Isabelle is not diagnosed in the book, but were she to be, she would probably be
diagnosed with Selective Mutism, a childhood anxiety disorder. Some
therapists might even diagnose her with Traumatic Mutism because of the
immediate onset and her total silence. Most children with SM are not completely
silent all the time. They are silent as a result of deep anxiety, but will talk
normally when they are in 'safe' environments. Isabelle would be a rare case
because she is completely silent for nine months.
Children with SM often have "severely inhibited temperaments" and are more prone to anxiety. When we become stressed, the amygdala (the brain's "emergency manager") responds to the potential crisis by overriding thought and instigating a reaction intended to protect the body. In children with SM, that reaction is silence. Fearful situations can be birthday parties, school, family gatherings, or routine errands. Many children with SM also have Sensory Integration ...