Various. Not a problem of storing it, a problem of breaking it down! Classic type 1 is Glucose -6-phosphatase deficiency. Depending on the type, gluconeogenesis as well as glycogenolysis may be impaired – some of the enzymes are involved in both – so hypoglycaemia with ketones, lactate and triglycerides high. Liver becomes enlarged with excessive glycogen, Glucagon has no effect.

Managed by regular meals and extra complex carbohydrate eg cornstarch, as for ketotic hypoglycaemia.

Glycogen synthase deficiency is sometimes included. If you can’t make glycogen then you get an immediate glucose dip post prandially, you don’t get a big liver (obviously) but other mechanisms work ok so lactate is normal (cf typical Glycogen storage disorder).

Pompe disease is a lysosomal disorder, infantile form affects heart, neurodevelopment (enzyme treatment available).

McArdle syndrome is myophosphorylase defect – pain/weakness/cramps on exertion, myoglobinuria, second wind phenomenon (rapid recovery with rest).