Autism Spectrum Disorders

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Basics

Description

  • 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
  • DSM-5: 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 the early development period, they may not be apparent until social demands exceed capacity.
  • Symptoms must cause functional impairment.
  • Severity levels
    • Level 1: requiring support
    • Level 2: requiring substantial support
    • Level 3: requiring very substantial support
  • 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 similar symptoms that could be better explained by intellectual disability or global developmental delay

Epidemiology

  • Incidence: estimated 1 in every 110 children in the United States diagnosed per year
  • Predominant age: onset in early childhood
  • Predominant sex: male > female (4:1)

Pediatric Considerations
Symptom onset can often be seen in children <3 years of age but may not become apparent until social demands exceed capacity.

Prevalence
  • According to the Centers for Disease Control and Prevention (CDC) in 2014, an estimated prevalence of 1 in every 59 children between the ages of 3 and 17 years carried a diagnosis of ASD.
  • This has been a steady increase since 2000 when the CDC reported the prevalence to be 1 in 150.
  • Systematic literature reviews suggest changes in prevalence can be largely accounted for by changes in definition and increased awareness.

Etiology and Pathophysiology

  • No single cause has been identified.
  • General consensus: A genetic abnormality leads to altered neurologic development.
  • No scientific evidence relating vaccines, such as vaccines for measles, mumps, rubella (MMR) or thimerosal causing ASDs
  • Pathophysiology is not fully understood.

Genetics
  • Genetic concordance: A 2009 Swedish population-based cohort study of 2 million subjects showed a cumulative risk of 59% for monozygotic twins.
  • Rate in siblings: The American College of Medical Genetics and Genomics practice guidelines lists 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
    • >30% if there are two or more affected children

Risk Factors

  • Male sex
  • Family history
  • Advanced paternal age
  • Very low birth weight
  • Maternal use of selective serotonin reuptake inhibitors (SSRIs) or valproate during pregnancy
  • Note: Epidemiologic evidence does not support an association between immunizations and ASD.

General Prevention

  • Screening for early intervention is associated with improved prognosis.
  • Routine screening for ASD with a validated tool is recommended at 18- and 24-month well-child visits to assist with early detection.

Commonly Associated Conditions

  • Intellectual disability
  • 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, and fetal alcohol syndrome (rare)
  • Seizures (increased risk if severe mental retardation)
  • Sleep issues: insomnia, circadian rhythm sleep–wake disorder, sleep-related movement disorder
  • Chronic constipation, diarrhea, abdominal pain

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