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Muscle Disorders
Published in Philip B. Gorelick, Fernando D. Testai, Graeme J. Hankey, Joanna M. Wardlaw, Hankey's Clinical Neurology, 2020
Kourosh Rezania, Peter Pytel, Betty Soliven
Glycogen is the main source of carbohydrates in the muscle; it is formed by a core protein called glycogenin and multiple branches of glucose chains. The concerted action of multiple enzymes is required for the synthesis, maturation, and degradation of the glycogen molecule. Several inherited disorders of glycogen metabolism (also called glycogenoses or glycogen storage diseases) have been described (Figure 27.16). Acid maltase deficiency and McArdle's disease are typical examples that present predominantly with weakness and exercise intolerance, respectively. The most common forms of glycogenoses associated with muscle involvement will be discussed in the next sections.
Macronutrientst, Micronutrients, and Metabolism
Published in Emily Crews Splane, Neil E. Rowland, Anaya Mitra, Psychology of Eating, 2019
Emily Crews Splane, Neil E. Rowland, Anaya Mitra
In animals and humans, circulating glucose that is not used immediately for ATP production is converted into a storage polymer, glycogen. Glycogen is present in cells as globular or ball-like structures with a core molecule (glycogenin) and both branched and straight chains of up to ~10 glucose molecules radiating out. During periods of fasting, glucose molecules can be cleaved from these glycogen balls to provide a source of glucose when none is being absorbed from the gut. Formation of glycogen from glucose dissipates some energy, so the net energy that can be derived from glycogen for metabolism is a little less than the dietary energy consumed.
LIVER METABOLISM
Published in David M. Gibson, Robert A. Harris, Metabolic Regulation in Mammals, 2001
David M. Gibson, Robert A. Harris
Initiation of glycogen synthesis requires glycogemn (enzyme 1). which thereafter remains covalently attached to the glycogen molecule through the hydroxyl group of a specific tyrosine residue. Glycogenin glycosylates itself with UDP-glucose, creating a chain of about eight glucose residues. Once synthesis is initiated in this manner, a glycogen molecule grows by repeated addition of activated glucose residues (UDP-glucose) followed by branching of terminal chains. Glycogen synthase (enzyme 2) uses UDP-glucose to elongate terminal chains of glycogen by forming a-1,4-linkages between glucose residues. Branching enzyme (enzyme 3; amylo (1.4 ->1.6) transglucosytase) creates branches by transferring seven-residue segments to the 6-carbon hydroxyl of a glucose four residues from existing branches
New discoveries in progressive myoclonus epilepsies: a clinical outlook
Published in Expert Review of Neurotherapeutics, 2018
Shweta Bhat, Subramaniam Ganesh
Gene therapy holds the greatest promise in the treatment of the etiological cause of PMEs if we can overcome the daunting technical difficulties. Tremendous attempts to achieve successful gene therapy in the treatment of PMEs are underway. For the normal functioning of NEU1 (mutated in sialidoses), it’s binding to protective protein/cathepsin A (PPCA) chaperone is paramount. By introducing liver-tropic recombinant Adeno-associated virus vector serotype 8 (AAV2/8 vector) expressing PPCA chaperone in all systemic tissues, residual activity of NEU1 was reported to be considerably increased in a mouse model of sialidosis I, when injected in tail veins [108]. Similarly, gene delivery approaches using AAV9 virus (is a dweller of the human brain, hence can cross blood-brain barrier and non-immunogenic) to deliver laforin and malin to brain tissue of mouse model of LD are being carried out. In an advent to prevent exaggerated LB formation, the introduction of CRISPR/Cas9 nucleases targeted against GS, PTG, and glycogenin are underway. Further, enzymatic digestion of LB can be brought about using amylase. AAV9 or inactivated diphtheria toxin-mediated amylase delivery into brain tissue are also attempted in the mouse model of LD [152]. Enzyme replacement therapy (ERT) using recombinant TPP1 was quite successful for NCL2 (TPP1 deficient) and now clinical trials are ongoing. Stem cell therapy where human CNS stem cells carry functional PPT1 and TPP1 are also under clinical trial [149].