Picture of a muscle-bound Sphynx cat

This is my second picture of a muscle-bound hairless (Sphynx) cat which shows the condition that they are suffering from very clearly. Click here to see the other image. It is a very peculiar condition. Perhaps it is advantageous to the cat to have these huge muscles? But apparently not (see below). Are there any downsides? This cat looks like a ‘heavy’ from a gang of mafiosi criminals standing on a street corner about to smoke a fag.

Firstly, myostatin-related muscle hypertrophy affects people and other animals. It’s a very rare condition causing reduced body fat and increased muscle. The individual affected has twice the usual amount of muscle mass. And they have increased strength usually but not commensurate with the increase bulk on my understanding. It is a genetically inherited condition i.e. a congenital condition.

My research indicates that the lack of myostatin results in excessive muscle growth but “impaired force generation”. That implies that the muscles that we see on this Sphynx cat does not necessarily translate to a proportionately higher strength.

In fact, it appears that the muscles created are weaker than wild-type muscles. Myostatin is a protein produced by the cat which inhibits muscle cell growth. If there are deficiencies in this protein the muscle piles up and the cat bulks up.

It gives the appearance that the cat has been in the gym lifting weights for the past five years! The condition is also seen rarely in cattle, sheep and some dog breeds including whippets (see photograph below which is equally extraordinary).

The condition is caused by the genetic mutation of a recessive gene which has to be homozygous in the affected animal. That means there has to be two copies of the gene in the animal, one inherited from one parent and the other inherited from the other parent. That’s my understanding. If a cat is heterozygous for the gene, they don’t have this bulked up appearance but they are also apparently unusually muscular.

If this sort of muscle mass was advantageous to survival, we would have seen a lot more of it within the domestic cat population and other species but we don’t. Therefore, we have to conclude that it is not beneficial in that respect.

It can have a negative impact because of the bulk. For example, I expect cats with the condition to have a slower top speed and have less endurance. If the animal is heterozygous to the condition it can help with speed such as for horses and whippets.

Below are some more articles on genetic mutations.