the neuronal nicotinic acetylcholine receptor gene family: CHRNA4(ENFL1 locus) and CHRNB2 (ENFL3 locus) coding for alpha4 and beta2 subunit, respectively. However, mutations in these genes account for only a minority (less than 10%) of cases. For a third ADNFLE locus (ENFL2) on chromosome 15q24 the gene was not identified. The involvement of the three loci in the pathogenesis of ADNFLE was investigated in 12 unrelated Italian families, selected on the basis of anamnestic and video-polysomnographic data. Compliant family members were typed for polymorphic markers spanning the analyzed chromosome regions. Linkage analyses excluded association of all chromosome regions with ADNFLE in 72% of cases. In two, four and one families it was impossible to ascertain or exclude association with ENFL1, ENFL2, or ENFL3, respectively, however, no mutations have been detected in the nicotinic receptor genes located in these regions. These data strongly suggest that ENFL1, ENFL2 and ENFL3 are minor loci for the disease and point to the existence of at least a fourth locus for ADNFLE.

Sleep epilepsy

BACKGROUND

Seizures during sleep have been recognized for centuries, and it is well known that both sleep and lack of sleep can influence the occurrence of ictal and interictal events. Sleep epilepsy refers to the subset of epilepsy in which seizures occur exclusively or predominantly during sleep. Primary generalized, secondarily generalized, and focal partial epilepsy syndromes can all manifest as sleep epilepsy. The spread of polysomnography has increased our ability to accurately diagnose sleep epilepsy and facilitated the discovery of an autosomal dominant sleep epilepsy.

REVIEW SUMMARY

This review summarizes the epidemiology of sleep epilepsy and reviews a number of epilepsies that can manifest as sleep epilepsy as well as some nonepileptic sleep disorders from which sleep epilepsy must be differentiated.

Mutational analysis of nicotinic acetylcholine receptor beta2 subunit gene (CHRNB2) in a representative cohort of Italian probands affected by autosomal dominant nocturnal frontal lobe epilepsy

Twenty-four autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE) probands were analyzed for the presence of V287L and V287M mutations in the CHRNB2 gene, which have been recently associated with the disease. In all patients, the involvement of the two additional loci reported as being associated with ADNFLE (CHRNA4 gene and chromosome 15q24 region) had been previously excluded. Mutational screening was performed by sequencing a polymerase chain reaction-amplified CHRNB2 DNA fragment, spanning the whole exon 5, which contains the V287L and V287M mutations and codes for approximately 65% of the mature protein. In none of the patients were mutations in the analyzed region of CHRNB2 found. These data, obtained in the largest ADNFLE cohort so far analyzed, demonstrate the rarity of the identified CHRNB2 mutations in ADNFLE patients.

Sleep disorders in children with neurologic diseases

Pediatric neurologic diseases are often associated with different kinds of sleep disruption (mainly insomnia, less frequently hypersomnia or parasomnias). Due to the key-role of sleep for development, the effort to ameliorate sleep patterns in these children could have important prognostic benefits. Study of sleep architecture and organization in neurologic disorders could lead to a better comprehension of the pathogenesis and a better treatment of the disorders. This article focuses on the following specific neurologic diseases: nocturnal frontal lobe epilepsy and abnormal motor behaviors of epileptic origin, evaluating differential diagnosis with parasomnias; achondroplasia, confirming the crucial role of craniofacial deformity in determining sleep-disordered breathing; neuromuscular diseases, mainly Duchenne's muscular dystrophy and myotonic dystrophy; cerebral palsy, evaluating either the features of sleep architecture and the importance of the respiratory problems associated; headaches, confirming the strict relationships with sleep in terms of neurochemical and neurobehavioral substrates; and finally a review on the effectiveness of melatonin for sleep problems in children with neurologic syndromes and mental retardation, blindness, and epilepsy.

A new biallelic polymorphism in intron 1 of the CHRNA4 gene may cause erroneous genotyping of a closely linked CA repeat marker

A new polymorphism in intron 1 of the neuronal nicotinic acetylcholine receptor alpha 4 subunit gene (CHRNA4) was identified. It consists of a G to T substitution located in the downstream flanking region of a previously reported CA repeat marker. This polymorphism whose frequency is about six percent in a control population occurs near the 3' end of the reverse primer generally used to type the CA repeat marker. Data are presented showing that the newly identified polymorphism causes erroneous genotyping of the CA repeat marker which can alter the results of linkage analysis for CHRNA4. The use of a different reverse primer located 34 nt downstream of the published sequence overcame errors in genotyping and identified two novel alleles of the CA repeat marker. Re-typing of the marker with the new proposed primer pair in a Caucasian control population of 107 unrelated individuals was also performed

The nicotinic receptor beta 2 subunit is mutant in nocturnal frontal lobe epilepsy

Clustered attacks of epileptic episodes originating from the frontal lobe during sleep are the main symptoms of autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE, MIM 600513). Despite the clinical homogeneity, three forms of ADNFLE have been associated with chromosomes 20 (ENFL1; ref. 1), 15 (ENFL2; ref. 2) and 1 (ENFL3; ref. 3). Mutations of the gene encoding the neuronal nicotinic acetylcholine receptor alpha 4 subunit (CHRNA4 ) have been found in ADNFLE-ENFL1 families, but these mutations account for only a small proportion of ADNFLE cases. The newly identified locus associated with ENFL3 harbours several candidate genes, including CHRNB2 (ref. 8), whose gene product, the beta 2 nicotinic acetylcholine receptor (nAChR) subunit, co-assembles with the alpha 4 nAChR subunit to form the active receptor.

NREM parasomnias: arousal disorders and differentiation from nocturnal frontal lobe epilepsy

Parasomnias emerging from NREM sleep such as sleep walking, sleep terrors and confusional arousals are considered arousal disorders. Nocturnal video-polysomnography is the gold standard to diagnosing and differentiating parasomnias from other arousals with atypical motor behaviors such as nocturnal frontal lobe epilepsy (NFLE). This form of nocturnal seizures with prominent dystonic-dyskinetic components, in some cases genetic, has been recently identified by means of detailed video-analysis of movements during sleep. The clinical picture of parasomnias (with onset in early childhood, rare episodes of long duration, absence of stereotypy, general disappearance after puberty) is different from that of NFLE (which first occurs between the age of 10 and 20, manifests frequent complex and repetitive behaviors of short duration excluding rare prolonged seizures, nocturnal agitation, some daytime complaints such as fatigue or sleepiness, persistence into adulthood). Patients show no difference from classical sleep parameters whilst microstructure analysis shows sleep instability and arousal fluctuations in parasomnias and NFLE. In children as well, at least in our experience, the differential diagnosis between the two disorders is difficult and requires one or more complete nocturnal video-polygraphic recording. In any case the diagnosis of NFLE should be considered in children with nocturnal motor episodes or nocturnal motor agitation, when the attacks persist; this diagnosis is probably more frequent than expected.