My therapist said it has more to do with learnt behavior than 🧬 genetics. You learn it consciously or subconsciously how to speak in certain situations and before you know it, it becomes your way of speaking... My two brothers do stutter besides me, and 3 don't. May dad only stammer a bit when he's angry 😡. Dad is actually an excellent speaker.. My big bro stammer but don't give fk about it, doing his business really well. My other little bro is Hafiz - learnt whole Quran by heart. Whenever wherever he leads prayer or do recitation, you can't notice. It's just me who's too self conscious.