MYOTONIA CONGENITA IN MINIATURE 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。在迷你雪纳瑞犬中，c - 1氯离子通道的突变是常染色体隐性遗传性先天性肌强直的原因。突变导致D5跨膜段的苏氨酸残基被蛋氨酸取代。建立了一个受感染和杂合子狗的群体，并对8只受感染的狗进行了检查。受影响的狗在刺激后表现出骨骼肌松弛延迟，弥漫性骨骼肌肥大，喘鸣，吠叫异常，步态僵硬，高跷，随着运动而改善。牙齿异常，包括断牙、乳牙和恒牙延迟出牙、乳牙延迟脱牙、恒牙未脱臼或部分出牙，均有文献记载。在没有其他动物患先天性肌强直有这样的牙齿异常被描述。临床和电生理症状在5周龄时首次出现。杂合子犬没有表现出疾病的临床或电生理症状。两只受影响的狗从4周龄开始接受普鲁卡因胺治疗；接受治疗的狗表现出肌肉僵硬和牙齿异常的改善。我们与范德比尔特大学遗传医学部主任Alfred L. George， Jr博士合作开发了一种基于pcr的先天性肌强直DNA检测方法。从美国、加拿大和其他国家的各个州获得了微型雪纳瑞的血液或脸颊拭子。提取DNA，用物种特异性引物扩增突变位点周围的片段。然后用Hpy CH4 III酶切340个PCR产物，Hpy CH4 III酶切正常等位基因两次，得到175、135和30 bp的片段。，而突变等位基因只被切割一次，产生175和165个片段。共筛查354只犬，正常犬79.1%，带菌者19.8%，感染犬1%（4只）。在携带者和正常狗的测试中，男女比例为1:2。在这组偏倚的狗中，突变等位基因频率为11%，来自59名携带者和所有4只受影响的狗的谱系均可获得。一个已知是携带者的受欢迎的父系被确定为所有具有突变等位基因的狗的共同祖先。我们最近的研究已经确定电性肌强直存在于携带者犬中，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.