Final answer:
Patients with Rett's syndrome generally show normal development until the ages of 6 to 18 months, at which point developmental regression typically begins, leading to a loss of previously acquired skills.
Step-by-step explanation:
Patients with Rett's syndrome typically develop normally until they reach the ages of 6 months to 18 months. This period is a critical time for observing early signs of Rett's syndrome, as it is usually after this age that the symptoms start to manifest.
Due to a regression in development, children with Rett's syndrome begin to lose previously acquired skills, such as purposeful hand movements and the ability to communicate. Although there can be some variability, this change in development is a distinctive feature of the syndrome.