Biomedical subjects

Mark Tarnopolsky

Publications and source records attributed to Mark Tarnopolsky.

16 recordsLinked to original sources

PubMed2026

Comprehensive functional testing in fibroblasts has strong utility to diagnose mitochondrial disease.

Genome sequencing is the first-line diagnostic method for primary mitochondrial diseases (PMDs), yet its effectiveness is limited by variants of uncertain significance or unresolved genetic findings. We systematically evaluated the clinical performance of fibroblast-based functional testing, comprised of respiratory chain enzyme assays, blue native polyacrylamide gel electrophoresis with in-gel activity staining (BN-PAGE), complex I assembly assay, and targeted protein abundance assessments, in a cohort of 204 genetically confirmed PMD patients, 51 healthy controls, and 53 patients with differential diagnoses. Individually, enzyme assays, BN-PAGE, and complex I assembly assay showed sensitivities of 46%, 40%, and 49%, with specificities of 93%, 98%, and 99%, respectively. Combined, the assays achieved an overall sensitivity of 76%, a specificity 93%, a positive predictive value 96%, and a negative predictive value of 67%. Sensitivity was highest for isolated respiratory chain deficiencies, nuclear DNA-encoded mitochondrial translation defects, cofactor deficiencies, and mitochondrial aminoacyl-tRNA synthetase disorders, whereas mitochondrial DNA variants and maintenance defects remained challenging. Secondary mitochondrial dysfunction was rare. The strong clinical utility of comprehensive fibroblast functional testing improves PMD diagnosis when used complementary to genomic sequencing.

Journal Article↗

PubMed2006

Genomic organization, promoter activity, and expression of the human choline transporter-like protein 1.

Choline transporter-like (CTL) proteins of the CTL1 family are novel transmembrane proteins implicated in choline transport for phospholipid synthesis. In this study, we characterized the 5'-flanking region of the human (h)CTL1 gene and examined some of the possible mechanisms of its regulation, including promoter activity, splicing, and expression. The transcription start site of the hCTL1 gene was mapped by 5'-rapid amplification of cDNA ends (RACE), and the presence of two splice variants, hCTL1a and hCTL1b, was investigated using isoform-specific PCR and 3'-RACE. The hCTL1 promoter region of approximately 900 bp was isolated from MCF-7 human breast cancer cells. The promoter was TATA-less and driven by a long stretch of GC-rich sequence in accordance with widespread expression of hCTL1 at both mRNA and protein levels. Deletion analyses demonstrated that a very strong promoter is contained within 500 bp of the transcription start site, and more upstream regions did not increase its activity. The core promoter that conferred the minimal transcription is within the -188/+27-bp region, and its activity varied in human breast cancer and mouse skeletal muscle cells. Multiple motifs within the promoter regulatory region bound nuclear factors from both cultured cells and normal human skeletal muscle. The motifs within the three regions [S1 (-92/-61 bp), S2 (-174/-145 bp), and S3 (-289/-260 bp)] contained overlapping binding sites for hematopoietic transcription factors and ubiquitous transcription factors, in line with the expected gene function. Genomic analyses demonstrated a high conservation of hCTL1 and mouse CTL1 proximal promoters. Accordingly, mRNA profiles demonstrated that human splice variants were expressed ubiquitously, as demonstrated for the mouse transcripts; however, they differed from the profiles of rat CTL1 transcripts, which were more restricted to neurons and intestinal tissues. The shorter hCTL1b variant contained the cytosolic COOH-terminal motif L651KKR654 for endoplasmic reticulum retrieval/retention. This retention signal was conserved in hCTL1b and rat and mouse CTL1b and is typical for transmembrane proteins of type 1 topology.

Adult↗

PubMed2006

Genetic risk factors associated with lipid-lowering drug-induced myopathies.

Lipid-lowering drugs produce myopathic side effects in up to 7% of treated patients, with severe rhabdomyolysis occurring in as many as 0.5%. Underlying metabolic muscle diseases have not been evaluated extensively. In a cross-sectional study of 136 patients with drug-induced myopathies, we report a higher prevalence of underlying metabolic muscle diseases than expected in the general population. Control groups included 116 patients on therapy with no myopathic symptoms, 100 asymptomatic individuals from the general population never exposed to statins, and 106 patients with non-statin-induced myopathies. Of 110 patients who underwent mutation testing, 10% were heterozygous or homozygous for mutations causing three metabolic myopathies, compared to 3% testing positive among asymptomatic patients on therapy (P = 0.04). The actual number of mutant alleles found in the test group patients was increased fourfold over the control group (P < 0.0001) due to an increased presence of mutation homozygotes. The number of carriers for carnitine palmitoyltransferase II deficiency and for McArdle disease was increased 13- and 20-fold, respectively, over expected general population frequencies. Homozygotes for myoadenylate deaminase deficiency were increased 3.25-fold with no increase in carrier status. In 52% of muscle biopsies from patients, significant biochemical abnormalities were found in mitochondrial or fatty acid metabolism, with 31% having multiple defects. Variable persistent symptoms occurred in 68% of patients despite cessation of therapy. The effect of statins on energy metabolism combined with a genetic susceptibility to triggering of muscle symptoms may account for myopathic outcomes in certain high-risk groups.

AMP Deaminase↗

PubMed2005

A novel mutation in the PYGM gene in a family with pseudo-dominant transmission of McArdle disease.

A Caucasian family appeared to transmit McArdle disease in an autosomal dominant manner and was examined for mutations in the myophosphorylase gene. The asymptomatic father was heterozygous for the R49X mutation in exon 1. The symptomatic mother was a compound heterozygote for R49X and a novel 2 bp deletion in exon 1 causing a frameshift at codon 25 (T25fs). Each of three children manifested symptoms of McArdle disease and was either a compound heterozygote for these two mutations or homozygous for R49X.

Adult↗

PubMed2005

Serum creatinine: a surrogate measurement of lean body mass in children with acute lymphoblastic leukemia.

BACKGROUND: Since creatinine is formed almost exclusively in skeletal muscle, the hypothesis of a relationship between serum creatinine (SC) and lean body mass (LBM), determined by dual-energy X-ray absorptiometry (DXA), was tested. METHODS: Two cohorts of patients were analyzed: 37 children with acute lymphoblastic leukemia (ALL) and 20 children with primary muscular disorders (PMD). The latter cohort was used as a comparative group. Statistical analyses were performed using linear regressions. RESULTS: A strong correlation was demonstrated between SC and LBM in the patients with PMD (r = 0.77) and in patients with ALL (r = 0.83 at diagnosis; r = 0.77 on therapy; and r = 0.56 off therapy). The correlation between SC and body size (body mass index) was much weaker (r = 0.38; r = -0.09; r = 0.29 at the successive observations in the ALL cohort and r = 0.05 in the PMD cohort). These data provide support for the initial hypothesis. CONCLUSIONS: Further investigations with a wider variety of diseases are needed for this will allow the consideration of SC as a general surrogate measure of LBM and consequently of nutritional status.

Biomarkers↗

PubMed2004

Exercise testing as a diagnostic entity in mitochondrial myopathies.

Exercise intolerance is one of the most common symptoms in patients with mitochondrial myopathies (MM). At the whole body level, this is characterized by a reduction in maximal oxygen consumption (VO2max) with an excessive carbon dioxide production (VCO2), increased rating of perceived exertion and a hyperdynamic circulatory response at a given exercise intensity. Fewer patients with MM display overt muscle atrophy and weakness even in the absence of a peripheral neuropathy. At the level of the skeletal muscle, the abnormal exercise response in MM patients is characterized by an increase in; delivery of oxygen relative to extraction (reduced myoglobin or hemoglobin desaturation), lactate production, phosphocreatine hydrolysis and time of post-exercise PCr and ADP recovery. Classically, the characterization of exercise intolerance is performed using cycle ergometry with measurements of VO2, VCO2, respiratory exchange ratio (RER = VCO2/VO2), heart rate, minute ventilation, rating of perceived exertion, and cardiac output (where available). Exercise protocols to maximum or for a given time period at a set workload can differentiate MM from controls with a sensitivity of 0.63-0.75 and a specificity of 0.70-0.90. Modified hand-grip exercise protocols, especially if coupled with simultaneous measurements of myoglobin/hemoglobin desaturation (near infra-red spectroscopy) or venous oxygenation, can achieve similar or higher levels of sensitivity and specificity. Similarly, exercise coupled with muscle phosphocreatine/Pi ratios, PCr, pH or ADP recovery kinetics, determined using magnetic resonance spectroscopy are useful in differentiating MM, but are limited by availability, experience and cost. In summary, aerobic exercise testing with some measurement of oxygen consumption can be performed in most institutions and can provide valuable information in the both the work-up of patients with suspected MM as well as in the monitoring of therapy in such patients.

Journal Article↗

PubMed2004

Creatine monohydrate supplementation does not increase muscle strength, lean body mass, or muscle phosphocreatine in patients with myotonic dystrophy type 1.

Creatine monohydrate (CrM) supplementation may increase strength in some types of muscular dystrophy. A recent study in myotonic muscular dystrophy type 1 (DM1) did not find a significant treatment effect, but measurements of muscle phosphocreatine (PCr) were not performed. We completed a randomized, double-blind, cross-over trial using 34 genetically confirmed adult DM1 patients without significant cognitive impairment. Participants received CrM (5 g, approximately 0.074 g/kg daily) and a placebo for each 4-month phase with a 6-week wash-out. Spirometry, manual muscle testing, quantitative isometric strength testing of handgrip, foot dorsiflexion, and knee extension, handgrip and foot dorsiflexion endurance, functional tasks, activity of daily living scales, body composition (total, bone, and fat-free mass), serum creatine kinase activity, serum creatinine concentration and clearance, and liver function tests were completed before and after each intervention, and muscle PCr/beta-adenosine triphosphate (ATP) ratios of the forearm flexor muscles were completed at the end of each phase. CrM supplementation did not increase any of the outcome measurements except for plasma creatinine concentration (but not creatinine clearance). Thus, CrM supplementation at 5 g daily does not have any effects on muscle strength, body composition, or activities of daily living in patients with DM1, perhaps because of a failure of the supplementation to increase muscle PCr/beta-ATP content.

Activities of Daily Living↗

PubMed2004

Resistance training effectiveness in patients with Charcot-Marie-Tooth disease: recommendations for exercise prescription.

OBJECTIVES: To determine the effects of a 12-week, home-based resistance exercise program on strength, body composition, and activities of daily living (ADLs) in men and women with Charcot-Marie-Tooth (CMT) disease and to design an ADL-based resistance exercise prescription template. DESIGN: Double-blind, placebo-controlled study. SETTING: Testing in a university setting; exercise in patients' homes. PARTICIPANTS: Twenty CMT patients who volunteered. INTERVENTION: Subjects progressively strength trained at home 3 d/wk for 12 weeks. MAIN OUTCOME MEASURES: Timed ADLs, isometric strength, and body composition. RESULTS: Absolute strength was greater in men with CMT in only 4 of 10 baseline measures (P<.05), but not when strength was normalized by lean mass. Training compliance was 87% with no gender differences. At baseline, women had 80% of normal strength in 4 of 10 measures, whereas men did not achieve 80% of normal strength in any measure. After training, women had 80% of normal strength in 8 of 10 measures, whereas men only had 80% of normal strength in 1. Training volumes and strength change scores showed no gender differences. ADLs improved after training with no gender differences (P<.05). An exercise prescription template was developed by using chair-rise time to estimate starting weights for lower body and supine rise for upper body. CONCLUSIONS: Resistance training improved strength and ADLs equally in men and women. We designed an exercise prescription recommendation, based on ADL performance.

Activities of Daily Living↗

PubMed2004

Injection of botulinum toxin A to the upper esophageal sphincter for oropharyngeal dysphagia in two patients with inclusion body myositis.

Inclusion body myositis (IBM) is a progressive degenerative skeletal muscle disease leading to weakening and atrophy of both proximal and distal muscles. Dysphagia is reported in up to 86% of IBM patients. Surgical cricopharyngeal myotomy may be effective for cricopharyngeal dysphagia and there is one published report that botulinum toxin A, injected into the cricopharyngeus muscle using a hypopharyngoscope under general anesthesia, relieved IBM-associated dysphagia. This report presents the first documentation of botulinum toxin A injection into the upper esophageal sphincter using a flexible esophagogastroduodenoscope under conscious sedation, to reduce upper esophageal sphincter pressure and successfully alleviate oropharyngeal dysphagia in two IBM patients.

Aged↗

PubMed2004

Corticotropin-releasing factor 2 receptor localization in skeletal muscle.

Our objective in this study was to localize the corticotropin-releasing factor 2 receptor (CRF2R) in rodent and human skeletal muscle. We found CRF2R protein to be abundant in neural tissues in skeletal muscle, including large nerve fibers and bundles, neural tissue associated with mechanoreceptors, muscle spindles, and the Golgi tendon organ. CRF2R protein was also abundant in blood vessels in skeletal muscle. CRF2R protein was also observed, although with less abundance, in the endo/perimysial regions in skeletal muscle. The localization of the CRF2R to blood vessels is consistent with the CRF2R-mediated vascular phenomena observed previously, but the observation of CRF2R in neural tissue in skeletal muscle is a novel finding with an unknown function.

Animals↗

PubMed2003

Diagnostic utility of a modified forearm ischemic exercise test and technical issues relevant to exercise testing.

The sensitivity and specificity of a modified forearm ischemic test (FIT) are described in the diagnosis of glycogen storage disease, myoadenylate deaminase deficiency, and mitochondrial disease. FIT and muscle biopsy results were reviewed from 99 patients (glycogen storage disease [GSD], myoadenylate deaminase deficiency [AMPD], mitochondrial disease [MITO], miscellaneous neuromuscular disorders, and controls). The influence of catheter placement and an antecedent sugar bolus were also assessed in healthy young men. The FIT had a sensitivity of 1.00 and a specificity of 1.00 for a diagnosis of GSD, whereas the corresponding values were 1.00 and 0.37 for AMPD deficiency. A baseline lactate of >2.5 mmol/L provided the highest sensitivity (0.62) and specificity (1.00) for MITO disease. A baseline and +1 min sample provided optimal sensitivity and specificity for GSD and AMPD deficiency. Catheter placement in any vein other than the ipsilateral antecubital resulted in attenuated lactate responses (P < 0.0001). A pre-FIT sugar bolus did not alter the postexercise lactate or ammonia response. Thus, a modified FIT was helpful in the diagnosis of GSD and excluding AMPD deficiency, but not in the diagnosis of MITO disease. Catheter placement is critical to the interpretation of a FIT, whereas pretesting diet is less important.

Adult↗

PubMed2003

Two children with muscular dystrophies ascertained due to referral for diagnosis of autism.

We report two children who were referred for diagnostic assessment for autism and were subsequently determined to have a muscular dystrophy (MD). Each child had a history of speech delay and social impairments, but also had motor delays that had not previously been investigated. Both children met diagnostic criteria for autism spectrum disorders on standardized assessment. Each child was hypotonic and had other mild motor impairments. Serum creatine kinase (CK) activity was markedly elevated in each child, and subsequent muscle biopsy led to diagnosis of Becker's MD and congenital (autosomal recessive) MD, respectively. These cases highlight the importance of a thorough neuromotor examination for all children with suspected autism spectrum disorders.

Autistic Disorder↗

PubMed2003

Activation of the CRF 2 receptor modulates skeletal muscle mass under physiological and pathological conditions.

Two receptors activated by the corticotropin-releasing factor (CRF) family of peptides have been identified, the CRF 1 receptor (CRF1R) and the CRF 2 receptor (CRF2R). Of these, the CRF2R is expressed in skeletal muscle. To understand the role of the CRF2R in skeletal muscle, we utilized CRFR knockout mice and CRF2R-selective agonists to modulate nerve damage and corticosteroid- and disuse-induced skeletal muscle atrophy in mice. These analyses demonstrated that activation of the CRF2R decreased nerve damage and corticosteroid- and disuse-induced skeletal muscle mass and function loss. In addition, selective activation of the CRF2R increased nonatrophy skeletal muscle mass. Thus we describe for the first time a novel activity of the CRF2R, modulation of skeletal muscle mass.

Amphibian Proteins↗

PubMed2003

Effect of creatine and weight training on muscle creatine and performance in vegetarians.

PURPOSE: To compare the change in muscle creatine, fiber morphology, body composition, hydration status, and exercise performance between vegetarians and nonvegetarians with 8 wk of creatine supplementation and resistance training. METHODS: Eighteen VG and 24 NV subjects (19-55 yr) were randomly assigned (double blind) to four groups: VG + creatine (VGCr, N=10), VG + placebo (VGPl, N=8), NV + creatine (NVCr, N=12), and NV + placebo (NVPl, N=12). Before and at the end of the study, muscle biopsies were taken from the vastus lateralis m, body composition was assessed by DXA, and strength was assessed using 1-RM bench press and leg press. Subjects participated in the same 8-wk resistance-training program. Creatine dosage was based on lean tissue mass (0.25 g.kg(-1) LTM.d(-1) x 7 d; 0.0625 g.kg(-1) LTM.d(-1) x 49 d). RESULTS: Biopsy samples indicated that total creatine (TCr=free Cr + PCr) was significantly lower in VG compared with NV at baseline (VG=117 mmol.kg(-1); NV=130 mmol.kg(-1); P<0.05). For Cr subjects, there was a greater increase in PCr, TCr, bench-press strength, isokinetic work, Type II fiber area, and whole-body lean tissue compared with subjects on placebo (P<0.05). Vegetarians who took Cr had a greater increase in TCr, PCr, lean tissue, and total work performance than nonvegetarians who took Cr (P<0.05). The change in muscle TCr was significantly correlated with initial muscle TCr, and the change in lean tissue mass and exercise performance. These findings confirm an ergogenic effect of Cr during resistance training and suggest that subjects with initially low levels of intramuscular Cr (vegetarians) are more responsive to supplementation.

Adult↗

PubMed2003

Acute and moderate-term creatine monohydrate supplementation does not affect creatine transporter mRNA or protein content in either young or elderly humans.

Animal studies have shown that supra-physiological creatine monohydrate (Cr-mH) supplementation for 3 months reduced skeletal muscle creatine transporter (CRT) content. The doses of Cr-mH (1-2 g/kg/day) used in these studies were between 5 and 10 times those usually used in human studies, and it is unclear whether a down-regulation of CRT would occur in humans at the recommended doses of 0.1-0.2 g/kg/day. We measured CRT, and citrate synthase (CS) protein content using Western blotting before and after 2 months of Cr-mH supplementation and weight training in young men (N = 11 Cr-mH (0.125 g/kg/ day); N = 8 placebo). CRT and CS were also measured before and after 4 months of Cr-mH supplementation and weight training in elderly (> 65 years) men and women (N = 14 Cr-mH (0.075 g/kg/day); N = 14 placebo). Finally, CRT mRNA was measured using competitive RT-PCR before and after 8-9 days of Cr-mH loading in young men and women (N = 14, CR-mH (mean = 0.18 g/kg/day); N = 13, PL). Total creatine content was significantly elevated after the Cr-mH supplementation period as compared to placebo in each of the studies. Neither Cr-mH supplementation, nor exercise training resulted in measurable alterations in CRT protein content and acute Cr-mH loading did not alter CRT mRNA. There were no gender differences in CRT mRNA or total creatine content in the young subjects and no gender differences in total creatine content or CRT protein content in the elderly subjects. Weight training in young men did not increase CS protein content, however, in the elderly there was a significant increase in CS protein content after exercise training (p < 0.05). These results demonstrated that Cr-mH supplementation during weight training resulted in increases in skeletal muscle total creatine without reductions in CRT protein and acute Cr-mH loading did not decrease CRT mRNA content.

Adenosine Triphosphate↗

PubMedDate not supplied

Protein requirements for endurance athletes.

Acute endurance exercise results in the oxidation of several amino acids. The total amount of amino acid oxidation during endurance exercise amounts to only 1-6% of the total energy cost of exercise. The branched chain amino acid, leucine, has been most often studied in relation to endurance exercise. Leucine is oxidized by the enzyme, branched-chain oxo-acid dehydrogenase (BCOAD). BCOAD is relatively inactive at rest ( approximately 4-7%) and is activated at the onset of exercise by dephosphorylation (to about 25%). After a period of endurance exercise training, the activation of BCOAD and amino acid oxidation are attenuated, however the total amount of BCOAD enzyme is up-regulated. A low energy and/or carbohydrate intake will increase amino acid oxidation and total protein requirements. With adequate energy and carbohydrate intake, low to moderate intensity endurance activity has little impact on dietary protein requirements and 1.0 gPRO/kg/d is sufficient. The only situation where dietary protein requirements exceed those for relatively sedentary individuals is in top sport athletes where the maximal requirement is approximately 1.6 gPRO/kg/d. Although most endurance athletes get enough protein to support any increased requirements, those with low energy or carbohydrate intakes may require nutritional advice to optimize dietary protein intake.

3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)↗