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

癫痫是一种复杂的大脑疾病，个体容易表现出自发性癫痫发作。特发性癫痫(IE)被归类为主要由遗传或推测遗传引起的癫痫，在这种癫痫中，没有明显的大脑结构异常或其他相关的潜在疾病导致癫痫发作。IE是家犬中最常见的慢性神经系统疾病，估计影响0.6%的狗，但在一些品种中明显更高，例如比利时牧羊犬17%-33%。生活质量也受到目前使用的抗癫痫药物(AEDs)副作用的限制，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。治疗患有癫痫的狗的兽医和受影响的狗的主人面临的进一步挑战是：(I)抗药性：对目前影响高达60%-86%的治疗狗的AEDs缺乏反应，以及(Ii)与IE共存的神经行为变化，这种变化在狗身上知之甚少，但在癫痫患者中非常普遍。我们自己的研究之前发现，只有14%的狗在治疗后癫痫发作消失，在IE发作后，恐惧/焦虑和防御性攻击性增加。这些共同特征使狗成为自发发生耐药癫痫的理想翻译模型。显然，有必要对狗的IE有更深入的了解，以确定(I)IE的发展，(Ii)对现有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，以便未来治疗或预防IE的努力有针对性和有效。到目前为止，癫痫和AED反应的遗传标记都取得了有限的成功，可能很难解释，而且只占易感性的有限比例。在这项研究中，我们转而调查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)，它反映了有机体的基因组与其环境之间的相互作用，是观察到的特征的更好的潜在指示器，可以作为治疗策略进行潜在的修改。虽然还没有发现IE的代谢组学标记，但已经在人类和小鼠中发现了焦虑的特征。微生物组还没有在IE的发育过程中被研究，但参与了AED的新陈代谢，并且通过大脑-肠道的相互作用与焦虑水平有关。这项研究计划将描述患有和不患有IE的狗的疾病表现类型、行为特征的变化、代谢产物的变化以及微生物组中微生物群的差异，以确定疾病、药物反应和行为体征的新生物标记物(以及这些因素之间的关联)，从而为潜在的疾病生物学提供新的视角，并提供新的治疗目标。我们将分两个阶段对这些新措施进行研究：第一，从我们医院招募的品种和年龄匹配的患有和不患有IE的狗的病例对照研究，以直接比较特征；第二，对来自英格兰南部的5000只幼犬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，作为IE发生的危险因素。将采集尿液和粪便样本进行代谢组和微生物组分析。行为测试将表征狗潜在的情感状态的各个方面，以揭示IE和抗药性是否与使个人倾向于执行与焦虑相关的行为的潜在特征有关。需要这种新颖而全面的方法来揭开IE、耐药和行为异常发生的机制。

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.