The defining feature of selective mutism is an ability and willingness to talk in certain settings with certain people (usually in the home with close family members), but a failure to speak in other settings where speech would be expected (such as at school with teachers and peers). It is an intriguing anxiety disorder where the typical patient is a young child.
The most notorious case of selective mutism on record, however, involves not one young child but rather a pair of children, identical twins who presented the disorder throughout their lives. In the 1986 best-seller The Silent Twins, author Marjorie Wallace documents the fascinating lives of Jennifer and June Gibbons, English twins with selective mutism who were eventually incarcerated for the many crimes they committed together as teens and adults, including theft and arson. Multiple attempts at treatment proved fruitless to improve the twins’ communication with others besides themselves. Only upon the death of one twin did the other increase her speech.
The Twin Factor
Though the Gibbons sisters’ criminal history is unusual for selective mutism, there is a growing sense among clinicians that their status as twins is not. It has long been known that certain demographic characteristics – such as female gender, immigrant status, and bilingual household – are risk factors of selective mutism. But a reading of the scientific literature on selective mutism suggests that twinship may constitute another risk factor.
The percentage of twins in the general population is 3.3 percent and for monozygotic (“identical”) twins is 0.4 percent.1 However, as early as 1999, twin researcher Nancy Segal noted that 5.7 percent of subscribers to a national newsletter on selective mutism were families with twins. In one of the first scientific studies of selective mutism, six percent of the participants were twins who shared the disorder.2 The presence of twins has since been noted in several samples of selectively mute children drawn by other researchers.3,4
Though the scientific literature on selective mutism is sparse, there have been at least six published case studies on selectively mute twins, all of them involving pairs of identical twin girls.5,6,7,8 The general consensus from these papers is that twins with selective mutism may be more difficult to treat than singletons. Repeatedly mentioned as maintaining factors are the twins’ close relationship and mutual reinforcement of each other’s lack of speech with peers.
How Can We Treat Selective Mutism in Twin Children?
Another paper has reported on the neuropsychological assessment of two more sets of selectively mute twins, both fraternal and female.9 Although each set of twins presented with differing neuropsychological profiles, both had tendencies to interact almost exclusively with each other, but showed improvements in communication when separated.
Whether the literature described above indicates a true over-representation of twins among selectively mute children, it does suggest that professionals who treat the disorder are likely to encounter one or more sets of twins over the course of their careers.
I specialize in the behavioral treatment of selective mutism and have treated three pairs of twins within the space of four years – dizygotic girls, monozygotic girls, and monozygotic boys. I, too, have found that it is preferable to place the siblings in separate classrooms to deflect against their tendency to speak only to each other (though I have successfully treated twins who were placed in the same classroom). And though it is admittedly a small sample, I have learned from my experiences with these children and from consultation with colleagues that treatment needs to involve both separate and joint sessions; that is, the twins need to speak to others when separated and when together.
Katherine K. Dahlsgaard, Ph.D., is a licensed clinical psychologist specializing in Cognitive Behavioral Therapy for children, adolescents, and young adults. She focuses on anxiety disorders, including selective mutism, social anxiety disorder, and OCD, among others. Dr. Dahlsgaard is an accomplished lecturer, published author on child development and mental health, and holds prominent positions at the Anxiety Behaviors Clinic and the Picky Eaters Clinic in The Children’s Hospital of Philadelphia.