Autism spectrum disorder is a clinically and etiologically heterogeneous group, affecting 1 in 59 children. The etiopathogenesis of these, basically, neurodevelopment disorders, has been the subject of research by numerous researchers for more than two decades, and involves complex genetic, environmental, and epigenetic mechanisms. Hundreds of genes have been identified that contribute to serious deficits in communication, social relations and patient behavior. So the main objective of the paper is to explain the way in which genetic modifiers and epigenetic changes have a key role in modulating the phenotypic spectrum of patients with autism spectrum disorder. The systematic review of literature is based on a review of the available scientific papers. Following PRISMA’s instructions, a systematic review of published papers in the period from 2016 to 2024 was performed. Our study included literature published in the MEDLINE/PubMed database in which the following keywords were used during the search: “autismspectrum disorder”, “pervasive developmental disorder”, “risk factors”, “genetics”, “phenotypic spectrumof ASD”, “genes”, “epigenetic mechanisms”. Тhe obtained results show that the genetic factor increases the risk for development of autism spectrum disorder. More genes have been identified that are involved in the development of autism spectrum disorder, such as: ADNP, ANK2, CHD2, CNTN4, DSCAM, etc. In addition to genetic variants, there is also evidence of de novo gene variants. At the same time, chromosomal deletions or duplications were found in patients, such as the following: 15q11.2, BP1-BP2, 16p11.2 and 15q13.3. Copy number variations are submicroscopic, structural variants in chromosomes that include duplications, deletions, translocations, and inversions, sometimes stretching several kilo bases. Many genes may be affected with these changes, but not all are necessarily drivers of disease. Epigenetic mechanisms, DNA methylation and chemical histone modification are mechanisms that affect gene expression without changing the primary structure of genes. Genetic research so far has enabled us to consider autism spectrum disorder from a different angle, and understand its etiopathogenesis as a complex interaction between genes and environmental factors as a predisposition for its occurrence