Glycogen storage disease debranching enzyme deficiency

Several types of glycogen-storage disease are now known in most cases, the accumulation of glycogen can be correlated with a relative deficiency of either n-glucose 6-phosphatase or the debranching-enzyme system (Type I and III disease, respectively). In a very few cases, the enzymic defect is either in branching enzyme or in phosphorylase (Type IV or VI disease, respectively) see Table VII. In the Type II and V diseases, the enzyme deficiencies are different from the above, but have not yet been fully identified. 

Glycogen Storage Disease Type III Debranching Enzyme Deficiency. 304... 

The debranching enzyme has two enzymatic activities a glycosyltransferase and an a-1,6 gly-cosidase activity. There are two forms of deb-rancher enzyme deficiency in glycogen storage disease type Ilia (85 % of patients), the enzyme is deficient in both liver and muscle, whereas in glycogen storage disease type nib (15 % of patients), the enzyme is only deficient in liver but is normal in muscle. The preservation of muscle enzyme activity is caused by mutations in exon 3 where a muscle promoter allows translational start using a secondary start site after the mutation. Isolated deficiency of only one of the two enzyme activities is very rare. 

Table 15.10. Glycogen storage disease type 3 (debrancher enzyme deficiency) ...

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