RE: metabolic / glycogen storage

May 31, 2005

Kim,

No, not all metabolic diseases are glycogen storages diseases. Pasting one

brief section from an e-medicine article which defines the different

categories. It is one of the best articles available on this subject. The

site does require free registration to view articles.

Barbara

http://www.emedicine.com/neuro/topic672.htm

Traditionally, the metabolic myopathies are divided into 3 categories, as

follows.

1. Glycogen storage diseases

Muscle cells transport glucose from the circulating blood, synthesize

glycogen, and then degrade it when energy demands increase. Muscle cell

membrane (ie, sarcolemma) is not freely permeable to glucose; therefore,

utilization of circulating glucose is limited by its rate of transportation

through the sarcolemma. Glycogen is the main form of carbohydrate storage in

the muscle. When energy is required for muscle contraction, glycogen is

degraded to glucose and provides the energy required for muscle work. Any

disturbance in either the synthesis or the degradation of glycogen could

result in glycogen storage disease (ie, glycogenoses).

2. Lipid storage diseases

Long-chain fatty acids are the major source of energy for the skeletal

muscle during sustained exercise and fasting. The passage of these fatty

acids through the mitochondrial membrane, for beta-oxidation, requires their

binding with carnitine. Carnitine is synthesized mainly in the liver and

actively transported into the muscle against a concentration gradient. Free

fatty acids are first converted to acyl coenzyme A (CoA) compounds by the

action of fatty acyl CoA synthetases. Then, the long-chain acyl CoA is bound

to carnitine by acylcarnitine transferases, such as carnitine

palmitoyltransferase I (CPT I). This occurs on the outer mitochondrial

membrane.

The new compound passes through the inner mitochondrial membrane by the

action of acylcarnitine translocase. Within the mitochondrial matrix,

carnitine palmitoyltransferase II (CPT II) splits the transferred compound

to free fatty acids and carnitine. In the mitochondria, beta-oxidation of

the long-chain fatty acids is then carried out. Carnitine deficiency,

deficiency of carnitine palmitoyltransferases, or a defect in beta-oxidation

of these fatty acids may lead to myopathies.

3. Disorders of purine nucleotide metabolism

Adenylate deaminase is an enzyme that catalyses transformation of adenosine

monophosphate (AMP) to inosine monophosphate (IMP) and ammonia. This

reaction mainly occurs during anaerobic exercise to replenish ATP, which is

an essential source of energy for the muscles. Whether myoadenylate

deaminase deficiency causes muscle disease remains a controversial subject.

Mitochondrial disorders

Mitochondrial disorders encompass a group of disorders resulting from

abnormalities of the respiratory chain. These are discussed in a separate

article.

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From: [mailto: ] On Behalf

Of klaga5

Sent: Tuesday, May 31, 2005 2:54 PM

To:

Subject: metabolic / glycogen storage

Are all metabolic diseases, glycogen storage diseases, or are some

metabolic disease not under that catigory?

Kim

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May 31, 2005