This is a copy of the most recent official Bengal HCM positive list.
https://spreadsheets.google.com/spreads ... utput=html
HCM is a dominant disease so only one parent needs to have HCM for offspring to be affected. The probability of an offspring from an affected parent also being affected is at least 50%.
With a positive cat, one of its parents will have the gene and its siblings will have a 50% chance of also having the gene. What has been found in Bengals is that some will be diagnosed or die very early of the disease, some will be diagnosed or die at about 3 years of age and some at 4,5,6 or even older, we do not know as yet in Bengals whether that is due to variation of the effects of one gene, or whether that is due to many different genes causing HCM. Many, many different genes have been found to cause HCM in humans so I cannot see it would be any different in cats.
HCM is difficult to manage because it is a progressive disease so a scan may be negative at 2 to be positive at 3 but by that time many cats have had loads of kittens. However as some cats will have signs very early on, scanning is important to do before breeding and annually thereafter to pick up the disease as quickly as possible and remove affected cats from breeding programs.
Of course inbreeding around a cat that has the disease will increase the chances of kittens being born with the gene. So inbreeding as well as locking in desirable traits can indeed "lock in" undesirable ones too, like genetic diseases.