Associated Features of selective mutism

Associated features of Selective Mutism may include excessive shyness, fear of social embarrassment, social isolation and withdrawal, clinging, compulsive traits, negativism, temper tantrums, or controlling or oppositional behavior, particularly at home. There may be severe impairment in social and school functioning. Teasing or scapegoating by peers is common. Although children with this disorder generally have normal language skills, there may occasionally be an associated Communication Disorder (e.g., Phonological Disorder, Expressive Language Disorder, or Mixed Receptive-Expressive Language Disorder). These communication problems are not the main reason for the mutism.

It is important to note that selective mutism is also associated with Anxiety disorders (especially Social Phobia), Mental Retardation, hospitalization, or extreme psychosocial.
For further details,please read the following articles on selective mutism :
Symptoms of selective mutism
What parents can do if they suspect their child has selective mutism
Treatment of selective mutism