(sucrase-isomaltase deficiency, congenital sucrase-isomaltase deficiency, CSID)

A life-long condition caused by one of several genetic mutations, in which sucrase-isomaltase (enzyme) is not produced or either partially functional or non-functional in the small intestine. The enzyme is needed for proper metabolism of sucrose and starch.
The patients cannot break down sucrose (found in fruits) and maltose (found in grains).

The symptoms are present only after sucrose or starch are eaten.
Flatulence can be related to recurring indigestion, irritable bowel syndrome, etc.

(Symptoms)
• Abdominal cramps, bloating
• Vomiting
• Diarrhea, constipation, excessive flatulence
• Hypoglycemia, headaches, heart palpitations, anxiety
• Poor weight gain and growth

(Diagnosis)
• Disaccharidase enzyme test
• Biopsy of the small intestine
• Sucrose hydrogen breath test
• ¹³C-Sucrose Breath Test
• 4-4-4 Simple oral sugar challenge

(Treatment)
• Diet modification: Eliminates or restricts the consumption of foods containing sucrose or starch (e.g. low-FODMAP diet).
• Enzyme replacement therapy: Replaces the action of the deficient enzyme.

(Mechanism)
It causes chronic gastrointestinal symptoms whenever the patient eats food containing sucrose or starch (carbohydrates). When they are not absorbed from the gastrointestinal tract, they travel to the large intestine, where:
• Watery diarrhea: The food takes excess water by osmosis.
• Excessive flatulence (gas) and acidic environment: The food is broken down by bacteria in the process of fermentation.

Cf. lactose intolerance, fructose malabsorption