Genetic Welfare Problems of Companion Animals

Ragdoll

Hypertrophic Cardiomyopathy

Outline: Approximately 30% of Ragdoll cats have a genetic mutation that makes it likely that they will develop hypertrophic cardiomyopathy (thickening of the muscle walls of the heart). Over time this condition leads to heart failure and/or other complications such as increased risk of blockage of major blood vessels by blood clots. Heart failure causes increasing discomfort and malaise in affected animals which can occur over a prolonged period. Blockage of blood vessels causes severe pain. Animals with the genetic mutation that causes this condition can be detected before the reach the age they are commonly bred at using a specific genetic test and ultrasound scanning of the heart. It is thought that the disease could be rapidly eliminated by not breeding from affected animals.

Summary of Information

(for more information click on the links below)

1. Brief description

Hypertrophic cardiomyopathy (HCM) is the commonest form of heart disease in cats and it is very common in the Ragdoll breed. With HCM the heart wall abnormally thickens (Liu et al 1981). This thickening causes multiple problems and at some stage prevents normal heart function. Heart failure develops. The severity of the heart failure progresses and causes death - either suddenly, due to the heart failing to pump blood adequately around the body or from the effects of a thromboembolus (a clot causing blockage of a blood vessel), or after progressive complications caused by poor circulation and fluid build up in the chest and lungs affecting breathing.

In HCM some of the heart muscle cells do not work adequately because of a genetic fault. The normal unaffected heart muscle cells therefore have to work harder to compensate and, over time, they increase in size (hypertrophy). This causes abnormal muscle thickness in a heart that cannot work adequately.

Cats with heart disease, but without heart failure, will very likely appear normal to their owners. Veterinary surgeons may notice abnormalities on examining the cat eg hearing a heart murmur or an abnormal heart beat or rhythm. Other signs of heart disease and failure are detected using diagnostic equipment such as a chest radiograph, electrocardiogram (ECG) and, most importantly for HCM, ultrasonography.

2. Intensity of welfare impact

The intensity of the welfare impacts of this disease depends on the degree of heart failure and secondary effects that it causes. Many cats with HCM do not have heart failure and have no welfare problems. However, in severe and terminal heart failure, the presence of fluid inside the lungs (pulmonary oedema), makes breathing very difficult and laboured; a condition that can be assumed to be very unpleasant.

Thromboembolic disease (in which a blood clot forms and blocks a blood vessel) can occur as a consequence of HCD, causing severe pain and distress. It is also difficult to treat and some cats may undergo treatments lasting from days to weeks and may still end up with the cat having to be euthanased. Unfortunately, Ragdolls, which are homozygous for the condition are often severely affected and develop heart failure and thromboembolisms before two years of age (Meurs 2010).

Investigations of heart disease and heart failure often need to be extensive. These procedures may be unpleasant for the cats involved.

Treatment usually requires regular oral medication (often dosing three times a day is required) and this in itself can be significantly stressful for some cats. As the heart disease progresses signs of heart failure usually return, despite treatment, leading to severe heart failure and an unpleasant death unless euthanasia is performed promptly.

3. Duration of welfare impact

Heart failure with episodes of breathing difficulties (that may be alleviated by treatment) often occurs progressively over a period of weeks to months. The welfare impacts will usually vary from mild to severe over this period depending on the success and impact of investigations and treatments on the individual. Some cats live for years on medication after an initial episode of heart failure and some die suddenly. Many Ragdolls develop clinical signs before two years of age (Meurs 2010).

4. Number of animals affected

Approximately 30% of Ragdolls in the UK carry a mutant gene that causes HCM. In the USA 28% were found to carry the gene with 8% being homozygous for it and likely to develop severe disease at an early age. Those cats with only one copy of the gene tend to experience milder disease.

5. Diagnosis

Heart disease is suspected either by the owner noticing one of the signs of heart failure listed (see ‘Clinical and pathological effects’ below) or by a veterinary surgeon detecting a sign of heart disease or heart failure during a routine examination. The diagnosis of HCM requires the use of ultrasonography. There is a genetic test available for one important gene mutation that is responsible for causing the condition in Ragdolls (but there may be other causal mutations yet to be discovered).

6. Genetics

HCM has been shown to be inherited in Ragdolls (Meurs et al 2007) The gene defect that has been identified as being associated with the disease appears to be dominant with variable penetration. Individuals with either one or two copies of the gene have a tendency to develop HCM and those that inherit two copies are much more severely affected (Meurs 2010).

A genetic test is available for the gene defect. Unfortunately, although this genetic test is very useful, there appear to be some Ragdoll cats that develop HCM despite being negative for the gene.

7. How do you know if an animal is a carrier or likely to become affected?

A genetic test is available but Ragdolls that test negative may still develop HCM. It is likely that this is due to other, currently unknown, genetic faults. Ultrasonography can be used as a way of screening potential breeding animals for the presence of HCM that is otherwise unapparent to owners and on routine veterinary examination and which are negative on genetic testing. It can also be used for early detection of heart failure in individuals known to carry the mutant gene for HCM so that suitable treatment can be instigated.

8. Methods and prospects for elimination of the problem

A scheme organised jointly by the UK’s Feline Advisory Bureau and the Veterinary Cardiology Society aims to eliminate HCM from Ragdolls and other affected breeds in the UK. This scheme uses both the genetic test and annual examinations including an ultrasound scan of the heart for all breeding animals. Cats with signs of HCM or that have one or two copies of the mutant gene should not be used for breeding.

For further details about this condition, please click on the following:
(these link to items down this page)

• Clinical and pathological effects
• Intensity of welfare impact
• Duration of welfare impact
• Number of animals affected
• Diagnosis
• Genetics
• How do you know if an animal is a carrier or likely to become affected?
• Methods and prospects for elimination of the problem
• Acknowledgements
• References

1.  Clinical and pathological effects

HCM is the commonest form of heart disease in cats (Tilley & Goodwin 2003). Cardiomyopathy means disease due to an enlargement of the heart muscle. The name of the condition is a description of what happens rather than its cause and, in fact, HCM can be caused by various diseases. The main cause in Ragdoll cats is the presence of one, or more, mutant genes that directly cause heart muscle to develop abnormally.

The heart is a four-chambered pump which is divided into left and right sides. Each side has two chambers: blood enters into the thin-walled upper chamber (atrium). It then flows into the larger, lower chamber (ventricle). The ventricles have thick walls composed largely of heart muscle. Between the chambers of the atria and the ventricles there are valves that prevent blood flowing backwards from the latter to the former. On contraction, blood flows from the ventricles into the major blood vessels. There are also valves at the junction of the ventricles and these blood vessels that preventing blood flowing backwards.

Figure 1. The four chambers of the heart and direction of blood flow. Note the four valves, which in a normal healthy heart prevent the backflow of blood and the thickness of the heart muscle (myocardium) surrounding the ventricles. (Image property of The Cardiomyopathy Association to whom we are grateful for permission for its reproduction here).

The right side of the heart receives blood from the whole of the body other than the lungs, via the venae cavae. The blood accumulates in the right atrium and during a heart beat it is sucked past the tricuspid valve into the right ventricle and then as the right ventricle contracts (squeezes) its muscular wall, the blood is pushed through the pulmonary valves into the pulmonary arteries that take it onto the lungs (to take up oxygen).

The left side of the heart receives this oxygenated blood from the lungs, via the pulmonary veins. The blood accumulates in the left atrium and during a heart beat it flows past the mitral valve into the left ventricle. Then, as the muscular wall of the left ventricle contracts, the blood is pushed through the aortic valves into the aorta and onto the other major arteries which carry it around the body to perform all the functions of blood circulation such as delivering oxygen and nutrients and sharing heat and metabolic products throughout the body.

As the left hand side of the heart has to pump blood around the major organs of the body, whilst the right hand side only has to push blood through the adjacent lungs, the muscles of the left ventricle have to be much stronger than the right. As strength is largely a function of muscle size the muscle wall of the left ventricle is thicker than the right.

The part of the heart’s relaxation and contraction cycle (that together make up the ‘heart beat’) when contraction (squeezing of blood) is occurring is referred to as systole and the relaxation phase is called diastole. In HCM the heart failure is largely a failure of the diastolic phase (Bonow & Udelson 1992).

To co-ordinate the contractions of the different parts of the heart’s muscle there is a pathway for coordinating nerve impulses. This can be damaged in HCM disrupting the control of the heart muscle

Figure 2. In a normal healthy heart, nerve signals travel through the heart muscle to stimulate coordinated contractions. However if the muscle tissue becomes thicker, as occurs in hypertrophic cardiomyopathy, the nerve signals are disrupted leading to irregular hearbeats. (Image property of The Cardiomyopathy Association to whom we are grateful for permission for its reproduction here).

In HCM the thickness of the ventricular walls is abnormally increased (Liu et al 1981). The heart is a complex, sophisticated organ and this muscle thickening causes multiple problems so that, at some stage, it can no longer function normally. Exactly what happens in an individual depends on which parts of the ventricles hypertrophy and over what time scale and to what degree, on whether valves are affected and on the degree to which blood supply to the heart muscle itself is compromised (Peterson et al 1993, Bonagura 1994). These different manifestations of the disease are outline below.

Figure 3. Hypertrophy can affect the various areas of the heart muscle, with varying effects and consequences. (Image property of The Cardiomyopathy Association to whom we are grateful for permission for its reproduction here).

1. The thickened wall usually can contract and squeeze out blood adequately. The problem is rather to do with the ventricle relaxing and filling again. This relaxation is important as it is this action that helps to suck the blood from the atria and allows it to fill adequately. When the ventricle is not relaxing enough it causes a backflow problem so that blood cannot enter the heart normally. This is called backward or congestive heart failure. When the left side of the heart is affected this causes fluid to build up in the lungs (pulmonary oedema). When the right side is affected the fluid instead builds up in the body and usually shows as fluid accumulating in the chest cavity (pleural fluid), the abdomen (ascites) or in the body generally (oedema). In each case the thin-walled atrium becomes affected and stretches (dilates). This causes further problems (see below).
2. The valves of the heart are attached to it’s muscle walls. As the walls thicken the valves can become distorted and leak. When the tricuspid and mitral valves are affected this allows blood to flow backwards into the atria during contraction which causes further backwards (back pressure) heart failure problems. When the pulmonary and aortic valves are affected then they can fail to open properly and so partially block the outflow of blood. One particular consequence of HCM is called systolic anterior motion of the mitral valve (SAM) (Bonagura 1994) when part of the mitral value (which should only be between the left atrium and the left ventricle) becomes caught up in the flow of blood in the left ventricular outflow path. Cardiologists specifically look for this when assessing the patients using ultrasound as it may be a sign of more severe disease.

Figure 4. Hypertrophic cardiomyopathy with asymmetric septal hypertrophy (ASH) can impact the function of the valves of the heart, leading to the backflow of blood as well as systolic anterior motion of the mitral valve (described above). (Image property of The Cardiomyopathy Association to whom we are grateful for permission for its reproduction here).

3. The thickened muscle often contains scar tissue which interferes with the conduction of the nerve messages through the heart and causes uncoordinated contractions (Bonagura 1994). Irregular heart beats can contribute to forward heart failure. Forwards heart failure is when the left ventricle provides inadequate blood flow to the body which can lead to weakness, collapse, fainting and sudden death.
4. The heart muscle itself needs blood, in the same way as other parts of the body. This is supplied through coronary arteries. As the muscle grows (hypertrophies) it sometimes does not have adequate blood vessels growing with it and this can lead to sections of the ventricular wall getting insufficient oxygen and dying. This causes problems akin to those of human heart attacks (myocardial infarction) when these coronary arteries suddenly block (Bonagura 1994).

There are also other important pathological consequences of HCM (and some similar cardiac diseases) in cats (Tilley et al 1977). A major problem arises due to the dilation of the atria mentioned above. Because of abnormalities of blood flow and because there may be damage to the atrial linings, blood clots may form. These do not cause a problem as long as they remain in an atrium but can do when sporadically pieces of clot break off. The detached clot is carried in the bloodstream until it reaches a narrowing that stops it. Further clotting then occurs around it. The blood supply to part of the body supplied by this vessel suddenly ceases and, depending on where this occurs, severe disease can be caused (Bonagura 1994). This is called thromboembolic disease.

Why does heart muscle in some individuals with HCM increase in size? Heart muscle increases in size, just like other muscles, in response to working harder. Any disease that causes the heart to work hard over a period of time will therefore cause the ventricular wall to thicken and eventually may cause heart disease and heart failure by the mechanisms outlined above.

The usual cause of HCM in cats (and humans) is that, due to a genetic fault, the individual is born with some of its heart muscle cells not working adequately due to abnormal proteins. The normal heart muscle cells have to work harder to compensate and over time as they work harder they increase in size. This causes an overall abnormally thick muscle and the consequences listed above.

There is an important distinction between heart disease and heart failure. Heart disease usually occurs a significant amount of time before heart failure. When any of the abnormalities of heart disease listed above are present it may be possible for a veterinary surgeon to detect them. When changes occur to affect the adequacy of the function of the heart then heart failure is present, which can be categorised into forward and backward heart failure. Both may be present.

The body is able to respond to heart disease and compensate for impending heart failure by various mechanisms, outlined below, although some of these themselves cause further problems (Bonagura 1994).

1. When it detects inadequate blood flow from the heart, the body causes the heart rate to increase such that blood supply to the organs is maintained. However, this raised heart rate may further restrict the ability of the ventricles to relax as there is less time between each contraction; time in which the ventricles can relax and fill. Increasing heart rate can cause backward heart failure to worsen and eventually the amount of blood that the heart can push forwards around the body also decreases. A further problem is that it is during relaxation that the heart muscle itself receives blood via its coronary arteries so when beating quickly its own oxygen supply can decrease and heart muscle can die.
2. Inadequate blood flow from the heart also causes the body to react as though there has been a loss of circulating blood volume. Hormones are released in response which cause fluid to be retained even though there actually has been no loss of blood. The amount of fluid in the body thus increases and this is one of the reasons that fluid accumulates in the lungs (pulmonary oedema) or elsewhere in the body (pleural fluid or oedema).

Cats with heart disease, but without heart failure, will very likely appear normal to their owners and will not have any welfare problems at that time (Tilley & Goodwin 2003). An owner might be able to detect a fast and abnormally strong heart beat if feeling their cat’s chest. Similarly, a veterinary surgeon may notice a high heart rate or pulse rate when examining a cat. The heart rate is measured by feeling the heart beat, or, more usually, listening to the heart beating using a stethoscope. The pulse rate is measured by feeling the pulsing of blood flowing through a major artery. In cats it is usually the femoral artery in the upper inside leg that is felt. In a normal individual the heart rate and pulse rate will be the same – each heart beat produces a pulse; but this is not always the case with heart failure – sometimes an ineffectual heart beat occurs that does not generate a pulse that can be detected. This is called a pulse deficit (Bonagura 1994).

A veterinary surgeon listening to a cat’s heart beating may also hear an abnormal noise, called a murmur. Hearing a heart murmur is the commonest way for heart disease to be detected in cats. It used to be thought that such murmurs occurred in up to 95% of cats with HCM (Tilley & Goodwin 2003) but Paige et al (2009) reported that only 31% of cats with HCM, and with no signs of heart failure, had an audible murmur. Murmurs are produced by abnormally turbulent blood flow. They usually indicate the presence of a structural abnormality of the heart, for example: an abnormal valve that is allowing backflow of blood or a bulging part of the heart wall that is causing abnormal flow. On detection of a murmur, further investigations should be carried out to find their cause and to determine the health of the heart (Bonagura 1994). Another change that a veterinary surgeon may detect when listening to a cat’s heart is a “gallop rhythm”. This is heard in around 40% of cats with HCM (Tilley & Goodwin 2003). Normally a cat’s heart beat has two sounds, “lub – dub”. With a gallop rhythm three sounds are heard and this is a reliable indication that heart disease is present (Bonagura 1994). Dysrhythmias such as a “gallop rhythm” are heard in around 25% of cats with HCM (Tilley & Goodwin 2003).

Other more sophisticated methods of detecting heart disease involve the use of radiographs, electrocardiographs and ultrasound. Radiographs of the chest may show evidence of heart enlargement but this is a relatively crude method. (Chest radiographs are very useful for detecting common signs of heart failure – see below). A disadvantage of chest radiographs is the need for a general anaesthetic.

Electrocardiography (ECG) records the electrical activity of the heart as it beats. This usually can be carried out in cats without sedation or anaesthesia and can provide information about the presence of heart disease.

The most powerful tool for examining the heart is ultrasonography. This enables measurement of the thickness of the heart muscle; the size of each chamber and the position and movement of each valve.

Heart failure occurs when there are complications of heart disease affecting other organs (eg the lungs or brain) that can be detected clinically or that are causing changes to the cat’s behaviour. There are several quite different ways that heart failure due to HCM can become apparent to an owner (Tilley & Goodwin 2003) as outlined below.

1. Decreased activity and appetite due to heart failure causing a build up of fluid in the chest cavity, or in the lungs, or because the heart is unable to supply enough blood to the major organs (backwards or forwards heart failures). In this case the gums and other mucus membranes will eventually look cyanotic (blue) rather than the normal pink (Bonagura 1994).
2. Breathing difficulties due to backward left sided failure. Blood that cannot get into the small, stiff-walled left ventricle pools in the left atrium, causing it to dilate, and also causes increased pressure in the pulmonary veins which carry blood from the lungs and which drain into the left. As back pressure builds up fluid forms in the lung tissue replacing the cavities that are normally air-filled. Often owners will only notice breathing difficulties when signs become severe and breathing is rapid or the cat is panting (breathing with their mouth open). Unlike dogs, cats do not pant unless distressed. Cats showing this need immediate veterinary attention. At this stage, investigations will usually find that much of the lung fields are full of fluid (pulmonary oedema) and/or that the lungs are being compressed by large volumes of fluid trapped between the lungs and the chest wall (pleural fluid). This fluid causes some cats to cough and this may be the first sign of heart disease and failure that an owner notices (Bonagura 1994).
3. Through the presence of a thromboembolus (Tilley et al 1977). As previously described, a clot formed in the left atrium can detach and cause blood loss to a distant part of the body. The commonest place of blockage by the clot is at the end of the largest artery, the abdominal aorta, where it splits into three to supply blood to each hind leg and the tail. Affected cats suddenly have severe problems with both back legs; often being completely paralysed. This condition is very painful and the cat will be extremely distressed, usually crying out.
   
   Embolisms can occur anywhere and if a clot lodges in smaller vessels then it may not be detected. Other common sites of major embolisms are the right front leg, causing pain and paralysis; the kidneys, causing acute kidney failure; the small intestine, causing death of a section of bowel, abdominal pain, anorexia (loss of appetite), vomiting and, without treatment – death; and in the brain causing a stroke-like episode, the exact signs will depend on where in the brain the blockage occurs (Bonagura1994).
   
   The clots can also form in the right atrium and if these detach they cause blockages in the supply of blood to the lungs (pulmonary embolism). The signs of these vary but they can cause breathing difficulties and shock.
4. Disease can show because of severely abnormal heart beats. These can be irregular heart beats that at times fail to supply enough blood to the organs or which can cause forward heart failure. These dysrhythmias can cause fainting episodes (Bonagura 1994).
5. As forward heart failure becomes worse and blood supply to the heart itself is inadequate, heart rate may drop and become subnormal. At this stage circulation throughout the body is severely compromised, fluid may build up in the lungs (pulmonary oedema) and in body cavities (pleural effusion in the chest and ascities in the abdomen) and in peripheral tissues (oedema seen mostly in the lower parts of the body – the legs and lower trunk. The body temperature drops due to inadequate circulation of blood. This process is called cardiogenic shock. Terminally, there is inadequate blood supply to the brain and fits, coma and death occur (Bonagura 1994).
6. Cats with hypertrophic cardiomyopathy sometimes show no signs of illness and even no signs of disease on routine veterinary examinations before dying suddenly (Kittleson et al 1999). Sudden death can occur because of a large thromboembolus. It can also occur in those cats with particularly thick left ventricular walls in which supply of blood via coronary arteries is inadequate leading to death of a large part of the muscle. This might be associated with a sudden increase in demand for heart activity such as occurs with a stressful event. Sudden death can also happen when a severe dysrhythmia occurs.

So, the signs of heart failure vary considerably (Tilley et al 1977). Many cats will have early heart failure without their owners being aware of it.

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2. Intensity of welfare impact

The intensity of the welfare impact varies greatly with the degree of heart failure and the presence or absence of secondary affects. Many cats with hypertrophic cardiomyopathy do not have heart failure and have no welfare problems. Severe and terminal heart failure has severe welfare implications. Pulmonary oedema, the presence of fluid inside the lungs, causes breathing difficulty and this can be assumed to be very unpleasant.

Thromboembolic disease (depending on where the clots occur) can cause severe pain, distress and paresis (inability to use the hindlimbs normally). It is also difficult to treat and some cats may undergo treatments lasting from days to weeks and may still end up with the cat having to be euthanased.

Unfortunately Ragdolls, which are homozygous for the identified genetic mutation, are severely affected and develop heart failure and thromboembolisms often before two years of age (Meurs 2010).

Investigations of heart disease and heart failure often need to be extensive. As well as repeated clinical examinations, blood tests, ECGs, ultrasound examinations and radiographs, often under anaesthesia, are required to manage these problems. These procedures may be unpleasant for the cat.

Treatments for both forward and backward heart failure are available and usually help to reverse signs of heart failure. Reversing actual heart disease is much more difficult although there is some evidence that the size of the left ventricular wall can be reduced sometimes. Treatment is usually dependant on regular oral medication; for hypertrophic cardiomyopathy this unfortunately often means dosing three times a day, a process which in itself can be significantly stressful for some cats. As the heart disease progresses signs of heart failure usually return, despite treatment, leading to severe heart failure and an unpleasant death unless euthanasia is performed.

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3. Duration of welfare impact

Homozygous Ragdolls (those in which both copies of the gene are of the mutant form) are often less than two years old when heart failure and thromboembolisms develop (Meurs 2010). Heart failure with episodes of breathing difficulties, alleviated by treatment, often occurs over a period of weeks to months. The welfare impact may be mild or severe over this period depending on the success of treatment and the impact of investigations and treatments on the individual. Some cats live for years on medication after an initial episode of heart failure and some die suddenly. The average life expectancy of one group of cats (of various breeds) with HCM was found to be 492 days (Ferasin et al 2003). Tilley & Goodwin (2003) stated that, in general, cats with HCM and no signs of heart failure have an average life expectancy of five years from diagnosis and those with heart failure of three months.

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4. Number of animals affected

Approximately 30% of Ragdolls in the UK carry the mutant gene that causes HCM (FAB no date). In the USA, 28% of Ragdolls carry the gene with 8% being homozygous for it ie they have two copies of the mutant gene. Homozygous individuals develop severe, early disease. Those which are heterozygous (have only one copy of the mutant gene) tend to develop a much milder form of the disease (Meurs 2010).

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5. Diagnosis

Heart disease is suspected either by the owner noticing one of the signs of heart failure listed above or by a veterinary surgeon detecting a sign of heart disease or heart failure on an examination for another reason or a routine check. In the UK, many cases of HCM in Ragdolls are detected through the ultrasonography screening scheme organised by the UK’s Feline Advisory Bureau (FAB) and Veterinary Cardiology Society (VCS) (see below) or by owners using the specific genetic screening test. This test detects the presence of the mutant gene (not whether the cat actually has heart disease or heart failure). However, many cats with this gene will go on to develop disease and failure.

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6. Genetics

Hypertrophic cardiomyopathy has been shown to be inherited in Ragdolls (Meurs et al 2007). A defect has been found in the myosin binding protein C gene (MYBPC3) with a change in a single nucleotide base - from cytosine to thymine - that alters the conformation of codon 820. The defect appears to be dominant with variable penetration so that individuals with either one or two copies of the gene have the tendency to develop HCM (Meurs 2010). Factors, other than the presence of the gene, have an important influence on whether or not HCM develops and the severity of disease. However, what these factors are is currently unknown.

Unfortunately, although the genetic test for congenital HCM is very useful, there appears to be a number of Ragdolls that develop HCM despite having tested negative for the presence of this gene. In humans, there are more than 1000 known defects in 10 genes that can cause HCM so it is likely that there are other genetic mutations in Ragdolls and other cat breeds and investigations to find these are underway (Meurs et al 2009). It is also possible that false negative genetic results occur sometimes (Lyons 2010).

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7. How do you know if an animal is a carrier or likely to become affected?

A genetic test is available for this condition and is available from several laboratories around the world, eg the Molecular Diagnostics Unit, University of Bristol Veterinary School http://www.langfordvets.co.uk/lab_pkdsampling.htm.

An individual only needs to be tested once during its lifetime but there are significant limitations to the genetic test. Ragdolls that have a negative test result may still develop HCM and it seems likely that this is because other, currently undiscovered, genetic defects can also induce it.

Routine ultrasonography can be used both as a way of screening potential breeding animals for the presence of HCM, that is not apparent to owners, and on routine veterinary examination. All Ragdoll kittens should have the genetic test prior to purchase (unless both their parents are known to be free of the mutation) and their parents should also have been declared healthy on an ultrasound examination.

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8. Methods and prospects for elimination of the problem

There are schemes in operation that may use both genetic testing and annual examinations, including an ultrasound scan of the heart, to identify affected individuals. One is organised by the UK’s Feline Advisory Bureau (FAB) and Veterinary Cardiology Society (VCS): it aims to eliminate HCM from Ragdolls in the UK. (see: http://www.langfordvets.co.uk/lab_pcrnews.htm or http://www.fabcats.org/hcm/).

Cats that have HCM, or that have one or two copies of the mutant MYBPC3 gene, should not be used for breeding.

Only microchipped cats can be listed on the FAB VCS register of HCM-negative Ragdolls. The veterinary surgeon must read the microchip to confirm the identity of the cat at the time of sampling for the genetic test or each time the cardiac ultrasound test is performed,

Examinations are arranged with individual veterinary cardiologists, a list of whom for the UK can be found at: http://www.fabcats.org/hcm/.

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9. Acknowledgements

UFAW is grateful to Rosie Godfrey BVetMed MRCVS and David Godfrey BVetMed FRCVS for their work in compiling this section

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10. References

Bonagura JD (1994) Cardiovascular diseases. In: Sherding RG ed The Cat: Diseases and Clinical Management, 2nd edition. Churchill Livingstone: New York. pp

Bonow RO and Udelson JE (1992) Left ventricular diastolic dysfunction as a cause of congestive heart failure. Mechanisms and management. Annals of Internal Medicine 117: 502-10

Feline Advisory Bureau (FAB) (no date) Hypertrophic cardiomyopathy in cats. On-line. http://www.fabcats.org/hcm/. Accessed 16.6.11

Ferasin L, Sturgess CP, Cannon MJ, Caney SMA, Gruffydd-Jones TJ and Wotton PR (2003) Feline idiopathic cardiomyopathy: a retrospective study of 106 cats (1994–2001). Journal of Feline Medicine & Surgery 5: 151-159

Kittleson MD, Meurs KM, Munro MJ, Kittleson JA, Liu SK, Pion PD and Towbin JA (1999) Familial hypertrophic cardiomyopathy in maine coon cats: an animal model of human disease. Circulation 99: 3172-80

Liu SK, Maron BJ and Tilley LP (1981) Feline hypertrophic cardiomyopathy: gross anatomic and quantitative histologic features. American Journal of Pathology 102: 388-95

Lyons L (2010) http://www.vetmed.ucdavis.edu/Catgenetics/HCM_statement_UCD_Lyons.pdf. accessed 16.6.2011

Meurs KM (2010) Genetic Screening of Familial Hypertrophic Cardiomyopathy in August JRs ed. Consulatations in Feline Internal Medicine Volume 6 p406-409. Saunders Elsevier: St Louis, USA

Meurs KM, Norgard MM, Ederer MM, Hendrix CP and Kittleson MD (2007) A substitution mutation in the myosin binding protein C gene in Ragdoll cats. Genomics 90: 261-264

Meurs KM, Norgard MM, Kuan M, Haggstrom J and Kittleson M (2009) Analysis of 8 sarcomeric candidate genes for feline hypertrophic cardiomyopathy mutations in cats with hypertrophic cardiomyopathy. Journal of Veterinary Internal Medicine 23: 840-3

Paige CF, Abbott JA, Elvinger F and Pyle RL (2009) Prevalence of cardiomyopathy in apparently healthy cats. Journal of the American Veterinary Medical Association 234: 1398-403

Peterson EN, Moise NS, Brown CA, Erb HN and Slater MR (1993) Heterogeneity of hypertrophy in feline hypertrophic heart disease. Journal of Veterinary Internal Medicine 7: 183-9

Tilley LP, Liu SK, Gilbertson SR, Wagner BM and Lord PF (1977) Primary myocardial disease in the cat. A model for human cardiomyopathy. American Journal of Pathology 86: 493-522

Tilley LP and Goodwin JK (2003) Hypertrophic cardiomyopathy. In: Norsworthy GD, Crystal MA Fooshee Grace S and Tilley LP Eds The Feline Patient, 2nd edition. pp 295 Lippincott Williams & Wilkins: Baltimore

© UFAW 2011

Credit for main photo above:

By Simone Johnsson (originally posted to Flickr as Yan) [CC-BY-SA-2.0 (http://creativecommons.org/licenses/by-sa/2.0)], via Wikimedia Commons