Congenital sucrase-isomaltase deficiency (CSID) is a genetic disorder that affects an individual’s ability to properly digest certain sugars. This condition impacts the small intestine’s capacity to break down complex sugars like sucrose and isomaltose. It stems from a deficiency in specific digestive enzymes.
Understanding Congenital Sucrase-Isomaltase Deficiency
The human digestive system relies on enzymes to break down food into smaller, absorbable components. The sucrase-isomaltase enzyme complex, located on the surface of cells lining the small intestine, plays a direct role in digesting sucrose, often called table sugar, and isomaltose, a sugar derived from starch digestion. Sucrose is a disaccharide made of glucose and fructose.
In individuals with CSID, mutations in the SI gene disrupt the production, structure, or function of this enzyme. These mutations prevent the efficient breakdown of sucrose into glucose and fructose, and isomaltose into glucose. Because these larger sugar molecules cannot be absorbed by the small intestine, they travel to the large intestine.
Once there, these undigested sugars ferment due to the action of normal gut bacteria. This fermentation produces gases and attracts water, contributing to the gastrointestinal symptoms associated with CSID. The condition is inherited in an autosomal recessive pattern, meaning an individual must inherit two copies of the mutated SI gene, one from each parent, to develop the disorder.
Recognizing the Symptoms
Symptoms of congenital sucrase-isomaltase deficiency become noticeable when an infant begins consuming foods containing sucrose, such as fruit juices, fruits, or solid foods. This usually occurs after weaning from breast milk or lactose-only formula. Breast milk does not contain sucrose, so breastfed infants may not show symptoms until later.
Common gastrointestinal symptoms include chronic watery diarrhea, abdominal pain, bloating, and excessive gas. Infants and young children may also experience poor weight gain, failure to thrive, and malnutrition due to malabsorption of nutrients. Other signs can include nausea, vomiting, and skin irritation around the buttocks from prolonged diarrhea.
While symptoms are often more pronounced in infants and young children due to their higher carbohydrate intake and faster intestinal transit time, adults with CSID can also experience persistent symptoms. These may be milder, presenting as increased bowel movement frequency, looser stools, abdominal distension, and flatulence. Adults might also experience episodic watery diarrhea after consuming sucrose-rich meals.
Getting a Diagnosis
Diagnosing congenital sucrase-isomaltase deficiency involves several methods, often starting with a detailed review of the patient’s dietary history and symptoms. The gold standard for diagnosis is a disaccharidase assay performed on a small intestine biopsy. This procedure involves taking a tissue sample from the small intestine during an endoscopy to measure the activity levels of sucrase and isomaltase enzymes.
Less invasive screening options include hydrogen breath tests, such as the sucrose hydrogen-methane breath test or the 13C-sucrose breath test. These tests measure the hydrogen, methane, or 13CO2 levels in a patient’s breath after ingesting a sucrose solution. Elevated levels indicate that undigested sucrose is fermenting in the large intestine.
Genetic testing, involving sequencing of the SI gene, can also confirm a diagnosis by identifying specific mutations. This method can be a less invasive alternative to biopsy and is useful for diagnosis and family screening. CSID symptoms can overlap with other gastrointestinal conditions like irritable bowel syndrome, which can sometimes delay an accurate diagnosis.
Living with the Condition
Managing congenital sucrase-isomaltase deficiency primarily involves dietary adjustments and enzyme replacement therapy. Strict avoidance of sucrose is a primary dietary management strategy, which can be challenging as sucrose is found in many fruits, juices, and processed foods. Limiting starch intake may also be necessary, as isomaltase is involved in starch digestion.
Enzyme replacement therapy with sacrosidase, marketed as Sucraid, is an FDA-approved treatment for sucrase deficiency in patients aged 5 months and older. This oral solution provides an exogenous sucrase enzyme, aiding in the breakdown of sucrose into absorbable glucose and fructose. Sucraid should never be heated or added to warm beverages or infant formula, as heat can inactivate the enzyme.
While sacrosidase helps with sucrose digestion, it does not specifically replace the deficient isomaltase, so dietary modifications for starch may still be required. Nutritional support and monitoring for deficiencies are also important aspects of care, especially in children to ensure proper growth and development. Although symptoms can sometimes improve with age for some individuals, lifelong management is often necessary to control symptoms effectively.