I have to disagree with you to some degree. There are definitely cases where the long canines are caused by disease or trauma. But, I have heard of a few cases where a kitten's adult teeth had just dropped and said kitten had "vampire fangs". I believe it is possible for a cat to have long or exaggerated canine teeth as a natural physical characteristic and not due to some sort of abnormal pathology. Though, just seeing pictures of vampire cats online, who knows what the cause is or what percentage is natural verse a health issue. I think when it appears in young cats, it is more likely to be a natural variant. But, if a cat, especially an older cat suddenly develops "vampire fangs", the cat should see a vet asap. Whether there is a specific gene that causes it, I have not clue. I am not an expert and don't pretend to be one. I am just fascinated by natural mutations in animals. I have seen a cat born with two sets of ears. So, to me at least, it is not out of the realm of possibility that some of these "vampire cats" are the result of a random mutation. If it weren't for random mutations, many cat breeds would not exist.That isn't caused by a gene. That is a cat in desperate need of a long overdue dental cleaning. Those fangs sticking out are being pushed out due to various things, perhaps oral tumors under the gums, or infected pockets. Those teeth will likely fall out eventually.