The Cause of Stuttering: Genetic and Brain Scanning Study Results

In stuttering, there are abnormalities in the connections between the speech planning part of the brain (A) and the speech execution part of the brain (B) on the left side.  This is a very limited part of the brain and does not affect intelligence or personality. This abnormality leads to moving the articulators (C) without a proper plan.  For approximately 70% of people this is caused by an easily identifiable inherited gene.  For the rest it is likely to be due to a latent gene or a gene that has been recessive for several generations. It may also be due to an abnormality of brain development due to damage (e.g., environmental toxins, bump on the head, high fever, infection, or lack of oxygen) at birth or in the first few years of development. 

Many people believe that if you have a gene for a disorder you will inevitably display that disorder but this is not true.  Genes are like light switches, they can be turned on and off by circumstances in the environment.  They may predispose a person to be smart, or stutter, or be an Olympic skater but if that switch never gets flipped that gene is not expressed.  A person will not stutter unless they have that gene, whether or not that gene is turned on and stays on depends on a number of factors.  Environmental factors like stress and interaction experiences do not cause stuttering but may “flip the switch” and turn on an existing stuttering gene.  Most experts agree that therapy before age 5 changes the brain and manipulates the expression of genes to prevent or at least significantly minimize long-term stuttering.

image indicating speech planning part of brain and image of articulators (lips)

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