Congenital sucrase-isomaltase deficiency (CSID) is a genetic disorder that causes maldigestion of sucrose and starch due to a deficiency or absence of the enzymes sucrase and isomaltase in infants, children, and adults (1). Symptoms include chronic or intermittent osmotic diarrhea and abdominal pain. This disorder can include severe diarrhea with failure to thrive in infants (2), and be mistaken for chronic nonspecific diarrhea without growth failure in toddlers and irritable bowel syndrome in adolescents and adults before diagnosis (3,4). It is important that a nutrition assessment be done upon diagnosis of CSID to determine the extent, if any, of malnutrition and failure to thrive. Diet education is crucial for achieving optimum nutrition status and minimization of symptoms of CSID. A registered dietitian can provide nutrition support to patients and their families.
There are a variety of steps that the dietitian needs to take for proper treatment of the patient with suspected or confirmed CSID (Fig. 1). A patient's dietary intake history (types and amounts of foods and beverages), food allergies (suspected or confirmed) and aversions, and what medications and supplements are being taken is helpful in assessing current nutrient intake and habits. A written 3-day dietary intake record with symptoms is an important tool because it can be assessed using a nutritional analysis program for nutrient intake adequacy and amounts of sucrose and starch being consumed. If a parent has not provided a 3-day food record, then a 24-hour dietary recall is helpful but not optimal. Bowel habits, pain episodes, and any other physical symptoms can also help determine food tolerance and problem foods (5).
An assessment of the child's growth history is essential in determining nutritional status. This assessment includes weight and height/length measurements over time, weight/height percentiles or body mass index percentiles and frontal occipital circumference measurements up to age 2 years. These are plotted on the World Health Organization growth charts from infancy to age 2 years and the Centers for Disease Control and Prevention growth charts after age 2 years (6). The Waterlow classification can be used to determine the degree of malnutrition present. Acute malnutrition (based on actual weight in kilograms divided by expected weight [kilograms] for height in centimeters at the 50th percentile on growth charts) and chronic malnutrition (based on actual height [centimeters] divided by expected height [centimeters] for age at the 50th percentile on the growth charts). There are 0 to 3 grades of malnutrition, from normal, mild, and moderate to severe (7). There are also other nutrition assessments that can be done such as visual assessment of possible vitamin deficiencies and biochemical analysis, but these will not be expanded upon in this article.
Upon assessing intake and growth, an estimation of calorie and protein requirements needs to be calculated. The Institute of Medicine Dietary Reference Intakes is a useful tool to determine calorie and protein needs. The calories and protein may need to be based on catch-up growth needs if the child is underweight and growth is stunted (8,9).
After diagnosis and determination of nutrition status, the parents and child (if the child is old enough) can be educated on the diet for CSID. It is important that the family work with a dietitian and medical doctor during this period of education. Every patient and family is different, so the diet education needs to be individualized. The first step is to make sure that the child's nutrition status is stable before introducing new foods into the diet to prevent relapse into poor nutritional status. The child may need to be on a supplemental formula to improve nutritional status, along with high-calorie foods that do not contain sucrose or starch. The child can consume acceptable infant and toddler formulas without sucrose or starch; meats, poultry, and seafood; dairy products such as cheese, plain yogurt, and cow's milk without sucrose or starch; and many vegetables when beginning the diet. A dietitian can help the family choose appropriate foods for the child. The CSID Parent Support Group Web site at CSIDinfo.com (10) provides helpful information for use by doctors and dietitians on introducing sucrose- and starch-containing foods into the diet. For foods not listed on the CSID Web site, the dietitian can analyze the foods with a nutrition analysis program.
When the child is nutritionally stable, sucrose-containing foods with ≤2% sucrose can be introduced one at a time (1). The food lists on the CSID Web site contain a variety of these foods. The Web site has food group lists, including fruits, vegetables, breads and starches, nuts, meats, fats, and oils. Each group lists the amount of fructose, sucrose, lactose, maltose, and starch per 100-g serving of the food (11). The child needs to try one food at a time for at least 3 to 7 days. The child needs to do this for 4 weeks. The child may be prescribed Sucraid (sacrosidase) (12), an oral enzyme solution used to aid in the digestion of sucrose, but it is important to determine which foods the child can eat without Sucraid, hence starting with the foods with ≤2% sucrose. At week 4, Sucraid can be introduced if available to the patient. Dosing is prescribed by the physician. With Sucraid the child can increase to 2% to 5% sucrose-containing foods and assess tolerance; then, at week 5, 5% to 7% sucrose; at week 6, 7% to 10% sucrose; at week 7, 10% to 15% sucrose; and so forth. Some patients can tolerate only up to 10% to 15% sucrose with Sucraid and some can tolerate up to 20% to 25% sucrose with Sucraid. For this reason it is important to be methodical and start the diet slowly to determine tolerance.
After sucrose tolerance is determined, starch can be introduced into the diet. There are no approved supplemental enzymes for starch digestion. A biopsy and breath test can help determine enzyme activity. Some children have no starch enzyme activity and have to avoid all starches and some have varying degrees of enzyme activity (4). With limited starch digestion, a patient may be able to consume up to 120 g of starch per day. A more liberal level of 240 to 360 g of starch per day can be tolerated by those with a higher level of enzyme activity.
The family needs to be educated about understanding food labels and how to recognize sucrose and starch in foods. The family should be provided with a handout on sugars and starches, a list of acceptable sugar substitutes, how to recognize them, and which are acceptable in the child's diet.
In infancy the most important diet component is breast milk or formula. If an infant is breast-feeding only, they should not have symptoms of poor digestion related to CSID until they are weaned (13). If they are taking formula, then they may have malabsorption problems depending on the source of carbohydrate in the formula. A formula with lactose as the carbohydrate source should be tolerated. Some formulas use starches or sucrose as the carbohydrate source, so it is important to determine which formula the child is using. A dietitian can help the family select the appropriate formula for the infant after diagnosis.
When the infant begins solids, he or she should not be given rice or any other baby cereal. An iron supplement without starch or sucrose should be given if the child is still breast-feeding. If the child is taking infant formula, he or she should be receiving an adequate amount of iron. It is best to start with nonstarchy pureed vegetables and fruits with <2% sucrose. Plain pureed meats can be added later. The formula feeding or breast-feeding should be continued until age 1 year at the least to provide adequate nutrients for growth. Sucrose-containing foods and starches should be introduced as discussed in the previous section.
If the child is diagnosed as having CSID when he or she is older, the guidelines for introducing foods should be used after he or she is nutritionally stable if applicable. All children with CSID should be given a sucrose-free vitamin mineral supplement because it can be more difficult to meet certain nutrient needs based on a child's intake. Also, fructose and glucose can be used in foods and beverages to provide extra calories for energy as can oils and many fats. A dietitian can help the family find these products.
If the patient and family determine that the diet for CSID is not working to completely relieve symptoms, then it should be noted that some patients also may have concurrent enzyme deficiencies or food intolerances causing gastrointestinal discomfort such as foods containing fermentable oligosaccharides, disaccharides, monosaccharides, and polyols. The patient also may benefit from eating low-glycemic-index, slower-digesting starches. Follow-up with both the physician and dietitian is crucial to provide optimum symptom treatment and to determine whether there are other underlying deficiencies or intolerances. When a child is diagnosed as having CSID, a complete nutrition and diet intake assessment along with education and follow-up is crucial to provide the best outcome. The family should have a relationship with a physician and registered dietitian who are knowledgeable about CSID to guide them through the diagnosis and education and ongoing follow-up.
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