It's interesting that you should mention smell, since I was born without a sense of smell - the term is anosmia. It is very poorly studied, and most studies deal with people who lose their sense of smell due to neurological diseases or head trauma.

In my case it's clearly genetic (my mom and her dad both can't smell), and almost no one studies it. From what I've read I'd much rather be born without a sense of smell than lose it, since that can be very traumatic.