Autism Spectrum Disorders (ASD), also known as Pervasive Developmental Disorders (PDDs), cause severe and pervasive impairment in thinking, feeling, language, and the ability to relate to others. These disorders are usually first diagnosed in early childhood and range from a much milder form, Asperger syndrome, to the more severe form, called autistic disorder (Autism), including other non-specific pervasive development disorders (PDD-NOS). ASD may include two rare disorders, Rett syndrome and childhood disintegrative disorder. ASD does NOT include attention-deficit disorder (ADD) or attention-deficit hyperactivity disorder (ADHD).