Introduction. Autism spectrum disorders (ASD) represent a group of pathologies that affect neurodevelopment, manifest from early childhood, but also persist into adolescence and adulthood. According to data from international specialized literature, every 54th child suffers from ASD. Autism is more common than some genetic syndromes, such as: Down syndrome/diabetes/AIDS, or some forms of cancer in children. ASD, a disorder with the fastest growing rate at 13% annually. The prevalence of ASD is around 14.7 per 1000 children. ASD and genetic diseases often co-occur, which is determined in 2530% of cases. The aim of the study is to research the etiological, genetic aspects, clinical polymorphism and developmental peculiarities of children with ASD in genetic diseases. Material and methods: We used the observational method of official studies, the synthesis and critical analysis of over 130 articles published from 2016-2023 on the platforms PubMed, Medscape, NEJM, GeneCards, Lecturio, AMBOSS. Results. Research in the literature suggests that there are numerous genetic conditions associated with ASD. The maternally inherited 15q11-q13 duplication is the most common chromosomal aberration reported in children with ASD. Fragile X syndrome – which is frequently associated with ASD and develops due to a dynamic mutation that consists in the expansion of CGG nucleotides, thus inactivating the FMR1 gene. Kleefstra syndrome is caused by submicroscopic 9q34.3 deletion or mutations in the EHMT1 gene leading to haploinsufficiency of this gene, characterized by ASD, moderate to severe mental retardation, microcephaly, facial dysmorphism, limited or even absent language. EHMT1 exhibits enzymatic activity in monomethylation and dimethylation of histone 3, lysine 9 (H3K9me1 and H3K9me2), which promotes heterochromatization and gene repression. During development, the EHMT1/EHMT2 repressive complex is involved in neuronal cell differentiation. Other genes are also involved in the pathogenesis of ASD, for example genes responsible for regulating transcription (MECP2, MEF2C, FOXG1), cell growth (TSC1, TSC2, PTEN), synaptic channels (SCN2A) and synaptic structure (CASK, CDKL5, FMR1, SHANK3). Conclusions. ASD in genetic diseases have still unclear etiopathogenetic mechanisms and require extensive research studies. Data from the specialized literature suggest that various polygenic and monogenic conditions, „de novo” mutations, but also epigenetic mechanisms can cause ASD in genetic diseases