Siamese Cats and Congenital Heart Disease

by Michael

The Siamese cat has a long list of genetic diseases; longer than any other purebred cat. This is a shame. It is still in the top three most popular cat breeds probably because the Siamese is loyal and vocal. There is plenty of interaction between cat and person. One of the diseases reported more commonly in Siamese cats than other cat breeds is congenital heart disease:

  • Aortic stenosis – aortic valve of the heart does not open fully causing reduces blood flow, which can lead to shortness of  breath and difficulties in breathing.
  • PDA – Patent ductus arteriosus – the word “patent” in this instance means “open”. The condition is an open  blood vessel that should have closed after birth.
  • Endocardial fibroelastosis – thickening of the heart muscle and replacement with fibrous tissue.
  • Atrioventricular valve malformation – malformed heart valve

Signs in kittens with heart defects are:

  • kittens are small for their age
  • kittens are in poor condition
  • they don’t play as much as normal
  • kitten tires quickly
  • difficulty breathing
  • throbbing heartbeat

Left -sided heart failure causes:

  • dyspnea – shortness of breath
  • rales – crackling noise when inhaling air
  • hydrothorax – serous fluid accumulating in the pleural cavity. “Serous” means watery. The pleural cavity is the space between two membranes that line the lungs.

Right-sided heart failure causes:

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  • distended pulsating jugular veins
  • ascites – excess fluid build up in the space between the tissues that line the abdomen and abdominal organs.
  • hepatomegaly – enlarged liver.

Briefly, although not a congenital heart condition, a disease called Mucopolysaccharidosis VI is found in Siamese cats. This is a deficiency of arylsulfate B activity resulting in storage of glycosaminoglycan dermatan sulfate. This has serious development consequences:

  • skeletal abnormalities such as eyes spaced too far apart, small ears, flattened face, depressed sternum,  flattened chest.
  • Kittens are smaller than average with larger forepaws than normal. At five months there are gait abnormalities taking short steps while keeping the head low. These kittens cannot jump normally. A quarter of these kittens have hind legs weakness or paralysis at ten months.

I mention this disease because a visitor asked if there was a sex-linked genetic disease that affects Siamese cats (the male) which causes growth retardation, distended abdomen, paraparesis (partial paralysis of the lower limbs). The disease that I have referred to may be the cause. It appears not to be sex-linked however.

Source: Medical, Genetic & Behavioral Aspects of Purebred Cats – ISBN0-9634124-0-X – pages 155 and 156. Edited by Dr Ross D Clark DVM.


Useful tag. Click to see the articles: Cat behavior

Note: sources for news articles are carefully selected but the news is often not independently verified.

Michael Broad

Hi, I'm a 74-year-old retired solicitor (attorney in the US). Before qualifying I worked in many jobs including professional photography. I love nature, cats and all animals. I am concerned about their welfare. If you want to read more click here.

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3 Responses

  1. Terry says:


    How dominant is the gene for congenital heart defects in Siamese cats? I currently have a kitten with pleural effusion that can’t be more than an eigth Siamese at the most, but has the skeletal structure of the breed (one of her litter mates has the markings). She’s currently on Lanoxin but I’ve read that Chylothorax is common in Siamese cats, and that seems to be idiopathic.

    I’m wondering what the rate of ventricular disease is over chylothorax and the incident rate overall, as several of her litter mates have already been adopted and might express this gene.

    • admin says:

      Hi Terry, I am sorry but I can’t answer your question. It is difficult, almost impossible, to find answers to questions like yours. I am not even sure if there is an available answer! You might have tried Google Scholar, already. A search in Google scholar might throw up some useful information but you’ll have to buy the article if the abstract does not contain the information that you are looking for. Good luck in your search. I might do further work on this so might end up writing about it.

  1. January 29, 2015

    […] and how many are due to inbreeding of purebred Siamese? The original gene pool was pretty small. Siamese Cats and Congenital Heart Disease | PoC Given that they used to be famous for longevity, I was kind of surprised to read that they could […]

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