Mode of inheritance of spinal muscular atrophy in Maine Coon cats

You may have heard of spinal muscular atrophy (SMA) in Maine Coon cats. It is one of those inherited diseases, several of which affect the Maine Coon, and as indicated in the title the muscles of the back become weakened which interferes with their normal activities such as jumping and walking. 

These are not Maine Coons. Image in the public domain (believed).

The cause is due to a loss of neurons in the first few weeks of life. The weakness becomes apparent at 3-4 months of age. Kittens walk with a strange gait and their hocks nearly touch the ground. The hock is the area from the end of the foot to the first part of the leg.

RELATED: 15 facts about spinal muscular atrophy in Maine Coon cats.

There should be no difficulty in diagnosing SMA being present in a Maine Coon cat. The disease is inherited as an autosomal (non-sex-linked) recessive mutated genetic trait.

Genes come in pairs. If a Maine Coon cat has one copy of the mutated gene and one copy without the mutation they are referred to as a carrier or heterozygous to that condition. The cat will not be affected by SMA but it can pass the mutation onto its offspring. The cat should only be mated with clear cats i.e. cats without any mutated genes.

There are three conditions that a cat can be in concerning SMA in terms of their ability to pass it on to offspring. The cat can be clear or 'homozygous normal' meaning there is no mutated gene and they will not develop SMA. The cat cannot pass on SMA to their offspring and it can be mated with any other cat.

Affected kittens with two copies of the mutated gene i.e. 'homozygous affected' will pass on the mutated gene to their offspring every time.

The chart below sets out the mode of inheritance of this disease with reference to the various combinations of mother (dam) and father (sire) and whether the parents are clear, carriers or affected as described above.

Chart showing mode of inheritance of SMA in Maine Coons. Image: Laboklin.