Heart and Hip Problems in Large Cat Breeds: What Owners Should Know

Several large breeds are more prone to hypertrophic cardiomyopathy (HCM), the thickening of the heart muscle: Cornell lists the Maine Coon, Ragdoll, Norwegian Forest Cat, Siberian and British Shorthair among them. Gene tests flag known mutations, but a positive test is not a diagnosis. Hip dysplasia is also common in screened Maine Coons. Your vet decides on screening.

This page explains what the conditions are, what the tests can and cannot tell you, and what to ask at your next visit. It does not diagnose or treat anything. If your cat is breathing fast, collapses or suddenly cannot use its back legs, call a vet straight away.

What is HCM, and which breeds are at risk?

HCM is a disease in which the wall of the heart’s main pumping chamber thickens. Langford Vets at the University of Bristol calls it “the most common form of heart disease found in domestic cats.” Cornell Feline Health Center lists breeds in which it is more prevalent: Maine Coon, Ragdoll, British Shorthair, American Shorthair, Sphynx, Bengal, Chartreux, Norwegian Forest, Siberian and Persian.

The difficulty is that “many cats with HCM do not appear to be ill,” in Cornell’s words. Cornell names echocardiography, an ultrasound of the heart, as “the gold standard” for diagnosis: non-invasive and very accurate.

What a gene test can and cannot tell you

Two breed mutations have tests. In Maine Coons the test looks for the MYBPC3 A31P variant; in Ragdolls, the R820W variant. How common the Ragdoll variant is depends on the population studied: a 2014 study of Ragdolls tested in the British Isles found it in 27 percent, while Langford Vets gives a figure of around 13 percent.

Cornell says genetic results should be interpreted with a veterinary professional, because “not all cats that have these mutations will develop the condition.” A 2013 study in the Journal of Veterinary Internal Medicine estimated the penetrance of A31P in Maine Coons at 0.08 for one copy and 0.58 for two, rising with age. Langford Vets says Maine Coons with two copies are “more likely to develop moderate to severe disease earlier in life,” and recommends considering heart ultrasound for cats with a positive result.

Hip dysplasia in Maine Coons

Hip dysplasia is a loose hip joint, caused by a shallow socket or a misshapen head of the thigh bone. Two screening studies suggest it is common in Maine Coons:

• US records. A study of Orthopedic Foundation for Animals records, published in the Journal of Feline Medicine and Surgery, found hip dysplasia in 24.9 percent of screened cats, 27.3 percent of males and 23.3 percent of females. The youngest affected cat was 4 months old. The authors caution against applying the figure to other groups.
• Swedish screening. A 2019 study of 5,038 pedigree Maine Coons found some radiographic signs in 37.4 percent, with no sex difference. It found a genetic link between hip dysplasia and body mass, and that selecting for healthier hips over eight generations improved scores.

Both studies counted cats sent for screening, so they are not your cat’s odds. They are a reason to watch a big cat’s movement.

Signs to mention to your vet, from International Cat Care’s arthritis guidance: reluctance to jump up or down, stiffness after rest, difficulty with the litter tray and less grooming. At home, the same source suggests steps or a ramp to high places and a litter tray with at least one low side. Keeping the cat lean matters too; see body condition in the care section.

Spinal muscular atrophy (SMA)

SMA is an inherited condition of Maine Coons that causes loss of the nerve cells controlling the limb muscles. Langford Vets says signs “become apparent by 3-4 months of age,” with an abnormal gait, and that affected cats are typically too weak to jump correctly by 6 months. It is autosomal recessive, so a cat must inherit two copies to be affected. Langford notes that affected cats “can live relatively normal lives indoors and appear not to be in pain.”

How the gear fits in

A cat with stiff hips or a heart condition still needs to climb, play and use its box. Low-entry litter boxes, wide steady perches and ramps help. See litter boxes for large cats and cat trees for large cats, and read how big Maine Coons get for size and lifespan.