Note, some people do have genetic conditions that affect their ability to take IQ tests - these include Down syndrome, phenylketonuria, even IBS if you’re giving them a test without bathroom breaks.

The point of knowing this is so you can treat it. You can raise the IQ of a phenylketonuric by not feeding them Diet Coke. It doesn’t seem like the HBD people would be happy seeing this, because they just want to prove someone is inherently superior and someone else isn’t.