Metabolic Myopathy

Question 1

What is the inheritance pattern of McArdle’s disease?

Answer 1

Autosomal recessive

Question 2

What enzyme is deficient in McArdles disease and what reaction does it supply?

Answer 2

Myophosphorylase

Glycogen —> glucose 1-phosphate

Question 3

What gene is affected by McArdle’s disease?

Answer 3

PYGM

Question 4

What are pathologic features of McArdle’s disease?

Answer 4

Sarcolemmal blebs/vacuoles
PAS positive vacuoles no reactivity to acid phosphatase
Phosphorylase activity absent in muscle but retained in blood vessels

Question 5

What are the 4 types of lipid storage myopathy?

Answer 5

Neutral lipid storage disease with myopathy (PNPLA2)
Neutral lipid storage disease with ichthyosis (CGI-58)
Primary carnitine deficiency (SLC22A5)
Multiple acyl-CoA deficiency (ETFA, ETFB, ETFDH)

Question 6

Muscle biopsy in lipid storage myopathy shows what features?

Answer 6

Many small sarcoplasmic vacuoles mainly in type 1 fibers, not rimmed
Positive Oil red O stain for lipids

Question 7

What gene is tested in late onset pompe disease?

Answer 7

GAA gene

Question 8

What EMG finding can be seen in pompe disease?

Answer 8

Myotonia in paraspinal muscles