Dino Ferrari Center, Neuroscience Section, Department of Pathophysiology and Transplantation, University of Milan, Neurology Unit, Istituto Di Ricovero e Cura a Carattere Scientifico Foundation Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy.
J Physiol Pharmacol. 2013 Oct;64(5):669-78.
Here we present the case of a 32-year-old female patient with myotonia congenita. She carried two mutations in the CLCN1 gene that encodes the chloride channel ClC-1: p.Phe167Leu, which was previously identified in several families, and p.Val536Leu, which has been previously reported but not yet characterized by electrophysiological investigations. The patient's symptoms included generalized stiffness, myotonia, and muscle cramps mostly localized in the lower limbs. These symptoms started during childhood and worsened over the following years. The symptoms were exacerbated by low outside temperature, rest, stress, and fasting and were improved by mild exercise, suggesting a warm-up phenomenon. The mutation p.Phe167Leu has previously been associated with a slight shift in the overall open probability. Here we further analysed this mutation to extrapolate the voltage-dependence of the fast and slow gates. In our experimental conditions, p.Phe167Leu exclusively affected the slow gate, increasing the minimum open probability and displacing the voltage-dependence toward depolarized potentials. p.Val536Leu showed more severe effects, dramatically influencing the slow gate as well as modifying properties of the fast gate. Co-expression of the mutants in a human cell line to reproduce the compound heterozygous condition of the patient produced channels with altered voltage-dependence of the slow gate but a restored fast gate. The alteration of the slow mechanism was reflected by the relative open probability, reducing the contribution of ClC-1 channels in maintaining the resting membrane potential of skeletal muscles and thus explaining the myotonic phenotype of the patient.
我们在此介绍一例先天性肌强直症患者，该患者携带两个 CLCN1 基因突变：p.Phe167Leu 和 p.Val536Leu。前者曾在多个家族中被发现，而后者虽然已有报道但尚未通过电生理研究进行特征分析。该患者的症状包括全身性肌肉僵硬、肌强直和肌肉痉挛，主要集中在下肢。这些症状始于儿童时期，随后几年逐渐加重。症状在低温、休息、压力和禁食时加重，而在轻度运动后改善，这提示存在预热现象。p.Phe167Leu 突变此前与整体开放概率的轻微偏移有关。在此，我们进一步分析了该突变，以推断快、慢门控的电压依赖性。在我们的实验条件下，p.Phe167Leu 仅影响慢门控，增加最小开放概率并将电压依赖性移向去极化电位。p.Val536Leu 则表现出更严重的影响，极大地影响了慢门控并改变了快门控的性质。将突变体在人类细胞系中共同表达，以再现患者的复合杂合状态，产生了具有慢门控电压依赖性改变的通道，但快门控得到恢复。慢机制的改变反映在相对开放概率上，降低了 ClC-1 通道在维持骨骼肌静息膜电位中的作用，从而解释了患者的肌强直表型。
