Proof that stuttering is physical came in 2009, when Chinese scientists determined that the brains of people who stutter have elevated levels of dopamine, a neurotransmitter known as the “feel-good chemical” because it creates sensations of well-being. “Irregular dopamine levels were linked to genetic mutations in stutterers,” said Gerald Maguire, an associate professor of clinical psychiatry and the Kirkup chair of stuttering treatment at the University of California at Irvine School of Medicine. “Indeed, dopamine may play a role in up to 70 percent of stuttering cases.”
Problems with three other genes likely cause stuttering in an additional 9 percent of cases, found a 2010 study at the National Institute of Deafness and Other Communication Disorders. “All three of these genetic glitches affect how cellular components in the brain are broken down and recycled,” said lead researcher Dennis Drayna, a geneticist at the institute. “The enzymes in key brain cells either don’t function, or are misrouted to the wrong part of the cell.”
Since they realized that stuttering is linked to brain chemistry, scientists have discovered that the drugs asenapine, olanzapine and risperidone, which all affect neurons in the brain, are clinically effective in treating it. “The Food and Drug Administration has yet to approve these drugs for this use, but some doctors are prescribing these medications ‘off-label’ to stuttering patients,” Maguire said. “Doctors are allowed to do this because the FDA has already sanctioned these drugs as safe and effective for other uses.”
https://www.pbs.org/wnet/need-to-know/health/stuttering-it-lurks-in-dna/9188/