Can stuttering be caused by trauma?

While trauma in the form of emotional distress can aggravate stuttering, it has not been found to cause it. Rather than a cause, stuttering is a trigger-- something that sets off a disorder in individuals who are genetically predisposed to developing the disorder. If trauma had caused stuttering, psychotherapy should be effective in treating it; yet psychotherapy has been unsuccessful. (https://www.stutteringhelp.org/stress-stuttering)