The expressive and receptive language development of a 5-year-old girl is severely impaired. The child also displays severe psychomotor retardation, poorly coordinated gait and trunk movements, and stereotypic hand movements. What other associated features would lead the PMHNP to suspect a diagnosis of Rett syndrome rather than autism spectrum disorder in this patient?

Choice A reason: Lack of social engagement is common in autism spectrum disorder and is not specific to Rett syndrome. Choice B reason: Lack of imaginative play is also a feature of autism but is not uniquely associated with Rett syndrome. Choice C reason: Deceleration of head growth (microcephaly) around 6 months of age is a hallmark of Rett syndrome, distinguishing it from autism, and, combined with motor regression and stereotypic hand movements, strongly supports this diagnosis. Choice D reason: Lack of eye contact can occur in both autism spectrum disorder and Rett syndrome, so it is not a differentiating factor.