Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by persistent deficits in social communication and interaction, alongside restricted, repetitive patterns of behavior, interests, or activities, with onset in early childhood.

Definition

Epidemiology

Prevalence estimated at 1–2% of children worldwide
More common in boys than girls (~4:1 ratio)
Symptoms typically apparent by 2–3 years of age
Global prevalence rising due to increased awareness and improved diagnosis
High variability in intellectual abilities and functional outcomes

Etiology

Genetic factors: multiple genes implicated (e.g., SHANK3, NRXN1, CHD8)
Environmental risk factors: advanced parental age, prenatal exposure to infections or toxins
Neurodevelopmental abnormalities: altered synaptic connectivity and brain network function
Family history increases risk
No single causative agent; multifactorial origin
Epigenetic and perinatal factors contribute to risk

Pathophysiology

Altered brain connectivity and synaptic development
Imbalance between excitatory and inhibitory neurotransmission
Abnormalities in cortical and subcortical regions: amygdala, prefrontal cortex, cerebellum
Altered neural plasticity and social cognition networks
Neuroinflammation and immune dysregulation proposed in some cases
Genetic and epigenetic mechanisms disrupt neuronal signaling pathways
Functional deficits manifest as social, communication, and behavioral impairments