«Clinical, neurophysiological and molecular-genetic aspects of the formation of a drug resistant epilepsy»

Tashkent Medical Academy. Neurology Department PhD. Tuychibaeva Nodira Miratalievna

Task Force of the ILAE Commission on Therapeutic Strategies proposed consensus on the definition of drug resistant epilepsy in order to improve medical assistance for patients and to promote the international research works:
“Drug resistant epilepsy may be defined as failure of adequate trials of two tolerated and appropriately chosen and used AED schedules (whether as monotherapies or in combination) to achieve sustained seizure freedom”
The overall framework of the definition comprises two “hierarchical” levels:
  • Level 1 provides a general template or scheme to categorize outcome to each therapeutic intervention (whether pharmacologic or no pharmacologic), including a minimum dataset about the intervention that would be needed for such purpose;
  • Level 2 provides a core definition of drug resistant epilepsy based on how many “informative” trials of antiepileptic drugs (AEDs) resulted in a “treatment failure” outcome (as defined in Level 1)
Outcomes to a given intervention are categorized based on whether it rendered the patient seizure‐free (Category 1) or not (Category 2). For the outcome to fall into either category, the intervention must be “appropriate” and “adequate”. Otherwise, the outcome is designated as undetermined (Category 3). Each category is then subdivided into A, B, and C, based on outcome with respect to adverse effects.
There are multiple hypotheses on the mechanisms of drug resistant epilepsy (an associated syndrome, initial response to AED, number and the type of seizures)Four current hypotheses, that may explain medical refractoriness of epilepsy: “the target", "the transporter (multi-drug transporter)", "network" and "intrinsic severity".

«Intrinsic severity».
  • Objective:
  • Epileptic encephalopathies of neonatal age and infancy
  • 1. Early (neonatal) myoclonic encephalopathy
  • 2. Early infantile epileptic encephalopathy with suppression-burst pattern on the EEG (Ohtahara syndrome).
  • 3. Severe myoclonic epilepsy of infancy (Dravet syndrome) etc.
  • Other forms of epilepsy
  • 1. Kozhevnikov-Rasmussen syndrome
  • 2. Progressive forms of epilepsy with myoclonus
  • 3. Landau-Kleffner syndrome (acquired epileptic aphasia)
  • 4. Epileptic encephalopathies in inborn errors of metabolism
  • Structural damages, which accounts for > 50% of adult DR cases, should be considered
  • Epilepsies caused by mesial temporal sclerosis, cortical dysplasia etc.
A subclinical mutation in Kcnq2 was found to dramatically increase epilepsy severity in mice bearing an epilepsy‐inducing mutation in Scn2a (Kearney et al., 2006), and, similarly, mutations in Scn2a and Kcnq2 were found to increase epilepsy severity in an Scn1a epilepsy mutant (Hawkins et al., 2011). Enhanced expression of Kcnv2 was also found to increase epilepsy severity in the Scn2a mutants (Jorge et al., 2011). Of interest, unique coding variants in KCNV2, the human ortholog of Kcnv2, were found in two children with epilepsy, one of which was highly refractory to AEDs.

Causes of therapeutic resistance

Subjective
  • 1. Type of anticonvulsant and form of epilepsy and the nature of the seizures does not match;
  • 2. Irrational polytherapy;
  • 3. Frequent replacement of anticonvulsant;
  • 4. Somatic condition of patient;
  • 5. Wrong attempt to cure all forms of epilepsy with a single drug;
«Target hypothesis»
  • Suggests an epilepsy-induced alteration of cellular targets of AEDs, leading to a reduction in sensitivity. These targets include various receptors and ion channels, but this hypothesis is principally based on studies with carbamazepine (CBZ) on voltage-gated sodium channels in hippocampal neurons.
  • Sodium channels of hippocampal CA1 neurons from patients with MTS were studied and compared with neocortical neurons from patients without MTS. The mechanism of action of CBZ, use-dependent block of voltage-dependent sodium channels, was completely lost in these DRE patients.
  • Subsequent studies attempting to address this found that other AEDs with a similar mechanism of action, such as valproate (VPA) and lamotrigine (LTG), did not display a loss or marked reduction in sodium channel sensitivity.
«Network hypothesis»
  • Proposes that seizure-induced structural brain alterations such as axonal sprouting, synaptic reorganization, neurogenesis, and gliosis can contribute to the formation of an abnormal neural network. This network avoids the inhibitory effect of an endogenous antiepileptic system and prevents AEDs from entering their targets, eventually leading to DRE.
  • This is supported by the clinical finding of surgical resection of an altered network counteracting AED resistance and leading to seizure reduction.
«Transport hypothesis»
 
The system of biotransformation and transporters operates for the elimination of AEP, and its activity is the main limiting factor determining the pharmacokinetics of drugs
Transporters of drugs and the I and II phases enzymes of biotransformation are considered to be the part of the system
  • Isoforms of cytochrome P450 are the main enzymes of I phase
  • Among the transporters, the greatest role in the processes of absorption, distribution and excretion of AEDs play the glycoprotein P, encoded by the gene MDR1 and transporters of organic anions and cations
Polymorphism of the genes of biotransformation system (CYP2D6, CYP2C9, CYP2C19) and drug transporters (MDR1, OATP-C, OAT-1, OAT-3, OCT-1) could significantly affect the pharmacokinetics and pharmacodynamics of AEDs and to have significant clinical consequences.
 
Pharmacogenetic

Studies genetic characteristics of patient in drug metabolic pathways and pharmacological response. These genetic characteristics represent polymorphism of gene proteins that are involved in the pharmacokinetics or pharmacodynamics of drugs
  • The object of the study: 383 patients with a diagnosis of epilepsy and 96 healthy patients who did not have history of epilepsy and paroxysmal States.
  • Subject of research: samples of venous blood and blood serum of patients with various forms of epilepsy for the study of the pharmacogenetic and pharmacokinetic parameters, as well as the results of clinical, neuroimaging, and neurophysiological research.
  • Research methods: The study used clinical and neurological data, carefully taken anamnesis, neuroimaging studies (MRI), neurophysiological studies (video EEG monitoring, PSG), therapeutic drug monitoring of antiepilepticdrugs in blood plasma (carbamazepine, valproic acid), molecular genetic determination of polymorphic gene variants of CYP2C19 *2; CYP2C19 *3; 1236 T/C gene MDR; 13435 T/C gene MDR1; 9896 C-G gene CYP2E1; 430С>Т geneCYP2C9
Thorough examination:
Clinical and history.
Semiotics and the evolution of epileptic seizures.
EEG-video monitoring.
Polysomnography.
MRI (1.5 to 3 Tesla) if necessary

Further comprehensive examination of the patients with video-EEG monitoring and polysomnograph enabled to determine that 320 children (60.15 %) had epileptic paroxysms, in 20 patients (5.2 %), the PNES diagnosis was verified, and 10.9 % of the patients had impaired sleep, that is 3.5 times greater (р≤0.01) than before admission to the hospital. The accuracy of initial diagnoses was evaluated accord-
ingly.
It is important to specify that during the examination the number of patients with the diagnosis of epilepsy of unclear etiology reduced with precise differentiation by syndromes → symptomatic focal epilepsy (structural defect-FKD) → idiopathic generalized epilepsy. However, within the group of IGE patients, before and after EEG demonstrated the cases of wrong diagnosis of focal frontal epilepsy (11.4 % of cases). When analyzing our findings, the attention is attracted by the fact that most difficulties are faced in verification of diagnosis of epileptic encephalopathies. The JМE diagnosis was also confirmed only in 30 % of cases. Thus, the cause of discrepancy of АED choice in unspecified epilepsy in 37.5 % of cases was a pseudoresistant course of epilepsy in JМE patients being its subjective cause. The analysis of АЭП therapy selection (seizure evolution) also revealed that in 25.8 % of cases,anti-seizure drugs were often changed not reaching a medium/average doses were used.
Thus, we have revealed that the diagnosis was wrong in 23.4 % of patients with epilepsy whereas the diagnosis coincided in 21.8 % of cases. The diagnosis was specified in 53.1% of cases. The reverse tendency is evident in patients with nonepileptic paroxysms: wrong diagnosis was made in overwhelming majority of cases (61.9 %) and was confirmed in 15.8 %.
In 42 patients with incorrectly interpreted epileptic paroxysms, EEG video polysomnography helped make the following diagnoses. It is worth mentioning that the common complaints were myoclonus of falling asleep in 26.1 % of cases, rhythmic movements at sleep (in 10 patients) that we interpreted as jactitation of the head (in 70 % of cases) and pelvic area. In addition, there were sleep apnea in 214 % of cases, one patient had central apnea (with Arnold Kiari's diagnosis, grades 2-3).
  • The second stage of our study was the comparative aspect of patients with an established diagnosis of epileptic syndrome.
  • In this regard, we divided the patients into 2 groups after 12 month of observation. The main group consisted of patients with drug resistant epilepsy. The second group was represented by patients with epilepsy with a positive response to antiepileptic therapy.
  • Each group itself was divided into 2 subgroups:
  • A. Patients with the structural defect of the brain.
  • B. Patients without structural defect of the brain.
Comparison of revealed epileptic syndromes in various groups:
Among the patients with PRE (pharmacoresistant epilepsy), there were subgroup of patients with temporal epilepsy and epileptic encephalopathy.
The profile of patients with sleep impairment pharmacoresistant and pharmacoresponsive epilepsy course. The analysis of quantitative characteristics of the sleep structure in the entire group of patients with epilepsy revealed that the patientswith epilepsy differ from healthy examinees by smaller presentation of delta-sleep (Ds), increased Ds and REM latent periods. In addition, the group of patients with epilepsy demonstrated greater presentation of Ст II than in the group of healthy people and in the group of patients with insomnia. The latter had reliably worse characteristics of sleep practically in all parameters than healthy people and patients with epilepsy.
Thus, the results of these two groups study suggest the following conclusions: the severity of pharmacoresistant epilepsy course is probably caused by overlapping various sleep impairments among which the sleep apnea syndrome leads (in 31.6 % of cases); the syndrome of rhythmical movements during sleep follows it (25 %), while disorders of awakening make 18.3 %, parasomnia linked with fast sleep accounts for 14.9 % and in 10 % other sleep disorders occur.
In the favorable course of epilepsy, the syndrome of obstructive apnea has also been observed; however, the frequency of its presentation corresponds to the mild course of apnea at night (7.6±0.54) in 16.6 % of the patients.
The research on polymorphism of C3435T and С1236Т of MDR1 gene and evaluation of their association with development pf pharmacoresistance in patient with epilepsy undergoing АED therapy. The frequency of distribution of the alleles and genotypes of 1236 С/Т polymorphism of MDR1 gene in the groups of patients and the controls has demonstrated high presentation of С1236 polymorphism of
MDR gene in Uzbek population. However, there is a trend to consider it only as a genetic marker of pharmacoresistance. Whereas according to the results of our research, the homozygous and heterozygotes mutation of MDR gene C3435T is an effective marker of pharmacoresistant epilepsy course.

Conclusions

The main reasons for pseudopharmacoresistant course of epilepsy are that AEDs don't match form and the type of epilepsy in 37.5% cases; unreasonable replacement of AEDs in 22.1 % of cases. The most frequent non-epileptic paroxysms are: in 10.9% of cases - sleep disorders and 5.2% of cases - PNES.
Drug resistant course of epilepsy is significantly worsening on the background of various sleep disorders: sleep apnea syndrome; (31,6%) Restless leg syndrome (25%), nREM awakening disorders (18,3%,) REM parasomnias (14.9 percent).
In patients with pharmacoresistant epilepsy stage II of nREM sleep becomes longer (259,3±43,1) and observed an increase in the latent period of sleep delta (P≤0.05) with a reduction of its overall representation.
1236 T/C and T 13435/C MDR1 gene polymorphisms has a high percentage of the prevalence in the Uzbek population. The presence of mutant allele or genotypes of this gene significantly (P <0.05) increases the risk of developing pharmacoresistant patients and is a reliable predictive criterion of the effectiveness and validity of ongoing antiepileptic first-line therapy.
It is shown that the combination of unfavorable alleles of the polymorphisms C3435T and MDR1 С1236Т is an independent risk factor for the development of pharmacoresistant epilepsy.

Personalized medicine

based on modern technologies (genetic, pharmaceutical, diagnostic, and informative-communicative). Its principal task is individual patient care within the public health system. Instead of out-of-date "one drug for all" approach doctors use human genome data, molecular markers of specific diseases in the conduction of targeted therapy and in the optimizing of treatment strategies.
 

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