α-Mannosidosis in the guinea pig: Cloning of the lysosomal α-mannosidase cDNA and identification of a missense mutation causing α-mannosidosis

α-Mannosidosis is a lysosomal storage disorder caused by deficient activity of the lysosomal α-mannosidase. We report here the sequencing and expression of the lysosomal α-mannosidase cDNA from normal and α-mannosidosis guinea pigs. The amino acid sequence of the guinea pig enzyme displayed 82-85% identity to the lysosomal α-mannosidase in other mammals. The cDNA of the α-mannosidosis guinea pig contained a missense mutation, 679C>T, leading to substitution of arginine by tryptophan at amino acid position 227 (R227W). The R227W allele segregated with the α-mannosidosis genotype in the guinea pig colony and introduction of R227W into the wild-type sequence eliminated the production of recombinant α-mannosidase activity in heterologous expression studies. Furthermore, the guinea pig mutation has been found in human patients. Our results strongly indicate that the 679C>T mutation causes α-mannosidosis and suggest that the guinea pig will be an excellent model for investigation of pathogenesis and evaluation of therapeutic strategies for human α-mannosidosis.