GSD type 0, in some ways, is very different to the other liver GSDs. The common problem with the other liver GSDs is an inability to release glucose from the glycogen stores. If you have GSD type 0, you are unable to build up your glycogen stores in the first place. If not properly managed, glucose will build to high levels after a meal because your body is unable to store it as glycogen but, once that glucose is used up, you will develop hypoglycaemia or low levels of glucose in the blood.
As mentioned, if you have GSD type 0, you may experience both high and low levels of blood glucose. High levels of blood glucose don’t tend to be seen in other forms of GSD.
Unlike other liver GSDs, when untreated, you will NOT get a build-up of glycogen because you cannot make glycogen. Hepatomegaly or an enlarged liver will therefore not be seen.
When glucose levels run low, your body needs to produce energy in other ways. One way to do this involves your body using its fat stores to produce ketones. The body can also start to use protein to produce energy.
Ketones are an alternative source of energy. In healthy individuals, ketone levels are typically very low. Extended fasting can lead to higher levels of ketones. Ketones are produced from the body’s fat stores. The brain needs a lot of energy to work properly but it cannot use fat to produce energy – it prefers glucose. However, the brain can get energy from ketones. If you have GSD type 0, turning fat into ketones helps your brain get energy when glucose levels are low. Ketones also help keep your muscles supplied with energy when your glucose levels are low. Although ketones can be a very useful source of energy, it is important that your ketone levels do not go too high. High ketone levels indicate that GSD control could be better..
Good dietary management aims to reduce the risk of your blood glucose levels going too low. This means that your body will not need to make ketones or break down your muscles to produce energy.