Autism Spectrum Disorder must begin in childhood (12-24 months).

• A. Must begin in childhood (12-24 months)
• B. Rett Syndrome
• C. Selective Mutism
• D. Intellectual Disability without Autism Spectrum Disorder

Answer: (A)

Autism Spectrum Disorder shows up in the early developmental period, meaning its signs are typically evident during early childhood, often within the first few years of life. The idea that onset occurs around 12 to 24 months aligns with how clinicians expect to see emerging social-communication difficulties and restricted, repetitive behaviors in toddlers. That early appearance is a hallmark that helps distinguish ASD from other conditions.

Rett syndrome, while it can involve autism-like features, is a distinct genetic disorder with a characteristic regression after a period of normal development, so it isn’t the standard onset pattern for ASD. Selective mutism is an anxiety disorder marked by the child’s failure to speak in particular social settings despite normal language development, not the core social-communication deficits of ASD. Intellectual disability without autism implies global cognitive impairment without meeting ASD criteria, though ASD can co-occur with intellectual disability, the question’s focus is on the timing pattern typical of ASD onset, which the statement captures.

So the best answer reflects the typical timing of ASD onset in early childhood.