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Maltase is one type of alpha-glucosidase enzymes located in the brush border of the small intestine. (3,4). This enzyme catalyzes the hydrolysis of disaccharide maltose into two simple sugars of glucose. Maltase is found in plants, bacteria, yeast, humans, and other vertebrates. It is thought to be synthesized by cells of the mucous membrane lining the intestinal wall (2).

Digestion of starch requires six intestinal enzymes. Two of these enzymes are luminal endo-glucosidases named alpha-amylases. The other four enzymes have been identified as different maltases, exo-glucosidases bound to the luminal surface of enterocytes. Two of these maltase activities were associated with sucrase-isomerase (maltase Ib, maltase Ia). The other two maltases with no distinguishing characteristics were named maltase-glucoamylase (maltases II and III). The activities of these four maltases are also described as alpha-glucosidase because they all digest linear starch oligosaccharides to glucose. (1,4)

History
The history of maltase discovery began when Napoleon Bonaparte declared a continental blockade in his “Berlin decree” in 1806. This initiated the search for alternative sources of sugar. In 1833 French chemists Anselm Payen and Jean-Francois Persoz discovered a malt extract that converted starch into glucose which they called diastase at the time (5). In 1880, H.T. Brown discovered mucosal maltase activity and differentiated it from diastase, now called amylase (4). In the 1960s advances in protein chemistry allowed Arne Dahlqvist and Giorgio Semenza to fractionate and characterize small intestinal maltase activities. Both groups showed there were four major fractions of maltase activity that were intrinsic to two different peptide structures, sucrase-isomaltase and maltase-glucoamylase (1,4,5,6). Fifty years later entering the genomic age, cloning and sequencing of the mucosal starch hydrolase confirmed Dahlqvist and Semenza’s findings (5).

Maltase Deficiency
Acid maltase deficiency (AMD) also known as Pompe disease was first described by Dutch pathologist JC Pompe in 1932 (7,8). AMD is a non sex linked autosomal recessive condition in which excessive accumulation of glycogen build up within lysosome vacuoles in nearly all types of cells all over the body (7,8,9). It is one of the more serious glycogen storage diseases affecting muscle tissue (10).

AMD is categorized into three separate types based on the age of onset of symptoms in the affected individual. Infantile (Type a), childhood (Type b), and adulthood (Type c). The type of AMD is determined by the type of gene mutation localized on 17q23. Mutation type will determine production level of acid maltase. AMD is extremely fatal. Type a generally die of heart failure prior to age one. Type b die of respiratory failure between ages three to twenty-four. Type c die of respiratory failure 10-20 years of the onset of symptoms (10).