GLYCOGEN-STORAGE-DISEASE TYPE-II - GENETIC AND BIOCHEMICAL-ANALYSIS OF NOVEL MUTATIONS IN INFANTILE PATIENTS FROM TURKISH ANCESTRY

Glycogen Storage Disease type II (GSDII) is caused by the deficiency o f lysosomal alpha-glucosidase (acid maltase). This paper reports on th e characterization of the molecular defects in 6 infantile patients fr om Turkish ancestry. Five of the 6 patients had reduced levels of the lysosomal alpha-glucosidase precursor. Conversion to mature enzyme was impaired in all cases, and the lysosomal alpha-glucosidase activity i n all patients fibroblasts was less than 0.5% of control. DNA sequence analysis revealed 3 new mutations. One mutation, found in 3 patients in homozygous form, was a double insertion in exon 19 (2471AG-->CAGG) leading to a frameshift after Pro 913. It is the first insertion mutat ion described in the lysosomal alpha-glucosidase gene. Two patients we re homozygous for missense mutations leading to the substitution of Se r to Pro at amino acid 566 (S566P) in one case and of Pro to Arg at am ino acid 768 (P768R) in the other. One patient was found to have a Gly to Arg missense mutation at amino acid 643 (G643R), previously identi fied in an adult patient (Hermans et al., 1993), combined with a silen t second allele. The latter 3 mutations were introduced in the wild ty pe lysosomal alpha-glucosidase cDNA and expressed in COS cells to anal yze their effect. Precursor species of 110 kD were formed but the matu ration was impaired. As a result there was an overall deficiency of ca talytic activity, which is in accordance with the findings in the pati ents fibroblasts and with the clinical phenotype. (C) 1998 Wiley-Liss, Inc.