EDIT: Let's cool it with the downvotes, dudes. We're not out to cut funding to your black hole detection chamber or revoke the degrees of chiropractors just because a couple of us don't believe in it, okay? Chill out, participate with the prompt and continue with having a nice day. I'm sure almost everybody has something to add.
It's not thought to be genetic otherwise it would be heritable and its clearly not. It would also have self extinguished before too long if it ever got a foothold in the first place.
It's likely a construction issue having something to do with something that happens in the womb rather than to do with the blueprints.