Investigating the relationship between epilepsy, drug-resistance and affective disorders in the domestic dog

Epilepsy is a complex brain disease, in which individuals are pre-disposed to show spontaneous seizures. Idiopathic epilepsy (IE) is classified as epilepsy of predominantly genetic or presumed genetic origin and in which there are no gross abnormalities of the structure of the brain nor other relevant underlying diseases causing seizure activity. IE is the most common chronic neurological condition in domestic dogs, estimated to affect 0.6% of dogs, but markedly higher in some breeds e.g. 17-33% in the Belgian Shepherd. Quality-of-life is also limited by side-effects of the currently used anti-epileptic drugs (AEDs), and quantity-of-life is potentially reduced due to an increased risk of premature death secondary to epilepsy. Further challenges faced by veterinarians treating dogs with epilepsy, and owners of affected dogs ARE (i) drug-resistance: a lack of response to currently available AEDs affecting up to 60-86% of treated dogs, and (ii) neurobehavioural changes comorbid with IE, which are poorly understood in dogs but highly prevalent in people with epilepsy. Our own studies have previously found that as few as 14% of dogs become seizure free on treatment, and increases in fear/anxiety and defensive aggression are seen following the onset of IE. These common features make the dog an ideal translational model for spontaneously occurring drug resistant epilepsy.

It is clear that there is a need to gain a deeper understanding of IE in the dog to identify risk factors for (i) the development of IE, (ii) the lack of response to available AED therapies, (iii) the development of behavioural changes, and (iv) the interplay between these factors, so that future efforts to treat or prevent IE are targeted and effective. Genetic markers of both epilepsy and AED response have had limited success thus far, may be hard to interpret and account for only a limited proportion of susceptibility. In this study we instead investigate biochemical by-products of metabolic pathways (the 'metabolome') and the microorganisms living in association with the body (the 'microbiome') which reflects the interaction between an organism's genome and its environment and are a better potential indicator of observed characteristics, which can be potentially modified as treatment strategy. Although metabolomic markers of IE have not yet been found, profiles of anxiety have been identified in humans and mice. The microbiome has not yet been studied in IE development, but is involved in the metabolism of AEDs, and changes have been associated with anxiety levels through brain-gut interactions.

This research programme will characterise types of disease presentation, the variation in behavioural characteristics, variation in metabolites in the metabolome, and differences in micro-organism populations in the microbiome in dogs with and without IE to identify novel biological markers of both the disease, drug response and behavioural signs (and associations between these factors) that could provide new perspectives on the underlying disease biology and provide new treatment targets. We will study these novel measures in two stages: firstly, a case-control study of breed and age-matched dogs with and without IE recruited from our hospital populations to directly compare profiles; secondly, a prospective cohort study of 5000 puppies from the South of England to identify physical and behavioural profiles measured before seizure onset that act as risk factors for IE development. Urine and faecal samples will be collected for metabolomic and microbiomic analysis. Behavioural testing will characterise aspects of the dogs' underlying affective state, to reveal whether IE and drug-resistance are associated with an underlying characteristic that predisposes individuals to perform anxiety-related behaviours. This novel and comprehensive approach is needed to unravel the mechanisms underlying IE, the occurrence of drug-resistance and behavioural abnormalities.

Idiopathic epilepsy (IE) is a neurological disease of major welfare concern in the dog. In addition to seizure activity and quality-of-life limiting side-effects of the currently used anti-epileptic drugs (AEDs), further IE-associated challenges include (i) drug-resistance, affecting up to 60-86% of dogs treated with AEDs, and (ii) neurobehavioural changes comorbid with IE including increased anxiety. A deeper understanding of these factors and their interplay is required to improve IE treatment. Genetic markers of IE and AED response have had limited success thus far, and may account for only a limited proportion of susceptibility. This research programme will characterise the (i) behavioural (ii) metabolomic and (iii) microbiomic profiles of dogs with and without IE to identify novel biomarkers of IE, drug-resistance and behavioural co-morbidities. Although metabolomic markers of IE are yet to be found, metabolic profiles of anxiety have been identified in humans and mice. The microbiome has yet to be studied in IE development, but is involved in the metabolism of AEDs, and has effects upon the hippocampal serotonergic system including anxiety levels via the microbiota-gut-brain axis. Two complimentary studies will be conducted: a case-control study of breed/age-matched dogs with/without IE recruited from our hospital populations; and a prospective cohort study of puppies to identify profiles measured before seizure onset that act as risk factors for IE. Urine and faecal samples will be collected for metabolomic and microbiomic analysis. Behavioural testing including open field tests, cognitive bias and habituation rates will characterise underlying affective states, to reveal whether IE and drug-resistance are associated with an underlying characteristic predisposing individuals to show anxiety-related behaviours. This novel and comprehensive approach is needed to unravel the mechanisms underlying IE and develop more targeted treatments in the future.

Approximately 10.5 million dogs are kept as companion animals in the UK, of which an estimated 0.6-0.8% are affected by idiopathic epilepsy (approximately 63,000 dogs). Idiopathic epilepsy (IE) is a quality of life issue for both the affected dog and their owner. Management of dogs with IE often requires a long-term commitment by owners, including medicating their dog several times per day, monitoring for side-effects and ongoing financial costs. Seizures can be unpredictable and appear uncontrollable, and can be stressful for the owner to witness and manage, with 60-86% of dogs with IE uncontrolled by anti-epileptic drug therapy. Failed treatment may lead to early euthanasia. Inherited diseases in the domestic dog including IE have been a focus of scientific research and public attention for the past decade, for example major reports from charities, government bodies and an independent inquiry. IE was identified by The Dog Advisory Council as one of their 'priority problems' in 2012. This unique project will identify biomarkers of and risk factors for the development of IE, drug-resistance and co-morbid behavioural abnormalities.

Stakeholders who will benefit include:

(1) Commercial companies: pet food and veterinary pharmaceutical companies have an interest in the treatment of chronic diseases such as idiopathic epilepsy. An estimated 550,000 direct and indirect jobs are generated by pet ownership in Europe, and the pet food industry and related supply and services represent a combined annual turnover of over 24 billion Euros. Increased knowledge of the aetiopathogenesis of IE and mechanisms of drug-resistance in dogs will be advantageous in R&D studies of AED development and drug efficacy, along with the new field of identifying existing or novel treatments that improve co-morbid behavioural problems.

(2) Veterinary practices: IE is a commonly treated problem in first opinion veterinary practice, as demonstrated by published 'VetCompass' epidemiological data from RVC. IE is a frustrating condition for vets to treat, with widely varying responses to the same drugs between patients with the 'same' diagnosis, and thus increasing our understanding of IE, along with novel ways to identify dogs likely or unlikely to respond to AEDs and/or be affected by behavioural co-morbidities would greatly aid vets in their treatment of IE, and improve vet-client relations by allowing more tailored treatment plans for individual dogs.

(3) Dog breeders and regulatory bodies such as breed societies and the Kennel Club will benefit through an increased understanding of early life risk factors and profiles of dogs who will go on to develop IE, to inform the selection of animals from which to breed. At present there is no way to identify which individuals within a breed are at risk of developing IE, and with age of onset between 6 months and 6 years of age, many dogs may be used in breeding before their first seizure, which may inadvertently lead to the perpetuation of this disorder. If novel biomarkers of IE are identified, screening may be possible in the future to highlight high and low risk dogs and inform breeding strategies.

(4) Dog owners: Owners of dogs with IE are recognised to experience distress due to the management of their dog's condition, and are often frustrated to pay for expensive and invasive advanced diagnostic testing (e.g. MRI and CSF analysis) to be given an idiopathic diagnosis. As such, these owners are very keen gain a greater understanding of IE, particularly related to improvements in treatment. Owners may eventually benefit from improved therapeutic management of IE in their dog.

(5) Dogs suffering from IE: Affected dogs will benefit from the more personalised selection of AEDs, or development of novel targeted AEDs that result in reduced seizure frequency and behavioural abnormalities. This could significantly improve their QoL and reduce early euthanasia due to poor seizure management.