selective mutism
in DSM–IV–TR and DSM–5, a rare disorder, most commonly but not exclusively found in young children, characterized by a persistent failure to speak in certain social situations (e.g., at school) despite the ability to speak and to understand spoken language. Age of onset is usually before 5 years, and the failure to speak lasts at least 1 month (not counting the first month at school, when many children are shy about talking). Generally, these individuals function normally in other ways, although some may have additional disabilities. Most learn age-appropriate skills and academic subjects. Currently, selective mutism is thought to be related to severe anxiety and social phobia, and it is classified as an anxiety disorder in DSM–5, but the exact cause is unknown. It was formerly called elective mutism.