Autism Spectrum Disorders
- Group of neurodevelopmental disorders of early childhood characterized by (i) persistent deficits in social communication and interaction and (ii) restricted, repetitive patterns of behavior, interests, or activities
- Diagnostic and Statistical Manual of Mental Disorders, 5th edition, text revision: umbrella term autism spectrum disorder (ASD), which encompasses a group of pervasive developmental disorders with designations for varying severities and associated symptoms
- ASD combines former diagnoses, including autistic disorder, childhood disintegrative disorder, Asperger disorder, pervasive developmental disorder not otherwise specified (PDD-NOS), early infantile autism, childhood autism, Kanner autism, high-functioning autism, and atypical autism, many of which are still used by ICD-10 coding.
- Although symptoms must be present in early development period, they may not be apparent until social demands exceed capacity.
- Symptoms must cause functional impairment. Severity levels:
- Level 1: requiring support—noticeable impairment
- Level 2: requiring substantial support—marked deficits
- Level 3: requiring very substantial support—severe impairments interfering with functionality
- Specifiers for associated symptoms include with catatonia; intellectual impairment; language impairment; known medical or genetic condition; and neurodevelopmental, mental, or behavioral disorders.
- Important to distinguish ASD from symptoms that could be better explained by intellectual disability or global developmental delay
Onset in early childhood; predominant sex: male > female (approximately 4:1 ratio)
Symptom onset can often be seen in children <3 years of age but may not become apparent until social demands exceed capacity.
- Centers for Disease Control and Prevention (CDC) in 2018: estimated prevalence of 1 in every 44 children between ages 3 and 17 years carried diagnosis of ASD
- Increase noted since 2000 when the CDC reported prevalence to be 1 in 150, likely due to changes in definition and awareness.
- In 2018, there was no difference in prevalence of non-Hispanic white children diagnosed with ASD compared to non-Hispanic black children. However, the number of Hispanics diagnosed with ASD is lower.
Etiology and Pathophysiology
- No single cause has been identified.
- Consensus: A genetic abnormality leads to altered neurologic development.
- Epidemiologic evidence does not support association between immunizations and ASD.
- Genetic concordance: A 2009 Swedish population-based cohort study of 2 million subjects showed a cumulative risk of 59% for monozygotic twins.
- The American College of Medical Genetics and Genomics practice guidelines list the risk of siblings of children diagnosed with ASD without an identifiable cause to be 7% if the affected child is female, 4% if the affected child is male, and >30% if there are two or more affected children.
- Male sex, advanced paternal age, family history, very low birth weight
- Perinatal insults including toxic exposures, teratogens, prenatal infections, use of selective serotonin reuptake inhibitors (SSRI) or valproate during pregnancy
- Screening for early intervention is associated with improved prognosis, yet median age of diagnosis in the United States is >4 years.
- Routine screening for ASD with a validated tool is recommended at 18- and 24-month well-child visits to assist with early detection.
- Screening is indicated after 24 months if parents or clinician have concerns about ASD as less severe presentations may pass earlier routine screening.
- Children with false positives for ASD frequently have some form of developmental disorder and benefit from early intervention.
- Screening difficult due to variability of signs and symptoms of ASD, and lack of unanimous consensus of social developmental milestones, thus leading to delayed diagnosis.
Commonly Associated Conditions
- Intellectual disability (seizure in severe cases)
- Attention deficit hyperactivity disorder (ADHD), anxiety, depression, or obsessive behavior
- Motor impairments including hypotonia, apraxia, toe walking, or gross motor delays
- Phenylketonuria (PKU), tuberous sclerosis, fragile X syndrome, Angelman syndrome, Rett syndrome, CHARGE syndrome, Joubert syndrome, Smith-Lemli-Opitz syndrome, Timothy syndrome, and fetal alcohol syndrome (rare)
- Sleep issues: insomnia, circadian rhythm sleep–wake disorder, sleep-related movement disorder
- Change in bowel habits, abdominal pain
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