If symptoms suddenly appear in an older child or teen with no hint of them previously, they may have any of a number of disorders, but not autism.
Signs That Might Indicate Autism
None of these signs alone indicates autism--but if they arise, they’re worth checking out.
Lack of communication skills. Very young children may not have spoken language, and late talking, in itself, is not necessarily a sign of autism. But if your child is not babbling, pointing, gesturing, pulling you, or otherwise communicating his or her wants and needs (once he or she is old enough to do so), bring the issue up to your pediatrician.
Problems with social interaction and joint attention. All young children “parallel play,” meaning that they sit in the same space with other people but play on their own. Most children, though, are also able to pay attention to the same thing as someone else, sharing the experience. If your child is only interested in playing alone, and is unable to engage with others, talk with your doctor.
Need for repetition. Most young children enjoy hearing the same stories, watching the same videos, and eating the same foods over and over again. Children with autism, however, may want to repeat the same meaningless actions over and over again, for no apparent reason. For example, a child with autism might flush the toilet over and over again, or make the same meaningless noises over and over. If you see this behavior in your child, check it out.
Sensory issues. Many people without autism dislike bright lights and loud noises. Some children with autism, however, can be so overwhelmed by sensory input that they fall apart completely. If your child is overwhelmed by sensory experiences, do check it out: it may not be autism, but it certainly an important concern to address.