It might be rare but some people are born with 6 fingers
Humans have 5 fingers on each hand, 2 legs , 2 arms, one head
It might be rare but some people are born deaf. Humans still have 5 senses , hearing sight touch taste and smell
Sometimes things aren't quite right. It can be distressing to those people
Because they know there is something wrong, something that is observable by others who can also see something wrong
If it's not complicated for them why do you want to make it so ?
Sex is binary - baby makers and baby havers and people who can't do one or the other are real humans with feelings not sone hypothetical creature to muse over