I just got back from a Continuing Education seminar where one of the speakers talked about liver diseases. There are several congenital and/or hereditary liver diseases that veterinarians see in practice that are expensive to diagnose and treat. Sometimes, even surgery is required to correct/treat the condition.
Not all insurance companies offer policies that cover congenital/hereditary diseases. Some companies offer limited coverage. There are several that cover hereditary, but not congenital diseases, and some companies cover both.
In my book, I outline all these differences and go more into detail as to why such coverage is important - from a veterinarian's perspective. You should make this important factor a key point when doing your research to find the best company and policy for your pet.
I was also reminded of something that I'll recommend to you. Perhaps your veterinarian already recommends it to you. When you take your pet in for an annual or semiannual wellness examination, it's a good idea to do some basic blood tests that can help uncover e.g. liver disease (even though your dog or cat may appear in perfect health to you) before it advances to the point that the prognosis for recovery isn't good. Sometimes our pets don't show symptoms until a disease is advanced and a good wellness program can detect disease even before your pet appears ill.
I'll give an example. Chronic hepatitis in dogs is more commonly seen in certain breeds, and some of those breeds have actually been identified as having a genetic basis for the disease. If you have one of those breeds and your pet's insurance policy excludes hereditary conditions, you'll end up paying for the diagnosis and treatment out-of-pocket - yourself.
One way to detect chronic hepatitis early-on is by detecting an elevated liver enzyme (ALT) usually between the ages of 2 and 5 years old. Chronic hepatitis isn't the only problem that can cause the ALT to be elevated, but it is a red flag that warrants further investigation. In some dogs, if the condition is not recognized until the dog is showing symptoms, the prognosis is unfavorable for response to treatment.