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Glycogen Storage Disease     



Glycogen Storage Disease (GSD) encompasses various metabolic disorders that affect glycogen metabolism.  Patients affected with GSD lack or are deficient in enzymes responsible for the conversion of glycogen into glucose.  Glucose serves as the primary energy source in the body.  It is stored as glycogen, a complex chain of molecules.  Glycogen is stored mainly in the liver and muscle cells and is converted into glucose through a series of enzymatic reactions as needed by the body.  Various types of GSD are differentiated by the enzyme involved.  They are either classified by number, defective enzyme or the individual who first described the condition.  There are currently eleven known types of GSD.


Symptoms present in GSD include an enlarged liver, low blood sugar, growth retardation, and an abnormal blood chemistry.  Each type of GSD also has its own specific symptoms.  Definitive diagnosis can only be made through a biopsy of the affected organ.  A primary treatment for individuals with GSD is a well-controlled diet that ensures consistent levels of blood glucose. Symptoms, if properly treated, may subside by the time the patient reaches adulthood.  In severe cases, an organ transplant may be the only option for the patient.


GSD is primarily inherited in an autosomal recessive pattern, but a few types have been linked to the X chromosome.  These are Type VI or Hers Disease, Type VIII, and Type IX.  All three are involved in the activity of the enzyme phosphorylase kinase (PHK) in the liver. PHK is involved in the initial breakdown of glycogen.  The X-linked forms of GSD primarily affect males.  Couples at risk of having a child with GSD can now take advantage of a new technology called Pre-Implantation Genetic Diagnosis (PGD).  PGD tests an embryo for some genetic defects prior to implantation.  The sex of the embryo can also be determined.  Through this mechanism, the chances of having an affected child is greatly reduced.  PGD is a relatively new technology and is continually being improved to include many other disorders.  Due to the complex inheritance patterns of diseases, including GSD, a thorough genetic evaluation is strongly recommended to determine whether PGD will be beneficial.



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Last modified: 06/09/04