Genetic basis of Spinal Muscular Atrophy in cats - especially documented in Maine Coon cats, is caused by a large deletion mutation on chromosome 1 affecting the LIX1 gene. The exact function of LIX1 is not fully understood, but it is highly expressed in the spinal motor neurons and is believed to be involved with RNA metabolism. The disease is inherited in an autosomal recessive pattern, meaning a cat must inherit two defective copies of this gene (one from each parent) to develop the disease. Carriers (with one mutated copy) do not show symptoms but can pass the mutation on to offspring.
Pathophysiology - The deletion causing SMA leads to a loss of motor neurons in the lower spinal cord. This results in progressive muscle weakness and atrophy, primarily affecting the hind limbs. Motor neurons lose their function, leading to impaired nerve signals to muscles, causing muscle wasting and unsteady gait. Clinical signs usually appear around 3 to 4 months of age, with symptoms including tremors, abnormal posture, difficulty jumping, and muscle weakness. The disease progresses over several months, stabilizing around 8 months, and while disabling, it is not painful or fatal. Cats generally retain mental alertness throughout.
Complications - Progressive muscle atrophy and weakness, starting in the hind limbs. Difficulty walking and jumping, with some severely affected cats using front legs to crawl. Potential respiratory involvement in severe cases. Disability due to muscle loss but not painful or life-shortening. Stable but variable severity of symptoms lasting for years.
Why This Matters to Breeders and Vets - Genetic testing for SMA is available and important to identify carriers and affected cats. Carriers are asymptomatic but matings between two carriers can produce 25% affected kittens. Breeders use testing to avoid breeding affected cats and reduce disease prevalence in Maine Coons. Veterinarians need to recognize early symptoms and differentiate SMA from other neuromuscular diseases. Knowledge of SMA helps manage affected cats' welfare and educate owners on prognosis and care.
Summary - Spinal Muscular Atrophy in cats is a hereditary, autosomal recessive neurodegenerative disorder caused by a deletion affecting the LIX1 gene, primarily in Maine Coons. It leads to progressive loss of lower spinal cord motor neurons, resulting in muscle weakness and atrophy, especially in the hind limbs, with symptoms appearing at about 3-4 months of age. While disabling, the condition is non-painful and non-fatal, with affected cats often living several years. Genetic testing is essential for breeders and vets to manage the disease and reduce its occurrence in cat populations.