The regulated turnover of glycogen plays a central, tissue-specific role in the maintenance of blood glucose levels and in the provision of glucose to tissues such as muscle and brain in response to stress. Defects in the enzymes involved in glycogen turnover are associated with abnormal responses to fasting and exercise that can differ widely in their presentation and severity. Additional symptoms can be the result of accumulation of abnormal products of glycogen metabolism (www.ommbid.com).
In this initial release, we have annotated two forms of myoclonic epilepsy of Lafora that are due to defects in proteins required for the turnover of the low levels of phosphoglycogen that accumulate in many tissues of the body. This module will be extended in future releases to cover diseases due to deficiencies in GYG1, the ubiquitously expressed form of glycogenin (GSD type XV), GYS2 and GYS1, the liver-specific and ubiquitously expressed forms of glycogen synthase (GSD type 0), GBE1, the single form of branching enzyme (GSD type IV), and in the endoplasmic reticulum-associated phosphatase (G6PC) and transporter (SLC37A4) required for export of glucose geneated by glycogen breakdown in liver (GSD type 1a and 1b, respectively). Severe congenital neutropenia type 4 (SCN4) is included in this group because its molecular basis is loss of glucose 6-phosphatase 3 (G6PC3) activity (Boztug et al. 2009). G6PC3 is a ubiquitously expressed isozyme of G6PC, the enzyme whose deficiency is the cause of glycogen storage disease type 1a (GSD 1a).
|glycogen storage disease||2747||[glycogenosis]|
|OMMBID Chapter 71: Glycogen Storage Diseases|