I am not really familiar with breed specific problems, but if you are saying that Persians are more prone to kidney problems, I would avoid all dry food and stick to lower phosphorus foods. High protein is a not cause of kidney problems. Cats in later stages of kidney failure may have trouble processing protein. Since cats are geared to get their moisture from their food and have a low thirst drive, feeding a dry food diet could cause chronic mild dehydration which is tough on the kidneys. Here is one vet's take on why dry food is not good for cats www.catinfo.org.