Prevalence | Varies with type MCAD 1/10 000 (8), (9) Others less common except in certain populations | Varies with type McArdle disease 1/100 000 (8), (9) Others less common | 1/8000 (8), (9) |
Inheritance pattern | Most are autosomal recessive (8), (9) | Most are autosomal recessive (8), (9) | Any pattern of inheritance is possible: maternally inherited through mitochondrial DNA or inherited through nuclear DNA in autosomal dominant or recessive or X-linked fashion (8), (9) |
Duration of exercise needed to trigger symptoms | Longer duration (> 30 min) (8), (9) | Shorter duration (< 30 min) (8), (9) | Variable (8), (9) |
History of second-wind phenomenon* | No | Often present (8), (9) | Not usually present (8), (9) |
Creatine kinase levels | Normal between episodes of symptoms (8), (9) | Elevated even between episodes of symptoms (8), (9) | Variable; may be normal (8), (9) |
Other organ systems involved | Depends on type Adult often present only with rhabdomyolysis Other symptoms may include encephalopathy, cardiomyopathy, peripheral neuropathy or hypoketotic hypoglycemia (8), (9) | Depends on type May have hepatomegaly and history of hypoglycemia; some types have cardiac involvement (8), (9) | Other organ systems frequently involved, with cardiac, endocrine and central nervous systemic involvement common (8), (9) |
Investigations leading to diagnosis | Acylcarnitine profile will suggest diagnosis, which can be confirmed by mutation analysis or fibroblast culture to assess specific enzymes in fatty acid β-oxidation pathway (8), (9) | Diagnosis often found on muscle biopsy showing increased glycogen stores; subtyping of the type of glycogen storage disease may require further enzyme or DNA analysis (8), (9) | Muscle biopsy with analysis for defects in mitochondrial DNA or nuclear DNA (8), (9) |