Contribution of Asian Haplotype of KCNJ18 to Susceptibility to and Ethnic Differences in Thyrotoxic Periodic Paralysis.

CONTEXT AND OBJECTIVES: Thyrotoxic periodic paralysis (TPP) is an acute complication of thyrotoxicosis that can be lethal. TPP is rare in Caucasians but often affects young men in East Asian populations. This study aimed to clarify the contribution of KCNJ18 to susceptibility to TPP in East Asian populations. PARTICIPANTS AND METHODS: The study comprised 635 participants including 13 Japanese patients with TPP, 208 Japanese patients with Graves disease without TPP, and 414 healthy control subjects from the Japanese (n = 208), Korean (n = 111), and Caucasian populations (n = 95). DNA samples from 29 participants (13 with TPP, 8 with Graves disease, and 8 controls) were sequenced for KCNJ18, and all participants (n = 635) were genotyped for six variants of KCNJ18 and a polymorphism of KCNJ2 (rs312691). RESULTS: Six single-nucleotide variants (SNVs) with amino acid substitutions were identified by direct sequencing of KCNJ18. Among these, four SNVs comprised three haplotypes under strong linkage disequilibrium. Haplotype 1 (AAAG) of KCNJ18 was significantly associated with susceptibility to TPP in the Japanese population (OR = 19.6; 95% CI, 1.5 to 256.9; P = 0.013). Haplotype frequencies in the general East Asian (Japanese and Korean) and Caucasian populations differed significantly (haplotype 1: 80.8% vs 48.4%, P = 1.1×10-27). CONCLUSION: A major haplotype of KCNJ18 in East Asian populations is significantly associated with susceptibility to TPP. The haplotype is much more common in East Asian than Caucasian populations, suggesting its contribution to the high prevalence of TPP in East Asian populations.

[Clinical and molecular genetic analysis of a family with normokalemic periodic paralysis].

OBJECTIVE: Periodic paralysis (PP) is one type of skeletal muscle channelopathies characterized by episodic attacks of weakness. It is usually classified into hyperkalemic periodic paralysis (HyperPP), hypokalemic periodic paralysis (HypoPP) and normokalemic periodic paralysis (NormoPP) based on the blood potassium levels. HypoPP is the most common type of these three and NormoPP is the rarest one. The aim of this study was to explore the clinical and genetic features of a Chinese family with normokalemic periodic paralysis (NormoKPP). METHOD: Clinical features of all patients in the family with NormoKPP were analyzed. Genomic DNA was extracted from peripheral blood leukocytes and amplified with PCR. We screened all 24 exons of SCN4A gene and then sequence analysis was performed in those who showed heteroduplex as compared with unaffected controls. RESULT: (1) Fifteen members of the family were clinically diagnosed NormoKPP, and their common features are: onset within infacy, episodic attacks of weakness, the blood potassium levels were within normal ranges, high sodium diet or large dosage of normal saline could attenuate the symptom. One muscle biopsy was performed and examination of light and electronic microscopy showed occasionally degenerating myofibers. (2) Gene of 12 patients were screened and confirmed mutations of SCN4A genes--c. 2111 T > C/p. Thr704Met. CONCLUSION: The study further defined the clinical features of patients with NormoKPP, and molecular genetic analysis found SCN4A gene c. 2111 T > C/p. Thr704Met point mutation contributed to the disease. In line with the autosomal dominant inheritance laws, this family can be diagnosed with periodic paralysis, and be provided with genetic counseling. And the study may also help the clinical diagnosis, guide treatment and genetic counseling of this rare disease in China.

Skeletal muscle channelopathies: nondystrophic myotonias and periodic paralysis.

PURPOSE OF REVIEW: The aim is to review the recent findings in relation to the genetics, pathophysiology, clinical phenotypes, investigation and treatment of the nondystrophic myotonias (NDMs) and periodic paralyses. RECENT FINDINGS: The number of pathogenic mutations causing NDMs and periodic paralyses in known genes continues to expand. In addition, a mutation has been identified in the ryanodine receptor gene manifesting as an atypical periodic paralysis phenotype. Another recent study indicated that thyrotoxic hypokalaemic periodic paralysis is determined by mutations in a novel gene encoding an inwardly rectifying potassium channel, Kir2.6. Work studying molecular mechanisms indicates that 90% of the known mutations causing hypokalaemic periodic paralysis (HypoPP) result in loss of positively charged arginine residues in the S4 segments of either SCN4A or CACNA1S, possibly creating a gating-pore current that may be important in the pathogenesis of HypoPP. Recent studies evaluating clinical features and health status in NDM patients have provided more detailed insights into the significant morbidity associated with these diseases. Ultrasound has been successfully used to demonstrate muscle abnormalities in NDM patients and magnetic resonance spectroscopy studies applied to HypoPP patients suggest that this technique can demonstrate both disease-related and treatment-related changes. SUMMARY: Recent discoveries in the skeletal muscle channelopathies have increased our understanding of the genetics and pathophysiology of these diseases. Studies reporting imaging techniques raise the possibility of improved disease monitoring and better outcome measures for clinical trials. Randomized controlled trials to establish an evidence base upon which to recommend standard treatments are required.

[The construction and preliminary investigation of the cell model of a novel mutation R675Q in the SCN4A gene identified in a Chinese family with normokalemic periodic paralysis].

OBJECTIVE: To construct and investigate the cell model of a novel mutation R675Q in the skeletal muscle Na channel type 4 alpha subunit gene (SCN4A) identified from a Chinese family with normokalemic periodic paralysis. METHODS: cDNA encoding the adult isoform of SCN4A was used as a template for in vitro site-directed mutagenesis by PCR method. The mutated plasmid was transiently transfected into HEK-293 cells by calcium phosphate precipitation. Twenty four and 48 hours after transfection, the expression level of SCN4A was detected by reverse transcription-polymerase chain reaction (RT-PCR) and Western blot. Whole cell voltage-clamp recording was used to study the current of sodium channels. RESULTS: The site-mutagenesis of the plasmid was confirmed by sequencing. The expression of SCN4A gene was significantly elevated 24 h and 48 h after transfection. The relative current of R675Q is smaller than that of wide type before reaching peak current under the same test voltage, but larger than that of wild type current after reaching peak current. They both had the largest peak current under 0 mV test pulse. CONCLUSION: A cell model of normokalemic periodic paralysis was successfully constructed. The R675Q mutation of the SCN4A gene enhances the activation and inactivation of the sodium channel, and the S4 transmembrane segment may have intimate relationship with the attack of weakness in normoKPP patients.

Mutations of sodium channel alpha-subunit genes in Chinese patients with normokalemic periodic paralysis.

OBJECTIVE: In this study, we aim to investigate the clinical features and Mutations of sodium channel alpha-subunit (SCN4A) genes in Chinese patients with normokalemic periodic paralysis (normoKPP). METHODS: Six unrelated Chinese families with normoKPP were analyzed in clinical features. Genomic DNA was extracted from peripheral blood leukocytes and amplified with PCR. We screened all 24 exons of SCN4A gene with denaturing high performance liquid chromatography (DHPLC) technology, and then sequence analysis was performed in those who showed heteroduplex as compared with unaffected controls. RESULTS: The laboratory tests were within normal ranges. Electromyograms and electrocardiograms were normal. One muscle biopsy was performed with the patient in family 4 after a brief attack of normoKPP. Examination of light microscopy showed no changes, but electronic microscopy showed occasionally degenerating myofibers. The mutations of SCN4A genes were as follows: (1) Met1592Val occurred in family 1. (2) Val-781-Ile occurred with the patient and her father in family 4. (3) Both the patients had a novel mutation g2101a predicting the amino acid exchange Arg675Gln in family 5, which may be a disease-causing mutation. CONCLUSIONS: In addition to Val-781-Ile and Met1592Val, the mutation g2101a (Arg675Gln) may be the novel mutation of SCN4A genes in Chinese patients with normoKPP.

Periodic paralyses.

The periodic paralyses are a group of muscle diseases with abnormalities of channels. These abnormalities result in paralysis or weakness with or without poor relaxation of muscle. Hypokalemic periodic paralyses, potassium-sensitive periodic paralyses, and paramyotonia congenita are reviewed. The clinical findings, pathophysiologic abnormalities, diagnostic evaluations, and possible treatments are included in this article.

[Periodic paralysis: anatomo-pathological study of skeletal muscles in 14 patients]. / Paralisia periódica estudo anátomo-patológico do músculo esquelético de 14 pacientes.

Periodic paralysis is a rare disease, characterized by transient weakness associated with abnormal levels of serum potassium. Muscle biopsy may show a wide range of abnormalities, vacuoles being more specifically linked to the disease. We analysed 17 muscle biopsies from 14 patients with periodic paralysis (14 hypokalemic, 2 hyperkalemic). All of them showed at least one histological abnormality. Fourteen specimens showed vacuoles that were peripheral, single, frequent and preferentially found in type I fibers. Frequency or severity of attacks did not correlate with the presence of vacuoles but those were more easily found in patients with long term disease. Ten biopsies showed tubular aggregates, specially on the patients with frequent crises or long term disease. A second biopsy was done in three patients and in two we observed a worsening of the histopathologic picture. One patient manifested interictal weakness with evident myopathic changes on the muscle biopsy. Nonspecific changes were found in variable degrees in 15 biopsies. Our study shows that vacuoles and tubular aggregates are frequent changes in periodic paralysis and therefore helpful for the diagnosis. Important myopathic findings in the muscle biopsy suggest a permanent myopathy which probably develops after severe crises or long term disease.

Paralisia periódica: estudo anátomo-patológico do músculo esquelético de 14 pacientes / Periodic paralysis: anatomo-pathological study of musculoskeletal of 14 patients

A paralisia periódica é entidade caracterizada por crises de fraqueza muscular relacionadas com alteraçöes do nível sérico de potássio. A biópsia muscular pode mostrar alteraçöes específicas ou inespecíficas. Nosso estudo tem como objetivo a análise de 18 biópsias musculares de 14 pacientes com paralisia periódica (14 hipocalêmica, 2 hipercalêmica). Todas as biópsias mostraram alguma alteraçäo histopatológica. Quatorze biópsias apresentavam vacúolos, que se caracterizavam por serem únicos, de localizaçäo periférica, de aparecimento frequente e preferentemente em fibras do tipo I. Os vacúolos eram mais visualizados naqueles pacientes com longa evoluçäo e sem relaçäo com a frequência de crises. Os agregados tubulares foram encontrados em 10 biópsias principalmente naqueles pacientes com crises frequentes e doença de longa evoluçäo. Em 3 pacientes foram realizadas 2 biópsias, notando-se piora das alteraçöes em 2. Um paciente evoluiu com quadro clínico de miopatia permanente, confirmado pela biópsia muscular. Alteraçöes inespecíficas foram encontradas em graus variáveis em 15 biópsias. Nosso estudo mostra que os vacúolos e os agregados tubulares säo achado frequentes na paralisia periódica, constituindo importante auxílio diagnóstico. Alteraçöes miopáticas evidentes à biópsia sugerem o aparecimento de miopatia permanente, quadro decorrente de doença de longa evoluçäo ou crises severas

Genotype-phenotype correlations in human skeletal muscle sodium channel diseases.

BACKGROUND: Over the past 3 years, the genetics of the myotonic diseases have been substantially elaborated. Three genetically different groups of myotonic disease can be discerned: (1) the chloride channel myotonias, (2) the adynamia-paramyotonia complex, and (3) myotonic dystrophy. METHODS AND RESULTS: Electrophysiology has suggested and molecular biology has proven that the diseases belonging to the adynamia-paramyotonia complex, ie, paramyotonia congenita, hyperkalemic and normokalemic periodic paralysis, and some rare forms of myotonic disease, are caused by point mutations in the gene encoding the alpha subunit of the sodium channel in adult human skeletal muscle, located on chromosome 17q23. Thirteen different mutations have been described by various groups in the United States and Germany. The various mutations causing a particular form of the complex are not located in the gene in a predictable or easily understandable regular manner. CONCLUSIONS: Further study of the genotype-phenotype correlations should not only increase our understanding of the variability of signs in this group of diseases, it could also provide us with a deeper insight in the function of the various regions of the sodium channel protein.

Multiple deletions of mitochondrial DNA in a patient with periodic attacks of paralysis.

In this study multiple deletions of mitochondrial genome were found in a patient presenting with periodic attacks of paralysis. Morphological studies revealed mitochondrial abnormalities along with typical histopathological features of periodic paralysis. Southern blot and PCR analysis revealed multiple mtDNA deletions. Our patient could be affected by two unrelated diseases, idiopathic periodic paralysis and presymptomatic mitochondrial myopathy. Alternatively, mtDNA alterations and oxidative deficiency might express themselves phenotypically as periodic paralytic attacks, although this correlation has never been reported.

Identification of a mutation in the gene causing hyperkalemic periodic paralysis.

DNA from seven unrelated patients with hyperkalemic periodic paralysis (HYPP) was examined for mutations in the adult skeletal muscle sodium channel gene (SCN4A) known to be genetically linked to the disorder. Single-strand conformation polymorphism analysis revealed aberrant bands that were unique to three of these seven patients. All three had prominent fixed muscle weakness, while the remaining four did not. Sequencing the aberrant bands demonstrated the same C to T transition in all three unrelated patients, predicting substitution of a highly conserved threonine residue with a methionine in a membrane-spanning segment of this sodium channel protein. The observation of a distinct mutation that cosegregates with HYPP in two families and appears as a de novo mutation in a third establishes SCN4A as the HYPP gene. Furthermore, this mutation is associated with a form of HYPP in which fixed muscle weakness is seen.

Calcium-tension relationships of muscle fibers from patients with periodic paralysis.

Lateral gastrocnemius muscle biopsies from a 26-year-old man with hyperkalemic periodic paralysis and a 23-year-old man with hypokalemic periodic paralysis were studied. Both patients came from families in which older relatives had developed a vacuolar myopathy in association with their periodic paralysis. Muscle fibers were chemically skinned, and individual fibers were studied with a low-compliance strain gauge. The tension generated by fibers was studied in baths with calcium concentrations from 10(-8) mol/L to 2.5 x 10(-5) mol/L. The Ca-tension relationships and maximal tensions (normalized to fiber cross-sectional area) of fast and slow twitch fibers were indistinguishable from those found in fibers from 5 normal subjects. The results reinforce earlier findings which suggested that loss of Ca-induced myofibril contraction was not the cause of paralysis in periodic paralysis.

Expression of heat shock protein epitopes in tubular aggregates.

Tubular aggregates may be found in a variety of conditions and have been associated with a wide range of chemical and ischemic insults. We report clinical and histological features in a case of myopathy with tubular aggregates. The structure of these tubular aggregates was examined using antibodies to cytoskeletal proteins and heat shock proteins. Epitopes of the 72 kD heat shock protein were expressed in the areas of abnormality in this case and in a case of hypokalemic periodic paralysis with tubular aggregates. Heat shock proteins have a role in the modulation of the tertiary structure of proteins and may be involved in the pathogenesis of tubular aggregates and other microtubular abnormalities in muscle.

Permanent muscle weakness in familial hypokalaemic periodic paralysis. Clinical, radiological and pathological aspects.

Myopathy accompanying familial hypokalaemic periodic paralysis (HPP) is much less well documented than the paralytic attacks from which the disease derives its name. Eleven affected members of a large kinship with HPP were studied clinically and radiologically for the presence of myopathy. In 4 patients muscle biopsies were also performed and in 1 of them the histological findings obtained at autopsy were compared with the CT scans of various muscles. In another patient not previously biopsied, the specimens of both amputated legs were examined histologically. The age of the studied individuals ranged from 33 to 74 yrs. The 4 youngest patients showed no clinical signs of myopathy. However, in 2 of them CT scans demonstrated discrete hypodense lesions in the leg muscles, whereas in the other 2, muscle biopsies showed a vacuolar myopathy. The other 7 patients, all older than 50 yrs, presented both clinical and CT evidence of myopathy of proximal and distal muscles ranging from very mild to very severe, males being slightly more affected than females. In all 11 patients a mean CT grading was made that was based on the abnormalities found in the different muscle groups. The myopathy appeared to be unrelated to the history of paralytic attacks, but a strong correlation was found between age and mean CT grading. It was concluded that HPP is a myopathy with permanent muscle weakness of late onset in all the patients. The expression of the paralytic attacks is variable.

Progressive myopathy in hyperkalemic periodic paralysis.

A progressive degenerative myopathy has been well described in hypokalemic periodic paralysis but is not as widely recognized in hyperkalemic periodic paralysis. We studied four families with the latter disease in which some members developed a progressive myopathy. Episodes of paralysis were prolonged, lasting for months in some cases, and in one case paralysis was sufficiently severe to require ventilatory support. The progressive myopathy tended to develop at a time when attacks of paralysis were decreasing in frequency. Muscle biopsy specimens showed variability in fiber size, internal nuclei, and fibers with vacuoles. Electron microscopy showed myofibrillary degeneration and tubular aggregates. An abnormal biopsy specimen was more common in older patients. Our experience suggests that a progressive myopathy is as common in hyperkalemic periodic paralysis as it is in the hypokalemic disorder.