Autism spectrum disorder

Autism spectrum disorder (ASD) is a common, highly heritable neurodevelopmental condition that manifests early in life. It is defined by a specific combination of social communication deficits and repetitive, restricted, or sensory behaviors. Because ASD is a heterogeneous disorder, individuals present with a wide range of strengths and challenges, often co-occurring with other psychiatric or neurological conditions such as ADHD, anxiety, and epilepsy. While the worldwide prevalence is estimated to be just under 1%, diagnostic rates vary significantly based on the methods of ascertainment and the availability of clinical services.

Research into the biological underpinnings of autism has moved away from simple genetic models toward a more complex understanding of polygenic risk and rare, de novo mutations. While hundreds of genes have been associated with autism, these variants often play roles in multiple brain functions, such as synaptic structure and chromatin regulation, rather than acting as single-cause drivers. Neuroimaging and electrophysiological studies have identified subtle anatomical and functional differences in the brains of autistic individuals, including atypical neural connectivity and excitation/inhibition imbalances. However, these findings are often difficult to replicate and have not yet yielded reliable, clinically validated biomarkers for diagnosis.

Diagnosis relies on clinical observation and developmental history, with recent diagnostic systems like the DSM-5 and ICD-11 adopting an umbrella term to better capture the spectrum of presentations. Early intervention is a primary focus, with developmental and behavioral models aiming to improve social engagement and communication. Despite this, the evidence base for many interventions remains limited by small sample sizes and a lack of comparative effectiveness research. As individuals transition into adulthood, the focus shifts from symptom reduction to promoting independence, employment, and mental health, though adult-specific services remain critically underdeveloped.