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

癫痫是一种复杂的脑部疾病，其中个体易于表现出自发性癫痫发作。特发性癫痫（IE）被分类为主要遗传或假定遗传起源的癫痫，并且其中没有引起癫痫发作活动的大脑结构的大体异常或其他相关基础疾病。IE是家犬中最常见的慢性神经系统疾病，估计影响0.6%的犬，但在某些品种中明显更高，例如比利时牧羊犬中为17-33%。目前使用的抗癫痫药物（AED）的副作用也限制了生活质量，并且由于继发于癫痫的过早死亡风险增加，生活质量可能会降低。治疗癫痫犬的兽医和受影响犬的主人面临的进一步挑战是（i）耐药性：对目前可用的AED缺乏反应，影响高达60-86%的治疗犬，以及（ii）与IE共病的神经行为变化，这在犬中知之甚少，但在癫痫患者中非常普遍。我们自己的研究以前发现，只有14%的狗在治疗时没有癫痫发作，并且在IE发作后看到恐惧/焦虑和防御性攻击的增加。这些共同特征使犬成为自发性耐药性癫痫的理想转化模型。很明显，有必要对犬的IE进行更深入的了解，以确定以下风险因素：（i）IE的发展，（ii）对可用的AED治疗缺乏反应，（iii）行为变化的发展，以及（iv）这些因素之间的相互作用，以便将来治疗或预防IE的努力具有针对性和有效性。到目前为止，癫痫和AED反应的遗传标志物取得的成功有限，可能难以解释，并且仅占易感性的有限比例。在这项研究中，我们研究了代谢途径的生化副产物（“代谢组”）和与身体相关的微生物（“微生物组”），这反映了生物体基因组与其环境之间的相互作用，并且是观察到的特征的更好的潜在指标，可以作为治疗策略进行修改。虽然尚未发现IE的代谢组学标志物，但已在人类和小鼠中确定了焦虑的概况。微生物组尚未在IE开发中进行研究，但参与了AED的代谢，并且通过脑肠道相互作用与焦虑水平相关。这项研究计划将研究疾病表现的类型，行为特征的变化，代谢物组中代谢物的变化，以及患有和未患有IE的狗的微生物组中微生物种群的差异，以确定疾病的新生物标志物，药物反应和行为体征（以及这些因素之间的关联），这可能为潜在疾病生物学提供新的视角，并提供新的治疗靶点。我们将分两个阶段研究这些新措施：首先，对从我们的医院人群中招募的有和没有IE的品种和年龄匹配的狗进行病例对照研究，以直接比较特征;其次，对来自英格兰南部的5000只小狗进行前瞻性队列研究，以确定癫痫发作前测量的身体和行为特征，这些特征作为IE发展的危险因素。将采集尿液和粪便样本进行代谢组学和微生物组学分析。行为测试将对狗的潜在情感状态进行分析，以揭示IE和耐药性是否与使个体倾向于进行焦虑相关行为的潜在特征相关。需要这种新的和全面的方法来解开IE的机制，耐药性和行为异常的发生。

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.