The exponential expansion of the publicly available human DNA sequence database has increasingly facilitated cloning by homology of genes for biochemically defined, functionally similar proteins. We hypothesized that an as-yet uncloned human alpha-glucosidase (human neutral alpha-glucosidase C or GANC) is a previously uncharacterized member of a paralogous human glycosyl hydrolase gene family 31, sharing sequence homology and related, but not identical, functions with other cloned human alpha-glucosidases. We now report both the in silico and physical cloning of two alleles of human neutral alpha-glucosidase (designated GANC on the human gene map). This cloning and correct identification and annotation as GANC was successful only because of the application of the biochemical and genetic information we had previously developed regarding this gene to the results of the in silico method. Of note, this glucosidase, a member of family 31 glycosyl hydrolases, has multiple alleles, including a "null" allele and is potentially significant because it is involved in glycogen metabolism and localizes to a chromosomal region (15q15) reported to confer susceptibility to diabetes.