What is Glycogen Storage Disease Type Ia?
Glycogen Storage Disease Type I (GSDI), also called von Gierke disease, is an inherited disorder that impairs the body's ability to break down a stored form of sugar, called glycogen. There are two genes associated with GSDI, and harmful genetic changes (mutations) in G6PC1 (formerly known as G6PC) cause GSDIa. In GSDIa, the body cannot maintain normal blood-sugar levels between meals, leading to low blood sugar (hypoglycemia). Additionally, glycogen builds up in organs, leading to an enlarged liver (hepatomegaly) and enlarged kidneys (nephromegaly).
Infants with GSDIa appear normal at birth, but usually begin to show symptoms when they start to sleep longer through the night. Low blood sugar can cause tiredness, irritability, and seizures. If not properly diagnosed, infants typically experience a medical crisis within the first few months of life.
Children diagnosed with GSDIa have swollen abdomens due to an enlarged liver, as well as delayed or stunted growth. Non-cancerous (benign) tumors in the liver are often seen around the time of puberty. Rarely, these can become cancerous. Changes in kidney function may occur as a patient reaches his or her twenties and may include kidney stones and a decreased ability to filter waste products. In advanced cases, dialysis and/or a kidney transplant may be needed. Other symptoms or complications that may develop include delayed puberty, thinning of the bones (osteoporosis), and a form of arthritis caused by uric acid crystals in joints (gout). Mental function is not affected by GSDIa.
How common is Glycogen Storage Disease Type Ia?
The incidence of glycogen storage disease type I (both Ia and Ib) is 1 in 100,000 live births. Approximately 80% of glycogen storage disease type I cases are GSDIa.
How is Glycogen Storage Disease Type Ia treated?
Individuals with GSDIa should be followed by a team of specialists who are familiar with the long-term management of glycogen storage disease to ensure appropriate monitoring and treatment for potential complications of the condition. The treatment of GSDIa involves careful monitoring of the patient's diet, both in the type of foods eaten and the frequency of meals. Individuals with GSDIa should avoid foods with sucrose (table sugar), fructose (sugar from fruits), and lactose and galactose (sugars found in milk). To maintain healthy blood sugar levels, individuals need to eat every 1-3 hours during the day and every 3-4 hours at night.
Infants and young children often need a feeding tube to tolerate frequent eating. A feeding pump may be needed at night and for emergency feedings, should their blood sugar drop to dangerously low levels. Children with GSDIa often develop problems eating and swallowing food orally and may need therapy to relearn sucking, swallowing, and sometimes speech.
Physicians recommend that individuals with GSDIa drink cornstarch mixed with water, soy formula, or soy milk. Cornstarch is digested slowly and therefore releases its glucose gradually, helping to safely extend the time between meals. Due to the restricted nature of the diet, multivitamins, calcium, and vitamin D are necessary.
What is the prognosis for an individual with Glycogen Storage Disease Type Ia?
With careful monitoring of diet and blood sugar levels, individuals with GSDIa typically have normal growth and live into adulthood. Without close monitoring of the diet, extremely low blood sugar levels can be fatal. Even with treatment, adolescence and adults may still develop kidney complications, high blood pressure, and cancerous liver tumors.