Choice A. Dilated cardiomyopathy is a feature of Duchenne muscular dystrophy, a genetic disorder that can present with gait abnormalities due to weakness but is not associated with intermittent breathing problems, repetitive movements, or speech regression. The increased incidence of sudden death in RS is related to cardiac electrical instability from autonomic dysregulation, not dilated cardiomyopathy.
Choice B. A happy demeanor is characteristic of Angelman syndrome, a neurodevelopmental disorder caused by the absence of the maternally inherited copy of the UBE3A gene. Patients can have repetitive hand flapping, a jerky gait, and seizures; however, developmental delay, rather than regression, is typical, and hyperventilation-hypoventilation episodes are not associated with this condition.
Explanation
Educational objective: Rett syndrome is characterized by a period of normal development followed by regression of speech, loss of purposeful hand use, stereotypical movements, and gait disturbance. Other features include early deceleration in head growth (ie, microcephaly), breathing abnormalities, autistic behaviors, and seizures.
Choice D. A musty odor is associated with phenylketonuria (PKU), an autosomal recessive metabolic disorder caused by phenylalanine hydroxylase deficiency. Untreated PKU causes intellectual disability, seizures, and skin abnormalities in early infancy. A period of normal development and intermittent breathing disturbances would not be seen
Choice E. Ophthalmologic abnormalities are not characteristic of RS. A cherry-red macula is seen with Tay-Sachs disease, a lysosomal storage disease that causes neurodevelopmental regression, particularly of motor skills, but not repetitive hand movements or episodic breathing problems.
