A Child shows head growth decelerating between ages of 6 months and 1 year. Which of the following is the most likely diagnosis?

Ans. D. Rett syndromeRett syndrome is a progressive condition that develops after some months of apparently normal development. Head circumference is normal at birth, and early developmental milestones are unremarkable. Between 5 and 48 months (usually between 6 months and 1 year), head growth begins to decelerate. Purposeful hand movements are lost, and characteristic midline hand wringing or hand washing stereotypies develop. Expressive and receptive language skills become severely impaired and are associated with marked mental retardation. In the preschool years, gait apraxia and truncal apraxia and ataxia develop.Down syndrome is the most common cause of mental retardation.Autistic disorder and learning disorders do not include changes in head growth.