GAA and Other metabolic disease: Glycogen storage disease type 2, or Pompe disease (PD, OMIM 232300) is an inborn metabolic disorder caused by the functional deficiency of the acid lysosomal α-glucosidase (GAA, acid maltase, E.C.3.2.1.20), the enzyme hydrolysing α-1,4 and α-1,6-glucosidic bonds in glycogen and belonging to family GH31 of the carbohydrate-active enzyme (CAZy) classification (www.cazy.org1).