Paroxysmal kinesigenic dyskinesia and myotonia congenita in the same family: coexistence of a PRRT2 mutation and two CLCN1 mutations

Paroxysmal Kinesigenic Dyskinesia: Genetics and Pathophysiological Mechanisms

Paroxysmal kinesigenic dyskinesia (PKD), the most common type of paroxysmal movement disorder, is characterized by sudden and brief attacks of choreoathetosis or dystonia triggered by sudden voluntary movements. PKD is mainly caused by mutations in the PRRT2 or TMEM151A gene. The exact pathophysiological mechanisms of PKD remain unclear, although the function of PRRT2 protein has been well characterized in the last decade. Based on abnormal ion channels and disturbed synaptic transmission in the absence of PRRT2, PKD may be channelopathy or synaptopathy, or both. In addition, the cerebellum is regarded as the key pathogenic area. Spreading depolarization in the cerebellum is tightly associated with dyskinetic episodes. Whereas, in PKD, other than the cerebellum, the role of the cerebrum including the cortex and thalamus needs to be further investigated.

Clinical and molecular characteristics of myotonia congenita in China: Case series and a literature review

Myotonia congenita (MC) is a rare genetic disease caused by mutations in the skeletal muscle chloride channel gene (CLCN1), encoding the voltage-gated chloride channel ClC-1 in skeletal muscle. Our study reported the clinical and molecular characteristics of six patients with MC and systematically review the literature on Chinese people. We retrospectively analyzed demographics, clinical features, family history, creatine kinase (CK), electromyography (EMG), treatment, and genotype data of our patients and reviewed the clinical data and CLCN1 mutations in literature. The median ages at examination and onset were 26.5 years (range 11–50 years) and 6.5 years (range 1.5–11 years), respectively, in our patients, and 21 years (range 3.5–65 years, n = 45) and 9 years (range 0.5–26 years, n = 50), respectively, in literature. Similar to previous reports, myotonia involved limb, lids, masticatory, and trunk muscles to varying degrees. Warm-up phenomenon (5/6), percussion myotonia (3/5), and grip myotonia (6/6) were common. Menstruation triggered myotonia in females, not observed in Chinese patients before. The proportion of abnormal CK levels (4/5) was higher than data from literature. Electromyography performed in six patients revealed myotonic changes (100%). Five novel CLCN1 mutations, including a splicing mutation (c.853 + 4A>G), a deletion mutation (c.2010_2014del), and three missense mutations (c.2527C>T, c.1727C>T, c.2017 G > C), were identified. The c.892 G > A (p.A298T) mutation was the most frequent mutation in the Chinese population. Our study expanded the clinical and genetic spectrum of patients with MC in the China. The MC phenotype in Chinese people is not different from that found in the West, while the genotype is different.

The study of exercise tests in paroxysmal kinesigenic dyskinesia

OBJECTIVE

To unravel if there was muscular ion channel dysfunction in paroxysmal kinesigenic dyskinesia (PKD) patients using the exercises tests (ET).

METHODS

Sixty PKD patients including 28 PRRT2 mutations carriers were enrolled in this study, as well as 19 hypokalaemic periodic paralysis (HypoPP) patients as the positive controls and 45 healthy subjects as the negative controls. ET including long exercise test (LET) and short exercise test (SET) was performed in the corresponding subjects.

RESULTS

In the LET, both the overall PKD patients and HypoPP patients had greater CMAP amplitude and area increments during exercise than healthy controls. At most 25% of PKD patients were identified from the normality with greater amplitude increment than the area. On the contrary, 50% of HypoPP patients were differentiated with greater area increment than the amplitude. More percentage of PRRT2- patients than PRRT2+ patients had abnormal average amplitude increment. Unexpectedly, five PKD patients had abnormal maximum CMAP amplitude decrements after exercise in the LET, and one had abnormal maximum immediate amplitude decrement in the SET.

CONCLUSIONS

Distinct ET manifestations were found in PKD patients compared to normal controls and HypoPP patients.

SIGNIFICANCE

Abnormal muscle membrane excitability might be involved in the mechanisms responsible for PKD.

PRRT2 mutations in a cohort of Chinese families with paroxysmal kinesigenic dyskinesia and genotype-phenotype correlation reanalysis in literatures

PURPOSE OF THE STUDY

Though rare, children are susceptible to paroxysmal dyskinesias such as paroxysmal kinesigenic dyskinesia, and infantile convulsions and choreoathetosis. Recent studies showed that the cause of paroxysmal kinesigenic dyskinesia or infantile convulsions and choreoathetosis could be proline-rich transmembrane protein 2 (PRRT2) gene mutations.

MATERIAL AND METHODS

This study analysed PRRT2 gene mutations in 51 families with paroxysmal kinesigenic dyskinesia or infantile convulsions and choreoathetosis by direct sequencing. In particular, we characterize the genotype-phenotype correlation between age at onset and the types of PRRT2 mutations in all published cases.

RESULTS

Direct sequencing showed that 12 out of the 51 families had three different pathogenic mutations (c.649dupC, c.776dupG, c.649C>T) in the PRRT2 gene. No significant difference of age at onset between the patients with and without PRRT2 mutations was found in this cohort of patients. A total of 97 different PRRT2 mutations have been reported in 87 studies till now. The PRRT2 mutation classes are wide, and most mutations are frameshift mutations but the most common mutation remains c.649dupC. Comparisons of the age at onset in paroxysmal kinesigenic dyskinesia or infantile convulsions patients with different types of mutations showed no significant difference.

CONCLUSIONS

This study expands the clinical and genetic spectrums of Chinese patients with paroxysmal kinesigenic dyskinesia and infantile convulsions and choreoathetosis. No clear genotype-phenotype correlation between the age at onset and the types of mutations has been determined.

Sequence CLCN1 and SCN4A in patients with Nondystrophic myotonias in Chinese populations: Genetic and pedigree analysis of 10 families and review of the literature

Myotonia congenita (MC), paramyotonia congenita (PC) and sodium channel myotonias(SCM) were belonged to Non-dystrophic myotonias, in which muscle relaxation is delayed after voluntary or evoked contraction. These diseases can not be simply distinguished only based on symptoms and signs but also on genetics: more than 100 mutations in the CLCN1 gene have been associated with MC, while at least 20 mutations in the SCN4A gene have been associated with PC and SCM. Most of these genetics studies have been conducted outside China, only several MC, PC, and SCM families accepted gene scan were reported in China. Therefore we analyzed genetic mutations in CLCN1 and SCN4A in 10 Chinese families clinically diagnosed with Non-dystrophic myotonias. Our result revealed 12 potential disease-causing mutations(3 mutations were novel) that were present in the probands and affected family members. We also reviewed all available literature on mutations linked to these 3 disease in Chinese populations. Our results may help identify genetic determinants as well as clarify genotype-phenotype relationships.