A press release issued by Banfield: The Pet Hospital states that
Young feline patients (especially cats under the age of one) appear to have the greatest risk of developing renal failure linked to the recalled diets.
Presumably this observation is based on cases seen at Banfield hospitals, but the press release does not give details. Because Banfield has veterinary hospitals across the United States and uses a centralized computer system, they are in a unique position to be able to aggregate data collected by veterinarians. Their press release notes that they are assisting the FDA but does not specify in what manner.