This is purely my hymblue opionion. I think at the very core, stuttering is neurological, and in most cases neurodevelolmental. Whether hereditary or not, I think genes certainly have an impact. And I think the research on that is very limited at this point. Example: My son and I have a mutated gene that has been noted for speech delays but it's not in any stuttering research. I think what compounds it is that stuttering can have other neurological comorbidities, such as ADHD, so depending on what gene may be involved, and if there is a comorbidity, it will affect the severity. ADHD is prevalent amongst stutters and since ADHD affects emotional regulation and hyperfixation that will amplify the engative feedback loop, feelings, sensitivity. Even if you don't have ADHD, that will still compound the stuttering. Then you combine that with this all leading to a heightened nervous system, it all turns into an unruly monster.