The signs of this disorder appear as early as one year old. Not responding to when called, lacking eye contact and other characteristics of typical children are the obvious signs.

Upon progression, with age, the children may fail to acquire even a single word, while others may be mute, echolalic or invent nonsensical language. It could also be followed by behavioral problems like hyperactivity, aggression, tantrums and others.

There could also be problems with eating, sleeping and toileting, or even medical or developmental difficulties such as seizures, a delay or regression in milestones, odd posture or gait and poor general understanding. One could also see restricted behaviors such as the flapping of hands, indifference to pain and others.

There will also be problems witnessed such as inability in making friends, adapting in a social setting and unable to read and understand facial expressions.