Search

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., (Copyright © 2019 Endocrine Society.)

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.

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.

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.

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.

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 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.

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.

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.

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.

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.

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.

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.

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.

Three patients with Hypokalemic Periodic Paralysis (HOPP)-associated progressive interattack muscle weakness, who became unresponsive or worsened by acetazolamide, responded favorably to dichlorophenamide, a more potent carbonic anhydrase inhibitor. Dichlorophenamide in single-blind placebo-controlled trials, considerably improved functional strength in two of the patients and had a moderate but definite effect in the third. Muscle groups graded 4/5 (MRC scale)returned to normal; very weak (0-3/5) atrophic muscles, improved to a minor degree. In one patient with acetazolamide-resistant paralytic attacks, dichlorophenamide also diminished the frequency and severity of the acute attacks. Dichlorophenamide had, in the present study, less effect than acetazolamide in reducing serum HCO3(-) and elevating Cl-. Its effectiveness may be related to the degree of sensitivity of certain HOPP patients to alterations of Cl- and/or HCO3(-) serum levels or to a different action of the drug unrelated to carbonic anhydrase inhibition or acidosis. Dichlorophenamide should be considered as an alternate to acetazolamide in the treatment of patients with HOPP-associated interattack muscle weakness who have become unresponsive or worsened by acetazolamide.

A 51 year-old male patient was affected by a dominantly inherited periodic paralysis. With large potassium supplements and ageing, the number and severity of attacks became considerably reduced. Increasing weakness and atrophy of the lower extremities were documented by clinical examination and by computer-assisted tomography of the muscles. A biopsy was taken in the vastus lateralis muscle without any attempt to induce a hypokalaemic paralytic attack. Light microscopy showed multiple intra- and extracellular vacuoles, rimmed vacuoles, myonecrosis, fatty degeneration and endomysial fibrosis. The endomysial nerve bundles were normal. Both fiber types were vacuolated. Quantitative studies revealed abnormal variability coefficients and increased atrophy factors for all types. Electron microscopy showed dilatations of the tubular system and of the sarcoplasmic reticulum communicating with large vacuoles limited by a single membrane. Other vacuoles were covered by a basement membrane and could contain collagen fibers or capillaries. Accumulation of myeloid bodies and of 10-13 nm filaments were also noted in the sarcoplasm. Cytoplasmic bodies were present. No tubular aggregates could be found. The nerve bundles were normal. These findings were in part similar to the ones reported by Gérard et al. (1978) in the son's biopsy during an induced paralytic attack. Significant findings in our case are the sequence of events leading to muscle fibre destruction, still detectable at an advanced stage of the disease. Myopathic changes represent a delayed but severe complication of the disorder.

The possibility has been raised that in familial periodic paralysis, the relatively large depolarization of the muscle fiber membrane seen during periods of paralysis might be attributable to a reduction in activity of the electrogenic Na(+)-K+ pump. The theoretical analysis presented here shows that although such hypotheses are qualitatively correct, the quantitative contribution of the electrogenic pump is too small to account entirely for the changes in membrane potential observed between the paralytic and interictal states.

In a case of congenital paramyotonia a muscle biopsy was performed and studied morphologically, histochemically and ultrastructurally. A clearcut pattern of changes has been observed with ATPase and oxidative enzymes. On electron microscopy special changes known as "tubular aggregates" were found. The relationship between the two findings, as well as the significance of such alterations in the range of periodic paralyses and myotonic phenomena, are discussed.

The authors studied 8 patients with Familial Periodic Paralysis on the clinical, hydroelectrolytic, electrophysiologic, histologic and therapeutic points of view. There was significant predominance in males. The onset of the symptoms in our group began under fifteen years of age. The clinical manifestations were similar to those referred in the literature. The hypokalemic form was found in all patients except in one case that had hyperkalemic form. Natremias on the superior border of the normality, were seen in 21.4% of the cases, and in 21.4% the natremias were higher; this fact suggested aldosterone liberation of the muscle. The histologic examination performed in 5 patients, was normal in 20% of them and, in those cases with repetitive and frequent crises, atrophic muscle fibers were seen. Prophylactic treatments were made. The patients with hypokalemic form received supplementary doses of potassium.

The observation of a 20 years old patient with a periodic paralysis is reported. During a crisis induced by 20 U of insulin and 150 g of glucose, transient hyperaldosteronism was found and the muscular biopsy performed in the left biceps brachii, disclosed vacuoles with a double membrane. The significance of these findings is discussed.

A large family with hypokalemic periodic paralysis was reexamined after 50 years. Two new cases were found in the third generation and 12 in the fourth generation. This family now includes 28 affected patients in four generations. The reexamination ascertained the presence of permanent muscle weakness (PMW) in all investigated affected sibs. This fact, and the fact that indications of the presence of PMW without paralytic attacks were found in only one subject, is strong evidence that both are manifestations of the same more or less fully penetrant dominant gene. A linkage study in this family could not localize the gene on the human genome, but close linkage with 25 genetic marker systems could be excluded.

Muscle changed found in five patients with periodic paralysis are described. Three patients had familial hypokaliemic paralysis, one had familial periodic paralysis with hyperkaliemia, and one had periodic attacks of muscular weakness with thyrotoxicosis. According to the stage in the clinical course at which biopsy was performed, several pathological patterns are described. Vacuolization was the main feature in the early stages of periodic paralysis. Later in the clinical course, tubular aggregates were the characteristic findings. In addition, degenerative changes of the muscle fibres were found in patient exhibiting a permanent myopathic condition. In thyrotoxic periodic paralysis, the longer the clinical course, the more severe the changes appeared to be. Possible mechanisms leading to such structural abnormalities remain in question.

In an ultrastructural study of biopsies of quadriceps femoris muscle from two patients during attacks of adynamia episodica hereditaria. Marked pinocytosis along the sarcolemma and an interfibrillary oedema were observed, together with a 'bamboo-like' shape of the myofibrils. Other non-specific abnormalities were also found.

Recommendations for histological criteria of diagnosis of dystrophic and congenital myotony as well as familial hypopotassemic periodic paralysis based on the results of skeletal muscles biopsies are presented.

A 47-year-old man with well-documented hypokalemic periodic paralysis demons-rated permanent myopathy as shown by biopsy. In addition there was clinical and biopsy evidence of progressive spinal muscular atrophy. The feature of the combination of these diseases is reported in a case and discussed.

The case history, skeletal muscle and heart muscle biopsy findings from an affected member of a family suffering from hypokalaemic periodic paralysis associated with permanent muscular weakness are reported. The patient, a female aged 35 years, while treated with 750 mg and later 1000 mg of acetazolamide daily, developed typical exercise angina pectoris. The ECG during exercise showed ST-segment depression. A coronary angiography was performed because coronary artery disease was suspected. To exclude cardiac muscle disease a biopsy of the left ventricular wall was taken. The angiography was normal. Ultrastructural analysis of the biopsy specimen showed an unusual amount of intermyofibrillary glycogen resembling, although far less abundant, the increase of glycogen found in the skeletal muscle biopsy specimen obtained from the same patient. The possible implications of these findings are discussed with reference to the normal echocardiographic findings in the family.

In a case of hypokalemic periodic paralysis with characteristic alterations of the sarcoplasmic reticulum (SR) in the skeletal muscle, subcellular calcium re-partition, as revealed with the pyroantimonate technique, appears disturbed during paralysis. Pyroantimonate precipitates, normally concentrated in the terminal cisternae of the SR, were localized in the T tubules, whereas the terminal cisternae appeared empty. The increase (about 14%) in muscular calcium during paralysis may result from the accumulation of calcium in the extracellular compartment (T tubules). Defects in calcium uptake and storage by the SR may be involved in the pathogenesis of the periodic paralysis syndrome.

The familial periodic hypokalemic paralysis is an infrequent disease characterized by paralytic attacks of sudden appearance affecting the muscles of the trunk and limbs. There is a marked hypokalemia during the paralytic episodes of the disease, and a family history in 80 percent of the cases. The differential diagnosis includes hyperthyroidism with periodic paralysis, congenital paramyotony and adynamia episodica hereditaria. Two typical cases of hypokalemic periodic paralysis are presented, with biological, electrophysiological, clinical, and ultrastructural pictures characteristics of the disease. The clinical manifestations of both patients are discussed, stressing the diagnostic importance of the electrophysiological study during the insulin test, and the interest of the histologic and ultrastructural studies. The spectacular response during the acute episodes to the intravenous perfusion of potassium salts, and the usefulness of the acetazolamide administration to prevent the paralytic episodes are emphasized.