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The muscle weakness that frequently accompanies osteomalacia and rickets may arise from a variety of causes. Particularly in patients with muscle weakness, identification of the metabolic disorder is important, since effective treatment is often possible.
BACKGROUND: Identifying the genetic basis of hypotonia and muscle weakness is critical for patient management and family counseling. However, diagnosis is often hindered by diverse genomic alterations, including repeat expansions, structural variants (SVs), and methylation defects. Standard-of-care testing, largely based on short-read sequencing, is limited in its ability to detect this heterogeneous variation landscape, leaving many patients undiagnosed or requiring lengthy sequential testing. Long-read sequencing represents a promising solution. However, its application as a first-tier diagnostic assay for hypotonia remains unexplored. METHODS: We retrospectively analyzed 227 patients with hypotonia to assess diagnostic yield, time-to-diagnosis, and costs associated with standard-of-care testing. A long-read whole-genome sequencing (LR-WGS) workflow with targeted analysis of hypotonia-associated genes was developed to detect and prioritize pathogenic SNVs, SVs, and CNVs, repeat expansions, and methylation changes at key disease loci. The workflow was validated in a reference-positive cohort with known diagnoses (n = 15) and applied to an unsolved cohort (n = 14). Variant interpretation followed ACMG guidelines and was confirmed with orthogonal methods. RESULTS: Standard-of-care testing achieved a diagnostic yield of 42% with an average time-to-diagnosis of 68.7 days; however, 30% of diagnosed patients experienced significant delays (average 169 days) due to sequential testing. The LR-WGS based approach identified all known pathogenic variants in the positive cohort, including SMN1 deletions, methylation defects at 15q11.2/Prader-Willi locus, FMR1 repeat expansions, and sequence and copy-number variants in > 100 genes underlying myopathies and muscular dystrophies. The targeted long-read pipeline reduced prioritized variant calls by 97.9-99.9% and, in the unsolved cohort, yielded one definitive diagnosis (de novo COL6A3 deletion) and one possible diagnosis (aberrant methylation and copy number at POMK), for an additional 14% yield. Among patients diagnosed after sequential testing (n = 29), LR-WGS is expected to reduce time-to-diagnosis by ~ 85% and decrease cumulative diagnostic delays, with projected healthcare cost savings of $396,000-439,000. Across the entire 227 patient cohort, LR-WGS is anticipated to reduce testing costs by 6.5%, yielding an average savings of $105 per patient. CONCLUSIONS: LR-WGS enables comprehensive discovery of genomic and epigenomic variants in hypotonia and muscle weakness, improving diagnostic yield, shortening diagnostic timelines, and reducing costs compared with current standard-of-care testing.
Pulmonary mechanics and respiratory muscle pressures were studied in 7 patients with severe respiratory muscle weakness. Minimal pleural pressures were grossly abnormal and showed little variation with lung volume. Both the maximal transpulmonary pressure and static expiratory compliance were low; therefore, the pressure-volume curves of the lungs resembled those obtained after strapping the chest in normal subjects. The low compliance may result from either microatelectasis or a generalized alteration in alveolar elastic properties and is probably a major determinant of both the total lung capacity and the breathing pattern of patients with neuromuscular disease. Airway and gas exchange function were less abnormal than the elastic properties of the lungs.
Frailty is a complex geriatric syndrome characterized by age-related declines in physiological function and cognitive reserve. To promote early prevention and intervention, minimally invasive and objective biomarkers that can detect frailty progression are required. We aimed to identify biomarkers associated with frailty progression and to elucidate their relevance to the Japanese version of the Cardiovascular Health Study (J-CHS) criteria, consist of five components (unintentional weight loss, self-reported exhaustion, muscle weakness, slow walking speed, and low physical activity). A total of 168 individuals (61 robust, 25 pre-frail, and 82 frail) enrolled in the NCGG (National Center for Geriatrics and Gerontology) Biobank were analyzed. Clinical information, blood-test data, aging-related factors, and gene-expression data were integrated for the analysis. First, linear regression identified one clinical factor, five aging-related factors, and 251 gene-expression factors associated with frailty. Subsequent logistic regression analyses examining each J-CHS components highlighted six candidate biomarkers. Cross-validation further suggested that three of these biomarkers-SMI, apelin, and GDF15-may represent potential biomarkers. Finally, retrospective and prospective analyses further demonstrated that those biomarkers were predictive of future muscle weakness, yielding a concordance index of 0.70. In conclusion, we validated and refined a biomarker panel consisting of SMI, apelin, and GDF15 that is associated with frailty, particularly muscle weakness (a major J-CHS component). These biomarkers may be useful for frailty assessment. Longitudinal analyses further suggested that they may be associated with the future development of muscle weakness in initially robust older adults, although validation in larger prospective cohorts is warranted.
Dyspnea is a common, disabling symptom in chronic heart failure, yet the underlying mechanisms remain unknown. The respiratory muscle pump is composed of skeletal muscles whose strength directly influences the pump's performance. Respiratory muscle weakness is important in the dyspnea experienced by some patients with pulmonary disease; however, the role of the respiratory muscle pump in the dyspnea of chronic heart failure has not previously been examined. To assess respiratory muscle strength and its relation to dyspnea during daily activity, we measured maximum inspiratory and expiratory mouth pressures as indices of respiratory muscle strength and the baseline dyspnea index in nine stable, chronic cardiac pump failure patients who had no evidence of primary lung disease, and in nine age- and sex-matched healthy control subjects. The chronic heart failure patients, when compared with their matched control subjects, had reduced inspiratory and expiratory muscle strength, and both inspiratory and expiratory muscle strength were significantly correlated with dyspnea during daily activity (r2 = 0.80, p = 0.001 and r2 = 0.45, p = 0.05, respectively). Inspiratory muscle strength accounted for all of the variance in dyspnea that was correlated with respiratory muscle strength when the relative contributions of inspiratory and expiratory muscle strength were examined. There was no correlation between lung volumes or spirometry and dyspnea in the heart failure patients. These findings indicate that patients with stable chronic heart failure have inspiratory and expiratory muscle weakness and further suggest that the respiratory muscle pump significantly contributes to the dyspnea during the activities of daily living.
A 43-year-old woman had noticed muscular weakness in her arms for four years before her admission. Muscle weakness and atrophy were prominent in the bilateral deltoid muscles, but muscular strength was almost unimpaired in the bilateral forearms and intrinsic muscles. There was no sign of sensory impairment except vibratory sensation. EMG revealed neuropathic NMU. X-P of the cervical spine showed enlargement of the spinal canal diameter, and MRI of the spinal cord revealed a large syrinx. On the basis of metrizamide CT and cranial MRI, a diagnosis of syringomyelia with Chiari malformation (type I) was made. Despite the presence of a large syrinx extending from C 1 to Th 11, the only detectable neurological sign was proximal weakness of the upper extremities simulating myopathy.
The symptom described as muscle weakness corrected by exercise appears to be part of the recessive form of congenital myotonia, of which it can constitute the dominant clinical manifestation in some cases. This symptom coincides with decrements of the action of potentials to repetitive stimulations in the electromyogram, which may be particularly severe in these same cases. These observations contribute to the modification and precision of the description of the recessive form of Thomsen's disease, but their pathogenicity remains unclear.
Rigid spine syndrome is a rare myopathy characterized by mild axial and proximal muscle weakness, limitation of neck and trunk flexion, scoliosis and mild joint contractures. We describe a 20-year-old woman with this syndrome who developed severe respiratory muscle failure disproportionate to the well-preserved extremity muscles. Nocturnal home care ventilation has completely restored her arterial oxygen desaturation during a 5-year follow-up.
Resting energy expenditure (REE) was assessed and its relationship to nutritional status, pulmonary function and respiratory muscle function was studied in 25 patients with pulmonary emphysema. The mean value of REE was 1413 +/- 251 Cal and the ratio of REE/REEpred was 1.398 +/- 0.23, suggesting the existence of a hypermetabolic state in these patients. REE/REEpred ratio was inversely correlated with plasma amino acid BCAA/AAA ratio and body muscle mass; and PImax. REE was inversely correlated with FEV1.0%. REE in the patient subgroup with severe hyperinflation (%RV > or = 200) was significantly higher than that in the subgroup with moderate hyperinflation. Malnourished patients showed significantly more severe hyperinflation than well-nourished patients. These findings suggest that augmented REE contributes to malnutrition in patients with emphysema, and that the increase in REE was related to the increase in mechanical work load on the basis of airway obstruction, respiratory muscle weakness and hyperinflation.
Newborn rats raised on a commercially available iodine-deficient diet developed severe muscle weakness, affecting predominantly their proximal hind limbs, that electrophysiologically and morphologically was determined to be myopathic in type. Follow-up dietary studies, utilizing different combinations of vitamins, minerals, casein and elemental iodine, demonstrated that the myopathy was the result of a deficiency of multiple dietary constituents, particularly casein, and was not due to a deficiency of iodine alone. These findings were compared with those observed in earlier investigations of a variety of nutritional myopathies. In the laboratory study of animals raised on experimental diets, it becomes important to consider the possible contributions of multiple dietary deficiencies in the evaluation of any abnormalities found.
An 83-year-old woman suddenly developed profound weakness of proximal and distal muscles in both upper limbs. Electromyography revealed abnormal changes but serum creatine kinase was normal. The weakness responded dramatically to steroid therapy. These unusual features of polymyalgia rheumatica are discussed.
Infusions of epinephrine or levarterenol bitartrate into a rabbit nerve-muscle preparation decreased the force of the evoked twitch of anterior tibial and gastrocnemius-soleus muscles. The adverse effect of the catecholamines was not directly on skeletal muscle. The alpha-receptor blocking drug phenoxybenzamine hydrochloride prevented the adverse effect of the catecholamines if it was given prior to catecholamine infusions and unmasked a weak augmentation of twitch tension. Taken with the finding of abnormal accumulation of catecholamine in human dystrophic muscles, the production of an experimental myopathy resembling human dystrophy by the monoamine oxidase inhibitor pargyline hydrochloride, and the finding of excessive levels of catecholamines in the tissues and urine of dystrophic animals, these experiments support the hypothesis that catecholamines could play a pathogenetic role in some dystrophic diseases of muscle.
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A myopathy, which improved with cyproheptadine hydrochloride therapy, developed in a patient with carcinoid syndrome of ten years' duration. Biopsy examination revealed advanced atrophy of type II muscle fibers, with type I fiber preponderance. Many of the small fibers had degenerated. Carcinoid myopathy may be due to excess circulating serotonin.