McArdle disease is characterized by the inability to break glycogen, as a result of glycogen phosphorylase (an enzyme required in glycogen metabolism) in muscle cells being deficient. It also leads to storage of Glycogen, which is an important source of energy. As its breakdown becomes difficult, energy for physical activities is released only through glucose.
The problem in McArdle's disease is that the glycogen cannot be broken down to be used for energy release and muscle damage is caused when the energy demand is greater than the aerobic pathway can supply.
The symptoms seem to reflect this. Sufferers find exercise difficult.
Glycogen storage disease type V (GSD V)
- Age: GSDS usually is common in children.
- A less severe form is correlated with late onset of the disease but severe form is seen with onset in first year of life. The majority of patients with McArdle disease are in the age group of 20 to 30.
- Late presentation is very rare.
- Incidence: The known incidence is in 1 – 2.3 in 100,000 cases.