The breakdown of glycogen to release glucose is done in several stages. One of the stages involves the production of something called glucose-1-phosphate (G1P) which can then be turned into glucose which can be used for energy. If you have GSD type VI, the enzyme needed to produce G1P is not working as well as it should be. This can lead to you having low levels of G1P and therefore low blood levels of glucose.
In most cases of GSD VI, the enzyme works more slowly than normal but it still works. Therefore, you will still make glucose but in lower quantities than other people. With you having less glucose than other people, your body needs to produce energy in other ways. One way to do this involves your body using its fat stores to produce ketones. Your 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 VI, 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 muscles to produce energy.
GSD type VI is often viewed as a milder form of GSD. If you have GSD type VI, it is still very important that you attend all your clinic appointments and follow the advice given to you by your Specialist Metabolic Team.