Biochemical diagnosis of type 1b glycogen storage disease.

A child with the classical signs and symptoms of Type 1 glycogen storage disease is presented, who on investigation was shown to have a recently described variant of this disease known as Type 1b glycogen storage disease. A reliable and simple procedure for the diagnosis and differentiation of Types 1 and 1b glycogen storage disease is described, as the conventional diagnostic approach of assaying glucose-6-phosphate phosphohydrolase in frozen tissue will not diagnose Type 1b glycogen storage disease. A portion of biopsy tissue should be maintained at a temperature near 0 degrees C (but not frozen) and the remainder frozen. Glucose-6-phosphate phosphohydrolase assays are carried out on the tissue homogenates of both portions. In Type 1 glycogen storage disease, glucose-6-phosphate phosphohydrolase activity will be low or absent in both frozen and unfrozen tissues. In Type 1b glycogen storage disease the frozen tissue homogenate will exhibit normal glucose-6-phosphate phosphohydrolase activity due to the disruption of the microsomes by ice crystals, while in the unfrozen tissue low levels of glucose-6-phosphate phosphohydrolase activity will be detected.