Rett's disorder, or Rett Syndrome, is a neurological disorder caused by a genetic mutation that occurs almost exclusively in girls. Children diagnosed with the disorder demonstrate autistic-like traits. By the definition of the diagnosis, the child develops normally through the first five months of life, and then sometimes between five and 30 months of age, loses previously acquired skills. It is also characterized by autistic traits that include a loss of social engagement (though this often develops later in life), hand-wringing movements, and severely impaired speech and language abilities, both in terms of expression and understanding others' words.
While the Rett's cause is genetic, fewer than one percent of known cases of the disorder have occurred in the same family.