It is rare for those with PWS to breed. Their learning disabilities, along with their inability to control their emotional swings, are incompatible with pair bonding: their overwhelming drive is hunger rather than sex or anything else. This is a recessive trait that burbles along without needing those who express it to breed in order for it to be passed along. Try not to channel Mengele before you get a basic understanding of genetics rather than guhnetiks, ok?