To be fair, not a single character in the Dune universe is a regular human. They're the equivalent of those plum-sized GMO strawberries at the grocery store.
In a 100 years it will be completely normal to have painless and routine medical transhuman enhancements. I'm getting a variable sized dick just as a courtesy enhancement!
But that's not what people mean when they say GMO in this context. Otherwise they would use GMO in front of every food item name unless they were referring to foraged goods with no domesticated equivalent.
I'm pretty sure that was in God Emperor. Heretics is the one where that same man acquires super sex powers that are so powerful he can overwhelm the sex powers of a clan of violent sex women and subjugate them to his will.