The authors, based on a large number of studies (including their own) regarding the toxic effects of heavy and radioactive metals on children of different ages and with varying degrees of chronic exposure to such metals, present the risks of developing somatic and genetic diseases. The main mechanisms of the influence of the radiation factor on the child’s body and the causes of the formation of radiation-induced diseases are shown.

   In modern society, there is an intensive increase in the incidence of hypertension among young people, which is mainly due to lifestyle features and associated risk factors.

   Purpose. To analyze the results of Russian and foreign scientific research concerning the study of risk factors in the development of hypertension in children and young people.

   Material and methods. A qualitative analysis of the current data available in the literature on the risk factors of hypertension and its prevention has been carried out.

   Results. It has been established that the occurrence of arterial hypertension in childhood is influenced not only by hereditary factors, but also by a number of environmental risk factors.

   Conclusion. Further research is needed to study new and established risk factors that need to be considered when conducting primary prevention of the disease in children and young people from the high-risk group.

   In recent years, the dynamics of mitochondrial transformations in cells have been of more concern to both representatives of basic science and researchers in the field of applied medicine. A growing number of observations demonstrate the important regulatory influence of mitochondrial dynamics on a variety of physiological and pathological processes in many, if not all, organ and tissue structures. The prospects for studying the features and regulators of these processes for understanding the pathogenesis of diseases, developing their new biomarkers, as well as treatment technologies seem increasingly significant.

   The purpose of this article is to review the facts obtained regarding mitochondrial dynamics, which, from the authors’ point of view, deserve the attention of pediatricians.

   The volume of relevant information turned out to be too extensive to fit into one article, which forced it to be divided into several successive publications. The first part provides information about the main processes included in the concept of “mitochondrial dynamics,” the importance of maintaining the balance of the latter for ontogenesis and tissue homeostasis, as well as data on its disturbances in diseases of the nervous system in children.

   Autism and autism spectrum disorders are neuropsychiatric diseases that begin to appear in children under 3 years. Over the past decade, the number of children with autism spectrum disorders has increased more than in 10-fold and continues to grow, accounting for 1–2 % of the world’s population. Currently, the diagnosis of autism spectrum disorders is based only on clinical and behavioral tests, and there are no biological and genetic markers that could contribute to the early detection of this disorder. The review, based on the analysis of modern literature data about epigenetic mechanisms which associated with autism, examines the influence of the DNA methylation profile in the formation of cognitive impairment and the possibility of using genes and their methylation status as diagnostic biomarkers in children with autism spectrum disorders. Literature data analysis shows that disorders of attention, speed of information processing, working memory, learning are based on genetic and epigenetic (methylation) changes in the expression of many genes: BDNF, CAPS2, CNTNAP2, GABRB3, FMR1, FOXP1, GTF2I, HSD11B2, MECP2, NF2, NGF, NR3C1, OXTR, PAK2, RELN, SLC6A4, UBE3A, etc. Most of these genes undergo hypermethylation, reducing the expression of its proteins, which impairs the development and formation of the nervous system in autism. In contrast, other genes are associated with methylation and oxidative stress are hypomethylated in autism spectrum disorders. Assessing the expression levels and methylation status of these genes can serve as genetic and epigenetic biomarkers for the differentiation and diagnosis of clinical symptoms, autism spectrum disorders severity, and facilitate the development of new treatments and rehabilitation procedures.

   Kyphoscoliotic type of Ehlers–Danlo syndrome occurs in the practice of doctors of different specialties. The main manifestations of the disease are congenital muscular hypotonia, progressive kyphoscoliosis, generalized joint hypermobility, dislocation/subluxation of the joints. In recent years, special attention has been paid to the fragility of blood vessels characteristic of patients, which usually has serious consequences.

   Purpose: the study aims at clarifying the clinical characteristics of type 1 kyphoscoliotic Ehlers–Danlo syndrome based on the analysis of the clinical findings observed in 2 patients with severe vascular disorders. Data from clinical and molecular genetic examination of 2 children (girl and boy) 17 and 13 years old from unrelated families are presented.

   The diagnosis of type 1 kyphoscoliotic Ehlers–Danlo syndrome was established in accordance with the diagnostic criteria according to the International Classification 2017. Children showed severe vascular disorders in the neonatal period, ruptures of medium-caliber arteries in adolescence. Genomic sequencing in both patients revealed a pathogenic nucleotide variant in the PLOD1 gene — duplication of the 11959421–11968422 chromosome 1 region in the homozygous state. The results of literature analysis and own observations of 2 patients with type 1 kyphoscoliotic Ehlers–Danlo syndrome indicate the severity and rather high incidence of vascular disorders, which should be considered when developing recommendations for the medical management of patients.

   Energy processes in muscles can be reflected by the creatine phosphokinase system of ATP resynthesis from ADP and creatine phosphate. The product of non-enzymatic degradation of creatine (creatine phosphate) is creatinine, which accumulates in the blood serum, and its concentration correlates with the volume of the patient’s muscle tissue, subject to the normal functioning of the kidneys.

   Purpose. To assess the perioperative serum creatinine level as a biological marker of muscle mass in patients with severe forms of cerebral palsy, IV–V level according to GMFCS, during orthopedic interventions on the hip joint.

   Material and methods. A prospective clinical observational study included 82 patients with severe forms of cerebral palsy, spastic dislocations (subluxations) of the hips, for which reconstructive or palliative interventions were performed on the hip joints. The trophological status of children was assessed before surgery, the level of serum creatinine was determined in the intraoperative period, on the first postoperative day, and on the fifth day after surgery.

   Results. The circumference of the middle third of the shoulder in 28 % of patients, as well as the thickness of the skin-fat fold over the triceps in 61 % of children were below the 10^th centile, which was regarded as malnutrition. The calculated proportion of body fat equal to 10 [8; 20] % in combination with the circumference of the muscles of the middle third of the shoulder suggest a combination of protein-energy deficiency and muscle mass deficiency in 1/5 of the patients. Creatinine indicators at all stages of observation corresponded to the minimum age norm or were below these values, tended to decrease and had a random agreement (W = 0,129).

   Conclusion. The level of creatinine in the blood serum correlates with the «shoulder muscle circumference» parameter in children with severe forms of cerebral palsy, severe movement disorders of IV–V level according to GMFCS. Plasma creatinine can be used as a biological marker of skeletal muscle mass in patients with severe cerebral palsy.

   The influence of the gut microbiota on the development of various diseases is of great interest to researchers. The conducted studies showed that in patients with chronic liver diseases, the dominant taxa of the gut microbiota were Bifidobacterium longum, Bifidobacterium adolescentis, Blautia massiliensis, and in healthy children — Neisseria flavescens. There is no comparative analysis of data on the taxonomic diversity of the intestinal microbiota in autoimmune and non-autoimmune liver diseases in children.

   Purpose. To investigate differences in the taxonomic diversity of fecal microbiota in patients with autoimmune and non-autoimmune liver diseases, as well as to evaluate potential biomarkers of 16S rRNA gene amplicons in these diseases by comparing the taxonomic composition.

   Material and methods. A metagenomic analysis of the intestinal microbiota of 24 children with chronic liver diseases (mean age 10,3 ± 4,7 years) was carried out with the isolation of the 16S rRNA gene region. The group included 18 children with autoimmune liver diseases and 6 children with non-autoimmune liver diseases.

   Results. The conducted study revealed 684 types of microorganisms in the studied samples of patients’ feces. The analysis of the conducted studies showed that no dominant taxa were found in the fecal samples of children with autoimmune liver diseases, while Veillonella dispar, Veillonella parvula, Cloacibacillus porcorum, Prevotella histicola and Bacteroides eggerthii were the dominant taxa in patients with non-autoimmune liver diseases.

   Conclusion. Studies have shown differences in the composition of the gut microbiota in children with autoimmune and non-autoimmune liver diseases.

   The article presents an analysis of cases of hospitalized children with fever of unknown origin. Purpose: to study the nosological structure of the causes of fever of unknown genesis in hospitalized children.

   Material and methods: a retrospective analysis of the medical histories of children hospitalized in the pediatric department was carried out for 2022–2023. All children underwent a comprehensive laboratory and instrumental examination.

   Results: the largest proportion (43,9 %) were school-age children who, in addition to fever, had complaints of weakness (87,8 %) and decreased appetite (85,4 %). Anemia (51,2 %), acceleration of ESR (47,6 %) and an increase in C-reactive protein (45,1 %) were most often recorded in the analyses. The causes of fever of unknown origin in 65,9 % of children were infectious diseases, in 19,5 % — autonomic dysfunction syndrome with a violation of thermoregulation, in 6,1 % — systemic connective tissue diseases, in 4,9 % — oncological pathology, in 2,4 % — inflammatory diseases of the gastrointestinal tract.

   The results of the study can be applied in pediatric practice, monitoring of children with infectious pathology.

   Erythema nodosum, which is often associated with infectious diseases, is one of the rare skin manifestations in the practice of pediatricians and pediatric infectious disease specialists.

   Purpose. The purpose was to study the clinical and laboratory manifestations of erythema nodosum in children.

   Material and methods. The study included 17 children with erythema nodosum aged 2 to 17 years who were hospitalized at the City Children’s Hospital No. 1 of Kazan.

   Results. In 6 (35 %) children, elevated values of antistreptolysin-O were detected, in 5 (29 %) — high titers of antibodies to Salmonella, in 2 (12 %) cases — IgM to Chlamidia pneumonia, in 2 (12 %) other children — IgM to capsid antigen of EBV, in one case (6 %) — IgM to Mycoplasma pneumonia. Increased erythrocyte sedimentation rate and C-reactive protein level was observed in 15 (88 %) and 12 (70 %) children, respectively. In 12 (70 %) of 17 children, increased level of soluble fibrin-monomer complex was detected in the blood.

   Conclusion. Erythema nodosum in children in most cases is associated with streptococcal infection and salmonellosis. The immune-inflammatory process in erythema nodosum is accompanied with an increase in the level of soluble fibrin-monomer complex in the blood.

   Syndromic craniosynostosis is a special group of hereditary pathologies. One of the syndromic craniosynostoses is Crouzon syndrome, an autosomal dominant pathology of the primary violation of the fusion of cranial sutures. It occurs with a frequency of 1:60,000 newborns. The disease leads to a number of secondary complications, such as exophthalmos, orthognathic problems, impaired vision, hearing, breathing, lag in neuropsychic development. The development of Crouzon syndrome is associated with a missense mutation in the fibroblast growth factor receptor-2 (FGFR2) gene. In modern medicine, a variant of Crouzon syndrome with black acanthosis is also known, the development of which is associated with a mutation in the FGFR3 gene. The similarity of clinical manifestations as with others syndromic craniosynostoses, also between 2 variants of Crouzon syndrome, leads to difficulties in differential diagnostic search. Knowledge and awareness of the full clinical presentation of this syndrome makes it possible to timely diagnose and treat, prevent possible severe complications and improve the quality of life of patients with Crouzon syndrome. This article describes 2 clinical cases with mutations in the FGFR2 and FGFR3 genes.

   Geroderma osteodysplasticum (OMIM #231070) is a rare autosomal recessive disorder characterized by congenital wrinkled skin on the dorsal surface of the limbs and abdomen; marked osteoporosis in childhood. Pathogenic variants of the nucleotide sequence in the GORAB gene, which encodes the GORAB protein located in the Golgi apparatus and plays a crucial role in vesicle transport in the Golgi complex, lead to the disease. This is the first report of 2 patients with this disease in Russia. A detailed description of the clinical-radiological and genetic characteristics of these patients with new nucleotide variants in the GORAB gene in a compound heterozygous state is presented: c.170C>G (p.Ser57Ter) and c.790G>C (p.Ala264Pro); c.295C>T (p.Gln99Ter) and heterozygous deletion on chromosome 1 (chr1:g.170531967–170539494del), affecting exons 1 and 2 of the gene. The main clinical manifestations of the syndrome were congenital wrinkled skin, sagging cheeks, hypoplasia of the cheekbones, prognathism, muscle hypotonia and joint hypermobility. Radiological signs included congenital bilateral dislocation of the hip, compression fractures of the vertebral bodies, and disruption of the continuity of the growth plate of the distal femur and proximal tibia, referred to as “insertion.” The rarity of the syndrome, as well as the similarity of clinical manifestations with a heterogeneous group of hereditary diseases accompanied by decreased skin elasticity, leads to a late correct diagnosis. This necessitates the description of the clinical-genetic characteristics of the disease, the study of the dynamics of the formation of its phenotypic manifestations, and the methods of molecular-genetic diagnostics.

   A clinical case of the development of portopulmonary hypertension in a child after splenorenal anastomosis is presented. The surgical intervention was performed to correct the congenital malformation — cavernous transformation of the portal vein, which led to portal hypertension and varicose veins of the esophagus and stomach. In the long-term postoperative period, pulmonary arterial hypertension, hypersplenism with bilinear cytopenia, and moderate liver failure developed. Combined therapy provided a temporary improvement of the patient status, therefore, during subsequent surgery, the size of the anastomosis was changed. This led to a sustained decrease in pulmonary artery blood pressure and clinical improvement in the boy’s condition.

    Autoimmune polyendocrine syndrome type 1 is a rare autosomal recessive hereditary pathology — a defect in the autoimmune regulator gene (AIRE), which develops with endocrine and non-endocrine manifestations in childhood. The disease is characterized by clinical polymorphism, which makes timely diagnosis difficult. The article describes a clinical case of an 11-year-old patient with autoimmune polyendocrine syndrome type 1, in whom the course of the disease was erased for a long period. The high quality of life of such patients is possible with timely, individually selected substitution therapy, followed by dispensary observation.

   Morozov Children’s City Clinical Hospital, almost in the first months of the development of the COVID-19 epidemic, began to admit not only patients with acute infection, but mainly with combined comorbid pathology. Based on a retrospective analysis of 290 medical records of children hospitalized with COVID-19 at the Children’s City Clinical Hospital, an analysis of children admitted to the hospital with predominantly comorbid pathology was carried out between April 2020 and September 2020. Six of these children had a fatal outcome. Most children were in the first 3 years of life (38,4 %) and puberty (37,3 %). The diagnoses of hospitalized patients were varied: pneumonia — 41 (14,4 %), surgical pathology and trauma — 69 (24,3 %), somatic pathology — 120 (42,3 %), including: diseases of the gastrointestinal tract, kidneys and urinary tract pathways, hematological diseases, neurological, type I diabetes mellitus, joint diseases, diseases of the newborn period, oncological diseases, diseases of the cardiovascular system. To diagnose covid pneumonia, along with rapid methods of SARS-COV2, computed tomography of the lungs was used. Analyzing the course of diseases in surgical children, it can be noted that coronavirus infection did not affect the course of the underlying disease. At the same time, COVID-19 infection in hematological patients provoked a worsening of the condition with symptoms of an acute respiratory viral infection (hyperthermia, weakness, cough, rhinitis). In patients with symptomatic focal epilepsy and in patients with increased intracranial pressure, SARS-COV-2 caused activation of seizures. It should be noted that the onset of type 1 diabetes was observed in 5 out of 6 admitted children. In these cases, COVID-19 infection was a provoking factor; it also caused an exacerbation in 1 child who had “long-term” diabetes. The article presents case histories and diagnoses of 6 children aged 3 years 9 months to 17 years with deaths, severe comorbid pathology (leukemia, brain stem tumor, immunodeficiency state), in whom COVID-19 infection aggravated the course of the underlying disease with the development of generalized combined bacterial infection, sepsis, bleeding.

   In recent years there has been an increase in cases of papillomatosis of the upper respiratory tract, including in childhood, which is a significant problem. More than 70 % of children have severe recurrent forms of the disease. It has been proven that the development of respiratory papillomatosis is associated with infection with human papillomavirus, more often HPV types 6 and 11. The development of respiratory papillomatosis in childhood may be a consequence of infection with the human papillomavirus of the respiratory tract at the time of birth, and HPV reactivation may occur after injury or infection. The treatment of this condition is a significant problem, since during surgical treatment, only the visible pathological process is excised, and no effect on the etiological factor is produced. Therefore, the most optimal can be considered to be vaccination against HPV with available vaccines at the stage of pregnancy planning in previously unvaccinated individuals, as well as vaccination against HPV in already infected individuals with existing respiratory papillomatosis. In our article, we present a case of successful vaccination of a 2-year-old child with an aggressive course of respiratory papillomatosis against HPV.