Epilepsy is a common neurological disorder in childhood defined as seizures that occur as a result of neuronal discharge in a specific region of the brain (Li 2020). The incidence of the disease in children varies between 33-82 per 100,000 per year (Wu 2019). Drug-resistant epilepsy (DRE) is defined as the persistence of seizures despite adequate anti-epileptic treatment with two or more antiepileptic drugs at efficacious daily doses, alone or in combination, and affects approximately 30% of children with epilepsy. Nowadays it has been defined as not pharmacoresponsive epilepsies. The most severe forms of treatment-resistant epilepsy usually begin in childhood (Patel 2016). In patients with epilepsy related to a genetic etiology, drug resistance is particularly frequent, especially in those with severe developmental and epileptic encephalopathies (Guery 2021).
Epileptic encephalopathy is defined by the presence of frequent epileptiform activity that causes slowing or regression of developmental skills. It is known that many of the epileptic encephalopathies have a molecular genetic basis. The fact that genetic etiology alone can cause developmental impairment means that individualized treatments should be developed to prevent the devastating consequences of this disease group. (Scheffer and Liao 2020). According to the 2010 ILAE (International League Against Epilepsy) classification and terminology commission, epileptic encephalopathy is defined as conditions in which epileptic activity causes serious cognitive and behavioral disorders and may worsen over time, beyond what is expected from the existing pathology (Berg 2010). Childhood EE are classified as infantile spasms, Dravet syndrome, Lennox-Gastaut syndrome, epileptic encephalopathy with Electrical Status during Slow Sleep (ESES), and Landau-Kleffner syndrome, etc. The common feature of these syndromes is that they are generally resistant to antiseizure drugs (ASD) (Engel 2001). The response to (ASD) is generally poor despite high dose polytherapy The most common application used in the treatment of EE patients is adrenocorticotropic hormone (ACTH). However, ACTH causes side effects with high morbidity and mortality, such as hyperglycemia, hypertension, immunodeficiency, and iatrogenic Cushing's syndrome (Khan 2012). However, because the quality of life is driven by several factors in patients with DRE, including the tolerability of the treatment, ASD management should try to optimize efficacy while anticipating the risks of drug-related adverse events. All patients with DRE should be evaluated at least once in a tertiary epilepsy center, especially to discuss eligibility for non-pharmacological therapies (Guery 2021). However, a second handicap from DRE is the risk of sudden unexpected death (SUDEP) and adverse effects on quality of life (QOL) at the individual patient level and family level, which should be considered in therapeutic management.
The etiology of epileptic encephalopathy is complex. Early diagnosis of IE in infants and children depends on a high level of suspicion and continuous monitoring. Risk factors include etiologies, clinical seizures, semiology, comorbidities (change in movements, social interaction), systemic symptoms (eg. markers), and research findings (eg EEG, metabolic scans, genetic studies) (Scheffer 2017). It is now accepted that most patients with DEE have a genetic etiology (Happ 2020; Hu 2012). Many of these genetic variants have been identified in patients previously thought to be constitutive or 'idiopathic'. Genetic analysis of a DEE cohort (n = 197) revealed that almost a third had pathogenic variants in known or novel genes (Scheffer 2016). An increasing number of genetic variants are implicated in the development of DEE (Wu 2019).
Other etiologies associated with IE include structural (eg, neurocutaneous diseases, cortical developmental disorders, brain tumors), metabolic (eg, vitamin-dependent epilepsies, amino acid disorders, non-ketotic hyperglycemia), and immune disorders (eg Rasmussen syndrome). (Sisodiya 2020). We included children with EE whose cause could not be found in our study. Known causes were excluded by performing a metabolic and epilepsy genetic panel on these patients beforehand.
As a result of the analysis of brain tissue obtained from patients and animal models, it was determined that gene expressions were greatly changed in the affected brain regions. Understanding what controls gene expression may open new avenues for the treatment or prevention of epileptic encephalopathy (Fisher 2014). Therefore, the development of new treatment targets and strategies in epileptic encephalopathies will reduce the risk of mortality and morbidity due to seizures and drugs used by individuals with this disease. For this purpose, identifying the relevant pathways and molecular mechanisms that coordinate gene expression is crucial for a better understanding of the pathogenic process and the development of new therapeutic approaches.
microRNA (miRNA) is a class of small (19-25 nucleotide), single-stranded, endogenous, non-protein-coding short RNA molecules that regulate gene expression either by promoting mRNA degradation or attenuating protein translation at the posttranscriptional level (Reschke 2015). miRNAs are initially transcribed by polymerase II (Pol II) as primary transcripts (pri-miRNA), processed into pre-miRNA, and finally converted to mature miRNA by RNases called Drosha and Dicer, respectively. The functional strand of mature miRNA is loaded into the RNA-induced silencing complex (RISC) containing the Argonaute 2 (Ago-2) protein. The RISC-loaded miRNA is then directed to silencing the target mRNA via mRNA degradation or translation inhibition. A given miRNA can have several binding sites to the same mRNA, and a single mRNA can be targeted by more than one miRNA, thus producing stronger effects. In line with this view, a single miRNA can regulate the expression of hundreds of genes, thus present important effects on cellular functions (Esquela and Kerscher 2006). They mainly function to lower protein levels in cells through sequence-specific binding to target mRNAs, leading to transcript degradation or translational repression.
More than 50% of the miRNAs identified are expressed in the brain. The brain has a variety of miRNAs that are crucial for the establishment and maintenance of normal development and cell phenotype. Acute and chronic nervous system diseases, including epilepsy, are associated with dysregulation of key components of the miRNA biogenesis pathway and altered expression of miRNA. miRNAs are implicated in many brain functions important for epileptogenesis, including cell death, neurogenesis, and synaptic plasticity (Karnati 2015). Studies on associating the development of epilepsy with miRNA have gained momentum in the last 10 years. Large-scale miRNA profiling studies that characterize changes in the expression of different miRNAs are carried out, especially in animal models and subsequent experimental studies with human blood and tissue samples (Mooney 2016). Recently, functional studies in rodents have shown that miRNAs can have potent effects on brain excitability, seizures, and epilepsy. It has been reported that targeting miRNAs, which play a key role in epilepsy, suppress or exacerbates seizures and alters brain excitability, which has a potential for miRNA-based therapeutics in epilepsy (Reschke and Henshall 2015).
In this study, it was aimed to determine the expression levels of 10 different miRNAs (hsa-miR-23a-3p, hsa-miR-34a-5p, hsa-miR-132-3p, hsa-miR-146a-5p, hsa-miR-134-5p, hsa-miR-30a-5p, hsa-miR-138-5p, hsa-miR-324-5p, hsa-miR-330-3p, hsa-miR-187-3p) thought to be deregulated in childhood epileptic encephalopathy patients and to reveal the disease formation process.