MTHFR gene mutation that reduces the body's ability to filter out toxins > 72 doses of vaccines with aluminum adjuvants on the childhood schedule > neurotoxic aluminum crosses the still developing blood brain barrier > brain damage to speech areas and/or aluminum conducts electricity which stimulates too much dopamine production in a speech area > stuttering this is my theory, for some reason there's a dearth of research on stuttering so it's impossible to prove right now of course for sure it's affected by your emotional state just like everything involving the brain is, but you're right, it's all just brain chemistry