Spinal Muscular Atrophy

Motor neurons in the spinal cord carry the signal that tells muscle to contract. In SMA the motor neurons serving the hind limbs are lost, and the muscle they supply wastes away from disuse. The cause is a deletion affecting the LIX1 gene.

Like PKdef, SMA is autosomal recessive: two copies to be affected, one copy to be a healthy and entirely invisible carrier.

Affected kittens are born looking normal and develop normally at first. From roughly three to four months the hind end starts to sway, the kitten stands with an unsteady wide-legged stance, muscle over the hips thins, and jumping becomes difficult and then impossible.

The condition is not painful and affected cats can live a long life, but they are permanently impaired and need an adapted indoor life. There is no treatment that restores the lost neurons — which places the entire burden on prevention.

SMA is essentially a Maine Coon problem: it was characterised in this breed and the mutation is carried in Maine Coon lines rather than being a general feline disease.

Because the first signs appear at three to four months, an affected kitten frequently leaves for its new home before anything is visible. The new owner discovers it. This is the clearest possible argument for testing the parents rather than watching the litter.

The same recessive logic applies as with PKdef, and so does the same rule: both parents tested, no carriers bred. Two clear parents cannot produce an affected kitten.

Testing is done at Langford Vets, University of Bristol, and the report for each cat is tied to that cat by microchip and registration number. A sample report is published on our genetic testing page.