Glycogen storage disease type 0

Glycogen storage disease type 0, often shortened to GSD 0, is an inherited metabolic condition in which the body cannot build glycogen, the branched sugar chain that stores glucose as a reserve of energy. Unlike the other glycogen storage diseases, which involve faulty breakdown or storage of glycogen that has already been made, this condition is a failure to make glycogen at all, so affected cells hold almost none. It occurs in two forms. In the muscle form, caused by changes in the GYS1 gene, children may have muscle pain and weakness or fainting after moderate exertion such as climbing stairs, some have a long QT heart rhythm disturbance, and the weakened pumping of the heart raises the risk of cardiac arrest and sudden death in childhood or adolescence. In the liver form, caused by changes in the GYS2 gene, infants develop low blood sugar and ketosis after long fasts, often once they begin to sleep through the night, with tiredness, pallor and nausea that ease after eating. Some people have mild features that go unnoticed for years, while others have developmental delay and poor growth. It is inherited in an autosomal recessive pattern. Very few people have been described, and it is thought to be underdiagnosed. This entry records the condition for reference and is not medical advice.