Pathology
When GDE activity is compromised, the body cannot effectively release stored glycogen, type III Glycogen Storage Disease (debrancher deficiency), an autosomal recessive disorder, can result. In GSD III glycogen breakdown is incomplete and there is accumulation of abnormal glycogen with short outer branches.
Most patients exhibit GDE defiency in both liver and muscle (TypeIIIa), although 15% of patients have retained GDE in muscle while having it absent from the liver (Type IIIb). Depending on mutation location, different mutations in the AGL gene can effect different isoforms of the gene expression. For example, mutations that occur on exon 3, effect the form which affect the isoform that is primarily expressed in the liver; this would lead to GSD type III.
These different manifestation produce varied symptoms, which can be nearly indistinguishable from Type I GSD, including hepatomegaly, hypoglycemia in children, short stature, myopathy, and cardiomyopathy. Type IIIa patients often exhibit symptoms related to liver disease and progressive muscle involvement, with variations caused by age of onset, rate of disease progression and severity. Patients with Type IIIb generally symptoms related to liver disease. Type III patients be distinguished by elevated liver enzymes, with normal uric acid and blood lactate levels, differing from other forms of GSD. In patients with muscle involvement, Type IIIa, the muscle weakness becomes predominant into adulthood and can lead to ventricular hypertrophy and distal muscle wasting.
Read more about this topic: Glycogen Debranching Enzyme
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