Extensive genetic heterogeneity in patients with acid alpha glucosidase deficiency as detected by abnormalities of DNA and mRNA

Acid maltase, or acid alpha glucosidase (GAA), is a lysosomal enzyme that hydrolyzes glycogen to glucose and is deficient in glycogen storage disease type II. We have previously isolated a partial cDNA (1.9 kb) for human GAA and detected abnormalities of mRNA in two infantile-onset and one adult-onset patient. We have now extended this study and examined mRNA and DNA from cell lines of eight additional infantile and three adult-onset patients. While five of the 10 infantile-onset patients expressed normal amounts and sizes of mRNA, the remaining five did not express detectable GAA mRNA. Two adult-onset patients had normal amounts and sizes of mRNA, while two adult-onset patients had mRNA of smaller size. Thus, half of the larger series of GAA-deficient patients also exhibited quantitative and/or qualitative abnormalities of mRNA. Of the five infantile-onset patients with normal mRNA, two exhibited an abnormal Sad fragment not found in DNA from 60 normals. To further characterize these patients, we determined GAA activity in several of the cell lines by using either the artificial substrate, 4-methylumbelliferyl-alpha-D-glucoside, or the natural substrate glycogen. Two adult-onset patients who both had normal size mRNA differed as to enzyme activity, with one patient exhibiting enzyme activity similar to that in infantile-onset patients. By combining these data with those for previously reported presence or absence of GAA-mutant protein cross-reacting to antibody, we provide evidence for a minimum of six different mutations in these 14 GAA-deficient cell lines.