Tulio E. Bertorini

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) Clinical, biochemical, and genetic features of an autosomal recessive mitochondrial disorder

We studied the clinical, biochemical, and genetic features of eight patients with the autosomal recessive mitochondrial syndrome mitochondrial neurogastrointestinal encephalomyopathy (MNGIE). MNGIE is clinically characterized by ophthalmoparesis, peripheral neuropathy, leukoencephalopathy, gastrointestinal symptoms (recurrent nausea, vomiting, or diarrhea) with intestinal dysmotility, and histologically abnormal mitochondria in muscle. Brain MRI scans were consistent with leukodystrophy in seven patients examined. Nerve conduction and EMG studies were compatible with a sensorimotor neuropathy; quantitative EMG of two patients suggested a myogenic process. Muscle mitochondrial enzyme analysis revealed a partial defect of cytochrome c oxidase activity in five patients; three had additional respiratory chain enzyme defects. Two patients had isolated complex I defects, and one had normal respiratory chain function. Southern blot analysis revealed multiple deletions of mitochondrial DNA in four of eight patients.

Muscle calcium and magnesium content in Duchenne muscular dystrophy

Calcium (Ca) and magnesium (Mg) content were determined in muscle of 27 patients with Duchenne muscular dystrophy, 36 with other neuromuscular diseases, and 22 whose muscle biopsy specimens were histochemically normal. Muscle Ca was significantly elevated in all diseases studied but was about 50% higher in Duchenne dystrophy patients (p < 0.0001). Mg was decreased by 44% in Duchenne dystrophy, compared with less striking deficits in other diseases (p < 0.005). In older, nonambulatory Duchenne dystrophy patients, Mg was significantly lower than in younger, ambulatory patients (p < 0.001); muscle Ca was the same in both groups. On the basis of noncollagen nitrogen concentration, muscle Mg depletion could not be attributed solely to reduced muscle mass. These findings strengthen arguments for a role of Ca in the pathogenesis of muscular dystrophy and may implicate Mg depletion as another pathogenetic factor.

Secondary reduction in calpain 3 expression in patients with limb girdle muscular dystrophy type 2B and Miyoshi myopathy (primary dysferlinopathies)

Dysferlin is the protein product of the gene (DYSF) that is defective in patients with limb girdle muscular dystrophy type 2B and Miyoshi myopathy. Calpain 3 is the muscle-specific member of the calcium activated neutral protease family and primary mutations in the CAPN3 gene cause limb girdle muscular dystrophy type 2A. The functions of both proteins remain speculative. Here we report a secondary reduction in calpain 3 expression in eight out of 16 patients with a primary dysferlinopathy and clinical features characteristic of limb girdle muscular dystrophy type 2B or Miyoshi myopathy. Previously CAPN3 analysis had been undertaken in three of these patients and two showed seemingly innocuous missense mutations, changing calpain 3 amino acids to those present in the sequences of calpains 1 and 2. These results suggest that there may be an association between dysferlin and calpain 3, and further analysis of both genes may elucidate a novel functional interaction. In addition, an association was found between prominent expression of smaller forms of the 80 kDa fragment of laminin alpha 2 chain (merosin) and dysferlin-deficiency.

CLINICAL FINDINGS IN MUSK-ANTIBODY POSITIVE MYASTHENIA GRAVIS: A U.S. EXPERIENCE

We performed a retrospective chart review on 53 muscle‐specific kinase antibody (MuSK‐Ab)‐positive myasthenia gravis (MG) patients at nine university‐based centers in the U.S. Of these, 66% were Caucasian, 85% were women, and age of onset was 9–79 years. Twenty‐seven patients were nonresponsive to anticholinesterase therapy. Myasthenia Gravis Foundation of America improvement status was achieved in 53% patients on corticosteroids, 51% with plasma exchange, and in 20% on intravenous immunoglobulin (IVIG). Thymectomy was beneficial in 7/18 patients at 3 years. Long‐term (≥3 years) outcome was very favorable in 58% of patients who achieved remission and/or minimal manifestation status. Overall, 73% improved. There was one MG‐related death. This survey reinforces several cardinal features of MuSK‐Ab‐positive MG, including prominent bulbar involvement and anticholinesterase nonresponsiveness. Facial or tongue atrophy was rare. Most patients respond favorably to immunotherapy. The best clinical response was to corticosteroids and plasma exchange, and the poorest response was to IVIG. Long‐term outcome is favorable in about 60% of cases. Muscle Nerve, 2009

Laminin α2 muscular dystrophy: Genotype/phenotype studies of 22 patients

Objective: To determine the number of primary laminin α2 gene mutations and to conduct genotype/phenotype correlation in a cohort of lamininα2-deficient congenital muscular dystrophy patients. Background: Congenital muscular dystrophies (CMD) are a heterogenous group of muscle disorders characterized by early onset muscular dystrophy and a variable involvement of the CNS. Laminin α2 deficiency has been reported in about 40 to 50% of cases of the occidental, classic type of CMD.1,2 Laminin α2 is a muscle specific isoform of laminin localized to the basal lamina of muscle fibers, where it is thought to interact with myofiber membrane receptor, such as integrins, and possibly dystrophin-associated glycoproteins.3,4 Methods: Seventy-five CMD patients were tested for laminin α2 expression by immunofluorescence and immunoblot. The entire 10 kb laminin α2 coding sequence of 22 completely laminin α2-deficient patients was screened for causative mutations by reverse transcription (RT)-PCR/single strand conformational polymorphisms (SSCP) analysis and protein truncation test(PTT) analysis followed by automatic sequencing of patient cDNA. Clinical data from the laminin α2-deficient patients were collected. Results: Thirty laminin α2-negative patients were identified (40% of CMD patients tested) and 22 of them were screened for laminin α2 mutations. Clinical features of laminin α2-deficient patients were similar, with severe floppiness at birth, delay in achievement of motor milestones, and MRI findings of white matter changes with normal intelligence. Loss-of-function mutations were identified in 95% (21/22) of the patients studied. SSCP analysis detected laminin α2 gene mutations in about 50% of the mutant chromosomes; PTT successfully identified 75% of the mutations. A two base pair deletion mutation at position 2,096-2,097 bp was present in 23% of the patients analyzed. Conclusions: Our data suggest that the large majority of laminin α2-deficient patients show laminin α2 gene mutations.

CINRG randomized controlled trial of creatine and glutamine in Duchenne muscular dystrophy

We tested the efficacy and safety of glutamine (0.6gm/kg/day) and creatine (5gm/day) in 50 ambulant boys with Duchenne muscular dystrophy in a 6‐month, double‐blind, placebo‐controlled clinical trial. Drug efficacy was tested by measuring muscle strength manually (34 muscle groups) and quantitatively (10 muscle groups). Timed functional tests, functional parameters, and pulmonary function tests were secondary outcome measures. Although there was no statistically significant effect of either therapy based on manual and quantitative measurements of muscle strength, a disease‐modifying effect of creatine in older Duchenne muscular dystrophy and creatine and glutamine in younger Duchenne muscular dystrophy cannot be excluded. Creatine and glutamine were well tolerated. Ann Neurol 2005;58:151–155

Randomized, blinded trial of weekend vs daily prednisone in Duchenne muscular dystrophy

Objective: To perform a double-blind, randomized study comparing efficacy and safety of daily and weekend prednisone in boys with Duchenne muscular dystrophy (DMD). Methods: A total of 64 boys with DMD who were between 4 and 10 years of age were randomized at 1 of 12 centers of the Cooperative International Neuromuscular Research Group. Efficacy and safety of 2 prednisone schedules (daily 0.75 mg/kg/day and weekend 10 mg/kg/wk) were evaluated over 12 months. Results: Equivalence was met for weekend and daily dosing of prednisone for the primary outcomes of quantitative muscle testing (QMT) arm score and QMT leg score. Secondary strength scores for QMT elbow flexors also showed equivalence between the 2 treatment groups. Overall side effect profiles of height and weight, bone density, cataract formation, blood pressure, and behavior, analyzed at 12 months, did not differ between weekend and daily dosing of prednisone. Conclusions: Weekend dosing of prednisone is equally beneficial to the standard daily dosing of prednisone. Analysis of side effect profiles demonstrated overall tolerability of both dosing regimens. Classification of evidence: This study provides Class I evidence that weekend prednisone dosing is as safe and effective as daily prednisone in preserving muscle strength and preventing body mass index increases in boys with DMD over a 12-month period.

Carnitine palmityl transferase deficiency Myoglobinuria and respiratory failure

A 51-year-old man presented with acute respiratory failure and myoglobinuria precipitated by an infection. Carnitine palmityltransferase (CPT) deficiency was documented in muscle, leukocytes, and liver. “he enzyme defect in liver, previously suspected and now documented, explained the decreased production of ketone bodies during fasting observed in this patient as well as others with muscle CFT deficiency. Decreased utilization of long-chain fatty acids and decreased availability of ketone bodies can deprive the muscle of crucial sources of energy and, in certain conditions, may precipitate myoglobinuria.

Parathyroid Ablation in Dystrophic Hamsters: EFFECTS ON CA CONTENT AND HISTOLOGY OF HEART, DIAPHRAGM, AND RECTUS FEMORIS

Cumulative evidence indicates that there is an increased accumulation of calcium in dystrophic muscle and that this may have a pathophysiological role in the progression of the dystrophic process. The accumulation may be related to a defect of the plasma membrane. Because parathyroid hormone (PTH) stimulates calcium influx into the cytosol, the chronic effects of surgical ablation of the parathyroid glands on muscle Ca, Mg, protein synthesis, and histology, as well as plasma creatine phosphokinase (CPK), Ca, and Mg, were studied in normal and dystrophic (BIO 14.6) hamsters. Thyroparathyroidectomized (TPTX) hamsters receiving replacement doses of l-thyroxine were killed at age 90 d, 55 d after TPTX. In intact dystrophic hamsters, the Ca content in the heart was 20 times higher than in normal animals and was reduced by half in TPTX dystrophic hamsters. Similar results were observed in diaphragm and rectus femoris. No abnormalities in Mg content were observed in intact or TPTX dystrophic hamsters. Ether-extractable fat of the heart and diaphragm was reduced in dystrophic hamsters and was not modified by TPTX. Protein synthesis was enhanced in the diaphragm of dystrophic hamsters but was not changed by TPTX. The concentration of CPK in plasma was elevated in dystrophic hamsters and fell significantly after TPTX. In the latter animals, microscopic examination of the heart showed lesser signs of dystrophy, particularly in the degree of fibrosis. To determine the degree of dystrophy at the age when TPTX was performed, identical analyses were made in 35-d-old hamsters. Definitive histological signs of dystrophy were observed, and although the Ca content in heart, diaphragm, and rectus femoris was elevated, the values were lower than in 90-d-old intact and TPTX dystrophic hamsters. This indicates that chronic TPTX in dystrophic hamsters reduces, but does not arrest, the dystrophic process. In normal hamsters, a 50% reduction in plasma Ca concentration was observed 6 h after TPTX; 55 d after TPTX, however, plasma Ca was within normal limits in both normal and dystrophic hamsters. No parathyroid tissue was observed in serial sections of the trachea and adjacent tissues in TPTX animals. This suggests that in chronically TPTX hamsters fed a standard laboratory diet, plasma Ca can be maintained by mechanisms independent of parathyroid function. THE DATA INDICATE THAT IN DYSTROPHIC HAMSTERS TPTX CAUSES A MARKED REDUCTION IN: (a) muscle Ca accumulation, (b) levels of plasma CPK and, (c) intensity of histological changes in the heart. These changes were independent of the levels of plasma Ca and were not observed in normal hamsters. We conclude that PTH accentuates the dystrophic process, probably by enhancing the already increased Ca flux into muscle (apparently caused by defective sarcolemma). We postulate that normal secretion of PTH may have a deleterious effect in congenital or acquired conditions associated with altered plasma membranes.

Calcium and magnesium content in fetuses at risk and prenecrotic Duchenne muscular dystrophy

We measured calcium (Ca) and magnesium (Mg) content in muscles of fetuses at risk of Duchenne muscular dystrophy (DMD) and in a premature infant who later developed typical DMD. There was a three- to six-fold increase in muscle Ca in the fetuses and in the premature infant. In contrast to our previous reports of reduced muscle Mg in DMD children, there was an 18 to 57% increase of Mg in the fetuses at risk. Opaque and Ca-positive fibers, rarely observed in normal fetuses, were numerous in fetuses at risk and in the premature infant. No necrotic fibers were detected in the fetuses or the premature infant. These findings suggest that excessive Ca accumulation precedes necrosis in DMD. Other factors related to growth and development that occur after birth may trigger the necrosis that follows muscle Ca accumulation.