Selective mutism is caused by the interaction between the nature of the child and external factors – nature and nurture. One can conceptualize this as various factors fitting into one of three groups – predisposing factors, precipitating factors, and maintaining factors:
Predisposing factors could include: Anxiety of child, shyness, timidity, hyper-sensitivity. Family history of shyness, anxiety or selective mutism –can include anxious parents, anxious behavior modeling by parents. Speech impairment of child – usually expressive language. Bilingualism, negative self image related to speech (e.g. doesn’t like sound of voice), neuro-developmental delay, often sensory processing disorder.
Precipitating factors (triggers) could include: School or kindergarten admission, frequent geographical moves, family belonging to linguistic minority, negative reactions to child talking – bullying, shouting etc.
Maintaining factors could include: Social Isolation of families, misdiagnosis (that is, the child is wrongly diagnosed as having oppositional behavior, autism, retardation etc.), lack of early and appropriate intervention. Lack of understanding by teachers, families, psychologists, reinforcement of the mutism by increased attention or affection, heightened anxiety levels caused by pressure to speak, ability to convey messages non verbally, over acceptance of mutism.
When there is a combination of predisposing factors, that heighten the child's vulnerability to SM, and triggers – events such as nursery school admission or a geographical move, the scales could tip and bring about the onset of SM. Predisposing factors include elements of the child's psychological and physiological make up which make him more vulnerable to selective mutism; this could includes an anxious or shy nature, a family history of shyness, and stubbornness and perfectionism. Many children with SM have some type of speech difficulty, including bilingualism. Maintaining factors facilitate the continuation of the condition – marring the child's chances of overcoming selective mutism.