Autism---also known as autistic disorder or classical ASD---is a neurodevelopmental disorder, part of a larger class known as autism spectrum disorders (ASD). Others in the class include Asperger's syndrome and Rett syndrome, but autism is the most severe, according to the National Institute of Neurological Disorders and Stroke (NINDS). For many kids, signs of autism show up in infancy, while others suddenly withdraw, regress or show behavioral changes months later. The symptoms are different for every child but involve development issues that fall under three crucial categories.
Behavior
Autism is characterized by "restricted, repetitive and stereotyped patterns of behavior," says the NINDS. A child with autism might develop specific rituals or routines and might become upset or throw a tantrum if they change even slightly. He may also move constantly or perform repetitive actions, such as spinning in circles, rocking, flapping his hands or even banging his head. He might be completely engrossed and fascinated by the small moving parts of an object, such as the spinning wheels on his toy car, or he might obsessively line his toys up in a row. He might also be extremely sensitive to sound, light or touch, and yet be completely oblivious to pain.
Language
Children with autism have difficulties with communication; they often start talking later than their peers or lose the ability to speak properly, even if they were previously able to say specific words or complete sentences. An autistic child may speak with a singsong pattern, a robotic voice or an otherwise abnormal rhythm or tone. She might also repeat words or phrases heard from others, but without any understanding of how to properly use them. You might notice that an autistic baby doesn't point or babble by her first birthday and doesn't say words by 16 months or short phrases by age 2.
Social Skills
It's not just about the words and voice; "the most severe autism is marked by a complete inability to communicate or interact with other people," according to the Mayo Clinic. An autistic child doesn't usually make eye contact when asking for something, can't easily start or continue a conversation and appears not to be aware of---or can't interpret---other people's feelings. He often doesn't seem to hear you and doesn't even respond to his name. He also prefers playing by himself and will retreat into his own world, not smiling and resisting physical contact, such as cuddling.
