Congenital sucrase-isomaltase deficiency

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Congenital sucrase-isomaltase deficiency (CSID) is an inherited metabolic disorder where you are unable to digest certain high sugar foods. When an infant is weaned, they start to consume fruits, fruit juices and other high sugar containing foods as part of their diet. In our body we have substances which can break down these sugars, so they can be absorbed and used for energy, these substances that break down these sugars are called enzymes. The instructions to make these enzymes are inherited from your parents. However, a person with CSID can either be born low levels of the enzymes or lack the enzymes to break down these sugars.

Congenital sucrose-isomaltase deficiency is estimated to affect 1 in every 5000 people within Europe. This disorder tends to be more prevalent within areas of Greenland, Alaska and Canada, it is estimated to affect every 1 in 20 people. CSID affects males and females equally.

Symptoms of CSID commonly occur once you have first ingested a high sugar product such as fruit or grains. Common signs and symptoms associated with this disease are:

• Watery diarrhoea
• Abdominal pain
• Bloating
• Nausea
• Irritability
• Vomiting
• Symptoms similar to reflux
• Poor mineral and nutrient absorption

Secondary symptoms associated with this metabolic disorder is dehydration and skin irritations

Children with this disorder may also develop malnutrition and fail to grow and develop at the expected rate as a result of the symptoms.  Symptoms and tolerance levels often improve with age. However, some individuals may not present with symptoms until puberty.

Congenital sucrase-isomaltase deficiency is diagnosed by taking a sample (biopsy) from your small intestine (where sugars are broken down and absorbed) to perform a test called a disaccharidase assay. This test is used to check the amount of the sugars you have absorbed by the small intestine. Another test which is used in diagnosing this metabolic disorder are sucrose breath tests. Genetic testing may sometimes be used as an alternative to diagnose or confirm CSID.

Diagnosis of this metabolic disorder can be complex; this is due to many of the symptoms being likened to other conditions such as irritable bowel syndrome and chronic diarrhoea.

Treatment needs to consistent with the advice of a specialist consultant and a specialised dietitian. This disorder is generally managed through a sucrose-restricted diet with careful management to ensure that you are acquiring enough nutrients. For children starch may also need to be limited in the diet. The diet and tolerance to foods is likely to change or improve with age therefore it is important to address dietary changes with your dietitian. Some individuals may benefit from an enzyme replacement therapy called Invertase (similar to the US version called Sacrodsidase, also known as Sucraid). This oral solution has been proven to be effective in improving nutritional status and reliving symptoms of CSID.

CSID can only be passed on to a child if both parents have a copy of the faulty gene. This is called autosomal recessive inheritance. A person who has a copy of the faulty gene is known as a carrier. If both parents are carriers, their child has a one in four chance of inheriting the disorder, and a one in two chance of being a carrier. This is the same for each child the parents have.

If the child only inherits one copy of the faulty gene, they will be a carrier but will not have the disorder. In some rare cases, carriers have had mild symptoms of the disorder for which they carry the faulty gene.

Once you are diagnosed, you can speak to a genetic counsellor. They can explain how you may have inherited CSID. They can also tell you about They can provide advice and support if you go on to have children of your own.

All information accurately referenced by Metabolic Support UK, however, should you require access to our references, please contact us by email: contact@metabolicsupportuk.org