Seizure Plus Research Articles

Generalized epilepsy with febrile seizure plus (GEFS+) spectrum: Novel de novo mutation of SCN1A detected in a Malaysian patient

In this report, we describe a 15-year-old Malaysian male patient with a de novo SCN1A mutation who experienced prolonged febrile seizures after his first seizure at 6 months of age. This boy had generalized tonic clonic seizure (GTCS) which occurred with and without fever. Sequencing analysis of voltage-gated sodium channel a1-subunit gene, SCN1A, confirmed a homozygous A to G change at nucleotide 5197 (c.5197A > G) in exon 26 resulting in amino acid substitution of asparagines to aspartate at codon 1733 of sodium channel. The mutation identified in this patient is located in the pore-forming loop of SCN1A and this case report suggests missense mutation in pore-forming loop causes generalized epilepsy with febrile seizure plus (GEFS+) with clinically more severe neurologic phenotype including intellectual disabilities (mental retardation and autism features) and neuropsychiatric disease (anxiety disorder).

Abstract P081: Voltage-Gated TTX-Sensitive Nav1.1 Brain Sodium Channels Are Important for Cardiac Contractile Function

Background: Mutations in voltage gated brain sodium channel Nav1.1 have been linked to many disorders, including Generalized Epilepsy with Febrile Seizures Plus (GEFS+) and Severe Myoclonic Epilepsy of Infancy (SMEI). Recent studies have identified TTX- sensitive Nav1.1 brain sodium channels in the SA node and ventricular T-tubules of the heart, though their role in cardiac function is still controversial. We tested the functional significance of Nav1.1 sodium channels in the heart by creating a novel knock-in of human epilepsy GEFS+ mutation SCN1A-R1648H at the Scn1a locus of a C57BL/6J X 129 mouse. Method: In vivo 2-D echocardiography was performed on 2 week old (juvenile) and 8 week old (adult) wild-type and heterozygote (Scn1aRH/+) mice after extracardiac neuronal block through intraperitoneal injections of atropine and propranolol (2.5mg/kg each). Calcium and contractility studies on adult ventricular cardiomyocytes isolated from the wild type and Scn1aRH/+ mice paced at 0.5Hz were followed by administration of TTX (100nM, a brain sodium channel inhibitor) and pacing at 2Hz. qRT-PCR and Western blot of the isolated cells and whole heart samples was also done. Results: A decrease in Nav1.1 gene expression in the Scn1aRH/+ juvenile (by 31%, 0.69 of 1) and adult (by 60%, 0.4 of 1) whole heart samples and isolated cells (p<0.05) was seen. Echocardiography revealed concentric hypertrophy in the juvenile Scn1aRH/+ mice by a significant increase in LV mass, LV mass/body weight ratio, and relative wall thickness (p<0.05). In the adult Scn1aRH/+ mice, systolic isovolumic contraction time (IVCT) was reduced (p=0.03) and decrease in diastolic function was evident through significant decreases in isovolumic relaxation time (IVRT) and E’/A’ ratio, and increase in E/E’ ratio. Isolated adult ventricular Scn1aRH/+ cardiomyocytes showed significant reduction in percent sarcomere shortening, maximum rate of contraction and relaxation, and time to peak contraction, exaggerated with TTX and pacing at 2Hz (p<0.5). Conclusions: Our study demonstrates the importance of voltage gated TTX-sensitive Nav1.1 brain sodium channels in cardiac contractile function and their possible role in cardiac complications in epilepsy.

Increased levels of HMGB1 and pro-inflammatory cytokines in children with febrile seizures

ObjectiveFebrile seizures are the most common form of childhood seizures. Fever is induced by pro-inflammatory cytokines during infection, and pro-inflammatory cytokines may trigger the development of febrile seizures. In order to determine whether active inflammation, including high mobility group box-1 (HMGB1) and pro-inflammatory cytokines, occurs in children with febrile seizures or epilepsy, we analyzed cytokine profiles of patients with febrile seizures or epilepsy.MethodsForty-one febrile seizure patients who visited the emergency department of Seoul National University Boramae Hospital from June 2008 to May 2009 were included in this study. Blood was obtained from the febrile seizure child patients within 30 minutes of the time of the seizure; subsequently, serum cytokine assays were performed. Control samples were collected from children with febrile illness without convulsion (N = 41) and similarly analyzed. Serum samples from afebrile status epilepticus attacks in intractable epilepsy children (N = 12), afebrile seizure attacks in generalized epilepsy with febrile seizure plus (GEFSP) children (N = 6), and afebrile non-epileptic controls (N = 7) were also analyzed.ResultsSerum HMGB1 and IL-1β levels were significantly higher in febrile seizure patients than in fever only controls (p < 0.05). Serum IL-6 levels were significantly higher in typical febrile seizures than in fever only controls (p < 0.05). Serum IL-1β levels were significantly higher in status epilepticus attacks in intractable epilepsy patients than in fever only controls (p < 0.05). Serum levels of IL-1β were significantly correlated with levels of HMGB1, IL-6, and TNF-α (p < 0.05).ConclusionsHMGB1 and pro-inflammatory cytokines were significantly higher in febrile seizure children. Although it is not possible to infer causality from descriptive human studies, our data suggest that HMGB1 and the cytokine network may contribute to the generation of febrile seizures in children. There may be a potential role for anti-inflammatory therapy targeting cytokines and HMGB1 in preventing or limiting febrile seizures or subsequent epileptogenesis in the vulnerable, developing nervous system of children.

Clinical Study and Molecular Genetic Analyses of Malaysian GEFS+ Patients

AbstractGeneralized epilepsy with febrile seizure plus (GEFS+) is a familial epilepsy syndrome characterized by phenotypic and genetic heterogeneity. Neuronal voltage gated sodium channel α-1 subunit gene, SCN1A is the most clinically relevant and associated with GEFS+. The objective was to study the clinical presentations of GEFS+ and analyze the SCN1A gene associated with Malaysian GEFS+ patients. Blood samples were collected from 30 unrelated GEFS+ patients and genomic DNA was obtained using the Qiagen DNA Blood Mini Kit following the manufacturer’s instructions. The 26 exons of SCN1A genes were analyzed by polymerase chain reaction (PCR) and denaturing high performance liquid chromatography (DHPLC). The aberrant profile peak from DHPLC analysis was confirmed by direct sequencing. The spectrum of phenotypes observed in Malaysian GEFS+ patients included febrile seizure (FS), febrile seizure plus (FS+) and afebrile generalized tonic clonic seizure (AGTCS). Direct sequencing of SCN1A revealed seven sequence variants including one novel SCN1A mutation that was associated with GEFS+. This suggests that mutation of the SCN1A gene is one of the prevalent causes of GEFS+ in Malaysia.

Mutations and deletions in PCDH19 account for various familial or isolated epilepsies in females

Mutations in PCDH19, encoding protocadherin 19 on chromosome X, cause familial epilepsy and mental retardation limited to females or Dravet-like syndrome. Heterozygous females are affected while hemizygous males are spared, this unusual mode of inheritance being probably due to a mechanism called cellular interference. To extend the mutational and clinical spectra associated with PCDH19, we screened 150 unrelated patients (113 females) with febrile and afebrile seizures for mutations or rearrangements in the gene. Fifteen novel point mutations were identified in 15 female patients (6 sporadic and 9 familial cases). In addition, qPCR revealed two whole gene deletions and one partial deletion in 3 sporadic female patients. Clinical features were highly variable but included almost constantly a high sensitivity to fever and clusters of brief seizures. Interestingly, cognitive functions were normal in several family members of 2 families: the familial condition in family 1 was suggestive of Generalized Epilepsy with Febrile Seizures Plus (GEFS+) whereas all three affected females had partial cryptogenic epilepsy. These results show that mutations in PCDH19 are a relatively frequent cause of epilepsy in females and should be considered even in absence of family history and/or mental retardation. © 2010 Wiley-Liss, Inc.

Sodium channels of SCNIA gene mutations in generalized epilepsy with febrile seizure plus (GEFS+) spectrum related to autism

Background Mutations in the a-subunit of the first neuronalsodium channel gene SCNIA have been demonstrated forgeneralized epilepsy \\lith febrile seizures plus (GEFS+), severemyoclonic epilepsy in infancy (SMEI), and borderline SMEI(SMEB). SCNIA mutations are also described in patients 'Withpsychiatric disorders such as autism.Objective To identify the mutations of SCNIA gene in patientswith GEFS+ spectrum which may be related to autism.Methods We examined four patients v.ith autism and GEFS+spectrum who were admitted to the Department of Child Health,Sardjito Hospital, Yogyakarta, Indonesia. Diagnosis of autism wasbased on DSM􀁟IV;ICD X criteria. Mutations in SCNIA wereidentified by PCRamplification and denaturing high􀁟performanceliquid chromatography analysis, Mth subsequent sequencing.Results There were four patients, all boys, aged 1.8 year to 7 years.The phenotypes of epilepsy were GEFS+ in one patient, SMEBin one patient and SMEI in two patients. Sequencing analysisrevealed a G􀁟to􀁟A heterozygous transition which was detectedat nucleotide c.4834G&gt;A (p.V1612I ) in exon 25. Other singlenucleotid polymorphisms (SNPs) were c.383 +66T&gt;C in intron 2,c.603-91G&gt;A and c.603-1060&gt; T in intron 4, c.965-21C&gt; T inintron 6, c.1028+21T&gt;Cin intron 7, c.2173G&gt;A in exon 12 andc. 2177-38C&gt;A, c.2177-12delT, c.2176+44C&gt; T in intron 12.Conclusion In this study, we reported the first cases Mth mutationin SCNIA gene in GEFS+ spectrum related to autistic patientsin Indonesian population, which showed a missense mutationp.V16121. [Paediatr lndones. 2010;50:125-32].

The First Genome-Wide Scan in a Tunisian Family With Generalized Epilepsy With Febrile Seizure Plus (GEFS+)

Generalized epilepsy with febrile seizure plus (GEFS+) is an autosomal dominant disorder. In the literature, 5 responsible genes were identified and 2 novel susceptibility loci for GEFS+ at 2p24 and 8p23-p21 were reported, indicating the genetic heterogeneity of this disorder. The aim of this report is to identify the responsible loci in a large affected Tunisian family by performing a 10cM density genome-wide scan. The highest multipoint logarithm of odds (LOD) score (1.04) was found for D5S407 in the absence of recombination. Two other interesting regions were found around marker D19S210 (LOD=0.799) and D7S484 (LOD=0.61) markers. To fine map these loci, additional markers in 2 regions on 5q13.3 and 7p14.2 were analyzed and positive LOD scores for both loci were obtained. Sequencing of the Sodium channel subunit beta-1 gene (SCN1B) (19q13.1) showed the absence of any causal mutation. Our findings emphasized the genetic heterogeneity of febrile seizures.

The Functional Effect of R1648H, a Sodium Channel Mutation that Causes Generalized Epilepsy with Febrile Seizures Plus in Splice Variants of SCN1A

SCN1A, the gene that encodes the alpha subunit of the voltage-gated sodium channel Nav1.1, is alternatively spliced at exon 5. SCN1A contains two copies of exon 5, denoted 5N and 5A (for ‘Neonatal’ and ‘Adult’ according to their developmental expression). There are 3 amino acid substitutions between the splice variants, all within the D1:S3/S4 extracellular linker. It is unknown how exons 5N and 5A alter channel function. Because patients with Generalized Epilepsy with Febrile Seizures plus (GEFS+) frequently exhibit age-dependent changes in seizure frequency and severity, we have asked whether the GEFS+-associated SCN1A mutation R1648H differentially affects Nav1.1-5N and Nav1.1-5A.

A BAC transgenic mouse model reveals neuron subtype-specific effects of a Generalized Epilepsy with Febrile Seizures Plus (GEFS+) mutation

Mutations in the voltage-gated sodium channel SCN1A are responsible for a number of seizure disorders including Generalized Epilepsy with Febrile Seizures Plus (GEFS+) and Severe Myoclonic Epilepsy of Infancy (SMEI). To determine the effects of SCN1A mutations on channel function in vivo, we generated a bacterial artificial chromosome (BAC) transgenic mouse model that expresses the human SCN1A GEFS+ mutation, R1648H. Mice with the R1648H mutation exhibit a more severe response to the proconvulsant kainic acid compared with mice expressing a control Scn1a transgene. Electrophysiological analysis of dissociated neurons from mice with the R1648H mutation reveal delayed recovery from inactivation and increased use-dependent inactivation only in inhibitory bipolar neurons, as well as a hyperpolarizing shift in the voltage dependence of inactivation only in excitatory pyramidal neurons. These results demonstrate that the effects of SCN1A mutations are cell type-dependent and that the R1648H mutation specifically leads to a reduction in interneuron excitability.

Influence of SCN1A Gene Mutation on Age of Onset of Febrile Seizures in GEFS+

Twelve multigenerational families with the generalized epilepsy and febrile seizure plus (GEFS+) syndrome and a known clinically relevant epilepsy gene mutation were examined for age of onset of febrile seizures (FS or FS+), in a study at the University of Melbourne, Australia, and centers in the Netherlands and Israel.

Does a SCN1A gene mutation confer earlier age of onset of febrile seizures in GEFS+?

SCN1A is the most clinically relevant epilepsy gene and is associated with generalized epilepsy and febrile seizure plus (GEFS+) and Dravet syndrome. We postulated that earlier onset of febrile seizures in the febrile seizure (FS) and febrile seizure plus (FS+) phenotypes may occur in the presence of a SCN1A mutation. This was because of the age-related onset of Dravet syndrome, which typically begins in the first year of life. We found that patients with FS and FS+ with SCN1A mutations had earlier median onset of febrile seizures compared to the population median. Patients with GABRG2 mutations had a similar early onset in contrast to patients with SCN1B mutations where onset was later. This study is the first to demonstrate that a specific genetic abnormality directly influences the FS and FS+ phenotype in terms of age of onset.

The Pathogenesis of Febrile Seizures: An Update

Febrile seizures(FS)is a specific epilepsy syndrome induced by fervescence in childhood,and it has been suspected to have a genetic basis.KCNQ2 and KCNQ3 genetic mutations related to benign familial neonatal convulsions(BFNC) have been confirmed, and mutations associated with generalized epilepsy with febrile seizure plus(GEFS+)were identified in SCN1A?SCN2A?SCN1B and GABRG2 genes. But the penetrance of FS and GEFS+ are incomplete and the clinical expression are very heterogeneous, suggesting that modifying genes and/or environmental factors strongly affect the phenotype.So the effects of temperature on ion channels associated with GEFS+ and FS are attracting increasing attention. Previous study has suggested that interleukin‐1β, a pyrogenic proinflammatory cytokine,is involved in the generation of febrile seizures or enhanced seizure susceptibility in animals, also recent research has been shown a mutation in the GABAA receptor subunit GABRG2 gene causing a temperature‐dependent intracellular trafficking defect‐misfolding and impaired assembly and ER retention, increased degradation, or rapid endocytosis would be worsened by fever resulting in febrile seizures.Moreover,our previous simulation studies have been shown that there is an obvious conformational change of M channel at 40?compared with that at 37?, and the fact that considerable temperature sensitivity in KCNQ2/KCNQ3 potassium channel has been verified.The intracellular trafficking defect of channel proteins caused by elevated temperature provides a new insight into the molecular pathomechanism of FS .

The GABRG2 Mutation, Q351X, Associated with Generalized Epilepsy with Febrile Seizures Plus, Has Both Loss of Function and Dominant-Negative Suppression

The GABA(A) receptor gamma2 subunit mutation, Q351X, associated with generalized epilepsy with febrile seizures plus (GEFS+), created a loss of function with homozygous expression. However, heterozygous gamma2(+/-) gene deletion mice are seizure free, suggesting that the loss of one GABRG2 allele alone in heterozygous patients may not be sufficient to produce epilepsy. Here we show that the mutant gamma2 subunit was immature and retained in the endoplasmic reticulum (ER). With heterozygous coexpression of gamma2S/gamma2S(Q351X) subunits and alpha1 and beta2 subunits, the trafficking deficient mutant gamma2 subunit reduced trafficking of wild-type partnering subunits, which was not seen in the hemizygous gene deletion control. Consequently, the function of the heterozygous receptor channel was reduced to less than the hemizygous control and to less than half of the wild-type receptors with a full gene dose. Pulse-chase experiments demonstrated that in the presence of the mutant gamma2S(Q351X) subunit, wild-type alpha1 subunits degraded more substantially within 1 h of translation. We showed that the basis for this dominant-negative effect on wild-type receptors was due to an interaction between mutant and wild-type subunits. The mutant subunit oligomerized with wild-type subunits and trapped them in the ER, subjecting them to glycosylation arrest and ER-associated degradation (ERAD) through the ubiquitin proteosome system. Thus, we hypothesize that a likely explanation for the GEFS+ phenotype is a dominant-negative suppression of wild-type receptors by the mutant gamma2S subunit in combination with loss of mutant gamma2S subunit protein function.

A Novel Inherited Mutation in the Voltage Sensor Region of SCN1A Is Associated With Panayiotopoulos Syndrome in Siblings and Generalized Epilepsy With Febrile Seizures Plus

We report 2 families harboring a novel SCN1A mutation, one of whom had Panayiotopoulos syndrome and the other a phenotype consistent with generalized epilepsy with febrile seizures plus. Two siblings had recurrent episodes of autonomic status epilepticus with focal features consistent with the diagnosis of Panayiotopoulos syndrome. Both have the SCN1A mutation p.Phe218Leu. The mutation was present in their father who has never had a seizure. The same mutation was identified in a child diagnosed with intractable childhood epilepsy with generalized tonic clonic seizures. From the age of 5, he developed complex focal seizures associated with left hippocampal sclerosis. The mutation was present in his mother, aged 25, who had febrile seizures and developed generalized tonic clonic seizures and his sister who had 1 febrile seizure. Our findings suggest that SCN1A mutations may cause susceptibility to an idiopathic focal epilepsy phenotype, the final phenotype depending on other (genetic or nongenetic) factors.

Linkage location and mutation analysis of generalized epilepsy with febrile seizures plus

To study the etiologic genes of generalized epilepsy with febrile seizure plus (GEFS+). Peripheral blood samples were collected from 25 persons of 2 families, including 2 probands. DNA was extracted from the peripheral blood leukocytes using phenol-chloroform method. Ten microsatellite markers spanning the critical regions of SCN1B, SCN1A, SCN2A, and GABRG2 genes were genotyped for linkage analysis by the software LINKAGE v5.1. The two-point linkage relation was determined by LOD score defining the approximate position of etiologic genes of the 2 GEFS+ families. Mutation analysis of the candidate etiologic genes in all members of these 2 families was performed. Results No sharing allele was discovered among the several microsatellite markers flanking SCN1A, SCN2A, and SCN1B genes, and the involvement of these genes in these 2 families could be excluded. In the family named Tian, sharing alleles were discovered among the markers D5S820, D5S422, and D5S1403 flanking GABRG2 gene. The two-point LOD scores at theta = 0 were 0.67, 1.0, and 0.79 for the marker D5S820, D5S422, and D5S1403, thus indicating possible linkage. In the family named Di, sharing allele was discovered only in the marker D5S1403 flanking the GABRG2 gene. Sequence analysis was performed for nine exons of the GABRG2 gene in these 2 families. Three single nucleotide variations were discovered on the exon 5 (c.588 C > T), exon 3 (c.604 C > T), and noncoding region of the exon 7. No mutation change of the GABRG2 gene was observed in these 2 families. No evidence supports the causal relation between the SCN1B, SCN1A, SCN2A, and GABRG2 mutation and the etiologic genes in the two families with GEFS+. It is still not clear what is the common etiologic genes of GEFS+.

GEFS+ is not related to the most common mutations of SCN1B, SCN1A and GABRG2 in two Tunisian families

The objective was to investigate whether the described mutations of the SCN1A, SCN1B and GABRG2 genes are associated to generalised epilepsy with febrile seizure plus (GEFS+) in two Tunisian families. We performed a genetic study of two multigenerational Tunisian families with GEFS+ spectrum. The molecular analysis included a PCR amplification of SCN1B, SCN1A and GAGRG2 exons, then a screening of the known SCN1B, SCN1A and GABRG2 gene mutations by direct sequencing. The data excluded the involvement of all known published mutations. However, an insertion of a T nucleotide at a heterozygous state within the intron 12 of the SCN1A gene has been identified in two probands and their parents. Our results corroborate the genetic heterogeneity of GEFS+ predominantly in epilepsy patients of different countries and ethnic groups.

Patients with a sodium channel alpha 1 gene mutation show wide phenotypic variation

We investigated the roles of mutations in voltage-gated sodium channel alpha 1 subunit gene (SCN1A) in epilepsies and psychiatric disorders. The SCN1A gene was screened for mutations in three unrelated Japanese families with generalized epilepsy with febrile seizure plus (GEFS+), febrile seizure with myoclonic seizures, or intractable childhood epilepsy with generalized tonic-clonic seizures (ICEGTC). In the family with GEFS+, one individual was affected with panic disorder and seizures, and another individual was diagnosed with Asperger syndrome and seizures. The novel mutation V1366I was found in all probands and patients with psychiatric disorders of the three families. These results suggest that SCN1A mutations may confer susceptibility to psychiatric disorders in addition to variable epileptic seizures. Unidentified modifiers may play critical roles in determining the ultimate phenotype of patients with sodium channel mutations.

Ion channels and epilepsy

ABSTRACT Ion channels play a central role in the generation and control of neuronal excitability. Genetic defects in ion channels are associated with several forms of human idiopathic epilepsies. These defects range from nonsense and missense point mutations to insertion, truncation and splice site mutations producing altered, non‐functional or negative‐dominant channel subunits. To date, 12 mutated genes have been identified. They code for Na + ( SNC1A, SNC2A, SNC1B ), K + ( KCNA1, KCNQ2, KCNQ3 ) and Cl ‐ ( CLCN2 ) channel subunits, as well as neurotransmitter receptor subunits including Cl ‐ channel GABAA receptor ( GABRA1, GABRG2 ) and cationic channel acetylcholine receptor ( CHRNA4, CHRNB2 ). One ion transporter Na + /K + ATPase gene ( ATP1A2 ) has also been identified. The epilepsy syndromes related to these genes are as diverse as benign familial neonatal (BFNC ‐ KCNQ2 and 3 ) and infantile (BFNIC ‐ SNC2A and ATP1A2 ) convulsions, episodic ataxia with seizures (AE2 ‐ KCNA1 ), generalized epilepsy with febrile seizure plus (GEFS+ ‐ SCN2A, 1A, 1B and GABRG2 ), autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE ‐ CHRNA4 and B2 ), severe myoclonic epilepsy of infancy (SMEI ‐ SNC1A ), juvenile myoclonic epilepsy (JME ‐ GABRA1 and CLCN2 ), and childhood and juvenile absence epilepsy (CAE, JAE ‐ SNC1B, GABRG2 and CLCN2 ). Despite the difficulty to correlate genotypes and phenotypes, these studies have increased our understanding of causal mechanisms of epilepsy and open a wide range of possibilities for developing better antiepileptic drugs and treatments.

Autism in Several Members of a Family With Generalized Epilepsy With Febrile Seizures Plus

The neurobiologic basis for autism is not well understood. In contrast, there have been several recent discoveries into the genetics of generalized epilepsy with febrile seizures plus, a group of epilepsy syndromes characterized by multiple seizure phenotypes. Here we describe a family with generalized epilepsy with febrile seizures plus and variably expressed autism spectrum disorder that does not show linkage to any of the four known generalized epilepsy with febrile seizures plus loci. A relationship between these two disorders has not previously been described.

Mutaciones de los canales neuronales de sodio y cloro asociadas a epilepsia generalizada con convulsiones febriles plus

La Epilepsia Generalizada con Convulsiones Febriles Plus (EGCF+), es una entidad relativamente común. Se caracteriza por convulsiones de tipo generalizado con una gran variabilidad fenotípica; se presenta desde los 3 meses de edad y persiste más allá de los 6 años; las convulsiones pueden ser precipitadas por fiebre pero se presentan también sin ella. La enfermedad se ha asociado a herencia autosómica dominante con penetrancia incompleta, en la que intervienen mutaciones de los genes que codifican los canales iónicos de sodio dependientes del voltaje y de los canales iónicos de cloro en las neuronas del Sistema Nervioso Central (SNC). El amplio fenotipo de la EGCF+ se ha encontrado en asociación con otras entidades como la Epilepsia Mioclónica Severa del Lactante (EMSL) y la Epilepsia Generalizada Tónico-Clónica Intratable de la Infancia (EGTCII), las cuales han presentado mutaciones comunes con las de la EGCF+, según informes recientemente publicados. Esta revisión pretende recopilar información de la literatura publicada sobre la EGCF+, con el objeto de brindar al lector un mejor conocimiento de esta entidad y de su asociación con las mutaciones que participan en su patogenia.