Autism spectrum disorder (ASD) is a neurodevelopmental condition characterized by persistent deficits in social communication and social interaction across multiple contexts, accompanied by restricted, repetitive patterns of behavior, interests, or activities. The neurobiology of ASD involves altered neural connectivity and synaptic development beginning in utero. Key pathological findings include abnormal cortical minicolumn structure (more numerous but narrower columns with reduced inhibitory interneuron function), excessive early brain growth (macrocephaly in the first 2 years) followed by plateauing, reduced long-range neural connectivity between frontal and posterior brain regions with increased local short-range connections, mirror neuron system dysfunction (contributing to impaired social imitation and empathy), and altered GABAergic/glutamatergic balance resulting in excitation-inhibition imbalance. Genetic factors account for approximately 80% of ASD risk, involving hundreds of genes related to synaptic formation, pruning, and neurotransmitter signaling (including SHANK3, MECP2, FMR1, CHD8, and 16p11.2 copy number variants). The M-CHAT-R/F (Modified Checklist for Autism in Toddlers, Revised with Follow-Up) is the AAP-recommended universal screening tool, administered at 18 and 24 months of age. It consists of 20 yes/no questions assessing social relatedness, joint attention, pointing, pretend play,...