Congenital Sucrase-Isomaltase Deficiency (CSID)

Some children are born with a decreased or absent ability to metabolize “table sugar” (sucrose) because their genes produce a defect version of the enzyme (sucrase-isomaltase) which is involved in the cleavage of “table sugar” (sucrose). The child  inherits a defect gene  both from the mother and the father to develop the disease, but depending on the type of genetic alteration, the severity of symptoms may vary.
“Table sugar” (sucrose) is a so called disaccharide and consists of two simple sugar molecules (monosacharides) linked together. In “table sugar” (sucrose) the two monosacharides are glucose and fructose. Humans cannot absorb sucrose directly from the intestine and the enzyme sucrase isomaltase needs to separate the two monosacharides glucose and fructose from one another so they can be absorbed from the intestinal tract and enter the blood stream.

Consequently, if the enzyme sucrase-isomaltase does not work properly,  “table sugar” (sucrose) is not turned in to glucose and fructose which can be absorbed, the intestine will hold a high concentration of “table sugar” (sucrose). Through a mechanism referred to as osmosis water will be retained in or even drawn into the intestine, resulting in  severe and frequent watery diarrhea . Onset of clinical symptoms is usually after the first year of life when consumption of food which contains “table sugar” (sucrose) increases. This commonly leads to a failure for the child to thrive. Other symptoms  include flatulence, dystrophy and abdominal pain.

The prevalence of CSID  has been reported to be around 0.2 %, but it  may vary  across different ethnic populations and the severity of symptoms may also vary. For example, it has been reported that 2-10 % of the Inuit population suffer from CSID. The disease is probably often missed or misdiagnosed and may be confused with a number of other diseases if not tested for specifically. Examples of differential diagnosis are congenital intestinal malformations, infectious and postinfectious diseases, lactose intolerance, endocrine disorders, pseudomembranous colitis, coeliac disease and cystic fibrosis.
Today it is possible to conduct a gene test which detects the most common mutations in the genes coding for the enzyme sucrase-isomaltase. An alternative  is to take a biopsy from the upper smaller intestine and measure the  sucrase-isomaltase activity.

The treatment of CSID involves a strict and life-long “table sugar” (sucrose) free diet. However, today this is very difficult to adhere to as much of the processed food we can buy today contains “table sugar” (sucrose) and especially among children the adherence to a diet free from “table sugar” (sucrose) might be problematic.

In USA there is an approved  pharmaceutical enzyme replacement therapy which can be used to compensate for the lack of an endogenous functioning enzyme. Such supplementation allows a more normal diet, including some intake of “table sugar” (sucrose) without the development of symptoms.