MYOTONIA CONGENITA IN MINIATURE SCHNAUZERS

该子项目是利用NIH/NCRR资助的中心赠款提供的资源的许多研究子项目之一。子项目和研究者（PI）可能从另一个NIH来源获得主要资金，因此可以在其他CRISP条目中表示。所列机构为中心，不一定是研究者所在机构。在小型雪纳瑞犬中，CIC-I氯离子通道的突变导致常染色体隐性遗传性先天性肌强直。该突变导致D5跨膜区段中的苏氨酸残基被甲硫氨酸取代。已经建立了一个受影响和杂合子狗的群体，并对8只受影响的狗进行了检查。受影响的犬表现出刺激后骨骼肌松弛延迟、弥漫性骨骼肌肥大、喘鸣、异常吠叫和僵硬、高跷步态，运动后可改善。牙齿异常，包括脱位，乳牙和恒牙列的延迟萌出，乳牙的延迟剥脱，以及恒牙的未萌出或部分萌出已被记录。在其他患有先天性肌强直的动物中，没有描述过此类牙齿异常。临床和电生理体征在5周龄时首次明显。杂合子狗没有表现出任何临床或电生理疾病的迹象。两只受影响的狗从4周龄开始用普鲁卡因胺治疗;治疗的狗表现出肌肉僵硬和成年后牙齿异常的改善。我们与Alfred L.博士合作开发了一种基于PCR的先天性肌强直DNA检测方法。范德比尔特大学遗传医学部主任小乔治。微型雪纳瑞的血液或脸颊拭子来自美国，加拿大和其他国家的各个州。提取DNA，用种特异性引物扩增突变位点周围的片段。然后用Hpy CH 4 III消化340通过PCR的产物，Hpy CH 4 III是一种限制酶，其切割正常等位基因两次，产生175、135和30 bp的片段。而突变等位基因仅被切割一次，产生175和165个片段。共筛选了354只犬，发现79.1%正常，19.8%为携带者，L1%（4只犬）受影响。携带者和正常犬的雌雄比为1.2。在这一偏向性犬组中，突变等位基因频率为1.1%，可从59个携带者和所有4只受影响犬获得谱系。一个流行的父系已知是一个载体被确定为一个共同的祖先，所有的狗与突变等位基因。我们最近的研究发现，携带者的狗中存在电性肌强直，这表明杂合子显示出一些疾病的证据。

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. In the Miniature Schnauzer dog, a mutation in the CIC-I chloride channel is responsible for autosomal recessive myotonia congenita. The mutation results in replacement of a threonine residue in the D5 transmembrane segment with methionine. A colony of affected and heterozygote dogs has been established and eight affected dogs have been examined. Affected dogs exhibited a delay in skeletal muscle relaxation following stimulation, diffuse skeletal muscle hypertrophy, stridor, an abnormal bark, and a stiff, stilted gait that improves with exercise. Dental abnormalities including disoclusion, delayed dental eruption of both deciduous and permanent dentitions, delayed dental exfoliation of the primary teeth, and unenipted or partially erupted permanent teeth have been documented. In no other animals affected with myotonia congenita have such dental abnormalities been described. Clinical and electrophysiological signs are first apparent at 5 weeks of age. Heterozygous dogs showed no clinical or electrophysiological signs of disease. Two affected dogs were treated with procainamide from 4 weeks of age onward; treated dogs showed amelioration of muscle stiffness and of dental abnormalities as adults. We have developed a PCR-based DNA test for myotonia congenita in collaboration with Dr. Alfred L. George, Jr , Director, Division of Genetic Medicine, Vanderbilt University. Either blood or cheek swabs from miniature schnauzers were obtained from the various states in the US, Canada, and other countries. DNA was extracted and the segment around the site of the mutation was amplified with species-specific primers. The 340 by PCR product was digested then with Hpy CH4 III, a restriction enzyme that cuts the normal allele twice resulting in fragments of 175, 135, and 30 bp., while the mutant allele is cut only once resulting in 175 and 165 by fragments. A total of 354 dogs were screened, and 79.1% were found normal, 19.8% were carriers, and L 1% (4 dogs) were affected. The male to female ratio was 1'2 among carriers as well as normal dogs tested. In this biased group of dogs, the mutant allele frequency was 1 1 ¿% Pedigrees were available from 59 carriers and all four affected dogs. One popular sire known to be a carrier was identified as a common ancestor to all of the dogs with a mutant allele. Our recent studies have identified electrical myotonia is present in carrier dogs indicating that heterozygotes show some evidence of disease.