In the Carbohydrate-Active enZymes database (CAZy) glycoside hydrolases (GHs) are classified presently into 156 GH families. In human, there are five known enzymes from the family GH31. Two (MGAM and SI) are intestinal glucosidases involved in saccharide digestion, the acidic glucosidase (GAA) is responsible for glycogen degradation in lysosomes and GANAB (glucosidase II) plays a role in the control of a proper protein folding in the endoplasmic reticulum. The fifth protein is called GANC. It is an α-glucosidase, which is able to release the terminal glucose from maltotriose and glycogen at neutral pH. Its subcellular localization and its physiological function have not been reported in scientific literature yet. Our phylogenetic analysis shows that GANC evolved in early vertebrates from the α-subunit of GANAB. We have thus used an in silico approach to identify changes leading from the α-subunit of GANAB to GANC. We have also searched for residues and regions, which are conserved and under influence of negative selection pressure and which could be important for the function of the enzymes. We have found three residues, which could be responsible for the difference in the substrate specificity reported between the α-subunit of GANAB and GANC. We have also retrieved expression and subcellular localization data, from the Human Protein Atlas database, which shows differences in the expression profiles between GANAB and GANC. Unlike GANAB, GANC seems to be expressed in the nucleoplasm and in the cytoplasm where it colocalizes with actin filaments. The signal sequence and the nuclear localization signal have also been analyzed.