What disorder manifests in females and is characterized by slowing head growth after two and a half years of age?

Rett's syndrome is a neurodevelopmental disorder that primarily affects females and is characterized by a series of developmental regression phases. One of the hallmark signs of Rett's syndrome is the slowing of head growth, which typically begins to present around the age of six months to two years, often becoming more pronounced after two and a half years of age. Individuals with Rett's syndrome may experience a loss of purposeful hand skills, language skills, and other developmental milestones, leading to significant challenges in their abilities to communicate and engage in daily activities.

The other disorders mentioned do not typically present with the specific symptom of slowing head growth in this manner after two and a half years of age. For instance, Fragile X syndrome may lead to developmental delays and cognitive challenges, but it has a different pattern of growth and is associated with different genetic factors. Autism Spectrum Disorder can also include developmental regression but does not specifically focus on head growth stagnation as a distinguishing feature. Down syndrome involves a different set of physical characteristics and developmental issues, which include cognitive delays but not the specific growth patterns observed in Rett's syndrome. Thus, Rett's syndrome is identified for its unique progression and symptomatology, particularly in females.