Some GSDs have different forms, e.g. infantile, juvenile, adult (late-onset). Some GSDs have different subtypes, e.g. GSD1a / GSD1b, GSD9A1 / GSD9A2 / GSD9B / GSD9C / GSD9D. GSD type 0: Although glycogen synthase deficiency does not result in storage of extra glycogen in the liver, it is classified with the GSDs as type 0 because it is another defect of glycogen storage and can cause similar problems. GSD type VIII (GSD 8): In the past, liver phosphorylase-b kinase deficiency was considered a distinct condition, however it has been classified with GSD type VI and GSD IXa1; GLYCOGEN STORAGE DISEASE IXa1; GSD9A1 OMIM — Online Mendelian Inheritance in Man it has been described as X-linked recessive inherited. GSD IX has become the dominant classification for this disease, grouped with the other isoenzymes of phosphorylase-b kinase deficiency. GSD type XI (GSD 11): Fanconi-Bickel syndrome (GLUT2 deficiency), hepatorenal glycogenosis with renal Fanconi syndrome, no longer considered a glycogen storage disease, but a defect of glucose transport. The designation of GSD type XI (GSD 11) has been repurposed for muscle lactate dehydrogenase deficiency (LDHA). GSD type XIV (GSD 14): No longer classed as a GSD, but as a congenital disorder of glycosylation type 1T (CDG1T), affects the phosphoglucomutase enzyme (gene PGM1). Phosphoglucomutase 1 deficiency is both a glycogenosis and a congenital disorder of glycosylation. Individuals with the disease have both a glycolytic block as muscle glycogen cannot be broken down, as well as abnormal serum transferrin (loss of complete N-glycans). As it affects glycogenolysis, it has been suggested that it should re-designated as GSD-XIV. Lafora disease is considered a complex neurodegenerative disease and also a glycogen metabolism disorder. Polyglucosan storage myopathies are associated with defective glycogen metabolism (Not McArdle disease, same gene but different symptoms) Myophosphorylase-a activity impaired: Autosomal dominant mutation on PYGM gene. AMP-independent myophosphorylase activity impaired, whereas the AMP-dependent activity was preserved. No exercise intolerance. Adult-onset muscle weakness. Accumulation of the intermediate filament desmin in the myofibers of the patients.Echaniz-Laguna A, Lornage X, Laforêt P, Orngreen MC, Edelweiss E, Brochier G, Bui MT, Silva-Rojas R, Birck C, Lannes B, Romero NB, Vissing J, Laporte J, Böhm J. A New Glycogen Storage Disease Caused by a Dominant PYGM Mutation. Ann Neurol. 2020 Aug;88(2):274-282. doi: 10.1002/ana.25771. Epub 2020 Jun 3. PMID 32386344. Myophosphorylase comes in two forms: form 'a' is phosphorylated by phosphorylase kinase, form 'b' is not phosphorylated. Both forms have two conformational states: active (R or relaxed) and inactive (T or tense). When either form 'a' or 'b' are in the active state, then the enzyme converts glycogen into glucose-1-phosphate. Myophosphorylase-b is allosterically activated by AMP being in larger concentration than ATP and/or glucose-6-phosphate. (See Glycogen phosphorylase§Regulation). Unknown glycogenosis related to dystrophy gene deletion: patient has a previously undescribed myopathy associated with both Becker muscular dystrophy and a glycogen storage disorder of unknown aetiology.Rose MR, Howard RS, Genet SA, McMahon CJ, Whitfield A, Morgan-Hughes JA. A case of myopathy associated with a dystrophin gene deletion and abnormal glycogen storage. Muscle Nerve. 1993 Jan;16(1):57-62. doi: 10.1002/mus.880160110. PMID 8423832.
Some GSDs have different forms eg infantile juvenile adult (late-onset) Some GSDs have different subtypes eg GSD1a / GSD1b GSD9A1 / GSD9A2 / GSD9B / GSD9C / GSD9D GSD type 0 Although glycogen synthase deficiency does not result in storage of extra glycogen in the liver it is classified with the GSDs as type 0 because it is another defect of glycogen storage and can cause similar problems GSD type VIII (GSD 8) In the past liver phosphorylase-b kinase deficiency was considered a distinct condition however it has been classified with GSD type VI and GSD IXa1; GLYCOGEN STORAGE DISEASE IXa1; GSD9A1 OMIM — Online Mendelian Inheritance in Man it has been described as X-linked recessive inherited GSD IX has become the dominant classification for this disease grouped with the other isoenzymes of phosphorylase-b kinase deficiency GSD type XI (GSD 11) Fanconi-Bickel syndrome (GLUT2 deficiency) hepatorenal glycogenosis with renal Fanconi syndrome no longer considered a glycogen storage disease but a defect of glucose transport The designation of GSD type XI (GSD 11) has been repurposed for muscle lactate dehydrogenase deficiency (LDHA) GSD type XIV (GSD 14) No longer classed as a GSD but as a congenital disorder of glycosylation type 1T (CDG1T) affects the phosphoglucomutase enzyme (gene PGM1) Phosphoglucomutase 1 deficiency is both a glycogenosis and a congenital disorder of glycosylation Individuals with the disease have both a glycolytic block as muscle glycogen cannot be broken down as well as abnormal serum transferrin (loss of complete N-glycans) As it affects glycogenolysis it has been suggested that it should re-designated as GSD-XIV Lafora disease is considered a complex neurodegenerative disease and also a glycogen metabolism disorder Polyglucosan storage myopathies are associated with defective glycogen metabolism (Not McArdle disease same gene but different symptoms) Myophosphorylase-a activity impaired Autosomal dominant mutation on PYGM gene AMP-independent myophosphorylase activity impaired whereas the AMP-dependent activity was preserved No exercise intolerance Adult-onset muscle weakness Accumulation of the intermediate filament desmin in the myofibers of the patientsEchaniz-Laguna A Lornage X Laforêt P Orngreen MC Edelweiss E Brochier G Bui MT Silva-Rojas R Birck C Lannes B Romero NB Vissing J Laporte J Böhm J A New Glycogen Storage Disease Caused by a Dominant PYGM Mutation Ann Neurol 2020 Aug;88(2)274-282 doi 101002/ana25771 Epub 2020 Jun 3 PMID 32386344 Myophosphorylase comes in two forms form 'a' is phosphorylated by phosphorylase kinase form 'b' is not phosphorylated Both forms have two conformational states active (R or relaxed) and inactive (T or tense) When either form 'a' or 'b' are in the active state then the enzyme converts glycogen into glucose-1-phosphate Myophosphorylase-b is allosterically activated by AMP being in larger concentration than ATP and/or glucose-6-phosphate (See Glycogen phosphorylase§Regulation) Unknown glycogenosis related to dystrophy gene deletion patient has a previously undescribed myopathy associated with both Becker muscular dystrophy and a glycogen storage disorder of unknown aetiologyRose MR Howard RS Genet SA McMahon CJ Whitfield A Morgan-Hughes JA A case of myopathy associated with a dystrophin gene deletion and abnormal glycogen storage Muscle Nerve 1993 Jan;16(1)57-62 doi 101002/mus880160110 PMID 8423832