It looks like this bicolor Sphynx cat has been quietly body building since he was a kitten. He is the Arnold Schwarzenegger of the cat world. And the hairlessness highlights his condition. The Reddit title is: “House cat suffering from Myostatin-related muscle hypertrophy – a rare condition that causes muscles to grow excessively large”. So, what is it?
The condition as you can see causes a gain in muscle mass. It means that there is a deficiency of myostatin protein due to a spontaneous genetic mutation.
Myostatin-related muscle hypertrophy is a rare condition characterised by reduced body fat and increased muscle mass. Individuals suffering from it have up to twice the usual amount of muscle mass and increased muscle strength. It is not known to cause any medical problems. It affects people and other animals as well.
In humans it is caused by a genetic mutation in the MSTN gene. This gene provides instructions for making a protein called myostatin. This protein is active for skeletal muscles such as for the legs in cats both before and after birth. The protein normally restrains muscle growth to prevent them growing too large. The mutation reduces the production of the functional myostatin which in turn leads to an overgrowth of muscle tissue.
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“The gym keeps him there to control the population of gym rats.” – Reddit user
In genetic terms the inheritance is ‘incomplete autosomal dominant’. The word “autosomal” means not sex-linked. In other words, either six can have the condition. If a person, or in this instance, a cat, carries both copies of the mutated gene i.e. they are homozygous to the condition they will have significantly increased muscle mass and strength. If they have one copy of the gene, they will also have increased muscle bulk but to a lesser degree.
The picture of the cat was shared on the r/Damnthatsinteresting subbreddit by user bsmith2123. Having written for this website for 14 years, this is the first time that I have seen this condition in a cat. And it is very interesting because, as mentioned, it has occurred in a hairless cat which makes the condition all the more visible. The picture is extraordinary. I can’t see any problem in him controlling his territory against invading cats. Although as he is hairless, he must be an indoor cat.
Only for the sake of convenience has I referred to the cat in the masculine. This could be a female. I refuse to refer to cats as ‘it’.