Multimorbidity in autism spectrum disorder: A comprehensive review

Autism spectrum disorder (ASD) is a heterogeneous neurodevelopmental condition defined by persistent differences in social communication and interaction, together with restricted and repetitive patterns of behavior and interests. Autism Spectrum Disorder rarely occurs in isolation; a substantial proportion of autistic individuals experience co-occurring psychiatric, developmental, neurological, gastrointestinal, sleep, feeding, motor and immune-related conditions that shape the clinical presentation, complicate diagnosis and influence long-term outcomes. This review synthesizes the major comorbidities associated with autism spectrum disorder and examines their impact on assessment and management across the lifespan. The evidence shows that anxiety, attention-deficit/hyperactivity disorder (ADHD), mood disorders, obsessive-compulsive disorder (OCD), intellectual disability (ID), epilepsy, gastrointestinal disturbances, sleep disorders and feeding and eating difficulties are especially common in ASD. These conditions often overlap with core autistic traits, contributing to diagnostic overshadowing, delayed recognition and delayed interventions. They may also intensify social withdrawal, irritability, repetitive behaviours and functional impairment, thereby increasing the burden on families and health-care systems. Biologically, comorbidities appear to arise from interacting genetic, neurobiological, environmental and immune-related pathways. Recognizing comorbidities is therefore essential not only for accurate diagnosis but also for individualized intervention. Effective care requires systematic screening, multidisciplinary assessment and targeted treatment that addresses both core autism spectrum disorder features and associated conditions. Early identification and integrated management can improve adaptive functioning, reduce symptom burden and enhance the quality of life.