Which of the following statements is true regarding Rett syndrome?

Ans. D. None of the aboveRett syndrome is a progressive condition that develops after 6 months of apparently normal development after birth. Head circumference at birth is normal, and early developmental milestones, including social interactions, are unremarkable. Between 6 and 48 months, most commonly between 6 and 12 months, a progressive encephalopathy develops. Head growth begins to decelerate, with resultant microcephaly. Motor abnormalities occur; purposeful hand movements are lost, and characteristic midline hand movements, such as hand wringing, emerge.Gait and truncal apraxia, ataxia, and poor coordination develop in the preschool years. Expressive and receptive language skills deteriorate and are associated with marked mental retardation (not normal intelligence). A loss of social interactional skills is observed during the preschool years. The etiology of the disease is unknown. A genetic basis for the condition is likely; Rett syndrome occurs only in girls, and case reports indicate complete concordance in monozygotic twins.Associated features include seizures (occurring in up to 75% of affected patients) and irregular respiration with episodes of hyperventilation, apnea, and breath holding.