Gelastic seizures due to hypothalamic hamartoma: rapid resolution after endoscopic tumor disconnection

SLC2A1 and Its Related Epileptic Phenotypes

Glucose transporter type 1 deficiency syndrome (GLUT1DS) is caused by heterozygous, mostly de novo, mutations in SLC2A1 gene encoding the glucose transporter GLUT1, the most relevant energy transporter in the blood–brain barrier. GLUT1DS includes a broad spectrum of neurologic disturbances, from severe encephalopathy with developmental delay, to epilepsy, movement disorders, acquired microcephaly and atypical mild forms. For diagnosis, lumbar puncture and genetic analysis are necessary and complementary; an immediate response to ketogenic diet supports the diagnosis in case of high suspicion of disease and negative exams. The ketogenic diet is the first-line treatment and should be established at the initial stages of disease.

KCNT1-Related Epilepsy: A Review

KCNT1 gene encodes the sodium-dependent potassium channel reported as a causal factor for several different epileptic disorders. The gene has been also linked with cardiac disorders and in a family to sudden unexpected death in epilepsy. KCNT1 mutations, in most cases, result in a gain of function causing a neuronal hyperpolarization with loss of inhibition. Many early-onset epileptic encephalopathies related to gain of function of KCNT1 gene have been described, most often associated with two phenotypes: malignant migrating focal seizures of infancy and familial autosomal-dominant nocturnal frontal lobe epilepsy; however, there is no clear phenotype–genotype correlation, in fact same mutations have been represented in patients with West syndrome, Ohtahara syndrome, and early myoclonic encephalopathy. Additional neurologic features include intellectual disability, psychiatric disorders, hypotonia, microcephaly, strabismus, and movement disorders. Conventional anticonvulsant, vagal stimulation, and ketogenic diet have been used in the absence of clinical benefit in individuals with KCNT1-related epilepsy; in some patients, quinidine therapy off-label has been practiced successfully. This review aims to describe the characteristics of the gene, the phenotypes related to genetic mutations with the possible genotype–phenotype correlations and the treatments proposed to date, discussing the comorbidities reported in the literature.

DNM1 Gene and Its Related Epileptic Phenotypes

The phenotypic variety associated to mutations in dynamin 1 (DNM1), codifying the presynaptic protein DNM1 has been increasingly reported, mainly related to encephalopathy with intractable epilepsy; currently, it is known the phenotype related to DNM1 gene mutations is relatively homogeneous with developmental delay, hypotonia, and epilepsy characterized by infantile spasms and possible progression to Lennox-Gastaut syndrome. By examining all the papers published until 2020 (18 articles), we compared data from 30 patients (extrapolated from 5 papers) with DNM1 mutations, identifying 26 patients with de novo mutations in DNM1. Nine patients (33.3%) reported the recurrent mutation p.Arg237Trp. A usual phenotype observed comprises severe to deep developmental delay and muscular hypotonia in all patients with epilepsy beginning with infantile spasms, which often evolved into Lennox-Gastaut syndrome. Data about GTPase or central domains mutations, and existing structural modeling and functional suggest a dominant negative effect on DMN1 function. Generally genetic epilepsies consist of a wide spectrum of clinical features, unlike that, DNM1-related CNS impairment phenotype is quite uniform. In up to one third of patients it has been found variant p.Arg237Trp, which is one of the most frequent variant detected in epileptic encephalopathies. The understanding of DNM1 function opens up the chance that this gene would become a new therapeutic target for epilepsies.

GRIN2A and GRIN2B and Their Related Phenotypes

Glutamate is the most relevant excitatory neurotransmitter of the central nervous system; it binds with several receptors, including N-methyl-D-aspartate receptors (NMDARs), a subtype of ionotropic glutamate receptor that displays voltage-dependent block by Mg2+ and a high permeability to Ca2+. GRIN2A and GRIN2B genes encode the GluN2A and GluN2B subunits of the NMDARs, which play important roles in synaptogenesis, synaptic transmission, and synaptic plasticity, as well as contributing to neuronal loss and dysfunction in several neurological disorders. Recently, individuals with a range of childhood-onset drug-resistant epilepsies, such as Landau–Kleffner or Lennox–Gastaut syndrome, intellectual disability (ID), and other neurodevelopmental abnormalities have been found to carry mutations in GRIN2A and GRIN2B, with high variable expressivity in phenotype. The first one is found mainly in epilepsy-aphasia syndromes, while the second one mainly in autism, schizophrenia, and ID, such as autism spectrum disorders. Brain magnetic resonance imaging alterations are found in some patients, even if without a clear clinical correlation. At the same time, increasing data on genotype–phenotype correlation have been found, but this is still not fully demonstrated. There are no specific therapies for the treatment of correlated NMDARs epilepsy, although some evidence with memantine, an antagonist of glutamate receptor, is reported in the literature in selected cases with mutation determining a gain of function.

SYNGAP1 and Its Related Epileptic Syndromes

Synaptic Ras GTPase-activating protein 1 (SYNGAP1) is abundantly expressed in the postsynaptic space in brain tissue and has a crucial role in the regulation of the excitatory/inhibitory balance and in brain development. It is estimated that SYNGAP1 loss of function variants have an incidence of 1 to 4/10,000 individuals, mostly occurring de novo, even if few cases of vertical transmission of mosaic mutations have been reported. Loss-of-function mutations within this gene have been related with an epileptic encephalopathy characterized by eyelid myoclonia with absences (EMA) and myoclonic-atonic seizures (MAE) with early onset, commonly resistant to antiepileptic drugs (AED). Epilepsy is often associated with other clinical features, including truncal and/or facial hypotonia and/or ataxia with a wide-based and unsteady gate. Other clinical signs are intellectual disability, developmental delay, and behavioral and speech impairment, in a context of a normal neuroimaging study. In selected cases, dysmorphic features, skeletal abnormalities, and eye involvement are also described. The diagnosis of the disorder is usually established by multigene panel and, in unsolved cases, by exome sequencing. Management of the affected individuals involves different specialists and is mainly symptomatic. No clinical trials about the efficacy of AED in SYNGAP1 encephalopathy have been performed yet and Lamotrigine and valproate are commonly prescribed. In more than half of cases, however, epilepsy is refractory to AED.

PCDH19-Related Epilepsies

Protocadherin-19 (PCDH19) is considered one of the most relevant genes related to epilepsy. To date, more than 150 mutations have been identified as causative for PCDH19-female epilepsy (also known as early infantile epileptic encephalopathy-9, EIEE9), which is characterized by early onset epilepsy, intellectual disabilities, and behavioral disturbances. More recently, mosaic-males (i.e., exhibiting the variants in less than 25% of their cells) have been described as affected by infant-onset epilepsy associated with intellectual disability, as well as compulsive or aggressive behavior and autistic features. Although little is known about the physiological role of PCDH19 protein and the pathogenic mechanisms that lead to EIEE9, many reports and clinical observation seem to suggest a relevant role of this protein in the development of cellular hyperexcitability. However, a genotype–phenotype correlation is difficult to establish. The main feature of EIEE9 consists in early onset of seizures, which generally occur in clusters lasting 1 to 5 minutes and repeating up to 10 times a day for several days. Seizures tend to present during febrile episodes, similarly to the first phases of Dravet syndrome and PCDH19 variants have been found in ∼25% of females who present with features of Dravet syndrome and testing negative for SCN1A variants. There is no “standardized” treatment for PCDH19-related epilepsy and most of the patients receiving a combination of several drugs. In this review, we focus on the latest researches on these aspects, with regard to protein expression, its known functions, and the mechanisms by which the protein acts. The clinical phenotypes related to PCDH19 mutations are also discussed.

FOXG1 Gene and Its Related Phenotypes

FOXG1 is an important transcriptional repressor found in cell precursor of the ventricular region and in neurons in the early stage of differentiation during the development of the nervous epithelium in the cerebrum and optical formation. Mutations involving FOXG1 gene have been described first in subjects with congenital Rett syndrome. They can cause seizure, delayed psychomotor development, language disorders, and autism. FOXG1 deletions or intragenic mutations also determinate reduction in head circumference, structural defects in the corpus callosum, abnormal movements, especially choreiform, and intellectual retardation with no speech. Patients with duplications of 14q12 present infantile spasms and have subsequent intellectual disability with autistic features, head circumference in the normal range, and regular aspect of corpus callosum. Clinical characteristics of patients with FOXG1 variants include growth deficit after birth associated with microcephaly, facial dysmorphisms, important delay with no language, deficit in social interaction like autism, sleep disorders, stereotypes, including dyskinesia, and seizures. In these patients, it is not characteristic a history of loss of acquired skills.

ALDH7A1 Gene and Its Related Pyridoxine-Dependent Epilepsy

Despite being classically reported as caused by mutations in solute carriers genes (SLC2A1), it has been recently shown that also mutations in ALDH7A1 can cause pyridoxine-dependent epilepsy (PDE). ALDH7A1 is a gene encoding for the antiquitin, an enzyme that catalyzes the nicotinamide adenine dinucleotide-dependent dehydrogenation of L-α-aminoadipic semialdehyde/L-Δ1-piperideine 6-carboxylate. It is a highly treatable disorder, but nevertheless it is still not certain when to consider this diagnosis and how to test for it. It is possible to identify a classical form and an atypical one of PDE associated with more than 70 mutations of ALDH7A1 gene. The typical form is characterized by the onset of seizures within the first month of life and can be treated with pyridoxine in monotherapy, as they are not responsive to traditional anticonvulsant therapy. The atypical forms are equally pyridoxine-dependent, but are characterized by a later onset of seizures, sometimes up to the age of 3 years. Several brain abnormalities have been associated with ALDH7A1 mutations. Seizure control is achieved by the administration of high-dose pyridoxine, which must be started in the patient as soon as possible. However, it has been observed that pyridoxine therapy does not prevent developmental delay in most cases; in these cases, it can be recommended and useful to supplement arginine with pyridoxine therapy associated with a dietary restriction of lysine.

TBC1D24 and Its Related Epileptic Encephalopathy

TBC1D24, mapped to 16p13.3, encodes a protein containing a Tre2/Bub2/Cdc16 (TBC) domain, belonging to the super-family of Rab GTPase activating proteins (Rab-GAP). These proteins regulate various functions, including the regulation of the traffic of the vesicular membrane. Several TBC1D24 mutations have been related to autosomal recessive neurological disorders, including severe developmental encephalopathies with malignant early childhood epilepsy, benign epilepsy, epileptic encephalopathy, and a complex neurological syndrome characterized by deafness, onychodystrophy, bone and neurological degeneration. Mutations of TBC1D24 have also been reported in patients with nonsyndromic deafness with dominant or recessive inheritance. Mechanisms underlying TBC1D24-associated disorders and the functions of TBC1D24 products in the generation of such complex spectrum of diseases remain partly unclear and future studies are needed to clarify this aspect, in order to improve the management of seizures and for the prevention of complication (including death) of newly diagnosed patients affected by TBC1D24-related disorders.

Calcium Channels Genes and Their Epilepsy Phenotypes

Calcium (Ca2+) channel gene mutations play an important role in the pathogenesis of neurological episodic disorders like epilepsy. CACNA1A and CACNA1H genes are involved in the synthesis of calcium channels. Mutations in the α1A subunit of the P/Q type voltage-gated calcium channel gene (CACNA1A) located in 19p13.13, which encodes for the transmembrane pore-forming subunit of CAV2.1 voltage-dependent calcium channel, have been correlated to a large clinical spectrum of epilepsy such as idiopathic genetic epilepsy, early infantile epilepsy, and febrile seizures. Moreover, CACNA1A mutations have been demonstrated to be involved in spinocerebellar ataxia type 6, familiar hemiplegic migraine, episodic ataxia type 2, early-onset encephalopathy, and hemiconvulsion–hemiplegia epilepsy syndrome. This wide phenotype heterogeneity associated with CACNA1A mutations is correlated to different clinical and electrophysiological manifestations. CACNA1H gene, located in 16p13.3, encodes the α1H subunit of T-type calcium channel, expressing the transmembrane pore-forming subunit Cav3.2. Despite data still remain controversial, it has been identified as an important gene whose mutations seem strictly related to the pathogenesis of childhood absence epilepsy and other generalized epilepsies. The studied variants are mainly gain-of-function, hence responsible for an increase in neuronal susceptibility to seizures. CACNA1H mutations have also been associated with autism spectrum disorder and other behavior disorders. More recently, also amyotrophic lateral sclerosis has been related to CACNA1H alterations. The aim of this review, other than describe the CACNA1A and CACNA1H gene functions, is to identify mutations reported in literature and to analyze their possible correlations with specific epileptic disorders, purposing to guide an appropriate medical treatment recommendation.

PRRT2 Related Epilepsies: A Gene Review

PRRT2 encodes for proline-rich transmembrane protein 2 involved in synaptic vesicle fusion and presynaptic neurotransmitter release. Mutations in human PRRT2 have been related to paroxysmal kinesigenic dyskinesia (PKD), infantile convulsions with choreoathetosis, benign familial infantile epilepsies, and hemiplegic migraine. PRRT2 mutations cause neuronal hyperexcitability, which could be related to basal ganglia or cortical circuits dysfunction, leading to paroxysmal disorders. PRRT2 is expressed in the cerebral cortex, basal ganglia, and cerebellum. Approximately, 90% of pathogenic variants are inherited and 10% are de novo. Paroxysmal attacks in PKD are characterized by dystonia, choreoathetosis, and ballismus. In the benign familial infantile epilepsy (BFIE), seizures are usually focal with or without generalization, usually begin between 3 and 12 months of age and remit by 2 years of age. In 30% of cases of PRRT2-associated PKD, there is an association with BFIE, and this entity is referred to as PKD with infantile convulsions (PKD/IC). PRRT2 mutations are the cause of benign family childhood epilepsy and PKD/IC. On the other hand, PRRT2 mutations do not seem to correlate with other types of epilepsy. The increasing incidence of hemiplegic migraine in families with PRRT2-associated PKD or PKD/IC suggests a common disease pathway, and it is possible to assert that BFIE, paroxysmal kinesigenic dyskinesia, and PKD with IC belong to a continuous disease spectrum of PRRT2-associated diseases.

SLC25A22 and Its Related Epileptic Encephalopathies

Epileptic encephalopathy is a condition in which seizures, electroencephalographic epileptiform abnormalities lead to a progressive deterioration of brain functions causing a significant psychomotor delay. One of the typical features of this heterogeneous and large group of severe disorders is the extremely early onset of seizures. The main causes of the epileptic encephalopathies include structural brain defects, inherited metabolic disorders; in this aspect, more than 100 genetic defects, including mutations in the solute carrier family 25 (SLC25A22) gene which encodes a mitochondrial glutamate carrier. To date, the main clinical phenotypes related to mutations of this gene are Ohtahara syndrome (or early infantile epileptic encephalopathy), early myoclonic encephalopathy and migrating partial seizures in infancy. In all the cases, prognosis is poor and no disease-modifying treatment is available in the present days.

Syntaxin Binding Protein 1 Related Epilepsies

Syntaxin binding protein 1 (STXBP1), commonly known as MUNC18–1, is a member of SEC1 family membrane trafficking proteins; their function consists in controlling the soluble N-ethylmaleimide-sensitive factor attachment protein receptors complex assembly, making them essentials regulators of vesicle fusion. The precise function and molecular mechanism through which Munc18–1 contributes to neurotransmitter releasing is not entirely understood, but several evidences suggest its probable role in exocytosis. In 2008, heterozygous de novo mutations in neuronal protein Munc18–1 were first referred as a cause of Ohtahara syndrome development. Currently, a wide examination of the published data proved that 3.1% of patients with severe epilepsy carry a pathogenic de novo mutation including STXBP1 and approximately 10.2% of early onset epileptic encephalopathy is due to an aberrant STXBP1 form codified by the mutated gene. STXBP1 mutations can be associated to a wide clinical heterogeneity. All affected individuals show developmental delay and approximately the 95% of cases have seizures and early onset epileptic encephalopathy, characterized by infantile spasms as the main consistent feature. Burst suppression pattern and hypsarrhythmia are the most frequent EEG anomalies. Other neuronal disorders include Rett syndrome and behavioral and movement disorders. Mild dysmorphic features have been detected in a small number of cases. No genotype–phenotype correlation has been reported. Management of STXBP1 encephalopathy requires a multidisciplinary approach, including epilepsy control and neurological rehabilitation. About 25% of patients are refractory to standard therapy. A single or combined antiepileptic drugs may be required. Several studies described vigabatrin, valproic acid, levetiracetam, topiramate, clobazam, and oxcarbazepine as effective in seizure control. Lamotrigine, zonisamide, and phenobarbital are also commonly used. To date, it remains unclear which therapy is the most effective. Severe morbidity and high mortality are inevitable consequences in some of these patients.

Gamma-Aminobutyric Acid Type A Receptor Genes and Their Related Epilepsies

Gamma-aminobutyric acid type A (GABA-A) receptor subunit gene mutations, which include GABRA1, GABRB3, GABRD, and GABRG2, are often involved in several genetic epilepsy syndromes and other neuropsychiatric diseases like autism spectrum disorder, schizophrenia, and anxiety. GABA-A are ligand-gated ionic channels, and are involved firstly in the fast inhibitory synaptic transmission of the central nervous system. The GABA receptors include the ionotropic GABA-A and GABA-C receptors and the metabotropic GABA-B receptors. According to the site in which mutations occur, they cause disorders in channel opening, “lock-and-pull” receptor system functioning, and capable of causing a specific epilepsy phenotype. The aim of this article is to summarize the most recent literature findings, considering genetic mutations, clinical features, genotype/phenotype correlation, and therapy about neurodevelopment diseases correlated to GABA receptors dysfunction, in particular epilepsy. According to our findings, we conclude that further mutation analysis could permit genotype–phenotype correlation and give more information about the best efficient treatment, even if—at present—more clinical and genetic studies are necessary.

WDR45 Gene and Its Role in Pediatric Epilepsies

WD repeat domain 45 (WDR45) gene has been increasingly found in patients with developmental delay (DD) and epilepsy. Previously, WDR45 de novo mutations were reported in sporadic adult and pediatric patients presenting iron accumulation, while heterozygous mutations were associated with β-propeller protein-associated neurodegeneration (BPAN), a subtype of neurodegeneration with brain iron accumulation disorders, characterized by extrapyramidal movement disorders and abnormal accumulation of iron in the basal ganglia. Overall, people harboring WDR45 mutations have moderate to severe DD and different types of seizures. The phenotype of adult patients is characterized by extrapyramidal movement, dystonia, parkinsonism, language impairment, and involvement of the substantia nigra and in the globus pallidus at brain magnetic resonance imaging. Importantly, there are no findings of brain iron accumulation in brain in BPAN patients in the first decade of life, thus suggesting a progressive course of the disease. Comparatively, the main phenotype of pediatric patients is epilepsy with early onset, most of which present infantile spasms and arrest or regression of psychomotor development. The phenotype of patients with WDR45 mutations is variable, being different if caused by somatic mosaicism or germline mutations, and presenting with a different spectrum of manifestations in males and females. The treatment of affected individuals is symptomatic. Regarding the seizures, specific, gene-based approaches with specific antiepileptic drugs are not currently available. The early diagnosis of BPAN could be useful in some aspects, such as providing families a supportive treatment to their affected children.

The Spectrum of KCNQ2- and KCNQ3-Related Epilepsy

KCNQ genes encode for a family of six transmembrane domains, single pore-loop, and K+ channel α-subunits that have a wide range of physiological correlates. In the brain, KCNQ2 and KCNQ3 heteromultimers are thought to underlie the M-current which is essential in raising the threshold for firing an action potential; mutations in these genes may cause several types of infantile epilepsies. KCNQ2-related disorders represent a continuum of overlapping neonatal epileptic phenotypes that range from KCNQ2 benign familial neonatal epilepsy (BFNE), a seizure disorder that occur in children who typically have a normal psychomotor development and are inherited as an autosomal dominant trait, to KCNQ2 early-onset epileptic encephalopathy (EOEE) as the result of a de novo pathogenic variant. KCNQ3-related disorders are rarer and include BFNE, benign familial infantile epilepsy and KCNQ3-related epileptic encephalopathy with intellectual disability with or without seizures and/or cortical visual impairment. For both KCNQ2- and KCNQ3-related disorders, it is possible to use several drugs for different classes of mutations (i.e., gain of function vs. loss of function), and usually their effects vary in relation to the clinical presentation and the phenotype of the patient. However, KCNQ2-EOEE patients have a worse response to treatment than KCNQ2-BFNE patients and usually become drug resistant with multiple daily seizures.

MECP2-Related Disorders and Epilepsy Phenotypes

MECP2 (methyl-CpG binding protein-2) gene, located on chromosome Xq28, encodes for a protein particularly abundant in the brain that is required for maturation of astrocytes and neurons and is developmentally regulated. A defective homeostasis of MECP2 expression, either by haploinsufficiency or overexpression, leads to a neurodevelopmental phenotype. As MECP2 is located on chromosome X, the clinical presentation varies in males and females ranging from mild learning disabilities to severe encephalopathies and early death. Typical Rett syndrome (RTT), the most frequent phenotype associated with MECP2 mutations, primarily affects girls and it was previously thought to be lethal in males; however, MECP2 duplication syndrome, resulting from a duplication of the Xq28 region including MECP2, leads to a severe neurodevelopmental disorder in males. RTT and MECP2 duplication syndrome share overlapping clinical phenotypes including intellectual disabilities, motor deficits, hypotonia, progressive spasticity, and epilepsy. In this manuscript we reviewed literature on epilepsy related to MECP2 disorders, focusing on clinical presentation, genotype–phenotype correlation, and treatment.

CDKL5 Gene: Beyond Rett Syndrome

CDKL5 is a gene located in the X-chromosome (Xp22) encoding a serine/threonine kinase involved in various signaling pathways, implicated in cell proliferation, axon development, dendrite growth, synapse formation, and maintenance. Mutations occurring in this gene have been associated with drug-resistant early-onset epilepsy, with multiple seizures type, and deep cognitive and motor development delay with poor or absent speech, ataxic gait or inability to walk, hand stereotypies and in a few cases decrement of head growth. Many aspects remain unclear about the CDKL5 deficiency disorders, research will be fundamental to better understand the pathogenesis of neurological damage and consequently developed more targeted and profitable therapies, as there is not, at the present, a gene-based treatment and the seizures are in most of the cases drug resistant. In this article, we summarize the actual knowledge about CDKL5 gene function and mostly the consequence given by its dysfunction, also examining the possible therapeutic approaches.

Aristaless-Related Homeobox (ARX): Epilepsy Phenotypes beyond Lissencephaly and Brain Malformations

The Aristaless-related homeobox (ARX) transcription factor is involved in the development of GABAergic and cholinergic neurons in the forebrain. ARX mutations have been associated with a wide spectrum of neurodevelopmental disorders in humans and are responsible for both malformation (in particular lissencephaly) and nonmalformation complex phenotypes. The epilepsy phenotypes related to ARX mutations are West syndrome and X-linked infantile spasms, X-linked myoclonic epilepsy with spasticity and intellectual development and Ohtahara and early infantile epileptic encephalopathy syndrome, which are related in most of the cases to intellectual disability and are often drug resistant. In this article, we shortly reviewed current knowledge of the function of ARX with a particular attention on its consequences in the development of epilepsy during early childhood.

The Spectrum of DEPDC5-Related Epilepsy

Disheveled EGL-10 and pleckstrin domain-containing protein 5 (DEPDC5) is a key member of the GAP activity toward rags complex 1 complex, which inhibits the mammalian target of rapamycin complex 1 (mTORC1) pathway. DEPDC5 loss-of-function mutations lead to an aberrant activation of the mTOR signaling. At neuronal level, the increased mTOR cascade causes the generation of epileptogenic dysplastic neuronal circuits and it is often associated with malformation of cortical development. The DEPDC5 phenotypic spectrum ranges from sporadic early-onset epilepsies with poor neurodevelopmental outcomes to familial focal epilepsies and sudden unexpected death in epilepsy; a high rate of inter- and intrafamilial variability has been reported. To date, clear genotype–phenotype correlations have not been proven. More studies are required to elucidate the significance of likely pathogenic/variants of uncertain significance. The pursuit of a molecular targeted antiepileptic therapy is a future challenge.

SCN1A and Its Related Epileptic Phenotypes

Epilepsy is one of the most common neurological disorders, with a lifetime incidence of 1 in 26. Approximately two-thirds of epilepsy has a substantial genetic component in its etiology. As a result, simultaneous screening for mutations in multiple genes and performing whole exome sequencing (WES) are becoming very frequent in the clinical evaluation of children with epilepsy. In this setting, mutations in voltage-gated sodium channel (SCN) α-subunit genes are the most commonly identified cause of epilepsy, with sodium channel genes (i.e., SCN1A, SCN2A, SCN8A) being the most frequently identified causative genes. SCN1A mutations result in a wide spectrum of epilepsy phenotypes ranging from simple febrile seizures to Dravet syndrome, a severe epileptic encephalopathy. In case of mutation of SCN1A, it is also possible to observe behavioral alterations, such as impulsivity, inattentiveness, and distractibility, which can be framed in an attention deficit hyperactivity disorder (ADHD) like phenotype. Despite more than 1,200 SCN1A mutations being reported, it is not possible to assess a clear phenotype–genotype correlations. Treatment remains a challenge and seizure control is often partial and transitory.

SCN1B Gene: A Close Relative to SCN1A

One of the first reported genes associated with epilepsy was SCN1B, which encodes for β-subunit of voltage-gated sodium channel of excitable cells and it is critical for neuronal function in both central and peripheral nervous system. β-subunits modulate the expression levels and functional properties of sodium channels and though their immunoglobulin domains may mediate interactions between channels and other proteins. Traditionally, SCN1B mutations were associated with generalized epilepsy with febrile seizures plus, a familial epilepsy syndrome characterized by heterogeneous phenotypes including febrile seizures (FS), febrile seizures plus (FS + ), mild generalized epilepsies, and severe epileptic encephalopathies. Throughout the years, SCN1B mutations have been also associated with Dravet syndrome and, more recently, with developmental and epileptic encephalopathies, expanding the spectrum associated with this gene mutations to more severe phenotypes.