Speech development is affected in children with autism, and related Autism Spectrum Disorders. Some may remain mute throughout their lives, though possibly communicating in other ways - images, visual clues, sign language, or typing on a keyboard. Those on the more severe end of the autism spectrum who do speak sometimes use language in unusual ways, retaining features of earlier stages of language development for long periods, or throughout their lives. Some speak only single words, while others repeat a phrase over and over. Some repeat what they hear, a condition called echolalia.
In milder cases on the autism spectrum, there can be problems in social interaction with peers. Children with Asperger's syndrome may be bullied at school due to their idiosyncratic behavior, interests, and impaired ability to perceive and respond in socially expected ways to nonverbal cues. They may also be extremely literal and have difficulty interpreting and responding to sarcasm or banter.
As with many so aspects of autism, PDD-NOS and Asperger's syndrome, early intervention is required to minimize the delays in a child's communication skills. This site contains links to fact sheets that provide useful strategies for children on the autism spectrum.