1% is not as rare as you think and due to confirmation bias and the fact that the majority of PWS are mild ones so you may be very hard to meet with another PWS but you can google many diseases/disorders that have lower incidence than 1%, some of which are more devastating than stuttering if you really want to compare the incidences. Afaik Down's Syndrome(no offense to the Down patients sorry) is way more rare than stuttering and it is way more devastating.