Rett's syndrome primarily affects which demographic?

Rett's syndrome is a neurodevelopmental disorder that predominantly affects females, resulting from mutations in the MECP2 gene, which plays a critical role in brain development and function. This condition is characterized by normal early development followed by a loss of purposeful hand skills and speech, along with the development of repetitive movements and other cognitive impairments.

The emphasis on girls in this context stems from the fact that Rett's syndrome manifests almost exclusively in females, with very few cases reported in males, who often do not survive the prenatal or infant stages if they carry the mutation. Therefore, the correct choice accurately identifies the specific demographic impacted by Rett's syndrome, highlighting the genetic mutation's specific effects on brain development in girls.

The other options provided do not accurately reflect the characteristics or demographics associated with Rett's syndrome, focusing instead on broader categories that are not specifically linked to this condition.