Genetic Sucrase-Isomaltase Deficiency

Congenitalsucrase-isomaltase deficiency is a disorder that affects a person's ability to digest certain sugars. People with this condition cannot break down the sugars sucrose and maltose. Sucrose (a sugar found in fruits, and also known as table sugar) and maltose (the sugar found in grains) are called disaccharides because they are made of two simple sugars. Disaccharides are broken down into simple sugars during digestion. Sucrose is broken down into glucose and another simple sugar called fructose, and maltose is broken down into two glucose molecules. People with congenital sucrase-isomaltase deficiency cannot break down the sugars sucrose and maltose, and other compounds made from these sugar molecules (carbohydrates).

Congenital sucrase-isomaltase deficiency usually becomes apparent after an infant is weaned and starts to consume fruits, juices, and grains. After ingestion of sucrose or maltose, an affected child will typically experience stomach cramps, bloating, excess gas production, and diarrhea. These digestive problems can lead to failure to gain weight and grow at the expected rate (failure to thrive) and malnutrition. Most affected children are better able to tolerate sucrose and maltose as they get older.

The prevalence of congenital sucrase-isomaltase deficiency is estimated to be 1 in 5,000 people of European descent. This condition is much more prevalent in the native populations of Greenland, Alaska, and Canada, where as many as 1 in 20 people may be affected.

Symptoms

Congenital sucrase-isomaltase deficiency usually becomes apparent after an infant is weaned and starts to consume fruits, juices, and grains and often is diagnosed under the age of 18 months. It may sometimes be diagnosed in older children or adults, however the frequency of CSID in adults has not yet been determined.

After ingestion of sucrose or maltose, an affected person will typically experience watery diarrhea, bloating, excess gas production, abdominal pain ("stomach ache"), and malabsorption of other nutrients. Other symptoms may include nausea, vomiting, or reflux-like symptoms.

In some children, these digestive problems can lead to failure to gain weight and grow at the expected rate (failure to thrive) and malnutrition. Most affected children are better able to tolerate sucrose and maltose as they get older.

Symptoms can vary for a variety of reasons including the timing of introduction of sucrose into a person's diet, and the amount of sugar and starch consumed. Infants who are breast-fed or fed lactose-containing formula will often not have symptoms of CSID until they ingest juices, solid foods, or medications that are sweetened by sucrose.

In some people symptoms may be milder than typically expected. Those with milder symptoms may not be diagnosed until later in childhood or in adulthood. In others with CSID the symptoms may mistakenly be thought due to something else, such as a functional GI disorder like irritable bowel syndrome with diarrhea (IBS-D) or dyspepsia.

Causes

Mutations in a gene (the SI gene) cause congenital sucrase-isomaltase deficiency. The SI gene provides instructions for producing the enzyme sucrase-isomaltase. This enzyme is found in the small intestine and is involved in the digestion of sugar and starch. It is responsible for breaking down sucrose and maltose into their simple sugar components. These simple sugars are then absorbed by the small intestine.

In addition to genetic variations, other factors including dietary, gut motility, and nutritional interactions can affect the severity of symptoms.

Dietary management of malabsorption disorders like GSID can be challenging. Talk to your doctor and a registered dietitian about what foods may cause digestion problems. Ask about alternatives. Learn how to read food labels and what to avoid. Be aware of possible sugar content of medicines, if needed.