Molecular diagnosis for GSD I by direct DNA testing and GSD II by linkage studies is available clinically.
FATTY ACID OXIDATION DISORDERS (MCAD DEFICIENCY)
During periods of fasting or prolonged aerobic exercise when glycogen stores are depleted, fatty acids become a main energy source by P-oxidation in the liver, and skeletal and cardiac muscles. The pathway for fatty acid oxidation occurs in the mitochondria and is complex, involving as many as 20 steps. A number of disorders involving different enzymes in the pathway have been identified. Although the symptoms of the disorders have pheno-typic overlap, there are several biochemical measurements that can aid in the diagnosis of these disorders, including plasma carnitine levels which are usually low, plasma acylcarnitines, and urine acylglycines (for review, see Reference 22). The most common of these disorders by far is medium-chain acyl-CoA dehydrogenase (MCAD) deficiency, which is discussed in detail below.
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