/u/Order_a_pizza has a wonderful answer. I'll just add some context to your question, as a genetics researcher (with a stutter). First off, neurological and behavioral traits are super complicated, and a complex condition like stuttering is unlikely to have one responsible gene or mutation, but rather many that all work together. FOXP2 has been implicated in speech pathologies, but there needs to be a lot more research done to say anything conclusive about what it does and how its mutations relate to phenotype. It was first identified when [one family with severe inherited stuttering](https://pubmed.ncbi.nlm.nih.gov/9462748/) was found to have this rare mutation. The thing is, everyone has mutations all over their genomes, including within FOXP2, so we can't say much about whether particular mutations cause stuttering or not. This [FOXP2 overview](https://www.ncbi.nlm.nih.gov/books/NBK368474/) talks about FOXP2 deficiencies in severe cases, but they even say that the prevalence of these mutations in the severe cases are super low. [This research article](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4099264/) found that, out of 875 stuttering cases, only one had a mutation in FOXP2. Common mutations and rare mutations were not much different between those with a stutter and those without. All that is to say, your genetics aren't as deterministic as people tend to think, and scientists often can't look at your genome and pinpoint exactly what is causing a problem. In the case of us people who stutter, it usually has nothing to do with FOXP2. Second point to bring up, the 23andMe-like genetic tests don't actually sequence the genome. They pick (many) known, specific points in your DNA sequence and ask "Does this predefined DNA base exist here?" The tests probably won't test for many of the more rare FOXP2 mutations that exist out in the population. /u/Order_a_pizza says they had exome sequencing done, which is actual sequencing and will let you know, without predetermining which mutations to look for, exactly what mutations you may have.