13C-Labeled-Starch Breath Test in Congenital Sucrase-isomaltase Deficiency

Background and Hypotheses: Human starch digestion is a multienzyme process involving 6 different enzymes: salivary and pancreatic a-amylase; sucrase and isomaltase (from sucrose-isomaltase [SI]), and maltase and glucoamylase (from maltase-glucoamylase [MGAM]). Together these enzymes cleave starch to smaller molecules ultimately resulting in the absorbable monosaccharide glucose. Approximately 80% of all mucosal maltase activity is accounted for by SI and the reminder by MGAM. Clinical studies suggest that starch may be poorly digested in those with congenital sucrase-isomaltase deficiency (CSID). Poor starch digestion occurs in individuals with CSID and can be documented using a noninvasive C-13-breath test (BT). Methods: C-13-Labled starch was used as a test BT substrate in children with CSID. Sucrase deficiency was previously documented in study subjects by both duodenal biopsy enzyme assays and C-13-sucrose BT. Breath (CO2)-C-13 was quantitated at intervals before and after serial C-13-substrate loads (glucose followed 75minutes later by starch). Variations in metabolism were normalized against C-13-glucose BT (coefficient of glucose absorption). Control subjects consisted of healthy family members and a group of children with functional abdominal pain with biopsy-proven sucrase sufficiency. Results: Children with CSID had a significant reduction of C-13-starch digestion mirroring that of their duodenal sucrase and maltase activity and C-13-sucrase BT. Conclusions: In children with CSID, starch digestion may be impaired. In children with CSID, starch digestion correlates well with measures of sucrase activity.