Congenital sucrase-isomaltase deficiency

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Congenital sucrase-isomaltase deficiency is a rare genetic disorder that affects an individual'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, grains, and other starchy food. After ingestion of sucrose or maltose, an affected individual will typically experience stomach cramps, bloating, excess gas production, and diarrhea. These digestive problems can lead to malnutrition and an inability to gain weight and grow at the expected rate (faltering weight).

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Variants (also known as 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. Variants 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. Rather than being absorbed by the small intestine, the undigested sugars move to the large intestine (colon). Here, they attract water and are consumed by normal bacteria in the colon, causing the intestinal discomfort seen in individuals with congenital sucrase-isomaltase deficiency.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

Congenital sucrase-isomaltase deficiency is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have variants. The parents of an individual with an autosomal recessive condition each carry one copy of the altered gene, but they may not show signs and symptoms of the condition.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

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.

Reported clinical features and what the terms mean

The following findings are associated with this condition in Orphanet. They are not a checklist for diagnosing yourself, and they do not all occur in every affected person. Some are examination, imaging or laboratory findings that cannot be recognised at home.

The frequency labels describe how often a finding was reported among people with the condition in the source. They do not give the chance that a person with that symptom has the condition. Definitions below reproduce HPO terminology; they explain the term, not the likely severity in an individual.

Abdominal pain · Very frequent (99-80%)

An unpleasant sensation characterized by physical discomfort (such as pricking, throbbing, or aching) and perceived to originate in the abdomen.

Diarrhea · Very frequent (99-80%)

Abnormally increased frequency (usually defined as three or more) loose or watery bowel movements a day.

Constipation · Frequent (79-30%)

Infrequent or difficult evacuation of feces.

Flatulence · Frequent (79-30%)

Passage of excessive amounts of gas and the feeling of abdominal fullness and bloating.

Gastroesophageal reflux · Frequent (79-30%)

A condition in which the stomach contents leak backwards from the stomach into the esophagus through the lower esophageal sphincter.

Nausea · Frequent (79-30%)

A sensation of unease in the stomach together with an urge to vomit.

Poor appetite · Frequent (79-30%)

A reduced desire to eat.

Vomiting · Frequent (79-30%)

Forceful ejection of the contents of the stomach through the mouth by means of a series of involuntary spasmic contractions.

Abdominal colic · Occasional (29-5%)

A type of abdominal pain that comes and goes in waves, most often starting and ending suddenly and being of severe intensity.

Abdominal distention · Occasional (29-5%)

Distention of the abdomen.

Bloody diarrhea · Occasional (29-5%)

Passage of many stools containing blood.

Bowel incontinence · Occasional (29-5%)

Involuntary fecal soiling in adults and children who have usually already been toilet trained.

Fatigue · Occasional (29-5%)

A subjective feeling of tiredness characterized by a lack of energy and motivation.

Failure to thrive · Very rare (<4-1%)

Failure to thrive (FTT) refers to a child whose physical growth is substantially below the norm.

Which doctor should you see?

The suggested department for discussing Congenital sucrase-isomaltase deficiency is Gastroenterology, with a gastroenterologist as the relevant type of clinician. General physician / Family Medicine; paediatrician for children. Referral depends on symptoms.

Additional services that may be relevant, depending on the findings, include: Clinical Genetics.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• Which digestive symptoms or nutritional changes matter most?
• What question would an endoscopy, scan or laboratory test answer if one is proposed?
• How should persistent pain, bleeding or difficulty eating be followed up?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for Congenital sucrase-isomaltase deficiency. That gap does not mean that treatment is unavailable. A clinician needs to establish the diagnosis and review current guidance before recommending medicines, procedures, rehabilitation or other support.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

The collected references do not establish a complete prevention or long-term outlook section for this entry. Missing information should not be interpreted as proof that prevention is impossible or that a particular outcome is inevitable. Ask what is known for the exact subtype, stage and personal circumstances, and which uncertainties remain.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.