Three novel FHL1 variants cause a mild phenotype of Emery-Dreifuss muscular dystrophy.

Emery-Dreifuss muscular dystrophy (EDMD) is a hereditary muscle disease, characterized by the clinical triade of early-onset joint contractures, progressive muscle weakness, and cardiac involvement. Pathogenic variants in FHL1 can cause a rare X-linked recessive form of EDMD, type 6. We report three men with novel variants in FHL1 leading to EDMD6. The onset of muscle symptoms was in late adulthood and muscle weakness was not prominent in either of the patients. All patients had hypertrophic cardiomyopathy and one of them also had cardiac arrhythmias. Western blot performed on muscle biopsies from two of the patients showed no FHL1 protein expression. We predict that the variant in the third patient also leads to the absence of FHL1 protein. Complete loss of all FHL1 isoforms combined with mild muscle involvement supports the hypothesis that loss of all FHL1 isoforms is more benign than the cytotoxic effects of expressed FHL1 protein with pathogenic missense variants.

Novel Homozygous Truncating Variant Widens the Spectrum of Early-Onset Multisystemic SYNE1 Ataxia.

Pathogenic variants in the SYNE1 gene are associated with a phenotypic spectrum spanning from late-onset, slowly progressive, relatively pure ataxia to early-onset, fast progressive multisystemic disease. Since its first description in 2007 as an adult-onset ataxia in French Canadian families, subsequent identification of patients worldwide has widened the clinical spectrum and increased the number of identified pathogenic variants. We report a 20-year-old Faroese female with early-onset progressive gait problems, weakness, dysphagia, slurred speech, orthostatic dizziness, and urge incontinence. Neurological examination revealed mild cognitive deficits, dysarthria, broken slow pursuit, hypometric saccades, weakness with spasticity, hyperreflexia, absent ankle reflexes, ataxia, and wide-based, spastic gait. Magnetic resonance imaging displayed atrophy of the cerebellum, brainstem, and spinal cord. Severely prolonged central motor conduction time and lower motor neuron involvement was demonstrated electrophysiologically. Fluorodeoxyglucose-positron emission tomography (FDG-PET) scan showed hypometabolism of the cerebellum and right frontal lobe. Muscle biopsy revealed chronic neurogenic changes and near-absent immunostaining for Nesprin-1. Next-generation sequencing revealed a previously undescribed homozygous truncating, likely pathogenic variant in the SYNE1 gene. The patient's mother and paternal grandfather were heterozygous carriers of the variant. Her father's genotype was unobtainable. We expand the list of likely pathogenic variants in SYNE1 ataxia with a novel homozygous truncating variant with proximity to the C-terminus and relate it to a phenotype comprising early-onset cerebellar deficits, upper and lower motor neuron involvement and cognitive deficits. Also, we report novel findings of focally reduced frontal lobe FDG-PET uptake and motor evoked potential abnormalities suggestive of central demyelination.

Myopathy can be a key phenotype of membrin (GOSR2) deficiency.

T1-weighted, cross-sectional MR images showing shoulder girdle, abdominal, paraspinal, gluteal and thigh muscles almost completely replaced by fat, whereas lower leg muscles are almost unaffected i a patient who is compound heterozygous for pathogenic variants in GOSR2.

Muscle biopsy and MRI findings in ANO5-related myopathy.

INTRODUCTION/AIMS: Mutations in the anoctamin 5 (ANO5) gene are a common cause of muscular dystrophy. We aimed to investigate whether inflammatory changes in muscle are present in patients with ANO5 myopathy when assessed by muscle biopsy and muscle magnetic resonance imaging (MRI). METHODS: Adults with pathogenic variations in ANO5 known to cause muscular dystrophy were included in our study. Muscle biopsies of pelvic and lower extremity muscles were reviewed retrospectively. Muscle MR short-tau inversion recovery (STIR) images of a subset of these patients were obtained prospectively. RESULTS: Muscle biopsies from 24 patients were reviewed. MR STIR images were performed in 17 of these patients. We found inflammatory changes in muscle biopsies of three patients and MRI revealed hyperintense signals on STIR images in 14 of 17 patients. DISCUSSION: In this study, we found that muscle edema is very common in patients with ANO5 myopathy and that some patients have inflammatory changes in muscle biopsies. Further studies are needed to determine whether the STIR+ lesions reflect inflammation.

No effect of resveratrol in patients with mitochondrial myopathy: A cross-over randomized controlled trial.

Mitochondrial myopathies (MM) are caused by mutations that typically affect genes involved in oxidative phosphorylation. Main symptoms are exercise intolerance and fatigue. Currently, there is no specific treatment for MM. Resveratrol (RSV) is a nutritional supplement that in preclinical studies has been shown to stimulate mitochondrial function. We hypothesized that RSV could improve exercise capacity in patients with MM. The study design was randomized, double-blind, cross-over and placebo-controlled. Eleven patients with genetically verified MM were randomized to receive either 1000 mg/day RSV or placebo (P) for 8 weeks followed by a 4-week washout and then the opposite treatment. Primary outcomes were changes in heart rate (HR) during submaximal cycling exercise and peak oxygen utilization (VO2 max) during maximal exercise. Secondary outcomes included reduction in perceived exertion, changes in lactate concentrations, self-rated function (SF-36) and fatigue scores (FSS), activities of electron transport chain complexes I and IV in mononuclear cells and mitochondrial biomarkers in muscle tissue among others. There were no significant differences in primary and secondary outcomes between treatments. Mean HR changes were -0.3 ± 4.3 (RSV) vs 1.8 ± 5.0 bpm (P), P = .241. Mean VO2 max changes were 0.7 ± 1.4 (RSV) vs -0.2 ± 2.3 mL/min/kg (P), P = .203. The study provides evidence that 1000 mg RSV daily is ineffective in improving exercise capacity in adults with MM. These findings indicate that previous in vitro studies suggesting a therapeutic potential for RSV in MM, do not translate into clinically meaningful effects in vivo.

A single c.1715G>C calpain 3 gene variant causes dominant calpainopathy with loss of calpain 3 expression and activity.

Recessively inherited limb girdle muscular dystrophy (LGMD) type 2A is the most common LGMD worldwide. Here, we report the first single missense variant in CAPN3 causing dominantly inherited calpainopathy. A 43-year-old proband, his father and two sons were heterozygous for a c.1715G>C p.(Arg572Pro) variant in CAPN3. Affected family members had at least three of the following; muscle pain, a LGMD2A pattern of muscle weakness and wasting, muscle fat replacement on magnetic resonance imaging, myopathic muscle biopsy, and elevated creatine kinase. Total calpain 3 protein expression was 4 ± 3% of normal. In vitro analysis of c.1715G>C and the previously described c.643_663del variant indicated that the mutant proteins lack autolytic and proteolytic activity and decrease the quantity of wild-type CAPN3 protein. Our findings suggest that dominantly inherited calpainopathy is not unique to the previously reported c.643_663del mutation of CAPN3, and that dominantly inherited calpainopathy should be considered for other single variations in CAPN3.

POPDC3 Gene Variants Associate with a New Form of Limb Girdle Muscular Dystrophy.

OBJECTIVE: The Popeye domain containing 3 (POPDC3) gene encodes a membrane protein involved in cyclic adenosine monophosphate (cAMP) signaling. Besides gastric cancer, no disease association has been described. We describe a new muscular dystrophy associated with this gene. METHODS: We screened 1,500 patients with unclassified limb girdle weakness or hyperCKemia for pathogenic POPDC3 variants. Five patients carrying POPDC3 variants were examined by muscle magnetic resonance imaging (MRI), muscle biopsy, and cardiac examination. We performed functional analyses in a zebrafish popdc3 knockdown model and heterologous expression of the mutant proteins in Xenopus laevis oocytes to measure TREK-1 current. RESULTS: We identified homozygous POPDC3 missense variants (p.Leu155His, p.Leu217Phe, and p.Arg261Gln) in 5 patients from 3 ethnically distinct families. Variants affected highly conserved residues in the Popeye (p.Leu155 and p.Leu217) and carboxy-terminal (p.Arg261) domains. The variants were almost absent from control populations. Probands' muscle biopsies were dystrophic, and serum creatine kinase levels were 1,050 to 9,200U/l. Muscle weakness was proximal with adulthood onset in most patients and affected lower earlier than upper limbs. Muscle MRI revealed fat replacement of paraspinal and proximal leg muscles; cardiac investigations were unremarkable. Knockdown of popdc3 in zebrafish, using 2 different splice-site blocking morpholinos, resulted in larvae with tail curling and dystrophic muscle features. All 3 mutants cloned in Xenopus oocytes caused an aberrant modulation of the mechano-gated potassium channel, TREK-1. INTERPRETATION: Our findings point to an important role of POPDC3 for skeletal muscle function and suggest that pathogenic variants in POPDC3 are responsible for a novel type of autosomal recessive limb girdle muscular dystrophy. ANN NEUROL 2019;86:832-843.

Preclinical Research in Glycogen Storage Diseases: A Comprehensive Review of Current Animal Models.

GSD are a group of disorders characterized by a defect in gene expression of specific enzymes involved in glycogen breakdown or synthesis, commonly resulting in the accumulation of glycogen in various tissues (primarily the liver and skeletal muscle). Several different GSD animal models have been found to naturally present spontaneous mutations and others have been developed and characterized in order to further understand the physiopathology of these diseases and as a useful tool to evaluate potential therapeutic strategies. In the present work we have reviewed a total of 42 different animal models of GSD, including 26 genetically modified mouse models, 15 naturally occurring models (encompassing quails, cats, dogs, sheep, cattle and horses), and one genetically modified zebrafish model. To our knowledge, this is the most complete list of GSD animal models ever reviewed. Importantly, when all these animal models are analyzed together, we can observe some common traits, as well as model specific differences, that would be overlooked if each model was only studied in the context of a given GSD.

IL-6 release from muscles during exercise is stimulated by lactate-dependent protease activity.

IL-6 is secreted from muscles to the circulation during high-intensity and long-duration exercise, where muscle-derived IL-6 works as an energy sensor to increase release of energy substrates from liver and adipose tissues. We investigated the mechanism involved in the exercise-mediated surge in IL-6 during exercise. Using interval-based cycling in healthy young men, swimming exercise in mice, and electrical stimulation of primary human muscle cells, we explored the role of lactate production in muscular IL-6 release during exercise. First, we observed a tight correlation between lactate production and IL-6 release during both strenuous bicycling and electrically stimulated muscle cell cultures. In mice, intramuscular injection of lactate mimicked the exercise-dependent release of IL-6, and pH buffering of lactate production during exercise attenuated IL-6 secretion. Next, we used in vivo bioimaging to demonstrate that intrinsic intramuscular proteases were activated in mice during swimming, and that blockade of protease activity blunted swimming-induced IL-6 release in mice. Last, intramuscular injection of the protease hyaluronidase resulted in dramatic increases in serum IL-6 in mice, and immunohistochemical analyses showed that intramuscular lactate and hyaluronidase injections led to release of IL-6-containing intramyocellular vesicles. We identified a pool of IL-6 located within vesicles of skeletal muscle fibers, which could be readily secreted upon protease activity. This protease-dependent release of IL-6 was initiated by lactate production, linking training intensity and lactate production to IL-6 release during strenuous exercise.

Palbociclib in combination with simvastatin induce severe rhabdomyolysis: a case report.

BACKGROUND: Palbociclib is a selective well-tolerated antineoplastic drug used in the treatment of advanced HER2-negative, estrogen-receptor positive breast cancer that has shown significant improvement in progression-free survival. We present a patient that developed severe rhabdomyolysis with tetra-affection and loss of gait after initiating the first cycle of Palbociclib concomitantly with Simvastatin 40 mg treatment. CASE PRESENTATION: A 71-year-old woman with metastatic breast cancer developed tetraparesis and near fatal rhabdomyolysis after initiation of first cycle Palbociclib. For 10 years prior to this treatment, the patient had been treated with Simvastatin without myalgia or other neuromuscular complaints prior to the first cycle of Palbociclib. The patient was admitted at the neurology department, where Palbociclib and Simvastatin were discontinued. The patient was aggressively hydrated and treated with intravenous immunoglobulin therapy with slowly remission and finally regaining independent gait function. Evaluation showed a negative myositis antibody work-up. Muscle magnetic resonance imaging showed edema in multiple foci, but skeletal muscle biopsy did not show necrosis. Post discharge genetic analysis showed single heterozygosity for nucleotide polymorphism rs4149056. CONCLUSION: We present a patient who developed severe rhabdomyolysis induced by a combination of Palbociclib and Simvastatin treatment. Rhabdomyolysis was most likely induced by toxic plasma concentrations of Simvastatin due to Palbociclibs inhibition of the CYP3A4 enzyme in combination with a decreased hepatic uptake of Simvastatin due to single nucleotide polymorphism rs4149056. The study underscores that combining Simvastatin and Palbociclib should be done cautiously and genetic testing of the rs4149056 SNP is warranted. If present, Simvastatin should be discontinued or replaced with a lesser myopathic statin in regard to patients risk of cardiovascular events.

Exercising with blocked muscle glycogenolysis: Adaptation in the McArdle mouse.

BACKGROUND: McArdle disease (glycogen storage disease type V) is an inborn error of skeletal muscle metabolism, which affects glycogen phosphorylase (myophosphorylase) activity leading to an inability to break down glycogen. Patients with McArdle disease are exercise intolerant, as muscle glycogen-derived glucose is unavailable during exercise. Metabolic adaptation to blocked muscle glycogenolysis occurs at rest in the McArdle mouse model, but only in highly glycolytic muscle. However, it is unknown what compensatory metabolic adaptations occur during exercise in McArdle disease. METHODS: In this study, 8-week old McArdle and wild-type mice were exercised on a treadmill until exhausted. Dissected muscles were compared with non-exercised, age-matched McArdle and wild-type mice for histology and activation and expression of proteins involved in glucose uptake and glycogenolysis. RESULTS: Investigation of expression and activation of proteins involved in glycolytic flux revealed that in glycolytic, but not oxidative muscle from exercised McArdle mice, the glycolytic flux had changed compared to that in wild-type mice. Specifically, exercise triggered in glycolytic muscle a differentiated activation of insulin receptor, 5' adenosine monophosphate-activated protein kinase, Akt and hexokinase II expression, while inhibiting glycogen synthase, suggesting that the need and adapted ability to take up blood glucose and use it for metabolism or glycogen storage is different among the investigated muscles. CONCLUSION: The main finding of the study is that McArdle mouse muscles appear to adapt to the energy crisis by increasing expression and activation of proteins involved in blood glucose metabolism in response to exercise in the same directional way across the investigated muscles.

Limb girdle muscular dystrophy due to mutations in POMT2.

BACKGROUND: Mutations in the gene coding for protein O-mannosyl-transferase 2 (POMT2) are known to cause severe congenital muscular dystrophy, and recently, mutations in POMT2 have also been linked to a milder limb-girdle muscular dystrophy (LGMD) phenotype, named LGMD type 2N (LGMD2N). Only four cases have been reported so far.ClinicalTrials.gov ID: NCT02759302 METHODS: We report 12 new cases of LGMD2N, aged 18-63 years. Muscle involvement was assessed by MRI, muscle strength testing and muscle biopsy analysis. Other clinical features were also recorded. RESULTS: Presenting symptoms were difficulties in walking, pain during exercise, delayed motor milestones and learning disabilities at school. All had some degree of cognitive impairment. Brain MRIs were abnormal in 3 of 10 patients, showing ventricular enlargement in one, periventricular hyperintensities in another and frontal atrophy of the left hemisphere in a third patient. Most affected muscle groups were hip and knee flexors and extensors on strength testing. On MRI, most affected muscles were hamstrings followed by paraspinal and gluteal muscles. The 12 patients in our cohort carried 11 alleles with known mutations, whereas 11 novel mutations accounted for the remaining 13 alleles. CONCLUSION: We describe the first cohort of patients with LGMD2N and show that unlike other LGMD types, all patients had cognitive impairment. Primary muscle involvement was found in hamstring, paraspinal and gluteal muscles on MRI, which correlated well with reduced muscle strength in hip and knee flexors and extensors. The study expands the mutational spectrum for LGMD2N, with the description of 11 novel POMT2 mutations in the association with LGMD2N. CLINICAL TRIAL REGISTRATION: NCT02759302.

Collagen XII myopathy with rectus femoris atrophy and collagen XII retention in fibroblasts.

INTRODUCTION: Mutation in the collagen XII gene (COL12A1) was recently reported to induce Bethlem myopathy. We describe a family affected by collagen XII-related myopathy in 3 generations. METHODS: Systematic interview, clinical examination, skin biopsies, and MRI of muscle were used. RESULTS: The phenotype was characterized by neonatal hypotonia, contractures, and delayed motor development followed by resolution of contractures and a motor performance limited by reduced endurance. DNA analyses revealed a novel donor splice-site mutation in COL12A1 (c.8100 + 2T>C), which segregated with clinical affection and abnormal collagen XII retention in fibroblasts. MRI disclosed a selective wasting of the rectus femoris muscle. DISCUSSION: COL12A1 mutations should be considered in patients with a mild Bethlem phenotype who present with selective wasting of the rectus femoris, absence of the outside-in phenomenon on MRI, and abnormal collagen XII retention in fibroblasts. Muscle Nerve 57: 1026-1030, 2018.

Differential glucose metabolism in mice and humans affected by McArdle disease.

McArdle disease (muscle glycogenosis type V) is a disease caused by myophosphorylase deficiency leading to "blocked" glycogen breakdown. A significant but varying glycogen accumulation in especially distal hind limb muscles of mice affected by McArdle disease has recently been demonstrated. In this study, we investigated how myophosphorylase deficiency affects glucose metabolism in hind limb muscle of 20-wk-old McArdle mice and vastus lateralis muscles from patients with McArdle disease. Western blot analysis and activity assay demonstrated that glycogen synthase was inhibited in glycolytic muscle from McArdle mice. The level and activation of proteins involved in contraction-induced glucose transport (AMPK, GLUT4) and glycogen synthase inhibition were increased in quadriceps muscle of McArdle mice. In addition, pCaMKII in quadriceps was reduced, suggesting lower insulin-induced glucose uptake, which could lead to lower glycogen accumulation. In comparison, tibialis anterior, extensor digitorum longus, and soleus had massive glycogen accumulation, but few, if any, changes or adaptations in glucose metabolism compared with wild-type mice. The findings suggest plasticity in glycogen metabolism in the McArdle mouse that is related to myosin heavy chain type IIB content in muscles. In patients, the level of GLUT4 was vastly increased, as were hexokinase II and phosphofructokinase, and glycogen synthase was more inhibited, suggesting that patients adapt by increasing capture of glucose for direct metabolism, thereby significantly reducing glycogen buildup compared with the mouse model. Hence, the McArdle mouse may be a useful tool for further comparative studies of disease mechanism caused by myophosphorylase deficiency and basic studies of metabolic adaptation in muscle.

Protein-carbohydrate supplements improve muscle protein balance in muscular dystrophy patients after endurance exercise: a placebo-controlled crossover study.

In healthy individuals, postexercise protein supplementation increases muscle protein anabolism. In patients with muscular dystrophies, aerobic exercise improves muscle function, but the effect of exercise on muscle protein balance is unknown. Therefore, we investigated 1) muscle protein balance before, during, and after exercise and 2) the effect of postexercise protein-carbohydrate supplementation on muscle protein balance in patients with muscular dystrophies. In 17 patients [7 women and 10 men, aged 33 ± 11 yr (18-52), body mass index: 22 ± 3 kg/m(2) (16-26)] and 8 healthy matched controls [3 women and 5 men, age 33 ± 13 years (19-54), body mass index: 23 ± 3 kg/m(2) (19-27)], muscle protein synthesis, breakdown, and fractional synthesis rates (FSR) were measured across the leg using tracer dilution methodology on two occasions, with and without oral postexercise protein-carbohydrate supplementation. In patients, muscle protein breakdown increased in the recovery period (11 ± 1 µmol phenylalanine/min) vs. rest (8 ± 1 µmol phenylalanine/min, P = 0.02), enhancing net muscle protein loss. In contrast, postexercise protein-carbohydrate supplementation reduced protein breakdown, abolished net muscle protein loss, and increased the muscle FSR in patients (0.04 to 0.06%/h; P = 0.03). In conclusion, postexercise protein-carbohydrate supplementation reduces skeletal mixed-muscle protein breakdown, enhances FSR, resulting in a reduced net muscle loss in patients with muscular dystrophies. The findings suggest that postexercise protein-carbohydrate supplementation could be an important add-on to exercise training therapy in muscular dystrophies, and long-term studies of postexercise protein-carbohydrate supplementation are warranted in these conditions.

Effect of sildenafil on skeletal and cardiac muscle in Becker muscular dystrophy.

OBJECTIVE: Patients with Becker muscular dystrophy (BMD) and Duchenne muscular dystrophy lack neuronal nitric oxide synthase (nNOS). nNOS mediates physiological sympatholysis, thus ensuring adequate blood supply to working muscle. In mice lacking dystrophin, restoration of nNOS effects by a phosphodiesterase 5 (PDE5) inhibitor (sildenafil) improves skeletal and cardiac muscle performance. Sildenafil also improves blood flow in patients with BMD. We therefore hypothesized that sildenafil would improve blood flow, maximal work capacity, and heart function in patients with BMD. METHODS: A randomized, double-blind, placebo-controlled crossover design with two 4-week periods of treatment, separated by 2-week washout was used. We assessed brachial artery blood flow during maximal handgrip exercise, 6-minute walk test, maximal oxidative capacity, and life quality; cardiac function was evaluated by magnetic resonance imaging (MRI) at rest and during maximal handgrip exercise. Muscle nNOS and PDE5 were tested with Western blotting in 5 patients. RESULTS: Sixteen patients completed all skeletal muscle evaluations, and 13 completed the cardiac MRI investigations. Sildenafil had no effect on any of the outcome parameters. No serious adverse effects were recorded. PDE5 and nNOS were deficient in 5 of 5 biopsies. INTERPRETATION: Despite positive evidence from animal models of dystrophinopathy and physiological findings in patients with BMD, this double-blind, placebo-controlled clinical study showed no effect of sildenafil on blood flow, maximal work capacity, and heart function in adults with BMD. This discrepancy may be explained by a significant downregulation of PDE5 in muscle.

A pilot study of muscle plasma protein changes after exercise.

INTRODUCTION: Creatine kinase (CK) and myoglobin (Mb) do not possess all good qualities as biomarkers of skeletal muscle damage. We investigated the utility of troponin I (TnI) and telethonin (Tcap) as markers and examined their temporal profiles after skeletal muscle damage. METHODS: Plasma profiles were measured before and after exercise in 3 groups: subjects affected by either Becker muscular dystrophy or McArdle disease, and healthy subjects. RESULTS: Mb and TnI appeared early in the blood, and the increase of TnI was only observed in patients with muscle disease. The CK increase was more delayed in plasma. Tcap was not detectable at any time. CONCLUSIONS: Our results suggest that TnI is a marker of more severe damage signifying sarcomeric damage, and it could therefore be an important supplement to CK and Mb in clinical practice. Tcap is not useful as a marker for skeletal muscle damage.

Quality of life in hypokalemic periodic paralysis - a survey.

Primary hypokalemic periodic paralysis (HypoPP) is a skeletal muscle channelopathy most commonly caused by pathogenic variants in the calcium channel gene, CACNA1S. HypoPP can present with attacks of paralysis and/or permanent muscle weakness. Previous studies have shown that patients with HypoPP can have impaired quality of life (QoL). In this cross-sectional study, we aimed to describe the QoL in patients with HypoPP caused by pathogenic variants in CACNA1S using The Individualized Neuromuscular Quality of Life (INQoL) questionnaire, a validated tool to measure the QoL of patients with neuromuscular diseases (higher score, worse QoL). We showed that muscle weakness and fatigue were the symptoms with the greatest impact on participants' lives and that "activities", in the life domain of the INQoL, was most affected by HypoPP. Furthermore, we showed that the total INQoL score increased with age. Low QoL was primarily driven by progressive permanent muscle weakness and not attacks of paralysis, although half of the participants reported that attacks of paralysis challenged their daily life. The results suggest that special attention should be given to muscle weakness and fatigue in patients with HypoPP.

Skeletal Muscle Involvement in Patients With Truncations of Titin and Familial Dilated Cardiomyopathy.

BACKGROUND: Genetic variants in titin (TTN) are associated with dilated cardiomyopathy (DCM) and skeletal myopathy. However, the skeletal muscle phenotype in individuals carrying heterozygous truncating TTN variants (TTNtv), the leading cause of DCM, is understudied. OBJECTIVES: This study aimed to assess the skeletal muscle phenotype associated with TTNtv. METHODS: Participants with TTNtv were included in a cross-sectional study. Skeletal muscle fat fraction was evaluated by magnetic resonance imaging (compared with healthy controls and controls with non-TTNtv DCM). Muscle strength was evaluated by dynamometry and muscle biopsy specimens were analyzed. RESULTS: Twenty-five TTNtv participants (11 women, mean age 51 ± 15 years, left ventricular ejection fraction 45% ± 10%) were included (19 had DCM). Compared to healthy controls (n = 25), fat fraction was higher in calf (12.5% vs 9.9%, P = 0.013), thigh (12.2% vs 9.3%, P = 0.004), and paraspinal muscles (18.8% vs 13.9%, P = 0.008) of TTNtv participants. Linear mixed effects modelling found higher fat fractions in TTNtv participants compared to healthy controls (2.5%; 95% CI: 1.4-3.7; P < 0.001) and controls with non-TTNtv genetic DCM (n = 7) (1.5%; 95% CI: 0.2-2.8; P = 0.025). Muscle strength was within 1 SD of normal values. Biopsy specimens from 21 participants found myopathic features in 13 (62%), including central nuclei. Electron microscopy showed well-ordered Z-lines and T-tubuli but uneven and discontinuous M-lines and excessive glycogen depositions flanked by autophagosomes, lysosomes, and abnormal mitochondria with mitophagy. CONCLUSIONS: Mild skeletal muscle involvement was prevalent in patients with TTNtv. The phenotype was characterized by an increased muscle fat fraction and excessive accumulation of glycogen, possibly due to reduced autophagic flux. These findings indicate an impact of TTNtv beyond the heart.

Hemoglobin concentration and blood shift during dry static apnea in elite breath hold divers.

Introduction: Elite breath-hold divers (BHD) enduring apneas of more than 5 min are characterized by tolerance to arterial blood oxygen levels of 4.3 kPa and low oxygen-consumption in their hearts and skeletal muscles, similar to adult seals. Adult seals possess an adaptive higher hemoglobin-concentration and Bohr effect than pups, and when sedated, adult seals demonstrate a blood shift from the spleen towards the brain, lungs, and heart during apnea. We hypothesized these observations to be similar in human BHD. Therefore, we measured hemoglobin- and 2,3-biphosphoglycerate-concentrations in BHD (n = 11) and matched controls (n = 11) at rest, while myocardial mass, spleen and lower extremity volumes were assessed at rest and during apnea in BHD. Methods and results: After 4 min of apnea, left ventricular myocardial mass (LVMM) determined by 15O-H2O-PET/CT (n = 6) and cardiac MRI (n = 6), was unaltered compared to rest. During maximum apnea (∼6 min), lower extremity volume assessed by DXA-scan revealed a ∼268 mL decrease, and spleen volume, assessed by ultrasonography, decreased ∼102 mL. Compared to age, BMI and VO2max matched controls (n = 11), BHD had similar spleen sizes and 2,3- biphosphoglycerate-concentrations, but higher total hemoglobin-concentrations. Conclusion: Our results indicate: 1) Apnea training in BHD may increase hemoglobin concentration as an oxygen conserving adaptation similar to adult diving mammals. 2) The blood shift during dry apnea in BHD is 162% more from the lower extremities than from the spleen. 3) In contrast to the previous theory of the blood shift demonstrated in sedated adult seals, blood shift is not towards the heart during dry apnea in humans.