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EDITORIAL
The heart of genetic testing If one thinks of almost any disease known to veterinary medicine, it is possible to think of a specific breed of dog or cat that is predisposed to that condition. In domesticating our companion animals, man has helped to reduce the gene pool of the canine and feline species, and in creating breeds has created a genetic “bottleneck” responsible for the breed predispositions we see today (Karlsson & Lindblad-Toh 2008). Owners and breeders of pedigree dogs and cats have, in the last few years, become more acutely aware of the issues affecting individual breeds, and it is fair to say that the majority of breed clubs in the UK consider health as an area for discussion and improvement. Clearly, the aim in any breeding programme is to produce healthy animals that also fit the description of the breed they represent, but trying to reduce the prevalence of a disease in a closely related population can be problematic. Some of the factors influencing the success of breeding programmes are the age of onset of the condition, the mode of inheritance of the disease and the prevalence of the condition in the population. When one considers additional factors at a genetic level, the penetrance of the mutation (i.e. the likelihood that an animal will develop the disease if it has the causative mutation), the effect of zygosity on disease phenotype and the prevalence of the mutation can all play an important role. One of the key steps to improve health in breeding programmes has been the introduction of genetic testing, which allows rapid identification of predisposed individuals prior to breeding from them. Breeding programmes to reduce the prevalence of cardiovascular disease in our small animal patients are some of the most challenging. The most common acquired heart diseases of dogs [myxomatous mitral valve disease (MMVD) and dilated cardiomyopathy (DCM)] and cats [hypertrophic cardiomyopathy (HCM)] are, in most cases, adult-onset conditions, meaning that an animal may have had a significant influence on the genetics of the breed before anyone becomes aware that it is affected by cardiovascular disease. While congenital cardiac diseases are also likely to have a genetic basis in many cases, the ability to identify these diseases in young dogs on echocardiography, usually prior to breeding, means that genetic testing becomes less important. Elucidation of the genetic cause of cardiovascular diseases in dogs and cats has been an area of intense research in recent years. In dogs with DCM, initial investigation of candidate genes known to be mutated in human DCM yielded no significant results (Stabej et al. 2004, 2005, Meurs et al. 2007, Wiermsa et al. 2008). A European-wide collaboration known as the LUPA project has been attempting to identify the genetic cause of DCM and early onset of MMVD in a number of breeds, in addition to a variety of other diseases of dogs that are common to canine and human populations (www.eurolupa.org). The group has utilised a method known as genome-wide association studies (GWAS) to identify conserved regions of the genome in affected dogs. Regions of interest in the genome of Cavalier King Charles spaniels with MMVD (Madsen et al. 2011) and in Dobermanns with DCM (Mausberg et al. 2011) have been identified using Journal of Small Animal Practice
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Vol 55
•
May 2014
•
large populations of dogs from across Europe. Work with other breeds is ongoing, but it appears unlikely that a single gene defect is responsible for DCM or early onset of MMVD. These results stand in contrast to genetic studies carried out in the USA, highlighting another problem with genetic testing that is proving increasingly important in cardiovascular disease. A mutation in the PDK4 gene in Dobermanns is reported to be associated with the development of DCM in the USA population, again identified by GWAS (Meurs et al. 2012). However, this mutation is not associated with DCM in the European population used in the LUPA project (Owczarek-Lipska et al. 2013). Therefore, it appears possible that despite these dogs being visually similar and developing a phenotypically indistinguishable form of DCM, there may be different causative mutations in different subpopulations of the same breed. Perhaps this is not surprising when one considers that mutations in more than 40 different genes (at the last count) have been associated with the development of DCM in humans (Garcia-Pavia et al. 2013). Alternatively, there may be a number of different mutations or genetic modifiers that must occur simultaneously in order for DCM to be phenotypically expressed, as is often the case in humans (Garcia-Pavia et al. 2013). A similar scenario exists with boxer dogs, where an 8-bp deletion in the Striatin gene has been identified in USA boxers with arrhythmogenic right ventricular cardiomyopathy (ARVC) (Meurs et al. 2010). This mutation is found in similar proportions in populations of both affected and unaffected boxers in the UK population, suggesting that this mutation is not the only cause of ARVC in boxers, although it may have some effect on disease expression in UK dogs (Dukes-McEwan et al. 2010). This has significant implications for breeders of boxers and Dobermanns in the UK and Europe, as the genetic tests offered in the USA cannot be used to identify affected dogs in other populations. In this edition of the journal, Casamian-Sorrosal et al. (2014) report the prevalence of causative mutations for HCM in Maine coon and ragdoll cats, where genetic testing of breeding animals is already widespread. The myosin-binding protein C A31P mutation in Maine coons has been shown to be associated with the development of HCM in populations of this breed in numerous countries (Fries et al. 2008, Mary et al. 2010, Wess et al. 2010). Nevertheless, in studies where echocardiography has been performed, HCM has been identified in homozygous wild-type animals (Mary et al. 2010, Wess et al. 2010), suggesting again that there is likely to be more than one mutation resulting in a phenotypically similar disease, even within subpopulations of cats. A great deal of work remains to be done in other breeds predisposed to HCM, and indeed in the diverse crossbreed population of cats, where HCM is still the most common cardiomyopathy (Ferasin et al. 2003). Casamian-Sorrosal et al. (2014) highlight the importance of understanding population demographics and prevalence in the subsequent use of genetic testing results. The high prevalence of causative mutations in UK cats highlights that affected cats
© 2014 British Small Animal Veterinary Association
239
Editorial
cannot simply be excluded from the breeding population, but equally emphasises the significant impact that genetic testing could potentially have in reducing the prevalence of a disease in a breeding program. It is our responsibility as veterinary surgeons to disseminate this information to breeders of dogs and cats so that the genetic tests are used accurately and not indiscriminately. Our knowledge of the genetics of cardiovascular disease in dogs and cats is expanding at an ever-increasing rate. A huge amount remains to be discovered, for example, the causative mutations in other specific breeds, the effect of genetic and environmental modifiers and the influence of homozygous or heterozygous status on the phenotype of the disease. Interestingly, the mutations and regions of interest described in canine DCM and ARVC so far (Werner et al. 2008, Meurs et al. 2010, 2012, Mausberg et al. 2011) are in regions of the genome not previously known to be associated with phenotypically similar conditions in humans, suggesting that the dog may be living up to its status as man’s best friend, by providing novel areas of research for the human field. Ultimately, the most important factor governing the success of genetic testing is probably the dissemination of this information to veterinarians, breeders and owners of affected breeds, to give them the best chance of improving the health of their pets. Hannah Stephenson Hannah Stephenson Specialist Veterinary Cardiology Lancashire References Casamian-Sorrosal, D., Chong, S. K., Fonfara, S., et al. (2014) Prevalence and demographics of the MYBC3-mutations in ragdoll and Maine Coons in the British Isles. Journal of Small Animal Practice 55, 269-273 Dukes-McEwan, J., Stephenson, H. M., Wotton, P. R., et al. (2010) Cardiomyopathy in boxers: the search for a genetic cause, and how you can help. Veterinary Times 40, 6-9
Ferasin, L., Sturgess, C. P., Cannon M. J., et al. (2003) Feline idiopathic cardiomyopathy: a retrospective study of 106 cats (1994-2001). Journal of Feline Medicine and Surgery 5, 151-159 Fries, R., Heaney, A. M. & Meurs, K. M. (2008). Prevalence of the myosin binding protein C mutation in Maine coon cats. Journal of Veterinary Internal Medicine 22, 893-896 Garcia-Pavia, P., Cobo-Marcos, M., Guzzo-Merello, G., et al. (2013) Genetics in dilated cardiomyopathy. Biomarkers in Medicine 7, 517-533 Karlsson, E. K. & Lindblad-Toh, K. (2008) Leader of the pack: gene mapping in dogs and other model organisms. Nature Reviews Genetics 9, 713-725 Madsen, M. B., Olsen, L. H., Häggström, J., et al. (2011) Identification of two loci associated with development of myxomatous mitral valve disease in Cavalier King Charles spaniels. Journal of Heredity 102 (Suppl 1), S62-S67 Mary, J., Chetboul, V., Carlos Sampedrano, C., et al. (2010) Prevalence of the MYBPC3-A31P mutation in a large European feline population and association with hypertrophic cardiomyopathy in the Maine Coon breed. Journal of Veterinary Cardiology 12, 155-161 Mausberg, T., Wess, G., Simak, J., et al. (2011) A locus on chromosome 5 is associated with dilated cardiomyopathy in Doberman Pinschers. PLoS ONE 6, e20042 Meurs, K. M., Fox, P. R., Norgard, M., et al. (2007) A prospective genetic evaluation of familial dilated cardiomyopathy in the Doberman pinscher. Journal of Veterinary Internal Medicine 21, 1016-1020 Meurs, K. M., Mauceli, E., Lahmers, S., et al. (2010) Genome-wide association identifies a deletion in the 3’ untranslated region of Striatin in a canine model of arrhythmogenic right ventricular cardiomyopathy. Human Genetics 128, 315-324 Meurs, K. M., Lahmers, S., Keene, B. W., et al. (2012) A splice site mutation in a gene encoding for PDK4, a mitochondrial protein, is associated with the development of dilated cardiomyopathy in the Doberman pinscher. Human Genetics 131, 1319-1325 Owczarek-Lipska, M., Mausberg, T. B., Stephenson, H., et al. (2013) A 16-bp deletion in the canine PDK4 gene is not associated with dilated cardiomyopathy in a European cohort of Doberman Pinschers. Animal Genetics 44, 239 Stabej, P., Imholz, S., Versteeg, S. A., et al. (2004) Characterization of the canine desmin (DES) gene and evaluation as a candidate gene for dilated cardiomyopathy in the Dobermann. Gene 340, 241-249 Stabej, P., Leegwater, P. A., Imholz, S., et al. (2005) The canine sarcoglycan delta gene: BAC clone contig assembly, chromosome assignment and interrogation as a candidate gene for dilated cardiomyopathy in Dobermann dogs. Cytogenetic and Genome Research 111, 140-146 Werner, P., Raducha, M. G., Prociuk, U., et al. (2008) A novel locus for dilated cardiomyopathy maps to canine chromosome 8. Genomics 91, 517-521 Wess, G., Schimner, C., Weber, K., et al. (2010) Association of the A31P and A74T polymorphisms in ythe myosin binding protein C3 gene and hypertrophic cardiomyopathy in Maine coon and other breed cats. Journal of Veterinary Internal Medicine 24, 527-532 Wiermsa, A. C., Stabej, P., Leegwater, P. A., et al. (2008) Evaluation of 15 candidate genes for dilated cardiomyopathy in the Newfoundland dog. Journal of Heredity 99, 73-80
Hannah Stephenson graduated from the University of Glasgow in 2005 and spent her first 2 years in mixed practice in Lancashire. She undertook a Junior Clinical Training Scholarship at the RVC before moving back up North to the University of Liverpool as a research assistant. This research investigated the genetic basis of dilated cardiomyopathy in dogs, as part of the LUPA project, and she has continued her research over the years investigating DCM in Great Danes more specifically. She undertook a residency in cardiology at Liverpool during which time she gained the RCVS certificate in small animal medicine. She was awarded the ECVIM diploma in cardiology in 2012, followed by RCVS specialist recognition in 2014. After a short time as a clinical lecturer at the University of Liverpool, she now runs a peripatetic cardiology referral service for veterinary practices in the North West.
240
Journal of Small Animal Practice
•
Vol 55
•
May 2014
•
© 2014 British Small Animal Veterinary Association
EDITORIAL
The heart of genetic testing If one thinks of almost any disease known to veterinary medicine, it is possible to think of a specific breed of dog or cat that is predisposed to that condition. In domesticating our companion animals, man has helped to reduce the gene pool of the canine and feline species, and in creating breeds has created a genetic “bottleneck” responsible for the breed predispositions we see today (Karlsson & Lindblad-Toh 2008). Owners and breeders of pedigree dogs and cats have, in the last few years, become more acutely aware of the issues affecting individual breeds, and it is fair to say that the majority of breed clubs in the UK consider health as an area for discussion and improvement. Clearly, the aim in any breeding programme is to produce healthy animals that also fit the description of the breed they represent, but trying to reduce the prevalence of a disease in a closely related population can be problematic. Some of the factors influencing the success of breeding programmes are the age of onset of the condition, the mode of inheritance of the disease and the prevalence of the condition in the population. When one considers additional factors at a genetic level, the penetrance of the mutation (i.e. the likelihood that an animal will develop the disease if it has the causative mutation), the effect of zygosity on disease phenotype and the prevalence of the mutation can all play an important role. One of the key steps to improve health in breeding programmes has been the introduction of genetic testing, which allows rapid identification of predisposed individuals prior to breeding from them. Breeding programmes to reduce the prevalence of cardiovascular disease in our small animal patients are some of the most challenging. The most common acquired heart diseases of dogs [myxomatous mitral valve disease (MMVD) and dilated cardiomyopathy (DCM)] and cats [hypertrophic cardiomyopathy (HCM)] are, in most cases, adult-onset conditions, meaning that an animal may have had a significant influence on the genetics of the breed before anyone becomes aware that it is affected by cardiovascular disease. While congenital cardiac diseases are also likely to have a genetic basis in many cases, the ability to identify these diseases in young dogs on echocardiography, usually prior to breeding, means that genetic testing becomes less important. Elucidation of the genetic cause of cardiovascular diseases in dogs and cats has been an area of intense research in recent years. In dogs with DCM, initial investigation of candidate genes known to be mutated in human DCM yielded no significant results (Stabej et al. 2004, 2005, Meurs et al. 2007, Wiermsa et al. 2008). A European-wide collaboration known as the LUPA project has been attempting to identify the genetic cause of DCM and early onset of MMVD in a number of breeds, in addition to a variety of other diseases of dogs that are common to canine and human populations (www.eurolupa.org). The group has utilised a method known as genome-wide association studies (GWAS) to identify conserved regions of the genome in affected dogs. Regions of interest in the genome of Cavalier King Charles spaniels with MMVD (Madsen et al. 2011) and in Dobermanns with DCM (Mausberg et al. 2011) have been identified using Journal of Small Animal Practice
•
Vol 55
•
May 2014
•
large populations of dogs from across Europe. Work with other breeds is ongoing, but it appears unlikely that a single gene defect is responsible for DCM or early onset of MMVD. These results stand in contrast to genetic studies carried out in the USA, highlighting another problem with genetic testing that is proving increasingly important in cardiovascular disease. A mutation in the PDK4 gene in Dobermanns is reported to be associated with the development of DCM in the USA population, again identified by GWAS (Meurs et al. 2012). However, this mutation is not associated with DCM in the European population used in the LUPA project (Owczarek-Lipska et al. 2013). Therefore, it appears possible that despite these dogs being visually similar and developing a phenotypically indistinguishable form of DCM, there may be different causative mutations in different subpopulations of the same breed. Perhaps this is not surprising when one considers that mutations in more than 40 different genes (at the last count) have been associated with the development of DCM in humans (Garcia-Pavia et al. 2013). Alternatively, there may be a number of different mutations or genetic modifiers that must occur simultaneously in order for DCM to be phenotypically expressed, as is often the case in humans (Garcia-Pavia et al. 2013). A similar scenario exists with boxer dogs, where an 8-bp deletion in the Striatin gene has been identified in USA boxers with arrhythmogenic right ventricular cardiomyopathy (ARVC) (Meurs et al. 2010). This mutation is found in similar proportions in populations of both affected and unaffected boxers in the UK population, suggesting that this mutation is not the only cause of ARVC in boxers, although it may have some effect on disease expression in UK dogs (Dukes-McEwan et al. 2010). This has significant implications for breeders of boxers and Dobermanns in the UK and Europe, as the genetic tests offered in the USA cannot be used to identify affected dogs in other populations. In this edition of the journal, Casamian-Sorrosal et al. (2014) report the prevalence of causative mutations for HCM in Maine coon and ragdoll cats, where genetic testing of breeding animals is already widespread. The myosin-binding protein C A31P mutation in Maine coons has been shown to be associated with the development of HCM in populations of this breed in numerous countries (Fries et al. 2008, Mary et al. 2010, Wess et al. 2010). Nevertheless, in studies where echocardiography has been performed, HCM has been identified in homozygous wild-type animals (Mary et al. 2010, Wess et al. 2010), suggesting again that there is likely to be more than one mutation resulting in a phenotypically similar disease, even within subpopulations of cats. A great deal of work remains to be done in other breeds predisposed to HCM, and indeed in the diverse crossbreed population of cats, where HCM is still the most common cardiomyopathy (Ferasin et al. 2003). Casamian-Sorrosal et al. (2014) highlight the importance of understanding population demographics and prevalence in the subsequent use of genetic testing results. The high prevalence of causative mutations in UK cats highlights that affected cats
© 2014 British Small Animal Veterinary Association
239
Editorial
cannot simply be excluded from the breeding population, but equally emphasises the significant impact that genetic testing could potentially have in reducing the prevalence of a disease in a breeding program. It is our responsibility as veterinary surgeons to disseminate this information to breeders of dogs and cats so that the genetic tests are used accurately and not indiscriminately. Our knowledge of the genetics of cardiovascular disease in dogs and cats is expanding at an ever-increasing rate. A huge amount remains to be discovered, for example, the causative mutations in other specific breeds, the effect of genetic and environmental modifiers and the influence of homozygous or heterozygous status on the phenotype of the disease. Interestingly, the mutations and regions of interest described in canine DCM and ARVC so far (Werner et al. 2008, Meurs et al. 2010, 2012, Mausberg et al. 2011) are in regions of the genome not previously known to be associated with phenotypically similar conditions in humans, suggesting that the dog may be living up to its status as man’s best friend, by providing novel areas of research for the human field. Ultimately, the most important factor governing the success of genetic testing is probably the dissemination of this information to veterinarians, breeders and owners of affected breeds, to give them the best chance of improving the health of their pets. Hannah Stephenson Hannah Stephenson Specialist Veterinary Cardiology Lancashire References Casamian-Sorrosal, D., Chong, S. K., Fonfara, S., et al. (2014) Prevalence and demographics of the MYBC3-mutations in ragdoll and Maine Coons in the British Isles. Journal of Small Animal Practice 55, 269-273 Dukes-McEwan, J., Stephenson, H. M., Wotton, P. R., et al. (2010) Cardiomyopathy in boxers: the search for a genetic cause, and how you can help. Veterinary Times 40, 6-9
Ferasin, L., Sturgess, C. P., Cannon M. J., et al. (2003) Feline idiopathic cardiomyopathy: a retrospective study of 106 cats (1994-2001). Journal of Feline Medicine and Surgery 5, 151-159 Fries, R., Heaney, A. M. & Meurs, K. M. (2008). Prevalence of the myosin binding protein C mutation in Maine coon cats. Journal of Veterinary Internal Medicine 22, 893-896 Garcia-Pavia, P., Cobo-Marcos, M., Guzzo-Merello, G., et al. (2013) Genetics in dilated cardiomyopathy. Biomarkers in Medicine 7, 517-533 Karlsson, E. K. & Lindblad-Toh, K. (2008) Leader of the pack: gene mapping in dogs and other model organisms. Nature Reviews Genetics 9, 713-725 Madsen, M. B., Olsen, L. H., Häggström, J., et al. (2011) Identification of two loci associated with development of myxomatous mitral valve disease in Cavalier King Charles spaniels. Journal of Heredity 102 (Suppl 1), S62-S67 Mary, J., Chetboul, V., Carlos Sampedrano, C., et al. (2010) Prevalence of the MYBPC3-A31P mutation in a large European feline population and association with hypertrophic cardiomyopathy in the Maine Coon breed. Journal of Veterinary Cardiology 12, 155-161 Mausberg, T., Wess, G., Simak, J., et al. (2011) A locus on chromosome 5 is associated with dilated cardiomyopathy in Doberman Pinschers. PLoS ONE 6, e20042 Meurs, K. M., Fox, P. R., Norgard, M., et al. (2007) A prospective genetic evaluation of familial dilated cardiomyopathy in the Doberman pinscher. Journal of Veterinary Internal Medicine 21, 1016-1020 Meurs, K. M., Mauceli, E., Lahmers, S., et al. (2010) Genome-wide association identifies a deletion in the 3’ untranslated region of Striatin in a canine model of arrhythmogenic right ventricular cardiomyopathy. Human Genetics 128, 315-324 Meurs, K. M., Lahmers, S., Keene, B. W., et al. (2012) A splice site mutation in a gene encoding for PDK4, a mitochondrial protein, is associated with the development of dilated cardiomyopathy in the Doberman pinscher. Human Genetics 131, 1319-1325 Owczarek-Lipska, M., Mausberg, T. B., Stephenson, H., et al. (2013) A 16-bp deletion in the canine PDK4 gene is not associated with dilated cardiomyopathy in a European cohort of Doberman Pinschers. Animal Genetics 44, 239 Stabej, P., Imholz, S., Versteeg, S. A., et al. (2004) Characterization of the canine desmin (DES) gene and evaluation as a candidate gene for dilated cardiomyopathy in the Dobermann. Gene 340, 241-249 Stabej, P., Leegwater, P. A., Imholz, S., et al. (2005) The canine sarcoglycan delta gene: BAC clone contig assembly, chromosome assignment and interrogation as a candidate gene for dilated cardiomyopathy in Dobermann dogs. Cytogenetic and Genome Research 111, 140-146 Werner, P., Raducha, M. G., Prociuk, U., et al. (2008) A novel locus for dilated cardiomyopathy maps to canine chromosome 8. Genomics 91, 517-521 Wess, G., Schimner, C., Weber, K., et al. (2010) Association of the A31P and A74T polymorphisms in ythe myosin binding protein C3 gene and hypertrophic cardiomyopathy in Maine coon and other breed cats. Journal of Veterinary Internal Medicine 24, 527-532 Wiermsa, A. C., Stabej, P., Leegwater, P. A., et al. (2008) Evaluation of 15 candidate genes for dilated cardiomyopathy in the Newfoundland dog. Journal of Heredity 99, 73-80
Hannah Stephenson graduated from the University of Glasgow in 2005 and spent her first 2 years in mixed practice in Lancashire. She undertook a Junior Clinical Training Scholarship at the RVC before moving back up North to the University of Liverpool as a research assistant. This research investigated the genetic basis of dilated cardiomyopathy in dogs, as part of the LUPA project, and she has continued her research over the years investigating DCM in Great Danes more specifically. She undertook a residency in cardiology at Liverpool during which time she gained the RCVS certificate in small animal medicine. She was awarded the ECVIM diploma in cardiology in 2012, followed by RCVS specialist recognition in 2014. After a short time as a clinical lecturer at the University of Liverpool, she now runs a peripatetic cardiology referral service for veterinary practices in the North West.
240
Journal of Small Animal Practice
•
Vol 55
•
May 2014
•
© 2014 British Small Animal Veterinary Association
