Type IX is closely related to type VI. 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 production of G1P does not work as well as it should because of a faulty enzyme. If you have GSD type IX, the problem occurs a stage earlier; the enzyme required to produce G1P can work but it doesn’t get ‘switched on’. Therefore, type VI and IX can produce very similar symptoms.
In both GSD type VI and GSD type IX there are low levels of G1P and therefore low blood levels of glucose.
With your body potentially having low levels of glucose, your body needs to produce energy in other ways. One way to do this involves the 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 IX, 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.
GSD type IX can be very variable in terms of severity. Some individuals are prone to regular ‘hypos’ whereas other individuals, without treatment, will show poor growth and an enlarged liver but don’t tend to get ‘hypos’.
Like GSD type VI, type IX is often viewed as a milder form of GSD. If you have GSD type IX, it is still very important that you attend all your clinic appointments and follow the advice given to you by your Specialist Metabolic Team.