SMA in Maine Coons: Understanding Spinal Muscular Atrophy#

I remember the first time I saw a kitten with SMA. It was at a cat show, years ago, huddled in a breeder’s “pet quality” pen. He was a stunning Red Tabby, bright-eyed and playful, but when he tried to jump for a teaser toy, his back end seemed to wobble and collapse. He didn’t seem in pain—he just looked like a drunk sailor trying to navigate a rocking ship.

“He has SMA,” the breeder told me, sadly. “He’s perfectly healthy otherwise, but his rear legs just don’t get the signal.”

Spinal Muscular Atrophy (SMA) is one of the specific genetic diseases that affects the Maine Coon breed. Unlike HCM (heart disease), which is a silent killer, SMA is visible, strange, and heartbreakingly manageable.

If you are buying a kitten, or if your young cat is starting to walk with a strange “sway,” this guide will explain exactly what is happening inside their spinal cord.

What is SMA? (The Science)#

SMA is a hereditary neurodegenerative disorder. Specifically, it causes the loss of motor neurons in the lower spinal cord.

Think of the spinal cord like a fiber-optic cable sending messages from the brain to the muscles. In a cat with SMA, the specific “cables” that connect to the hind legs and lower back begin to fray and die off. The muscles, receiving no signals to move, begin to atrophy (waste away) from disuse.

It is caused by a deletion in the LIX1 gene. It is an Autosomal Recessive trait. This is crucial for breeders and buyers to understand:

Clear: The cat has no copies of the gene.
Carrier: The cat has one copy. They are perfectly healthy but can pass it on.
Affected: The cat has two copies (one from mom, one from dad). They will show symptoms.

The Symptoms: The “Sway”#

SMA is a juvenile disease. You won’t see it in a newborn, and you won’t see it develop suddenly in a 5-year-old cat. The timeline is very specific.

3-4 Months Old: This is when symptoms usually appear. The kitten might seem a bit clumsy. You might notice a slight tremor in their hind legs when they are standing still eating.

5-6 Months Old: The classic symptom appears—the SMA Sway. When the cat walks, their rear end sways from side to side dramatically. When they stand, their hocks (ankles) might touch each other (cow-hocked).

Jumping Issues: This is usually the dealbreaker for the cat. They will try to jump onto the sofa, but their rear legs don’t provide the thrust, and they might scramble or fall.

Amelia’s Note: Importantly, SMA is not painful. The cat doesn’t feel hurt. They are fully mentally alert, they eat well, and they play. They just have a physical disability.

Diagnosis: The DNA Swab#

In the past, vets had to do expensive electromyography (EMG) or muscle biopsies to diagnose this. Today, we have a simple cheek swab.

If your kitten is showing these signs, do not wait. Order a specific SMA DNA test from UC Davis or Wisdom Panel.

Breeders: If you are buying a kitten, the parents must be tested. Two carriers should never be bred together. If a breeder says “We don’t test for SMA because it’s rare,” walk away. It is rare because good breeders test for it.

Quality of Life: Can They Live Happy Lives?#

This is the hardest question I get asked. “Should I euthanize a kitten with SMA?”

Generally, No. Unlike human SMA (which can be fatal and affect breathing), Maine Coon SMA is usually restricted to the hind limbs and lower back. It is not typically fatal.

Most SMA cats live a normal lifespan (12-15 years). They live as “indoor-only” special needs cats. They need:

Ramps: To get onto sofas and beds (see our Senior Mobility Guide for ramp ideas).
Low Litter Boxes: High sides are difficult for them to step over.
Carpet/Rugs: Slick hardwood floors are a nightmare for SMA cats because they can’t grip.

However, the atrophy can sometimes progress to affect the front legs or breathing in severe cases, though this is less common.

The Bottom Line#

SMA is a preventable tragedy. It only exists because two carriers were bred together. If you are a pet owner, you likely never have to worry about this if you bought from a responsible breeder who showed you the negative test results for the parents.

If you have an SMA cat, know that they can be wonderful, loving companions. They may walk funny, but their hearts and purrs are just as big as any other Maine Coon.

References#

Fyfe, J.C. et al. (2006). “An ~140-kb deletion associated with feline spinal muscular atrophy implies an essential LIX1 function for motor neuron survival.” Genome Research.
UC Davis Veterinary Genetics Laboratory. Spinal Muscular Atrophy (SMA) in Maine Coon Cats.
Journal of Heredity. (2007). “Inheritance of spinal muscular atrophy in Maine Coon cats.”
Cornell Feline Health Center. Genetic Diseases of the Maine Coon.
OFA (Orthopedic Foundation for Animals). DNA Testing Statistics for Maine Coons.