Spinal muscular atrophy (SMA) is a hereditary neurodegenerative disease of the Maine Coon characterized by progressive loss of motor neurons in the spinal cord. Without innervation, muscles atrophy gradually and symmetrically, especially in the limbs and trunk. Affected kittens begin weakness around 3-4 months and develop a progressive but disabling neuromuscular condition. There is no treatment; DNA testing prevents the production of affected litters.

Restricted to the Maine Coon. The carrier frequency described in breed surveys is moderate and variable by country and line (limited data). Systematic testing in breeding animals keeps cases at low levels in the populations that apply it.

- Onset between 12 and 16 weeks of life, rarely earlier
- Symmetrical muscle weakness and atrophy, more marked in the hind limbs and trunk
- Abnormal gait with short steps and tendency to rest in sternal recumbency
- Difficulty jumping and maintaining elevated postures
- Thin musculature and muscle tremors
- Slow deterioration that usually stabilizes without recovering what was lost
- Preservation of general condition, appetite and behavior

SMA of the Maine Coon was described in the late 1990s and early 2000s in cats of the breed in North America, being characterized as a motor neuron neurodegeneration with neurogenic muscle atrophy. Genetic studies identified a genomic deletion affecting the LIX1 gene, responsible for the disease in the breed. Since the availability of the carrier test, Maine Coon breeders incorporated it into the usual breeding panels (along with HCM and PKD screening), notably reducing cases.

- Test Maine Coon breeding animals before the first mating, along with the usual breeding panel of the breed
- Never cross carrier with carrier: 25% risk of affected kittens
- A carrier can be crossed with a clear individual, prioritizing clear offspring to eliminate the allele
- In kittens with progressive muscle weakness from 3-4 months, request neurological assessment and genetic testing
- Record the results alongside the pedigree and share them with the breed club

The differential diagnosis includes hereditary feline myopathies, muscular dystrophy due to dystrophin deficiency (described in domestic short-haired cats and crosses), polyneuropathies (diabetic, deficiency-related) and myositis. Electromyography shows denervation and muscle biopsy shows grouped neurogenic atrophy; creatine kinase is normal or slightly elevated. Affected cats can live as companion animals with an adapted environment (ramps, low heights), although they must never be used in breeding.

1. Fyfe JC et al. 2006, deleción de ~140 kb asociada a la atrofia muscular espinal felina (PMID 16899656)
2. Wakeling EN et al. 2012, degeneración del motoneurona inferior en el modelo felino de SMA (PMID 22120001)
3. Kopke MA et al. 2022, miopatía miotubular ligada al X (MTM1) en un Maine coon: diagnóstico diferencial (PMID 35962713)
4. OMIA:001402 Atrofia muscular espinal felina