Which disease occurs only in females and presents normal development until 6 to 18 months of age followed by rapid mental deterioration?

Rett's syndrome is a neurodevelopmental disorder that predominantly affects females and is characterized by normal early development followed by a period of regression, typically between the ages of 6 to 18 months. During this regression, children with Rett's syndrome experience a loss of acquired skills, such as communication and purposeful hand movements, and may show significant cognitive decline.

The reason this condition is unique to females stems from its genetic basis, which involves mutations in the MECP2 gene located on the X chromosome. Males who inherit a mutation in this gene often do not survive to the age when symptoms typically manifest, making Rett's syndrome a disorder that primarily affects females.

Understanding the progression of symptoms, including the distinctive developmental trajectory and the age of regression, is crucial in identifying Rett's syndrome. This information helps differentiate it from other neurological disorders that may have overlapping symptoms but do not present the same pattern of initial normal development followed by rapid decline.