This is also known as atypical autism. Two key characteristics are difficulties with social interaction skills and communication. Signs are often visible in babies but a diagnosis is usually not made until around age 4.
Social functioning skills
Once a child with PDD-NOS enters school, he or she will often be very eager to interact with classmates, but may act socially different from peers and be unable to make genuine connections. As they age, the closest connections they make are typically with their parents. Children with PDD-NOS have difficulty reading facial expressions and relating to feelings of others. They may not know how to respond when someone is laughing or crying. Literal thinking is also characteristic of PDD-NOS. They will most likely have difficulty understanding figurative speech and sarcasm.
Inhibited communication skills are also a sign of PDD-NOS. Infants with the disorder may not babble; as they age, they may not speak at the age at which speech develops in typical people. Once verbal communication begins, vocabulary is often limited. Some characteristics of language-based patterns are repetitive or rigid language, narrow interests, uneven language development, and poor nonverbal communication.