Hmm... Could it be they just didn't have a proper nutritional diet?
You can also die if you don't eat. Is that also a 'broken' gene?
It's amazing the arrogance of some...
My cat wouldn't eat fruit on a bet. Once in a blue moon he'll eat some leafy stuff just to throw up. Even as do cats and dogs, we have a gene for making vitamin C so that we don't have to eat it. But ours is broken.
Thus your response is so far inadequate. You are refusing to see the problem so you don't have to answer it. That doesn't look very convincing to anyone who has already seen the problem for himself and was waiting for a real answer.
It's amazing the powers some attribute to willful ignorance.