| Copyright 2009. Any questions please contact the webmaster at emau@emaucats.com |
 |
|
Egyptian Mau Breed Council
|
|
Chairman’s Report - Professor Melissa Bateson The discovery that the Egyptian Mau is one of the breeds in which an altered version of the gene that codes for the enzyme pyruvate kinase (PK) exists is important news for our breed, and necessitates immediate action by our Club and Breed Advisory Committee. In some other breeds, such as the Somali, individual cats that have two copies of this altered version of the gene (known as ‘affected’, homozygous or ‘KK’ cats) develop a form of anaemia, called PK Deficiency (or PK Def), that can result in severe disease and ultimately euthanasia. Luckily a simple test exists for the altered version of the gene, meaning that it is theoretically possible to eliminate cats carrying the altered gene from the gene pool. Some other breeds, including the Somali, have, via a programme of genetic testing and selective breeding, completely eliminated the K version of the gene, and hence PK Deficiency disease. The question facing us is whether it would be in the interests of the Egyptian Mau breed to follow a similar path? We have a huge responsibility as the guardians of the future of our breed to get this decision right. For many breeders the answer seems to be simple: if we can eliminate a potentially unpleasant genetic disease then we would be irresponsible and unethical not to do it. However, my own view, having reviewed the available evidence and taken expert advice is that we currently do not have the evidence to support this course of action. The crux of the problem is that not all cats with the KK genotype develop PK Deficiency disease. Moreover, there seem to be big breed differences in whether these cats develop disease or not. In breeds such as the Singapura and Egyptian Mau there is no evidence that KK cats get sick. But isn’t it better to be safe than sorry and opt for elimination despite the lack of evidence for disease? I would argue not, because the costs of elimination are potentially high, and I’m not just talking about the financial costs. I feel strongly that we need further evidence that we have a disease problem in KK cats before recommending testing and elimination of the altered gene. Aside from the risks of narrowing our gene pool, there are also other genetic health problems in Egyptian Maus that mean we cannot take a one-dimensional approach to PK Def. For example, a proportion of our kittens have umbilical hernias, some of which involve a major deformity. I have worked very hard educating breeders to select breeding cats without this trait, and it has often meant neutering the kittens with the best type or temperament in a litter. If we had been constrained by also selecting against the K gene whole lines might have been lost, or alternatively cats with small hernias would have been put on the active register, perpetuating a potentially lethal deformity (over the years I have had to have emergency surgery on 3 kittens with strangulated hernias, and if these kittens has been in pet homes with owners that did not immediately recognise the symptoms they would probably have died). There is currently no genetic test for umbilical hernias. The hernias are often transitory and can be easily missed. It would be bad news for the breed if in trying to eliminate a possible problem (PK Def) we ended up exacerbating a known problem (hernias). It used to be common practice for breeders to mend a hernia on a kitten and use it for breeding or to ignore small transitory hernias. The lack of a test means that this cannot be verified. If everyone starts focusing on PK Def, which can be verified, an unintended consequence is likely to be that other known genetic problems currently without tests will increase in frequency. Good breeding is about making the right decision over which kittens to breed from. The decisions that are ethically correct are not necessarily the decisions that are easiest to verify because there are not genetic tests for all the known problems. Hence I believe that the PK Def test has the potential to bias our breeding programme in a way that could be very damaging to the breed. Forcing breeders to focus on PK Def will inadvertently suggest to them that this disease is more important than others. This is why we need more evidence before we recommend testing. The benefits of testing have to outweigh the costs. I have discussed these issues at length with my father Patrick Bateson, and we are both of the view that given the current evidence, recommending genetic testing for PK Def would be irresponsible for the breed at this point. Of course further evidence might well come to light that will change our views, and we need to think hard about the best way to obtain the necessary evidence. The take home message for the time being is not to panic. The K gene has been in our breed’s gene pool since the first Maus came to the UK in 1998 (it is in cats from my original import lines), and we do not yet have any confirmed cases of Maus getting sick with PK Def. We therefore clearly do not currently have a major problem with this disease in our breed and should not allow our breeding decisions to be swayed by the availability of a genetic test.
What should be done about PK deficiency in Egyptian Maus? Professors Patrick and Melissa Bateson Technology is developing rapidly so that scientists are able with greater and greater ease to identify genes that may be associated with particular diseases. Such a case was reported by Robert Grahn and his colleagues in BMC Veterinary Research in 2012. A mutant gene linked with pyruvate kinase (PK) deficiency in the red blood cells is associated in some breeds with decreased longevity of the red blood cells resulting in anaemia. Additional signs of the inherited disease include severe lethargy, weakness, weight loss, jaundice, and abdominal enlargement. Of 36 Egyptian Maus tested by Grahn and his colleagues, 27 did not carry the mutation, 9 carried it in the heterozygous form and none carried it in the homozygous form. The authors recommend that, along with many other breeds, Egyptian Maus should be tested for the mutant gene. Some owners have already done so. However, the authors note that homozygous cats that should have disease-associated presentations are not being actively reported to vets by breed owners. The authors conclude that the lack of presentation of sick cats is puzzling. They should not be puzzled. Very few mutant genes code for particular diseases in the sense that they and no other genes make the difference between having the disease and not having it. In breeds carrying the PK-deficiency mutation expression of the disease is variable in the age of onset, severity and may not occur at all. This already suggests that additional factors are required to induce disease. We consulted three expert geneticists. They all agreed that interaction of mutations with the genomic background is likely and in some cases is well established. Genetic evidence for single gene mutations should be treated with appropriate caution even if the mutant gene is sometimes associated with inherited disease. Egyptian Maus may not express the disease associated with the PK-deficiency gene. If carriers of the gene have been identified, not using them for breeding would be premature. Moreover, decreasing the number of cats used for breeding would increase the risk that the breed would become inbred, bringing with it all the well-known consequences of inbreeding. We recommend that if owners have had their cats tested and have found that any one of them is homozygous for the mutant gene, they should watch carefully for clinical signs of the disease and report any adverse signs to the Club. Conversely untested cats that develop anaemia should be tested for the mutant gene and once again the results reported to the Club. Meanwhile we recommend that breeders should continue to mate their cats that are heterozygous for the mutant gene until much more evidence becomes available.
What do we currently know about PK def in Egyptian Maus
by Professor Melissa Bateson
American breeder and judge Melanie Morgan has been compiling a data base of identified Egyptian Maus that have been tested for PK def. to date. I analysed the contents of this data base in July this year and report the following results. The data base contained results of genetic tests from 54 identified Egyptian Mau cats. The breakdown of numbers of cats with the three possible genotypes is shown in Table 1. Table 1: Frequency of the K allele in Egyptian Maus
*Note: This column gives the expected number of cats of each genotype based on the assumption that there is no selection acting on the K allele. Given that each cat has two copies of the allele we can compute the frequency of the K allele in our population as 25% (i.e. 23 copies of K from the carriers plus 4 copies of K from the ‘affected’ cats which equals 27 copies of the K allele out of a total of 108 alleles). Using this frequency we can then compute the expected numbers of cats of each genotype using the Hardy-Weinberg equilibrium. The expected numbers of cats does not differ significantly from the observed numbers (chi-square=0.996 with 2df, p>0.05). Despite over 40% of tested cats being carriers of the K allele, less than 4% of cats are of the homozygous or ‘affected’ KK genotype. If ‘affected’ cats were dying young (i.e. prior to the age at which most were tested) then there would be fewer KK cats than expected based on the number of carriers. However, a statistical analysis reveals that the number of KK cats is not significantly lower than expected. Therefore, these data provide no evidence that KK cats are dying young. The known KK cats are being carefully monitored for any signs of development of anaemia, and to my knowledge there is no evidence that any known KK cats have developed symptoms consistent with PK def disease. Determining the long-term health of known KK cats will be very important in establishing whether Egyptian maus are susceptible to PK def. Maugazine the official publication of The Egyptian Mau Club 1
|
|
|