The disease caused by mutations in the CDKL5 gene (encoding cyclin-dependent kinase 5, CDK5) belongs to the group of early (infantile) epileptic encephalopathies caused by alterations in the genome. Currently, the disease is called “developmental encephalopathy and epileptic encephalopathy type 2”. This disorder is a complex combination of symptoms that develop due to deficiency or absence of the CDKL5 gene product, which is serine/threonine kinase. The CDKL5 gene is located on X chromosome; the disease has an X-linked dominant inheritance pattern. This literature review summarizes relevant studies analyzing the disease caused by CDKL5 gene mutations, including its genetic and epidemiological aspects, clinical manifestations, characteristics of epilepsy, principles of diagnosis, and therapeutic approaches. We present a case series of several patients with genetic disorders involving the CDKL5 gene.

Angelman syndrome (AS) is a genetic disorder caused by a mutation in the maternal copy of the UBE3A gene and characterized by typical clinical manifestations (such as mental retardation, difficulty walking, and laughter) and specific changes on the electroencephalogram (EEG).
The aim of this study was to analyze age-specific characteristics of the main EEG patterns, including high-amplitude frontal delta activity with spikes, slow-wave delta-theta activity with spikes in the posterior regions, and diffuse continuous rhythmic theta activity. In addition to that, we assessed the frequency of a rare and highly specific for AS EEG pattern: notched slow waves.
We have identified and described additional criteria for EEG during sleep: high index of pathological slow-wave activity and the ratio of pathological slow-wave activity index to epileptiform activity index during sleep. We also analyzed all EEG patterns at the age most significant for the detection of this syndrome (up to 3 years) and their age-specific dynamics.
We covered the frequency and characteristics of EEG patterns rare in AS patients, such as three-phase bifrontal delta waves, reactive pathological activity in the posterior areas, EEG patterns of focal seizures originating from the posterior areas, benign epileptiform discharges of childhood, and migrating continuous slow-wave activity.
We analyzed the differences between main EEG patterns in AS and frontal and occipital intermittent rhythmic delta activity (fIRDA and OIRDA patterns).

Alexander disease is a form of leukoencephalopathy caused by mutations in the GFAP gene. There are three forms of the disease: infant, juvenile and adult. We present the clinical case of a patient born in 2004 (16 years old) with a debut of the disease at the age of 4 years with complex ticks. further neurological symptoms progressed and appeared atactic gait, intention tremor by performing coordination tests, muscle hypotension, decreased tendon reflexes, nasal voices, and behavior changes.
Magnetic resonance imaging revealed changes in the white matter of both frontal lobes. An analysis was made of 59 genes of the panel “Leukodystrophy/leukoencephalopathy” by the method of mass parallel sequencing on the Ion S5. A mutation of the GFAP gene (Nm_002055), 4 exon c.758C>A, p.ALA253Asp in a heterozygous state, not described in Human Gene mutation Database, was detected. The patient was confirmed to have a diagnosis of Alexander disease. According to tractography, a decrease in the number of fibers in the frontal lobes was found.
The patient is currently receiving symptomatic treatment.

The article presents a description of a clinical case of a child 3 years 8 months old with Rett syndrome caused by the mutation of p.Val485fs in the MECP2 gene. According to electroencephalography data at the age of 1 year and 6 months, diffuse continued epileptiform activity in the form of high-amplitude (up to 300 μV) acute – slow wave complexes (continuous spike-waves during slow-wave sleep, CSWS) with an index of 90–100 % was revealed. At the control examination at the age of 2 years and 10 months diffuse epileptiform activity was replaced by multifocal activity with an index of up to 70–80 % at certain epochs, in general, not exceeding 50–60 %. During the entire observation period there were no epileptic seizures. It remains unknown whether the presence of CSWS at such an early age is a predictor of a more severe course of Rett syndrome – in our observation the girl did not acquire walking skills and a delay in psychic and speech development was evident already before the 12 month of life. more research is needed on the frequency of the CSWS phenomenon and its role in the development of clinical features in Rett syndrome.

Developmental encephalopathy with epilepsy or epileptic encephalopathy, associated with a heterozygous mutation in the IRF2BPL gene, is a rare severe disorder. It’s manifested by developmental delay or regression of skills until or after epilepsy onset. Patients have a specific facial phenotype, movement disorders with dystonia and choreoathetosis, ataxia, dysarthria, dysmetria, and dysdiadochokinesis. Epilepsy is a common manifestation of the disease (around 70 % of cases), from the age of 6 months to 26 years. Semiology of seizures is vary, including infantile spasms, myoclonic, tonic or clonic seizures with nonspecific electroencephalographic changes. magnetic resonance imaging shows normal brain development at an early age and cortical and cerebellar atrophy developing over time. The authors present a clinical case describing a patient with a causative de novo variant (c.2152delT) in the IRF2BPL gene in Russia.
This patient was included to common table in an article entitled “De novo truncating variants in the intronless IRF2BPL are responsible for developmental epileptic encephalopathy” (DOI: 10.1038/s41436-018-0143-0).