Autism is a lifelong neurological disability that affects a person's ability to communicate, understand language, play and participate in social relationships. Autism is classified as a developmental disability because it interferes with the typical rate and patterns of childhood development. The first signs of autism usually appear as developmental delays before the age of three. Diagnoses closely related to autism include Pervasive Developmental Disorder, Asperger's syndrome and Rett's syndrome. These diagnoses are included in the category of Autism Spectrum Disorder.