The study examined transient beta events (TBE) during electroencephalography (EEG), which reflect activity between the thalamus and cerebral cortex. Compared to typically developing children, some children with idiopathic Autism Spectrum Disorder (ASD) had elevated TBE frequency. The majority of children with Phelan-McDermid Syndrome, Rett Syndrome, and SYNGAP1-related disorder also showed increased TBE frequency. TBE frequency appears to be a promising biomarker for stratifying patients with distinct properties across ASD and neurogenetic conditions.