What Causes CSID? Will You Outgrow CSID?

Certain mutations in the sucrase-isomaltase gene (SI) cause Congenital Sucrase-Isomaltase Deficiency (CSID). The SI gene provides genetic instructions to the cells for producing the sucrase-isomaltase enzymes. These enzymes are found in the brush border of the small intestine and are responsible for breaking down sucrose and maltose into their simple sugar components. Once these simple sugars are broken down, they are absorbed by the small intestine and into the bloodstream.

Genetic mutations that cause CSID do so by providing genetic instructions that alter the sucrase-isomaltase enzyme structure, disrupt production of the enzyme, or impair the functioning of the enzyme. These changes prevent the enzyme from breaking down sucrose and maltose, causing the gastrointestinal symptoms associated with CSID.

CSID is a rare, inherited disorder that is not outgrown, although some factors may mitigate the gastrointestinal symptoms over time. Congenital means “present at birth,” and the enzyme deficiency is not acquired due to infection or other external influence. Proper sucrose digestion requires production of new sucrase-isomaltase enzymes each time food is consumed. Those with CSID lack the ability to produce sucrase-isomaltase, so CSID is a chronic disorder that will never be outgrown.