The body normally stores extra sugar as glycogen in the liver, then breaks it back down into glucose between meals to keep blood sugar steady. Glycogen storage disease type 1a occurs when the enzyme associated with that last step, glucose-6-phosphatase, doesn't work.¹ Glycogen builds up in the liver and kidneys instead of being released as usable sugar. As a result, both organs enlarge, and blood sugar can drop to dangerous levels within just a few hours without eating.

Babies usually appear healthy at birth, and symptoms typically don't appear until between 3 and 4 months of age. They can include an enlarged belly, low blood sugar, seizures, and abnormal lab values that often lead to a frightening, unexplained hospitalization before anyone knows the cause.¹ A closely related condition, type 1b, comes from a change in a different gene and adds a higher risk of infections, but the two are similar enough that some clinicians treat them as one disease. This page is specifically about type 1a and G6PC.

This isn't a condition that's treated and resolved. Instead, it's managed daily and indefinitely. Frequent small feedings, often including uncooked cornstarch are typically required and often, infants and young children need a feeding tube to help them receive appropriate nutrition.¹ Even with careful management, long term complications can still develop, including kidney disease and benign liver tumors that occasionally require surgery or, in severe cases, an organ transplant.¹

This is why testing matters. Carrier screening is most ideal before conception, because it's the one point where you have the most options. If both partners are carriers, you can explore paths like IVF with preimplantation genetic testing, using a donor egg or sperm, or prenatal diagnosis early in pregnancy, that let you make informed decisions before a child is born with GSD1a, not just prepare to manage it afterward. Testing doesn't just prepare a family for a diagnosis; it can help you avoid one. 

There's a genuine reason for hope. Researchers are actively developing gene and enzyme replacement therapies aimed at the root cause of GSD1a — restoring the missing enzyme itself, rather than just managing symptoms through diet. At least one of these approaches have shown promising results in clinical trials, meaning the direction of research is encouraging.²  Knowing your carrier status now means being positioned to act quickly as new treatment options become available. 

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Glycogen storage disease type 1a is inherited in a pattern called autosomal recessive. A carrier has one working copy of G6PC and one nonworking copy. Carriers have no symptoms because the one working copy is enough.³ If both parents are carriers, each pregnancy has a 25% chance of the child being affected, a 50% chance of the child being an unaffected carrier, and a 25% chance of the child inheriting two working copies of the gene.³

Carrier rates vary sharply by ancestry, driven by specific mutations that are more common in different communities. These mutations are often referred to as “founder mutations”:

• Ashkenazi Jewish descent: about 1 in 71³
• Ohio Amish community: about 1 in 50, tied to one specific shared founder variant⁴
• General population: roughly 1 in 150 people⁵

A positive result means you carry one working copy and one nonworking copy of G6PC.³ You are not affected by glycogen storage disease type 1a, but you can pass the nonworking copy to a child. It is critical to have your partner tested, regardless of their ancestry, as the risk of having an affected child is impacted by  whether they carry a change in the same gene too. This also applies if you're using a sperm or egg donor.

A negative result means you have a significantly lower chance of being a carrier. It greatly lowers your risk without bringing it all the way to zero, since no screen can detect every possible gene change.

If both partners carry a change in G6P, each pregnancy has a 25% chance of being affected by Glycogen storage disease 1a.¹ If you are already pregnant, prenatal testing for GSD 1a, such as chorionic villus sampling (CVS) or amniocentesis, can diagnose whether a current pregnancy is affected prior to birth.¹ Genetic counseling is strongly recommended at this stage, and every jscreen result comes with access to a board certified genetic counselor to walk through what your specific results mean and what your options are. We highly recommend testing prior to conception, which allows for the greatest range of reproductive options.