CONGENITAL HYPOTHYROIDISM IN GIANT SCHNAUZERS

本子项目是利用由NIH/NCRR资助的中心赠款提供的资源的众多研究子项目之一。子项目和研究者（PI）可能已经从另一个NIH来源获得了主要资金，因此可以在其他CRISP条目中表示。列出的机构是中心的，不一定是研究者的机构。这些研究是与John Fyfe博士合作进行的，在宾夕法尼亚大学担任初级教员期间，他在这项资助下开始了这项研究，并在他转到密歇根州立大学担任教职后继续进行。常染色体隐性非原发性先天性甲状腺功能减退症（CH）在巨型雪纳瑞犬中有报道。我们获得了这种疾病的携带者，它随后被培育成一只正常的小猎犬。与雪纳瑞犬的回交再现了这种疾病。在最初的报告中，没有犬促甲状腺素（TSH）的实验室测试，虽然这种疾病被认为不是甲状腺的原发性疾病，但不可能确定缺陷是在垂体还是下丘脑的水平上。对狗进行TSH测试使我们能够解决这个问题。对f1回交交配产生的窝仔的前瞻性研究表明，在3至8周龄之间，受影响的犬垂体对促甲状腺激素释放激素（TRH）无反应，无论是外源性给药还是内源性产生甲状腺功能减退。面对不可降解的甲状腺激素影响的幼崽不产生TSH，表明下丘脑-垂体轴无法上调TSH的产生。Fyfe博士与转诊中心合作，已经开始描述这种疾病的分子基础。该疾病的主要群体由密歇根州立大学的Fyfe博士维持，但转诊中心向Fyfe博士提供了一只异交雌性，以增加CH连锁家族的遗传异质性。Fyfe博士获得了R03拨款，以确定该疾病的分子基础。异交和回交交配的结果表明，可能不止一个基因参与产生这种形式的先天性甲状腺功能减退症。遗传连锁调查已经排除了两个候选基因，TRH受体和TSHb基因。我们目前正在检查trh介导的信号级联中其他参与者的基因标记物，以寻找与该犬家族内分泌紊乱的关联。此外，在与Henthorn博士的合作下，我们已经启动了一项基因组扫描，以寻找联系，以开发比较位置候选基因。已发现与CFA 20有初步联系。受影响犬垂体的免疫组织化学和电镜检查结果表明，促甲状腺激素正在经历一种未折叠的蛋白质应激反应，可能是由于无法正确处理和包装TSH。在上述项目中获得的研究和知识直接为近期玩具狐梗犬常染色体隐性CH伴甲状腺肿的识别和鉴定提供了依据。这是CH的一种严重形式，会导致侏儒症，并在出生后的前两周内无法茁壮成长。Fyfe博士实验室的研究表明，受影响的狗甲状腺缺乏甲状腺过氧化物酶（TPO）活性，并且狗是TPO基因无义突变的纯合子。在人类中也有类似的TPO突变。通过Fyfe博士实验室的测试项目确定的疾病携带者可用于建立繁殖群体。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. These studies, conducted in collaboration with Dr. John Fyfe, were begun under this grant at the University of Pennsylvania during the time he was a junior faculty member and have continued since his move to a faculty position at Michigan State University. Autosomal recessive non-primary, congenital hypothyroid dwarfism (CH) was reported in giant schnauzer dogs. We obtained a carrier of this disorder, which was subsequently bred to a normal beagle. Backcrosses to the schnauzer line reproduced the disorder. At the time of the original report, a laboratory test for canine thyrotropin (TSH) was not available and while the disorder was recognized not to be a primary disease of the thyroid, it was not possible to determine whether the defect lay at the level of the pituitary or the hypothalamus. The availability of a TSH test for the dog enabled us to resolve this question. Prospective studies of litters resulting from F1-backcross matings demonstrate that between 3 and 8 weeks of age the affected dog pituitary becomes unresponsive to thyrotropin releasing hormone (TRH), either administered exogenonously or produced endogenously in response to hypothyroxemia. In the face of undectedable thyroid hormone affected pups do not produce TSH, indicating an inability of the hypothalamic-pituitary axis to upregulate TSH production. Dr. Fyfe, in collaboration with the Referral Center, has begun to characterize the molecular basis of this disease. The main colony with this disorder is maintained by Dr. Fyfe at Michigan State University, but an outcross female was provided to Dr. Fyfe by the Referral Center to increased genetic heterogeneity in the CH linkage family. Dr. Fyfe received an R03 grant to determine the molecular basis of the disorder. Results of outcross and backcross matings suggest that more than one gene may be involved in producing this form of congenital hypothyroidism. Genetic linkage investigations have eliminated two gene candidates, the TRH receptor and TSHb genes. We are currently examining markers in genes of other participants in the TRH-mediated signaling cascade for association with the endocrine disorder in this family of dogs. Additionally, in collaboration with Dr. Henthorn we have initiated a genome scan for linkage in order to develop comparative positional candidate genes. Tentative linkage has been found to CFA 20. Results of immunohistochemical and electron microscopic examination of affected dog pituitary glands suggest that the thyrotrophs are experiencing an unfolded protein stress response, perhaps due to inability to properly process and package TSH. The studies and knowledge gained in the above project directly provided the basis for the recent recognition and characterization of autosomal recessive CH with goiter in toy fox terrier dogs. This is a severe form of CH causing dwarfism and failure to thrive in the first 2 weeks of life. Studies in Dr. Fyfe¿s laboratory demonstrated that affected dog thyroid is deficient in thyroid peroxidase (TPO) activity, and the dogs are homozygous for a nonsense mutation in the TPO gene. Similar TPO mutations have been described in humans. Carriers of the disorder identified through a testing program in Dr. Fyfe¿s laboratory are available for establishment of a breeding colony.