Introduction
Autism Spectrum Disorder_Disease Background 1
Autism spectrum disorder (ASD) is the consolidation of autistic disorder, Asperger’s disorder, and pervasive developmental disorder, representing a single continuum of mild to severe deficits in social communication and restrictive repetitive behaviors or interests. This encompasses disorders previously referred to as early infantile autism, childhood autism, Kanner’s autism, high-functioning autism, atypical autism, pervasive developmental disorder not otherwise specified, childhood disintegrative disorder, and Asperger’s disorder.
Autism spectrum disorder is a neurodevelopmental disorder that begins in childhood that involves persistently impaired social interaction, persistently impaired reciprocal communication, presence of restricted and repetitive patterns of behaviors, interests, or activities, presence of symptoms from early childhood, and limited or impaired everyday functioning.
Epidemiology
The prevalence rate of autism spectrum disorder (ASD) is ≥1% in children and young individuals. One in 31 children aged 8 years across the United States has been identified with ASD in 2022. Autism spectrum disorder prevalence is rising across Asia, with an overall regional estimate of 0.36% that peaks in East Asia (0.51%) compared to lower rates in West Asia (0.35%) and South Asia (0.31%). In India, prevalence ranges from 0.74-1.68% per 100 children 2-9 years of age, affecting one in every 68 children.
The estimated prevalence rate in siblings of a child with autism spectrum disorder is 10%. Autism spectrum disorder is more frequent in boys. About ≥1% of children have regression or stasis of language and social behavior, usually occurring between ages 1 and 2 years.
Pathophysiology
Autism Spectrum Disorder_Disease Background 2
Genetic Factors
Brain development alteration, specifically neural connectivity, which affects social communication development, results in restricted interests and repetitive behaviors. It has been proposed that interactions between multiple genes or gene combinations are responsible for autism spectrum disorder and that exposure to environmental modifiers helps contribute to variable gene expression.
Neurobiologic Factors
Atypical neural connectivity as a result of abnormal neuronal differentiation during prenatal development contribute to the development of autism spectrum disorder.
Parental or Maternal Age
Advanced paternal or maternal age has been postulated to cause de novo spontaneous mutations and/or genetic imprinting alterations leading to the development of autism spectrum disorder.
Environmental and Perinatal Factors
Examples of environmental and perinatal factors are exposure to toxins or teratogens, perinatal insults, and prenatal infections (eg rubella, cytomegalovirus). The effect depends on the timing and duration of exposure, toxin concentration, mechanism of action, and distribution in the central nervous system. These modulate existing genetic factors predisposing to autism spectrum disorder.
Risk Factors
Risk factors in the development of ASD include advanced parental or maternal age, prematurity, neonatal encephalopathy, and genetic vulnerability.