• Clinical science

Autism spectrum disorder


Autism spectrum disorder (ASD) encompasses the previously separate diagnoses of autistic disorder, Asperger disorder, Rett disorder, childhood disintegrative disorder, and pervasive developmental disorder-not otherwise specified (PDD-NOS). ASD is a neurodevelopmental condition characterized by qualitative impairment in social interaction and communication as well as repetitive stereotyped behavior, interests, and activities. These features are present early in development and cause impairment of social and academic functioning. Diagnosis is based on careful assessment of behavior, cognitive development, and language skills. Treatment, which should be initiated early, involves educational and behavioral management, medical therapy, and family counseling.


  • Prevalence: 14.7/1000 in the US [1]
  • Sex: > (4:1)
  • Age: symptoms typically evident before 2–3 years of age


Epidemiological data refers to the US, unless otherwise specified.


  • Complex, multifactorial
    • Genetics: strong underlying predisposition; ; many genes have been found to be associated with autism spectrum disorders
    • Environmental factors (e.g., toxin exposure, prenatal infections) may increase the risk of ASD; however, no specific causes have been identified.

Studies have shown that there is no link between the MMR vaccine and autism.


Clinical features

  • Core features
    • Persistent impairment in communication and social interaction (inability to form relationships, abnormal language development, reduced empathy, difficulties in adjusting behavior to social situations, and poor eye contact)
    • Restricted, stereotyped patterns of behavior, interests, and activities (e.g., hand flapping, excessive touching/smelling, lining up toys, adverse response to sounds, and echolalia)
  • Additional features
    • Intellectual impairment
    • Language impairment
  • Associated conditions



  • Comprehensive evaluation of
    • Social interaction and communication skills
    • Language and comprehension skills
    • Behavior
    • Cognitive development
    • Associated conditions
  • Hearing and vision testing: to rule out comorbidities or other causes of developmental delays and behavioral disorders.
  • Genetic testing: fragile X syndrome, tuberous sclerosis (if any of these conditions is suspected)


Differential diagnoses

Differential diagnoses of impaired social interaction
Factor Autism spectrum disorder (ASD) Global developmental delay [13] Attention deficit hyperactivity disorder (ADHD) [14] Selective mutism [15] Rett syndrome [16] Hearing impairment
Age of onset
  • Before 2–3 years of age
  • Before 5 years of age
  • Usually before 6 years of age
  • Before 5 years of age
  • 7–24 months of age
  • Congenital or acquired later in life
  • > (4:1)
  • >
  • >
  • >
  • Seen almost exclusively in girls
  • =
Motor skills
  • Normal
  • Normal
  • Normal
  • Loss of fine motor skills
  • Typical hand wringing
  • Normal
Language use
  • Impaired
  • May have mixed expressive/receptive language delay
  • Normal
  • Impaired
  • Impaired
  • Impaired
  • Restricted, stereotyped patterns of behavior, interests, and activities
  • May show repetitive behaviors
  • Inattention and hyperactivity
  • Fails to speak in specific situations
  • Unusual eye movements
  • Sudden, odd facial expressions
  • Long bouts of laughter, hand licking, and grasping of hair or clothing
  • Not startled by loud sounds
  • Not turning head in direction of sounds
  • Communicates with hand gestures (e.g., pointing)
  • Temper tantrums
Physical features
  • Acceleration of head growth
  • May be abnormal depending on the etiology
  • Normal
  • Normal
  • May be abnormal depending on the etiology

The differential diagnoses listed here are not exhaustive.


  • Early behavioral and educational management
    • Competence training: social skills, communication skills
    • Establishing clear and consistent structures
  • Family support and counseling (e.g., parental education on interaction with the child and acceptance of his/her behavior)
  • Medical treatment

Risperidone and aripiprazole are the only FDA-approved drugs for controlling irritability in patients with autism spectrum disorder.



  • Indicators of poor prognosis: severe core symptoms, cognitive impairment (low IQ), poor or absent language skills, late initiation of treatment
  • Impaired social interaction often persists into adulthood.
  • The majority of patients are dependent even as adults on their family and familiar surroundings.
  • Individuals with good language and cognitive ability usually learn to cope with their particularities.
  • Approx. 50% of individuals with language impairment do not develop the ability to speak.
  • Adolescents: Insensitive behavior towards peers often results in social exclusion.