Epidemiology

Etiology

Males > Females (4:1 ratio).
Strong genetic component (high concordance in monozygotic twins).
Risk Factors: Advanced paternal age, maternal use of valproate, low birth weight.
Associations: Fragile X syndrome, Tuberous Sclerosis, Rett syndrome (though Rett is a distinct entity).

ASD is characterized by a combination of two core symptom domains that impair daily functioning:

Persistent deficits in social communication and interaction:
- Social-emotional reciprocity: Difficulty with back-and-forth conversation, initiating social interaction, and sharing interests.
- Nonverbal communication: Poorly integrated verbal and nonverbal cues, abnormal eye contact, and difficulty understanding gestures or facial expressions.
- Developing & maintaining relationships: Trouble making friends or adjusting behavior to social contexts.
Restricted, repetitive patterns of behavior, interests, or activities (at least 2 of the following):
- Stereotyped movements or speech: Repetitive motor movements (e.g., hand-flapping), lining up toys, or echolalia (repeating words/phrases).
- Insistence on sameness: Extreme distress at minor changes, inflexible adherence to routines, and ritualized behaviors.
- Highly restricted, fixated interests: Abnormal intensity or focus on particular subjects or objects.
- Sensory issues: Hyper- or hyporeactivity to sensory input like pain, temperature, or specific sounds/textures.

Differential Diagnosis
- Rett Syndrome: Occurs almost exclusively in females; characterized by normal development until 5–18 months followed by regression, loss of purposeful hand skills, and stereotypic hand-wringing.
- Selective Mutism: Child does not speak in specific situations (e.g., school) but speaks normally at home; social reciprocity is preserved.
- Social (Pragmatic) Communication Disorder: Deficits in social communication without the restrictive/repetitive behaviors of ASD.
- Intellectual Disability: Global delays; often comorbid with ASD.
- Landau-Kleffner Syndrome: Acquired epileptic aphasia (regression of language skills due to severe epilepsy).

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