Introduction: Intensive chemotherapy protocols and hematopoietic stem cell transplantation (HSCT) in children with cancer frequently lead to severe complications, such as mucositis and immune dysfunction. A growing body of evidence indicates that these complications are closely associated with the patient’s nutritional status and the composition of the gut microbiome, which becomes profoundly destabilized as a result of cytotoxic therapy and antibiotic use. Background: The aim of this review is to critically evaluate the current state of knowledge on the interplay between gut dysbiosis, metabolomic profiles—with particular emphasis on short-chain fatty acids (SCFAs)—and treatment-related toxicity in pediatric patients, as well as to delineate pathways toward personalized nutritional therapy. Methods: A narrative review was conducted, including clinical and preclinical studies published between January 2015 and October 2025. PubMed/MEDLINE, Embase, Cochrane Library, and other databases were searched, focusing on changes in microbiome composition, correlations between gut-derived metabolites and the severity of complications (sepsis, graft-versus-host disease [GvHD], mucositis), and the effects of targeted nutritional interventions (probiotics, prebiotics, postbiotics, and fecal microbiota transplantation [FMT]) on microbiome modulation during anticancer therapy. Results: The analysis demonstrates that pediatric oncologic treatment leads to a marked reduction in microbial diversity, including the loss of protective Clostridiales taxa (e.g., Faecalibacterium), accompanied by an overgrowth of Proteobacteria pathobionts. Metabolomic profiling indicates that low SCFA levels (e.g., butyrate < 20–50 µmol/g) are a strong predictor of severe mucositis, prolonged neutropenia, and an increased risk of sepsis. Interventions aimed at restoring eubiosis and enhancing SCFA production show potential in strengthening the intestinal barrier, modulating immune responses, and enabling maintenance of the planned relative dose intensity (RDI) of chemotherapy by reducing treatment-related toxicity. Conclusions: Gut microbiome profiling and fecal metabolomics represent promising prognostic tools in pediatric oncology. There is an urgent need for further research employing “omics”-based approaches to develop precise, individually tailored nutritional protocols. Such strategies, including postbiotics and FMT, may minimize treatment-related adverse effects and improve long-term clinical outcomes in pediatric patients.

Background. Rett syndrome (RTT) is a rare, genetic neurological disease caused by a mutation of the methyl-CpG-binding protein 2 (MECP2) gene that mainly affects girls. There is no currently available causative treatment for this disease; trofinetide is the only drug dedicated to alleviating symptoms. Aim. The aim is to present potential medicines in clinical trials that have been observed to have a therapeutic benefit in the treatment of Rett syndrome. The article contains also descriptions of pathophysiology and symptoms of Rett syndrome, which can be affected by undermentioned pharmaceuticals. Material and methods. The study used Google Scholar, PubMed, and Scopus databases as its data sources. Other information was obtained from the Clinicaltrials.gov registry and database, and reports of companies conducting drug research. The literature was filtered by keywords: ‘Rett syndrome‘, ‘clinical trials’ and ‘gene therapies‘. Results. The treatment of Rett syndrome focuses on alleviating symptoms and improving the quality of life. Trofinetide is the only substance approved by the US Food and Drug Administration (FDA), which helps to reduce behavioral problems and improve social functioning. Currently, research is underway on genetic therapies, including gene replacement therapy, which may provide more effective treatment options in the future. Additionally, research is being conducted on other drugs that reduce symptoms in patients with RTT. Conclusions. Great hopes are associated with research on gene therapies, which are currently in clinical trial phases. In the future, this could bring significant benefits to patients; their implementation may not only improve aspects of the disease, such as respiratory issues, but also can result in better survival outcomes.