Congenital sucrase-isomaltase deficiency

Other Names

CSID; Congenital sucrose-isomaltase malabsorption; Sucrose-isomaltase malabsorption, congenital; Disaccharide intolerance, 1; Sucrose intolerance congenital; SI deficiency; Sucrase-isomaltase deficiency, congenital

Pathophysiology

Congenital sucrase-isomaltase deficiency (CSID) is a genetic condition that affects a person's ability to digest certain sugars. People with this condition cannot break down the sugars sucrose (a sugar found in fruits, and also known as table sugar) and maltose (the sugar found in grains).

Presentation

CSID usually becomes apparent after an infant begins 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 thrive and malnutrition.

Disaccharides

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.

Deficiency of sucrase-isomaltase

People with congenital sucrase-isomaltase deficiency cannot break down the sugars sucrose and maltose, and other compounds made from these sugar molecules (carbohydrates).

Epidemiology

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.

Cause

• Mutations in 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 responsible for breaking down sucrose and maltose into their simple sugar components.
• These simple sugars are then absorbed by the small intestine.
• Mutations that cause this condition alter the structure, disrupt the production, or impair the function of sucrase-isomaltase.
• These changes prevent the enzyme from breaking down sucrose and maltose, causing the intestinal discomfort seen in individuals with congenital sucrase-isomaltase deficiency.

Inheritance

Autosomal recessive inheritance, a 25% chance

• This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations.
• The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

Symptoms

• Affected infants usually develop symptoms soon after they first ingest sucrose, which is found in modified milk formulas, fruits, or starches. Symptoms may include explosive, watery diarrhea resulting in abnormally low levels of body fluids (dehydration), abdominal swelling (distension), and/or abdominal discomfort.
• In addition, some affected infants may experience malnutrition, resulting from malabsorption of essential nutrients, and/or failure to thrive, resulting from nutritional deficiencies.
• In some cases, individuals may exhibit irritability; colic; abrasion and/or irritation (excoriation) of the skin on the buttocks as a result of prolonged diarrhea episodes; and/or vomiting.
• Symptoms of this disorder vary among affected individuals, but are usually more severe in infants and young children than in adults.
• For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed.
• 80%-99% of people have these symptoms

• Diarrhea(Watery stool)

30%-79% of people have these symptoms

• Vomiting(Throwing up)

5%-29% of people have these symptoms

• Abdominal colic
• Abdominal distention(Abdominal bloating)

Diagnosis

• CSID can be diagnosed by taking a small sample of tissue (biopsy) from the small intestine for a specific test known as a disaccharidase assay.
• Other tests may include a sucrose hydrogen breath test in which an abnormally high level of hydrogen will be detected in the breath of an affected individual after sucrose ingestion.
• Genetic testing may be indicated in some cases.

Treatment

• CSID is typically treated by modifying a person's diet to reduce the amount of sucrose.
• Because many foods contain sucrose and other complex sugars, it can be difficult to completely remove sucrose from the diet.
• Sacrosidase is an oral medication containing the enzyme that does not work properly in people with this condition.
• By taking this medication, those with CSID can eat sucrose-containing foods because this enzyme will break down sucrose.
• This medication must be taken with each meal or snack.

Medications

• The medication(s) listed below have been approved by the Food and Drug Administration (FDA) as orphan products for treatment of this condition.

Sacrosidase (Brand name: Sucraid®) Oral replacement therapy of the genetically determined sucrase deficiency, which is part of congenital sucrease-isomaltase deficiency.

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NIH genetic and rare disease info

• NIH info on Congenital sucrase-isomaltase deficiency

Congenital sucrase-isomaltase deficiency is a rare disease.