Searching for molecular abnormalities in genetic diseases by the use of a double labeling technique. II. Deficiency of a basic protein in fibroblasts of patients with Pompe's disease.

We used a double labeling technique to search for molecular defects in two fibroblast strains obtained from patients with Pompe's disease. Analysis of the double labeled subcellular fractions by sodium dodecyl sulfate (SDS) electrophoresis did not reveal any abnormalities except in the "mitochondrial-lysosomal" fraction. In this fraction ratio deviations indicated that in Pompe's disease there was a significant decrease in counts of a protein with molecular weight of about 29,000. After solubilization by freeze-thawing this protein was shown to have an isoelectric point of 7.9 in contrast to the alpha-glucosidase which focused at about pH 4.7. Two-stage gel studies demonstrated an estimated 90% reduction of this protein in Pompe's disease. Two-stage studies of acid alpha-glucosidase did not show any abnormal ratios of leucine incorporation. Similar although quantitatively less pronounced results were obtained in the study of skin fibroblasts from a patient with adult glycogen storage disease type II.