The phenotypic and genotypic features of a Scottish cohort with McArdle disease.

This retrospective study evaluated the phenotypic and genotypic features of 14 patients with McArdle disease attending the West of Scotland adult muscle clinic. Although all patients experienced exercise-induced cramps, exercise intolerance and hyperCKaemia, only 71% (n = 10) experienced the second wind phenomenon, rhabdomyolysis and/or myoglobinuria. We observed a high rate of fixed muscle weakness (50%; n = 7), coronary artery disease (36%; n = 5), and psychological comorbidity (50%; n = 7). Although 79% had symptom onset in the first decade of life, the mean age at presentation and at genetic diagnosis was 43.8 years and 47.7 years, respectively. 93% had at least one copy of the common PYGM pathogenic variant, c.148C > T, p.(Arg50*), with 50% (n = 7) of the cohort being homozygous. Our cohort highlights the phenotypic variability seen in McArdle disease and underscores the potential for late-onset presentations. It emphasises the need for improved awareness and recognition of this condition amongst neurologists, rheumatologists and general physicians. A history of exercise intolerance and second wind phenomenon may not always be volunteered by the patient, underscoring the need to ask specific questions in clinic to extrapolate the relevant symptoms in this patient cohort.

Exercise Induced Myoglobinuria is Determined by Haptoglobin Polymorphism.

BACKGROUND: In professional soccer players (n = 27), confounders of quantitative myoglobinuria following physical training were assessed in order to improve interpretation of post-exercise myoglobinuria. METHODS: Urine samples were collected in the morning before training sessions, 48 to 72 hours following a game. Urine myoglobin was assayed using immunoturbidimetry. Blood was drawn 48 hours following training session. Creatinine was assayed using a Jaffe method. Creatine kinase (CK) activity was assayed according to the IFCC reference method. Serum myoglobin was assayed using the same assay as the one used for urine. Hp polymorphism was assessed on hemoglobin supplemented serum. Serum Hp concentration was assayed nephelometrically. Training intensity was assessed using a wearable GPS tracking system. Physical load monitoring included the covered total distance, the distance at different speed zones, and the number of sprints/accelerations/decelerations/jumps. Multiple regression analysis was used to detect the determinants of post-exercise myoglobinuria. RESULTS: Myoglobinuria negatively correlated with serum haptoglobin (Hp) concentration. Athletes presented with Hp values, which were lower than the Hp phenotype reference ranges, which can be explained by depletion of circulating Hp stores. Myoglobinuria was most pronounced in players carrying a Hp 2-2 phenotype, which is associated with the lowest Hp reference range. Myoglobin clearance was inversely correlated with Hp 2-2 concentration. Correlation between myoglobinuria and biomarkers of muscle damage was weak. Neither age nor glomerular filtration rate were found to be confounders of myoglobinuria. When comparing myoglobinuria with training intensity, the number of sprints, average acceleration speed, and maximal speed were determining factors for predicting exercise-induced myoglobinuria. CONCLUSIONS: In athletes, plasma myoglobin binding capacity is depleted. Moderate myoglobinuria not only should be regarded as a muscle damage marker, but also should be interpreted as an indicator for Hp depletion. Apart from its significance as a biomarker for muscle damage and rhabdomyolysis, myoglobinuria in athletes should be a warning that the heme binding capacity of plasma Hp is depleted, indicating an exhausted defense against Fenton chemistry induced free radicals. Fenton chemistry is associated with free radical formation, which is to be avoided because of the causative relationship with inflammatory processes and tissue damage.

Acute recurrent rhabdomyolysis in a Chinese boy associated with a novel compound heterozygous LPIN1 variant: a case report.

BACKGROUND: LPIN1-related acute recurrent rhabdomyolysis (RM), first reported in 2008, is an autosomal recessive inherited metabolic disease. In recent years, LPIN1 gene variants have been identified as one of the main causes of severe RM in children in Western countries. The disease is extremely rare in China, and we report a case of acute recurrent RM caused by a novel compound heterozygous LPIN1 variant. CASE PRESENTATION: A 15-year-old Chinese boy presented with myalgia after strenuous exercise, accompanied by transient increases in serum creatine kinase and myoglobin and persistent hyperuricaemia and hyperbilirubinaemia. Genetic analysis using high-throughput genomic sequencing and Sanger sequencing revealed that there was a compound heterozygous variant in the LPIN1 gene of the proband: the paternal c.2047A > G(p.I683V) was an unreported missense variant, and the maternal c.2107_2108 insAGG(p.Q703delin sQE) was an unreported in-frame variant. CONCLUSIONS: In children with RM, LPIN1 variants should always be considered in the differential diagnosis. The clinical features of our case are atypical, which highlights the importance of an accurate diagnosis by genetic testing. If detected early, the condition may be controlled, and the prognosis may be improved.

Lipin 1 deficiency causes adult-onset myasthenia with motor neuron dysfunction in humans and neuromuscular junction defects in zebrafish.

Lipin 1 is an intracellular protein acting as a phosphatidic acid phosphohydrolase enzyme controlling lipid metabolism. Human recessive mutations in LPIN1 cause recurrent, early-onset myoglobinuria, a condition normally associated with muscle pain and weakness. Whether and how lipin 1 deficiency in humans leads to peripheral neuropathy is yet unclear. Herein, two novel compound heterozygous mutations in LPIN1 with neurological disorders, but no myoglobinuria were identified in an adult-onset syndromic myasthenia family. The present study sought to explore the pathogenic mechanism of LPIN1 in muscular and neural development. Methods: The clinical diagnosis of the proband was compared to the known 48 cases of LPIN1 recessive homozygous mutations. Whole-exome sequencing was carried out on the syndromic myasthenia family to identify the causative gene. The pathogenesis of lipin 1 deficiency during somitogenesis and neurogenesis was investigated using the zebrafish model. Whole-mount in situ hybridization, immunohistochemistry, birefringence analysis, touch-evoke escape response and locomotion assays were performed to observe in vivo the changes in muscles and neurons. The conservatism of the molecular pathways regulated by lipin 1 was evaluated in human primary glioblastoma and mouse myoblast cells by siRNA knockdown, drug treatment, qRT-PCR and Western blotting analysis. Results: The patient exhibited adult-onset myasthenia accompanied by muscle fiber atrophy and nerve demyelination without myoglobinuria. Two novel heterozygous mutations, c.2047A>C (p.I683L) and c.2201G>A (p.R734Q) in LPIN1, were identified in the family and predicted to alter the tertiary structure of LPIN1 protein. Lipin 1 deficiency in zebrafish embryos generated by lpin1 morpholino knockdown or human LPIN1 mutant mRNA injections reproduced the myotomes defects, a reduction both in primary motor neurons and secondary motor neurons projections, morphological changes of post-synaptic clusters of acetylcholine receptors, and myelination defects, which led to reduced touch-evoked response and abnormalities of swimming behaviors. Loss of lipin 1 function in zebrafish and mammalian cells also exhibited altered expression levels of muscle and neuron markers, as well as abnormally enhanced Notch signaling, which was partially rescued by the specific Notch pathway inhibitor DAPT. Conclusions: These findings pointed out that the compound heterozygous mutations in human LPIN1 caused adult-onset syndromic myasthenia with peripheral neuropathy. Moreover, zebrafish could be used to model the neuromuscular phenotypes due to the lipin 1 deficiency, where a novel pathological role of over-activated Notch signaling was discovered and further confirmed in mammalian cell lines.

Use of dexamethasone in idiopathic, acute pediatric rhabdomyolysis.

Current rhabdomyolysis treatment guidelines vary based on the etiology and diagnosis, yet many cases evade conclusive diagnosis. In these cases, treatment options remain largely limited to fluids and supportive therapy. We present two cases of acute rhabdomyolysis diagnosed in the emergency department: a 5-year-old boy with sudden onset bilateral flank pain, and a 13-year-old boy with 2-3 days of worsening pectoral and shoulder pain. Each patient had a prior similar episode requiring hospitalization in the past. The 5-year-old had no inciting trauma or trigger, medication use, or illness. The 13-year-old previously had an upper respiratory infection during the week prior and had been strenuously exercising at the time of onset. Genetic testing results were unknown for both patients during their hospitalizations, and insurance and other barriers led to delay. Later results for the first patient revealed a heterozygous deletion in intron 19 on the LPIN1 gene interpreted as a variant of unknown significance. During their hospitalizations, both children were started on intravenous (i.v.) fluids, and creatine kinase (CK) initially trended downward, but then began to rise or plateau. After reviewing the cases, prior literature, and anecdotal evidence of benefit from corticosteroid therapy in rhabdomyolysis with our consultant metabolic physicians, dexamethasone was initiated. In both patients, dexamethasone use correlated with relief of patient symptoms, significantly decreased CK value, and our ability to discharge these patients home quickly. Our cases, discussion, and literature review all lead to the consideration of the use of dexamethasone in conjunction with standard therapy for acute rhabdomyolysis.

Myoglobinuria as first clinical sign of a primary alpha-sarcoglycanopathy.

UNLABELLED: Myoglobinuria is a frequent complication of metabolic myopathies and may also occur in Duchenne and Becker dystrophies but is not a typical sign of limb-girdle muscular dystrophy. We describe an unusual presentation of alpha-sarcoglycanopathy with myoglobinuria at the onset of the disease. The boy presented an episode of dark urine, identified as presence of blood by a urine dipstick, occurred 10 days after an episode of fever and sore throat treated with antibiotics. He was admitted to the hospital and investigated for post-infectious nephritis, but further analysis revealed the presence of myoglobinuria. Immunohistochemistry on muscle tissue revealed absent expression of α-sarcoglycan confirmed by detection of a homozygous mutation in the alpha-sarcoglycan gene. Myoglobinuria has been previously reported four times in sarcoglycanopathies but only once in alpha-sarcoglycanopathy. CONCLUSION: The present observation reinforces the idea that the myoglobinuria should be considered a manifestation of a primary sarcoglycanopathy even as the only recognizable sign at the debut of the disease.

Novel mutations in myopathic form of carnitine palmitoyltransferase II deficiency in a Chinese patient.

BACKGROUND: Carnitine palmitoyltransferase II (CPT II) deficiency is one of the most common disorders of oxidative fatty acid metabolism. In this disorder, long-chain acylcarnitines cannot be converted to acyl CoA and there is impairment of ß-oxidation of fatty acids. RESULTS: In the 3 distinct clinical subtypes of CPT II deficiency, adult onset myopathic form shows mild clinical manifestations, characterized by recurrent rhabdomyolysis after intense physical stress. In this study, we report a case with adult myopathic form of CPT II deficiency presenting recurrent exercise-induced myoglobinuria. CONCLUSION: The acylcarnitine profile showed characteristic CPTII deficiency profile and sequencing of the CPT2 gene showed 2 novel missense mutations p. H369Q and p G497S.

Clinical and molecular characterization of McArdle's disease in Brazilian patients.

McArdle's disease, a glycogen storage disease type V, is caused by a deficiency of the enzyme myophosphorylase, encoded by the PYGM gene. Worldwide distribution of mutations has revealed interesting data about the prevalence of mutations and population migrations. Currently, more than 100 mutations in the PYGM gene have been described, with some recurrent mutations in the different populations. However, no molecular studies of McArdle's disease were reported in Brazilian patients. Here, we describe the clinical phenotype and genotype of 10 patients from 8 unrelated Brazilian families. Among the 10 patients (3 females, 7 males), eight presented with the typical phenotype, with exercise intolerance, cramps, and myalgia; one patient showed permanent muscle weakness; and one patient showed a mild phenotype. Molecular analysis identified 5 different mutations in the 8 families, both in homozygosis or compound heterozygosis state. Four of them had already been described (p.R50X, p.T692kfs30, p.K609K, and p.G455R), and one, pI513V, is a novel heterozygous mutation. The common nonsense p.R50X mutation was found in 6 of the 8 families, being therefore the commonest mutation in the Brazilian population as well. Other mutations previously reported in European patients were also found in the patients in this study, which was expected considering the European ancestry of the Brazilian population.

Recurrent myoglobinuria and deranged acylcarnitines due to a mutation in the mtDNA MT-CO2 gene.

Mitochondrial myopathies commonly present with exercise intolerance typified by breathlessness and fatigue on exercise. In contrast, exercise-induced rhabdomyolysis and myoglobinuria occur rarely. We present a 43-year-old man with a lifelong history of exercise intolerance associated with myalgia and recurrent episodes of exercise-induced myoglobinuria. From early childhood, he had weekly episodes of myoglobinuria, which became infrequent (every 3 months) as an adult. Carnitine transporter defect was suspected, because carnitine levels were low in muscle. During childhood, he was treated with carnitine (4-5 g daily), but without effect. With the advent of acylcarnitines, profiles mimicking but not diagnostic for multiple acyl-CoA dehydrogenase deficiency (MADD) were found. This led to treatment with riboflavin (100 mg/day for 3 years), again without effect. Clinical examination, including echocardiography, revealed no signs of involvement from other organs, and all relatives were asymptomatic.

Knock-in mice for the R50X mutation in the PYGM gene present with McArdle disease.

McArdle disease (glycogenosis type V), the most common muscle glycogenosis, is a recessive disorder caused by mutations in PYGM, the gene encoding myophosphorylase. Patients with McArdle disease typically experience exercise intolerance manifested as acute crises of early fatigue and contractures, sometimes with rhabdomyolysis and myoblobinuria, triggered by static muscle contractions or dynamic exercises. Currently, there are no therapies to restore myophosphorylase activity in patients. Although two spontaneous animal models for McArdle disease have been identified (cattle and sheep), they have rendered a limited amount of information on the pathophysiology of the disorder; therefore, there have been few opportunities for experimental research in the field. We have developed a knock-in mouse model by replacing the wild-type allele of Pygm with a modified allele carrying the common human mutation, p.R50X, which is the most frequent cause of McArdle disease. Histochemical, biochemical and molecular analyses of the phenotype, as well as exercise tests, were carried out in homozygotes, carriers and wild-type mice. p.R50X/p.R50X mice showed undetectable myophosphorylase protein and activity in skeletal muscle. Histochemical and biochemical analyses revealed massive muscle glycogen accumulation in homozygotes, in contrast to heterozygotes or wild-type mice, which did not show glycogen accumulation in this tissue. Additional characterization confirmed a McArdle disease-like phenotype in p.R50X/p.R50X mice, i.e. they had hyperCKaemia and very poor exercise performance, as assessed in the wire grip and treadmill tests (6% and 5% of the wild-type values, respectively). This model represents a powerful tool for in-depth studies of the pathophysiology of McArdle disease and other neuromuscular disorders, and for exploring new therapeutic approaches for genetic disorders caused by premature stop codon mutations.

Recurrent myoglobinuria in a sporadic patient with a novel mitochondrial DNA tRNA(Ile) mutation.

The differential diagnosis of myoglobinuria includes multiple etiologies, such as infection, inflammation, trauma, endocrinopathies, drugs toxicity, and primary metabolic disorders. Metabolic myopathies can be due to inherited disorders of glycogen metabolism or to defects of fatty acid oxidation. Primary respiratory chain dysfunction is a rare cause of myoglobinuria, but it has been described in sporadic cases with mutations in genes encoding cytochrome b or cytochrome c oxidase (COX) subunits and in four cases with tRNA mutations. We describe a 39-year-old woman with myalgia and exercise-related recurrent myoglobinuria, who harbored a novel mitochondrial DNA mutation at nucleotide 4281 (m.4281A>G) in the tRNA-isoleucine gene. Her muscle biopsy revealed ragged-red and COX-deficient fibers. No deletions or duplication were detected by Southern blot analysis. The m.4281A>G mutation was present in the patient's muscle with a mutation load of 46% and was detected in trace amounts in urine and cheek mucosa. Single-fiber analysis revealed significantly higher levels of the mutation in COX-deficient (65%) than in normal fibers (45%). This novel mutation has to be added to the molecular causes of recurrent myoglobinuria.

Pseudometabolic presentation of dystrophinopathy due to a missense mutation.

Exercise intolerance with myalgia, muscle stiffness, and recurrent rhabdomyolysis due to mutations in the DMD gene can mimic metabolic myopathies leading to delayed or inaccurate diagnoses. In this retrospective chart review, we report 3 unrelated boys with exertional myalgia, muscle stiffness, myoglobinuria, and normal neurological examination due to an identical point mutation in the DMD gene: a hemizygous T-to-C change in exon 15 (c.1724T>C) resulting in an amino acid substitution of leucine to proline at codon 575. Two of the 3 boys had normal dystrophin immunostaining and Western blot analysis in muscle. This missense mutation has been reported twice before, with at least 1 patient exhibiting rhabdomyolysis. Our report, however, is the first to describe in detail the clinical findings associated with this specific mutation. Further studies and clinical reports are needed to better understand the pathogenicity of the mutation.

Permanent muscle weakness in McArdle disease.

McArdle disease is an autosomal recessive muscle glycogenosis. In the typical clinical presentation, only exercise-related symptoms are noted. Nevertheless, permanent weakness may occur, usually late in life. In this study we report on the clinical and genetic features of fixed muscle weakness in McArdle disease. Among the 80 McArdle patients being followed at the Institute of Myology of the Salpêtrière Hospital, 9 patients have permanent weakness. The diagnosis of McArdle disease was confirmed by muscle biopsy and genetic investigations. Two patterns of muscle weakness and wasting were noted: (1) proximal and symmetric in 5 patients; and (2) asymmetric, mimicking facioscapulohumeral dystrophy (FSHD) in 4 patients. Computerized tomography scan showed fatty infiltration in the shoulder and pelvic girdle muscles. There was no clear correlation between genotype and the severity of muscle weakness. Proximal muscle weakness appeared after the age of 40 years and affected 11% of subjects in our series of 80 McArdle patients. Among patients over 40 years of age, 37.5% had muscle weakness.

Myopathic form of phosphoglycerate kinase (PGK) deficiency: a new case and pathogenic considerations.

We describe an 18-year-old man with muscle cramps and recurrent exertional myoglobinuria, without hemolytic anemia or brain dysfunction. Phosphoglycerate kinase (PGK) deficiency was documented in muscle and erythrocytes and molecular analysis of the PGK1 gene identified a novel mutation, T378P. This is the ninth case presenting with isolated myopathy, whereas most other patients show hereditary non-spherocytic hemolytic anemia alone or associated with brain dysfunction, and a few patients have myopathy plus brain involvement. Although the diverse tissue involvement in PGK deficiency remains unclear, all mutations in myopathic patients tend to cluster in the C terminal domain, adjacent to the substrate-binding pocket. This may lead to a failure in the closure of the N terminal and C terminal domains and loss of stability due to lack of inter-domain communication during the catalytic process.

Mutations in LPIN1 cause recurrent acute myoglobinuria in childhood.

Recurrent episodes of life-threatening myoglobinuria in childhood are caused by inborn errors of glycogenolysis, mitochondrial fatty acid beta-oxidation, and oxidative phosphorylation. Nonetheless, approximately half of the patients do not suffer from a defect in any of these pathways. Using homozygosity mapping, we identified six deleterious mutations in the LPIN1 gene in patients who presented at 2-7 years of age with recurrent, massive rhabdomyolysis. The LPIN1 gene encodes the muscle-specific phosphatidic acid phosphatase, a key enzyme in triglyceride and membrane phospholipid biosynthesis. Of six individuals who developed statin-induced myopathy, one was a carrier for Glu769Gly, a pathogenic mutation in the LPIN1 gene. Analysis of phospholipid content disclosed accumulation of phosphatidic acid and lysophospholipids in muscle tissue of the more severe genotype. Mutations in the LPIN1 gene cause recurrent rhabdomyolysis in childhood, and a carrier state may predispose for statin-induced myopathy.

Genetic determinants of statin intolerance.

BACKGROUND: Statin-related skeletal muscle disorders range from benign myalgias--such as non-specific muscle aches or joint pains without elevated serum creatinine kinase (CK) concentration--to true myositis with >10-fold elevation of serum CK, to rhabdomyolysis and myoglobinuria. The genetic basis of statin-related muscle disorders is largely unknown. Because mutations in the COQ2 gene are associated with severe inherited myopathy, we hypothesized that common, mild genetic variation in COQ2 would be associated with inter-individual variation in statin intolerance. We studied 133 subjects who developed myopathy on statin monotherapy and 158 matched controls who tolerated statins without incident or complaint. RESULTS: COQ2 genotypes, based on two single nucleotide polymorphisms (SNP1 and SNP2) and a 2-SNP haplotype, all showed significant associations with statin intolerance. Specifically, the odds ratios (with 95% confidence intervals) for increased risk of statin intolerance among homozygotes for the rare alleles were 2.42 (0.99 to 5.89), 2.33 (1.13 to 4.81) and 2.58 (1.26 to 5.28) for SNP1 and SNP2 genotypes, and the 2-SNP haplotype, respectively. CONCLUSION: These preliminary pharmacogenetic results, if confirmed, are consistent with the idea that statin intolerance which is manifested primarily through muscle symptoms is associated with genomic variation in COQ2 and thus perhaps with the CoQ10 pathway.

Tarui disease and distal glycogenoses: clinical and genetic update.

Phosphofructokinase deficiency (Tarui disease) was the first disorder recognized to directly affect glycolysis. Since the discovery of the disease, in 1965, a wide range of biochemical, physiological and molecular studies have greatly contributed to our knowledge concerning not only phosphofructokinase function in normal muscle but also on the general control of glycolysis and glycogen metabolism. Studies on phosphofructokinase deficiency vastly enriched the field of glycogen storage diseases, making a relevant improvement also in the molecular genetic area. So far, more than one hundred patients have been described with prominent clinical symptoms characterized by muscle cramps, exercise intolerance, rhabdomyolysis and myoglobinuria, often associated with haemolytic anaemia and hyperuricaemia. The muscle phosphofructokinase gene is located on chromosome 12 and about 20 mutations have been described. Other glycogenoses have been recognised in the distal part of the glycolytic pathway: these are infrequent but some may induce muscle cramps, exercise intolerance and rhabdomyolysis. Phosphoglycerate Kinase, Phosphoglycerate Mutase, Lactate Dehydrogenase, beta-Enolase and Aldolase A deficiencies have been described as distal glycogenoses. From the molecular point of view, the majority of these enzyme deficiencies are sustained by "private" mutations.

Exercise-induced cramp, myoglobinuria, and tubular aggregates in phosphoglycerate mutase deficiency.

We report two patients in whom phosphoglycerate mutase (PGAM) deficiency was associated with the triad of exercise-induced cramps, recurrent myoglobinuria, and tubular aggregates in the muscle biopsy. Serum creatine kinase (CK) levels were elevated between attacks of myoglobinuria. Forearm ischemic exercise tests produced subnormal increases of venous lactate. Muscle biopsies showed subsarcolemmal tubular aggregates in type 2 fibers. Muscle PGAM activities were markedly decreased (3% of the normal mean) and molecular genetic studies showed that both patients were homozygous for a described missense mutation (W78X). A review of 15 cases with tubular aggregates in the muscle biopsies from our laboratory and 15 cases with PGAM deficiency described in the literature showed that this clinicopathological triad is highly suggestive of PGAM deficiency.

Intronic mutation in the PGK1 gene may cause recurrent myoglobinuria by aberrant splicing.

A 33-year-old man with mental retardation and recurrent myoglobinuria demonstrated a deficiency in the phosphoglycerate kinase 1 (PGK1) activity of his muscles and erythrocytes. His PGK1 gene had intronic G-to-A substitution 5 nucleotides downstream from the normal exon 7 5' splice site (IVS7 + 5 G>A). This novel mutation results in a frame shift due to the insertion of 52 bp of intron 7 in the mature mRNA by aberrant splicing.