Glycogen Storage Disease is an inherited metabolic disorder.

Glycogen Storage Disease Type 1 is the most common form of GSD.

Glycogen Storage Disease (GSD) is a group of rare genetic disorders caused by enzyme deficiencies. These enzymes are responsible for storing or breaking down glycogen into glucose for the body to use as energy.  Without the ability to access this stored energy, the body's blood glucose levels will drop dangerously low, resulting in severe hypoglycemia, seizures, coma, and potentially death.

There are over 10 known types of Glycogen Storage Disease, which can affect the liver, the muscles, or both.  Each type of GSD has slightly different symptoms and different treatment. Glycogen Storage Disease Type 1 (GSD1) is the most common form of GSD.    

Glycogen Storage Disease Type 1 (GSD1)

Glycogen Storage Disease Type 1 (also known as GSD1, von Gierkes Disease, or glucose-6-phosphatase deficiency) affects approximately 25% of the GSD population worldwide.  There are two different types of GSD1:  GSD1a and GSD1b.  GSD1a is caused by a deficiency of the glucose-6-phosphatase (G6Pase) enzyme in the liver.  GSD1b is caused by a deficiency in glucose-6-phosphate translocase, or transporter (G6PT) enzyme, that helps in transporting G-6-Pase enzyme from one point to another.  These two enzymes work together to help the body break down glycogen into glucose.  

What does this mean?  Glucose is the main source of energy for the body. Food provides the glucose our body needs to function properly.  When we eat a meal, our body uses the glucose from the food to fuel our cells.  Excess glucose from each meal is sent to the liver, converted into glycogen, and stored for future use. As we get further and further away from a meal, certain proteins called enzymes turn that glycogen back into glucose and send it out into the body for energy.  In GSD1, the body cannot break down glycogen or release glucose from the liver.  

Since people with GSD1 are not able to use stored glycogen for energy, they are unable to maintain normal blood glucose (blood sugar) levels between meals.  They will become severly hypoglycemic within a few short hours after eating. Much like a car that runs out of fuel, the body will shut down once the energy from the food is used up. People with GSD1 need a constant, external source of glucose in order to survive.  

GSD1a is the most prevalent type of Glycogen Storage Disease, representing over 80% of all diagnosed cases of GSD1.  It is estimated to affect approximately 600 people in the U.S. and 6,000 worldwide.