Impaired digestive function of sucrase-isomaltase in a complex with the Greenlandic sucrase-isomaltase variant.

Sucrase isomaltase (SI) is the most prominent disaccharidase in the small intestine. Congenital sucrase-isomaltase deficiency (CSID) is an autosomal recessive disorder caused by variants in the SI gene. A homozygous frameshift mutation, c.273_274delAG (p.Gly92Leufs*8), has been identified in CSID in the Greenlandic population. This variant eliminates the luminal domain of SI and results in loss of its digestive function. Surprisingly, the truncated mutant is transport-competent and localized at the cell surface; it interacts avidly with wild type SI and negatively impacts its enzymatic function. The data propose that heterozygote carriers of p.Gly92Leufs*8 may also present with CSID symptoms.