<unk>  (SM) is an umbrella term for the condition of otherwise well-developed children or adults who cannot speak or communicate under certain settings. The exact causes that affect each person may be different and yet unknown. There have been attempts to categorize, but there are no definitive answers yet due to the under-diagnosis and small/biased sample sizes. Many people are not diagnosed until late in childhood only because they do not speak at school and therefore fail to accomplish assignments requiring public speaking. Their involuntary silence makes the condition harder to understand or test. Parents often are unaware of the condition since the children may be functioning well at home. Teachers and pediatricians also sometimes mistake it for severe shyness or common stage fright. Most children and adults with<unk>  are hypothesized to have an inherited predisposition to anxiety. They often have inhibited temperaments, which is hypothesized to be the result of over-excitability of the area of the brain called the amygdala. This area receives indications of possible threats and sets off the fight-or-flight response. Behavioral inhibitions, or inhibited temperaments, encompass feelings of emotional distress and social withdrawals. In a 2016 study, the relationship between behavioral inhibition and<unk>  was investigated. Children between the ages of three and 19 with lifetime<unk> , social phobia, internalizing behavior, and healthy controls were assessed using the parent-rated Retrospective Infant Behavioral Inhibition (RIBI) questionnaire, consisting of 20 questions that addressed shyness and fear, as well as other subscales. The results indicated behavioral inhibition does indeed predispose<unk> . Corresponding with the researchers’ hypothesis, children diagnosed with long-term<unk>  had a higher behavioral inhibition score as an infant. This is indicative of the positive correlation between behavioral inhibition and<unk> . Given the very high overlap between social anxiety disorder and<unk>  (as high as 100% in some studies), it is possible that social anxiety disorder causes<unk> . Some children or adults with<unk>  may have trouble processing sensory information. This could cause anxiety and a sense of being overwhelmed in unfamiliar situations, which may cause the child or adult to "shut down" and not be able to speak (something that some autistic people also experience). Many children or adults with<unk>  have some auditory processing difficulties. About 20–30% of children or adults with<unk>  have speech or language disorders that add stress to situations in which the child is expected to speak. Despite the change of name from<unk> " to<unk> ", a common misconception remains that a<unk> ly mute child is defiant or stubborn. In fact, children with<unk>  have a lower rate of oppositional behavior than their peers in a school setting. Some previous studies on the subject of<unk>  have been dismissed as containing serious flaws in their design. According to a more recent systematic study it is believed that children or adults who have<unk>  are not more likely than other children or adults to have a history of early trauma or stressful life events. Many children or adults who have<unk>  almost always speak confidently in some situations.
Selective mutism
Autism spectrum  disorder  1
Nonverbal autism
Tourettism
Akinetic mutism
Klismaphilia
Taurodontism
Autism spectrum