Gupta, Sandeep K.; Chong, Sonny K. F.; Fitzgerald, Joseph F.
Intestinal mucosal biopsies are obtained for histologic examination. The specimens can also be used for biochemical assay of disaccharidase activities (DAs). The disaccharidase play a vital role in the digestion of carbohydrates, and their deficiency can result in carbohydrate malabsorption, intolerance, or both. Disaccharidase deficiency can be a primary process or can be caused by a secondary phenomenon, which may be differentiated using histologic examination of intestinal mucosal specimens and biochemical assay of DAs (1). A cornerstone of interpretation of biochemically determined DAs is availability of normal DAs.
Disaccharide activities have been reported in intestinal mucosa in children, but interpretation of the data is debatable. In many instances the control group has included patients on whom insufficient clinical information is provided, or who had diarrhea (1-14). In some studies DAs have been reported in children who had no diarrhea and had normal intestinal mucosal histology (15,16), which would constitute a "normal" sample, but the sample size was either small of the results were not compared with DAs in children with small intestinal mucosal disease and/or diarrhea. In addition, the association between intestinal villus height and DAs is unclear. Although a positive correlation had been demonstrated in some studies (1,12,17), other reports do not support this relationship (2,18,19).
Therefore, the relationship between patient symptoms, intestinal mucosal morphology, and DAs is not entirely established. We report an analysis of DAs in children grouped by age, symptoms, and intestinal mucosal histology. We reviewed DAs in children who did not have diarrhea and who had normal intestinal mucosal histology to establish normal values. We compared these values with DAs determined in children with diarrhea, with and without intestinal mucosal disease. Lastly, a survey was conducted by questionnaire to assess the efficacy of dietary modification in patients with hypolactasia.
MATERIALS AND METHODS
We reviewed DAs and histology of 246 endoscopically obtained intestinal mucosal specimens from 232 children. These patients underwent esophagogastroduodenoscopy (EGD) during a 3-year period from September 1, 1990, through August 31, 1993, at the James Whitcomb Riley Hospital for Children, Indiana University Medical Center, Indianapolis, Indiana, U.S.A. The patients were divided into two groups based on the absence (group 1) or presence (group 2) of diarrhea. The main symptoms of the patients in group 1 were recurrent abdominal pain, vomiting, gastroesophageal reflux, hematemesis, and failure to thrive. All patients in group 2 had diarrhea; patients included those with celiac disease, inflammatory bowel disease, parasitic infestation (including giardiasis and cryptosporidiosis), and congenital sucrase-isomaltase deficiency. The patients were further divided into two age groups, less than 24 months and 24 months or more, in that lactase activity is inversely proportional to age and may decrease after late infancy (12).
Intestinal Mucosal Biopsy
Intestinal mucosal specimens were obtained from the distal duodenum or proximal jejunum during EGD. The instruments used were a fiberendoscope (Olympus GIF-XP20; Olympus American, Melville, NY, U.S.A.) in children weighing less than 12 kg and a videoscope (GIF-100; Olympus) in larger children. Immediately after biopsy, the specimens were oriented on filter paper and transported in formalin to the surgical pathology laboratory. The specimens for DAs were immediately placed on dry ice for shipment to the reference laboratory.
Each biopsy was carefully oriented, sectioned, and stained with hematoxylin-eosin. For purposes of this study, we reviewed the histology report on each patient. The mucosal histologic changes were classified as normal (normal villus architecture; villus height > crypt depth; Fig. 1), mild (mild villus blunting; villus; height = crypt depth, and/or evidence of parasitic infestation; Fig. 2), (moderate villus blunting; villus height < crypt depth), or severe (total villus atrophy; Fig. 3).
Lactase, maltase, palatinase, and sucrase activities were determined at our reference laboratory, State University of New York, Buffalo, New York, U.S.A. by the method of Dahlquist (12). Enzymatic activities are reported in units (U; micromoles of substrate hydrolyzed per minute at 37°C per gram of protein).
Sixty patients had lactase deficiency (lactase <15.0 U, based on the values provided by our reference laboratory). Lactose avoidance and/or lactase supplementation were recommended. A questionnaire was sent to 34 of these patients, to assess the efficacy of our recommendation. The remaining 26 patients were not included because they had parasitic infestation (giardiasis, cryptosporidiosis), celiac disease, or cow's milk protein allergy or were receiving feedings by jejunostomy tube, among other disqualifying factors. Briefly, the questionnaire inquired into the child's main symptoms, which recommendations were accepted, and the effect of the accepted recommendations on individual symptoms and overall well-being of the child.
A logarithmic transformation was performed to normalize the data (2). Differences between groups were determined by one-way analysis of variance. Differences between group means were assessed using Fisher's protected least-square difference (LSD).
Of the 232 patients, 111 were boys and 121 were girls. Ages ranged from 1 month to 17 years (mean age, 5.9 years). In group 1 (142 patients, 144 biopsies), 62 were boys and 80 were girls. Of these, 20 (12 boys) were aged less than 24 months (mean age, 14.4 months) and 122 (50 boys) were aged 24 months or more (mean age, 9.1 years). In group 2 (90 patients, 102 biopsies), 45 patients (25 boys) were aged less than 24 months old (mean age, 11.3 months) and 47 (25 boys) were aged 24 months or more (mean age, 4.7 years). Two patients in group 2 fell in both age groups because of the different times at which they underwent EGD (Table 1). All patients in group 1 had normal intestinal mucosal histology, whereas patients in group 2 had varying histologic abnormalities (Table 2).
The DAs from patients in group 1 represent normal values. They were free of diarrhea and had normal intestinal mucosal histology and represent as pure a sample as is ethically feasible to obtain (Table 3). The geometric mean (95% confidence interval [CI]) of the DAs in children aged less than than 24 months was (in U): lactase 36.7 (13.4-100.4), maltase 178.5 (88.9-356.3), palatinase 12.7 (3.8-41.5), and sucrase 60.0 (24.0-148.1). In children aged 24 months or more, the values for lactase, maltase, palatinase, and sucrase were 23.2 (3.9-108.1), 167.6 (78.8-355.9), 12.7 (4.9-32.9), and 51.0 (20.5-126.0), respectively. Only lactase activity decreased with age (p < 0.05).
The DAs in patients who had diarrhea (group 2) are shown in Tables 4 (aged less than 24 months) and 5 (aged 24 months or more). These patients are separated into subgroups based on intestinal mucosal histology: normal, mild changes, and moderate/severe changes). Results from group 1 subjects are also shown for comparison.
One-way analysis of variance of the log function of the DAs indicated significant differences between the group means of each enzyme log lactase, maltase, palatinase, and sucrase. Simultaneous individual comparisons of variance of individual means within the disaccharidase categories demonstrated significant differences among only a few groups. No differences in DAs were noted in patients with and without diarrhea if the mucosal histology was normal (group 1A vs. 2A). In patients with diarrhea, DAs were commensurate with the degree of mucosal injury. In younger patients, DAs were significantly depressed only in moderate to severe enteropathy (group 1A vs. 2C), whereas older children had significantly lower DAs with mild and moderate to severe degree of mucosal damage (group 1A vs. 2B and 1A vs. 2C).
Replies were received from 27 (79%) of the 34 patients mailed the questionnaire. Of these, 20 (12 boys; mean age, 9.2 years) were in group 1, and symptoms in 15 (75%) of the 20 improved with lactase supplementation and/or lactose avoidance. The mean lactase value in these 20 patients was 9.3 U. The mean lactase activity in those in whom symptoms did not improve was higher than in those whose symptoms responded to therapy (11.1 vs. 7.4 U). The remaining 7 (5 boys; mean age, 7.6 years) respondents had diarrhea (group 2), and 5 of those had normal histology (group 2A); all 7 (100%) responded to lactose avoidance and/or lactase supplementation. The mean lactase activity in these 7 patients was 7.6 U.
The disaccharidases, synthesized in membrane-bound polysomes, are membrane glycoproteins. They are located on or within the microvilli and protrude on the outer, luminal surface of the intestinal cell membrane. Each disaccharidase includes a hydrophobic region that serves as a membrane anchor, and an intraluminal hydrophilic region that is the active site. There are two main classes of disaccharidases: β-glycosidase (lactase) and α-glucosidases (sucrase-isomaltase, maltase-glucoamylase, and trehalase).
Reduced DAs may result in defects in carbohydrate absorption. Whereas carbohydrate malabsorption refers to inability to digest and absorb carbohydrates normally, with or without clinical symptoms, carbohydrate intolerance refers to symptoms from sugar malabsorption. Disaccharidase deficiency can be primary or secondary, the latter occurring with damaged functional and histologic integrity of the small intestine, as in celiac disease and acute infectious enteritis. Patients with primary, genetically determined defects of early and late onset (glucose-galactose malabsorption, sucrase-isomaltase deficiency, and adult-type hypolactasia) experience carbohydrate malabsorption without alterations in the intestinal mucosal histologic appearance.
Because it may not be possible to predict carbohydrate malabsorption accurately based on dietary and symptom history, laboratory methods are used (20). Such methods as breath hydrogen tests, oral tolerance tests, and the measurement of fecal excretion of 13C-enriched sugars assess carbohydrate malabsorption, but they neither measure DAs directly nor determine whether the disaccharidase deficiency is primary or secondary (7). Additionally, their applications are often limited by patient age.
Disaccharidase activities may be established from intestinal biopsy specimens by a rapid test, which is semiquantitative (21), or by biochemical testing. We have determined intestinal mucosal DAs biochemically in a large cohort of patients who could constitute a normal population. We have established normal ranges for DAs based on two broad age groups. Disaccharidase activities in these children show the typical developmental pattern as previously reported (7,12); sucrase, maltase, and palatinase levels remain relatively constant with increasing age, whereas lactase activity decreases significantly.
We compared these normal ranges of DAs with the values obtained in children with diarrhea and intestinal mucosal alterations. Activities of all four disaccharidases were altered in inverse relation to the degree of intestinal mucosal injury. Although lactase is thought to be the enzyme most susceptible to injury (12), we did not find such a trend. The DAs were not significantly different between patients with and without diarrhea in the presence of normal intestinal mucosal histology (groups 1A and 2A). Our data suggest that DAs correlate better with mucosal histologic alterations than with symptoms. It is, however, difficult to predict with certainty the DAs based on symptoms and/or intestinal mucosal histology, and vice versa. Some of our patients in group 1 (without diarrhea, normal intestinal mucosal histology) had hypolactasia that responded to lactase supplementation and/or lactose avoidance, shown by our analysis of questionnaire responses.
In conclusion, if information regarding DAs is required, it should be obtained biochemically. Lactase deficiency may need treatment regardless of mucosal histology.
Acknowledgement: The authors thank Gail Waltz CPNP, MSN, Myra Macapagal, and Dr. Qinyuan Lou for assistance with data collection and the questionnaire study; Mary M. Davis, M.D., for providing the photographs, and Ms. Vicki Haviland for her expert secretarial assistance.
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Clinical Quiz Section
Short cases with accompanying photographs of diagnostic biopsies, endoscopic findings, or physical characteristics are welcomed for the Clinical Quiz section. Please send a short history, glossy photograph, and answers to quiz questions to:
ESPGHAN Clinical Quiz Editor; Dr. Riccardo Troncone; Department of Pediatrics; University Federico II; Via S. Pansini, 5; 80131 - Naples; ITALY; Tel: 39-81-7463394; Fax: 39-81-5469811
NASPGN Clinical Quiz Editor; Dr. Joseph F. Fitzgerald; Department of Pediatrics; James Whitcomb Riley Hospital for Children; 702 Barnhill Drive; Indianapolis, IN 46202-5225; Tel: 317-274-3774; Fax: 317-274-8521
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