Dogs live with humans, and have access to medical care nearly as sophisticated as ours. We are also close in other ways: sharing approximately 85% of our genome – that is our complete sets of genes – any naturally occurring gene mutation that may cause a disease in dogs is likely to cause a similar condition in humans, and vice versa. Dogs can serve as models of human disease; for example, treatments such as gene therapy can be tried in dogs before going into clinical trials in humans, which can benefit both species.
The sequencing of the canine genome greatly increased the speed and efficiency with which genes that cause disease can be detected. It has also facilitated research into the origin of dogs and the search for genes that underlie specific traits in dogs, such as height and skull shape, and many hereditary diseases. Next generation sequencing (NGS), including whole exome sequencing (WES) – technologies which allow geneticists to determine the precise order of nucleotides within DNA and RNA molecules much more quickly and cheaply than before –and the establishment of publically available databases has also allowed for easier identification of genes and mutations that may cause disease.
LGMDs are a varied group of Mendelian disorders … characterized by muscle wasting and weakness in the muscles of the shoulders and hips
Our group made use of these technologies to study a form of Limb-girdle muscular dystrophy (LGMD) in Boston terrier dogs. LGMDs are a varied group of Mendelian disorders – diseases caused by single genes that are inherited according to Mendel’s laws – characterized by muscle wasting and weakness in the muscles of the shoulders and hips. Four affected dogs from three unrelated families were identified by their primary veterinarians, and referred for specialized investigation.
临床检查和病理学结果证实，所有受影响的狗都患有LGMD和免疫组织病理学测定，它们使用与某些组织结合的抗体揭示其存在的抗体，这表明一种肉体糖性疾病 - 这是一种由四个基因中的突变引起的疾病对于某种类型的蛋白质，称为肉糖果。肉体肿瘤病是常染色体隐性，具有类似于Duchenne肌肉营养不良的严重症状。
有六种肉糖蛋白，其中四种（α，β，δ，γ）参与肌肉中的结构和信号功能。从受影响的狗的肌肉中缺少肌聚糖，使我们的候选基因编码这些蛋白质的基因，整个外显子组测序使我们能够同时研究它们。
从四只狗中的两只狗和其中一只狗的几个亲戚那里获得了DNA。对总共5只狗进行了整个外显子组测序，其中包括患有这种疾病和专性载体的两只狗 - 一只没有这种疾病但必须基于家族史的分析来携带基因突变的狗。在一只受影响的狗（情况3）中，我们发现两个核苷酸（DNA的建筑物块）被删除在其中一个sarcoglycan基因中。该狗的义务载体父母和另一个亲戚也有一份删除副本。
The other affected dog (Case 1) did not share this mutation, which was very surprising to us, given that they were the same breed. Breed structures limit genetic diversity, because dogs are only bred to other dogs of the same breed. This increases the chance that any two dogs will be related, and that they will carry a mutation that is “identical by descent”, that is, inherited from a shared ancestor. For this reason, most dogs in a breed with the same disease will share the same gene mutation.
This is also a good reminder to the animal breeding and veterinary community that even within one breed, a disease may be caused by more than one mutation
Further analysis showed that Case 1 had a different deletion in the same gene as Case 3. We hypothesize that the dogs have very similar phenotypes because the same portion of the protein coded by the gene is eliminated in the two different mutations.
We screened 200 more Boston terriers from North America and Europe, as well as a large variety of other breeds, and these mutations were not found outside of these two cases and family members. This is good news for the breed, as it appears that these are “private mutations”, found only in these two families. Although we have developed genetic tests for these two mutations, it will not be necessary for breeders of Boston terriers to add LGMD testing to their routine genetic screening at this time.
这也很好地提醒了动物育种和兽医界，即使在一个品种中，疾病也可能是由多个突变引起的。因此，测试实验室指出在编写报告时已经测试了哪些特定突变是最佳实践。
The two mutations were found in the sarcoglycan genesgcd，因此该疾病被归类为肢体肌肉营养不良2F（LGMD2F）（在肌肉营养不良症命名系统中，数字2表示它是一个常染色体隐性基因，而F代表该基因名称）。LGMD2F是人类肉体糖果肿大的最不常见的形式，因此我们关于第一个大型肉毒杆菌病模型的报告也可能引起人类医学的关注。
这项工作还证明了整个外显子组测序的实用性，以鉴定极少数受影响的动物中的突变。这可以比过去更快地确定突变，因为没有必要从大型家庭群体中收集样本。因此，早期建立了一项基因检测计划，以区分正常和未受影响的载体动物可以防止疾病通过品种人群无意间扩散。
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