Animal Health Trust Bloat Proposal_2012 Cathryn Mellersh

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1 Genetic Investigation of Bloat in the Irish Setter Phase A Introduction Gastric dilation (GD) and gastric dilation-volvulus (GDV), commonly referred to as bloat, are life-threatening conditions affecting large and giant-breed dogs [1-3]. During a bloat attack air accumulates in the stomach, putting pressure on the other organs and diaphragm, compressing large veins in the abdomen and preventing blood from returning to the heart. Filled with air, the stomach can easily rotate (volvulus) which pinches off its blood supply causing the stomach to begin to die and the entire blood supply to be disrupted. The condition affects apparently healthy dogs, usually with little warning, and treatment frequently requires surgical intervention to reposition and suture the stomach to prevent it from twisting again (a procedure called gastropexy). It is likely that bloat is a truly complex disease, having both genetic and environmental components. Significance to Canine Health Data from a health survey of purebred dogs, undertaken in 2004 by the Kennel Club/British Small Animal Veterinary Association Scientific Committee [4], indicated that GDV was a cause of morbidity for dogs of 44 breeds and a cause of death in 65 breeds, representing 2.5% of all deaths reported. The four breeds with the highest prevalence were the Grand Bleu de Gascogne (21.4%), the Bloodhound (14.3%), the Otterhound (9.0%) and the Irish Setter (7.2%). In the 2004 Kennel Club health survey 5.3% of Irish Setter deaths reported were due to GDV, accounting for the death of 24 dogs out of the 451 that were reported [2]. Around 1000 Irish Setters are registered with the Kennel Club in the UK each year. If the above figures are Page 1 of 7

2 extrapolated to the whole population then it is expected that around 50 Irish Setters will die each year from GDV in the UK alone. Preliminary Data In 2010, questionnaires were sent to the owners of 2,010 Irish Setters for which the Animal Health Trust (AHT) holds samples of DNA (Mellersh, 2010, unpublished). These samples were originally submitted to the AHT for genetic testing for progressive retinal atrophy (PRA) or canine leukocyte adhesion deficiency (CLAD), or had been provided for research purposes. Information was reported for 430 individual dogs. Owners were questioned on nine specific health conditions that have been highlighted as being of particular concern to those involved with the Irish Setter breed by the 2004 Health survey described above [4], one of which was GDV. In addition, owners were invited to provide information on any other health conditions seen in their dogs. Where named dogs had died, the possible cause and age of death was requested. The opportunity to indicate that named dogs had experienced no health problems was also provided. At the time of the survey response 251 dogs were no longer alive. GDV was reported to be the cause of death of 12 out of these 251 dogs (4.8%), which is comparable to the figure of 5.3% of Irish Setters that die from GDV reported by the Kennel Club health survey [2]. An additional 26 dogs had survived at least one attack of bloat, meaning 38 out of the 430 dogs (8.8%) included in the survey had been affected by GD or GDV, again a comparable figure to the 7.2% prevalence figure reported previously [2]. This survey was undertaken in collaboration with the Kennel Club and the Irish Setter Association in the UK. Identifying Genetic Risk Factors for Bloat Bloat clearly is a major concern for the Irish setter. Identifying genetic risk factors associated with the occurrence of bloat would be beneficial for two main reasons. Firstly, bloat-associated mutations could form the basis of genetic tests that breeders could use to determine the genotype of individual dogs and plan matings that would produce offspring with minimal risk of developing bloat. Secondly, understanding which genes play a part in increasing an individual dog s risk of bloat might shed Page 2 of 7

3 light on environmental factors or morphological traits that are risk factors for the condition. Earlier in 2011 staff from the Animal Health Trust applied to the American Kennel Club Canine Health Foundation (AKC CHF) for funding to undertake an ambitious study to identify both genetic and epidemiological risk factors for bloat. Unfortunately the AKC CHF declined to fund the study, mainly due to the high cost of the proposal. The Animal Health remains committed to investigating the genetic basis of bloat, but considering the overall cost of the study have decided to break the project down into its component phases and seek funding and undertake the individual stages sequentially. The study is, therefore, now being considered in two separate phases: Phase A Data collection and estimation of heritability. Phase B DNA sample collection from bloat cases and controls and genetic analysis. Below are full details and estimated costs for Phase A of the study. Page 3 of 7

4 Phase A - Study design The aim of Phase A is to i) identify Irish setters that have suffered at least one attack of bloat (cases) and dogs that are over the age of 10 yo, have been cared for by the same owner from an early age (<1 yo) and have never suffered an attack of bloat during their life (controls) and ii) to calculate the heritability of bloat. The heritability will provide us with an estimate of how much of an individual dog s risk of bloat is attributable to its genetics (as opposed to environmental factors and random chance), and therefore how easy it will be to identify genetic risk factors for the condition and reduce the prevalence by breeding strategies. If the estimate of heritability is large enough in magnitude and significantly determinable from zero we will proceed to Phase B of the study, which will comprise a genetic investigation. Step 1. An initial, brief correspondence will be distributed to the owners of all Irish Setters registered with the Kennel Club that will be between the ages of 1 12 years old (yo) at the time of questioning. Owners will receive a brief explanation of the study and will be asked if their dogs have ever suffered an attack of bloat. They will also be asked if they are willing to be contacted again, to provide more information about their dogs. It is expected that the owners of approximately 11,000 dogs will receive this initial correspondence, of which approximately 7% or ~770 dogs will have suffered at least one attack of bloat. If we achieve a 25% response rate from owners agreeing to assist with the study, we will identify approximately 190 cases and an equivalent number of controls that are over the age of 10 yo and our study design is based on these numbers. However, because this survey will target a single health condition that Irish Setter breeders and owners are very concerned about we may realize an actual response rate of ~50% which would mean that we would identify >350 cases. As the AHT has realized this level of response in previous targeted breedspecific health surveys we are optimistic that this level of response can be achieved. We could also use this initial correspondence to identify dogs that are affected by additional, potentially inherited conditions, such as megaesophagus. This will not affect the cost of Phase A and will generate data that could be used in future studies. Page 4 of 7

5 Step 2. Animal Health Trust Bloat Proposal_2012 A second correspondence will then be sent to the owners of all the cases and all the controls identified in Stage 1. The second correspondence will contain a brief questionnaire containing simple questions about the bloat attacks their dog has suffered. The owners will also be asked to take a small number of simple body measurements of their dog. Step 3. Once we have identified a sufficient number of cases and controls we will estimate the heritability of bloat. To do this we will use each dog s case/control status and pedigree information provided by the Kennel Club database revealing the relationships between them. We anticipate that a response rate of 33% will provide us with ~250 cases, which should enable us to obtain a moderately accurate heritability estimate. By collecting data about body size and shape it will also be possible to investigate the association, if any, between body shape and risk of bloat. If we obtain an accurate estimate of heritability 0.4 we will proceed to Phase B. A heritability of this size would indicate the risk of an individual dog developing bloat is sufficiently controlled by its genetics (as opposed to its environment) for us to identify genetic risk factors and go on to develop genetic tools to reduce the prevalence of the condition. Phase B. The owners of all the cases and controls will be asked to sample their dog s DNA by taking a simple cheek swab and return it to the AHT. Once these samples have been collected the Animal Health Trust will be very well placed to apply for funding for Phase B of the study, which will be to undertake genetic analysis of the cases and controls to identify genetic risk factors for bloat. The findings from Phase A, and the numbers of cases and controls identified and sampled, will determine the precise details and cost of Phase B so these will not be provided at this stage. Phase A - Budget price per item number Total Page 5 of 7

6 ( ) needed ( ) Step 1 - initial correspondence ,250* 4,125 Step 2-2nd correspondence ** 350 Research assistant: 40% FTE for 6 months*** 3,440 Total 7,915 * It is estimated the ~11,000 KC registered Irish setters between the ages of 1 12yo will be owned by ~8,250 owners, which is the equivalent to 4 dogs per 3 owners. ** The estimate of 700 is based on a 50% response rate, so might, in reality, be lower. *** A research assistant will be required to collate information collected during Step 1, distribute the 2 nd correspondence and collate data collected during Step 2. The heritability will be calculated by Dr. Tom Lewis, who is currently employed by the AHT to work in the Kennel Club Genetics Centre at the AHT, so no additional funding is required for this purpose. Phase A Time Frame Once we have secured sufficient funding to proceed the project will proced along the following time lines: Stage Period from start of Phase A to distribution of intial correspondence Deadline for returning initial correspondence Period from completion of Step 1 until distribution of second correspondence Deadline for returing second correspondence Estimation of heritabiity and data analysis Total Weeks Completion of Step 1 Completion of Step 2 Completion of Step 3 References 1. Ward, M.P., G.J. Patronek, and L.T. Glickman, Preventive Veterinary Medicine, (4): p Page 6 of 7

7 2. Evans, K.M. and V.J. Adams, Journal of Small Animal Practice, (7): p Glickman, L.T., et al., Journal of the American Veterinary Medical Association, (9): p Adams, V.J., et al., Journal of Small Animal Practice, : p Page 7 of 7