13C-breath tests for sucrose digestion in congenital sucrase isomaltase-deficient and sacrosidase-supplemented patients

Exploring congenital sucrase-isomaltase deficiency in autism spectrum disorder patients with irritable bowel syndrome symptoms: A prospective SI gene sequencing study

Congenital sucrase-isomaltase deficiency (CSID) is an inherited metabolic disorder causing chronic gastrointestinal symptoms and malnutrition when untreated. Most CSID patients are likely to remain under- or misdiagnosed. This study aimed to investigate prevalence of CSID among patients with autism spectrum disorder (ASD) presenting with irritable bowel syndrome (IBS) symptoms via prospective SI gene sequencing. A prospective cross-sectional study was conducted on 98 ASD patients exhibiting gastrointestinal symptoms consistent with IBS. Participants were assessed according to Rome IV criteria and underwent SI gene sequencing. Demographic, clinical, and dietary data were collected and analyzed. Sucrose content in various fruits and vegetables was evaluated using three-day food record, and gastrointestinal symptoms were rated on Likert scale. Seven patients (7%) were diagnosed with CSID based on SI gene analysis, revealing six different variants, including four novel mutations. One patient was homozygous for one variant, and six patients were heterozygous. Clinical presentations predominantly included diarrhea, abdominal pain, and bloating, with two patients showing growth retardation. One patient was diagnosed in adulthood. Food allergy and lactose intolerance were the misdiagnoses prior to CSID diagnosis in two patients. Real prevalence of CSID is likely underestimated. Clinical heterogeneity and non-specific symptoms contribute to diagnostic challenges. Gastrointestinal symptoms consistent with IBS in ASD patients should include CSID in differential diagnosis. Early genetic screening for SI variants in ASD patients with IBS symptoms can facilitate timely diagnosis and management, improving outcomes. Heterozygous variants of the SI gene should also be considered, as heterozygous patients can exhibit typical CSID symptoms.

Is there dietary macronutrient malabsorption in children with environmental enteropathy?

Assessing the digestive and absorptive capacity of the gastro-intestinal tract (GIT) using minimally- or non-invasive methods, particularly in children, has been difficult owing to the complex physiology and variability in functional measurements. However, measuring GIT function is increasingly important with the emerging relevance of childhood environmental enteropathy (EE) as a mediating factor in linear growth faltering, severe acute malnutrition, poor oral vaccine uptake and impaired cognition. In EE, sub-optimal nutrient digestion and absorption (malabsorption) forms the critical link to the conditions mentioned above. The present narrative review discusses probable mechanisms that can cause malabsorption of macronutrients, along with mechanistic and experimental evidence, in children (if not, in adults) with EE. The strengths and limitations of the human experimental studies are examined in relation to a battery of existing and potential tests that are used to measure malabsorption. From the available studies conducted in children, lactose and fat malabsorption are more likely to occur in EE. Breath tests (non-invasive) measuring carbohydrate (13C-starch/sucrose/lactose), fat (13C-mixed triglyceride) and dipeptide (benzoyl-L-tyrosyl-L-1-13C-alanine) malabsorption with modifications to the existing protocols seem suitable for use in children with EE. Future research should focus on understanding the degree of macronutrient malabsorption using these tests, in different settings, and link them to functional outcomes (such as growth, muscle strength, cognition).

Performance of empirical and model-based classifiers for detecting sucrase-isomaltase inhibition using the13C-sucrose breath test

The13C-sucrose breath test (13C-SBT) has been proposed to estimate sucrase-isomaltase (SIM) activity and is a promising test for SIM deficiency, which can cause gastrointestinal symptoms, and for intestinal mucosal damage caused by gut dysfunction or chemotherapy. We previously showed how various summary measures of the13C-SBT breath curve reflect SIM inhibition. However, it is uncertain how the performance of these classifiers is affected by test duration. We leveraged13C-SBT data from a cross-over study in 16 adults who received 0, 100, and 750 mg of Reducose, an SIM inhibitor. We evaluated the performance of a pharmacokinetic-model-based classifier,ρ, and three empirical classifiers (cumulative percent dose recovered at 90 min (cPDR90), time to 50% dose recovered, and time to peak dose recovery rate), as a function of test duration using receiver operating characteristic (ROC) curves. We also assessed the sensitivity, specificity, and accuracy of consensus classifiers. Test durations of less than 2 h generally failed to accurately predict later breath curve dynamics. The cPDR90 classifier had the highest ROC area-under-the-curve and, by design, was robust to shorter test durations. For detecting mild SIM inhibition,ρhad a higher sensitivity. We recommend13C-SBT tests run for at least a 2 h duration. Although cPDR90 was the classifier with highest accuracy and robustness to test duration in this application, concerns remain about its sensitivity to misspecification of the CO2production rate. More research is needed to assess these classifiers in target populations.

Diagnosing sucrase-isomaltase deficiency: a comparison of a 13C-sucrose breath test and a duodenal enzyme assay

BACKGROUND

Reduced activity of the sucrase-isomaltase (SI) enzyme can cause gastrointestinal symptoms. Biochemical measurement of SI activity in small intestinal biopsies is presently considered the gold standard for the diagnosis of SI deficiency, but this invasive test is not suitable as a routine diagnostic tool.

AIM

To evaluate a 13C-sucrose-breath test (13CSBT) as a diagnostic tool for SI deficiency in an adult population.

METHODS

13CSBT results were compared to sucrase activity measured in duodenal biopsies.

RESULTS

Forty patients with gastrointestinal symptoms were included in the study, 4 of whom had celiac disease and the rest (n = 36) had normal histological findings. Nine patients (22.5%) had low sucrase activity measured using duodenal biopsies. No correlation was observed between enzymatic sucrase activity and the 13CSBT results. The 13CSBT-curves for the celiac patients versus patients with normal duodenal histology demonstrated that the patients with celiac disease were within the lower range of the distribution.

CONCLUSION

We observed a mismatch between the 13CSBT results and the biochemically measured sucrase activity, suggesting that SI activity is not uniformly distributed throughout the small intestines. This methodological discrepancy should be acknowledged when diagnosing SI deficiency.

Diet management in congenital diarrheas and enteropathies - general concepts and disease-specific approach, a narrative review

Congenital diarrheas and enteropathies (CODE) are a group of rare, heterogenous, monogenic disorders that lead to chronic diarrhea in infancy. Definitive treatment is rarely available, and supportive treatment is the mainstay. Nutritional management in the form of either specialized formulas, restrictive diet, or parenteral nutrition support in CODE with poor enteral tolerance is the cornerstone of CODE treatment and long-term growth. The evidence to support the use of specific diet regimens and nutritional approaches in most CODE disorders is limited due to the rarity of these diseases and the scant published clinical experience. The goal of this review was to create a comprehensive guide for nutritional management in CODE, based on the currently available literature, disease mechanism, and the PediCODE group experience. Enteral diet management in CODE can be divided into 3 distinct conceptual frameworks: nutrient elimination, nutrient supplementation, and generalized nutrient restriction. Response to nutrient elimination or supplementation can lead to resolution or significant improvement in the chronic diarrhea of CODE and resumption of normal growth. This pattern can be seen in CODE due to carbohydrate malabsorption, defects in fat absorption, and occasionally in electrolyte transport defects. In contrast, general diet restriction is mainly supportive. However, occasionally it allows parenteral nutrition weaning or reduction over time, mainly in enteroendocrine defects and rarely in epithelial trafficking and polarity defects. Further research is required to better elucidate the role of diet in the treatment of CODE and the appropriate diet management for each disease.

Genetic and acquired sucrase-isomaltase deficiency: A clinical review

Genetic sucrase-isomaltase deficiency (GSID) is an inherited deficiency in the ability to digest sucrose and potentially starch due to mutations in the sucrase-isomaltase (SI) gene. Congenital sucrase-isomaltase deficiency is historically considered to be a rare condition affecting infants with chronic diarrhea as exposure to dietary sucrose begins. Growing evidence suggests that individuals with SI variants may present later in life, with symptoms overlapping with those of irritable bowel syndrome. The presence of SI genetic variants may, either alone or in combination, affect enzyme activity and lead to symptoms of different severity. As such, a more appropriate term for this inherited condition is GSID, with a recognition of a spectrum of severity and onset of presentation. Currently, disaccharidase assay on duodenal mucosal tissue homogenates is the gold standard in diagnosing SI deficiency. A deficiency in the SI enzyme can be present at birth (genetic) or acquired later, often in association with damage to the enteric brush-border membrane. Other noninvasive diagnostic alternatives such as sucrose breath tests may be useful but require further validation. Management of GSID is based on sucrose and potentially starch restriction tailored to the individual patients' tolerance and symptoms. As this approach may be challenging, additional treatment with commercially available sacrosidase is available. However, some patients may require continued starch restriction. Further research is needed to clarify the true prevalence of SI deficiency, the pathobiology of single SI heterozygous mutations, and to define optimal diagnostic and treatment algorithms in the pediatric population.

Intestinal Disaccharidase Deficiency in Adults: Evaluation and Treatment

PURPOSE OF REVIEW

Disaccharidase deficiency in adults causes carbohydrate malabsorption, resulting in symptoms which significantly overlap with irritable bowel syndrome (IBS). This article discusses the diagnosis and treatment of disaccharidase deficiency within the context of recent literature.

RECENT FINDINGS

Disaccharidase deficiency in adults is more common than previously thought, which includes lactase, sucrase, maltase and isomaltase enzymes. Deficiency in disaccharidases, which are produced by the intestinal brush border, will interfere with the breakdown and absorption of carbohydrates and may result in abdominal pain, gas, bloating and diarrhea. Patients deficient in all 4 disaccharidases are known as having "pan-disaccharidase" deficiency, which has a distinct phenotype with more reported weight loss than patients deficient in one enzyme. IBS patients who do not respond to low FODMAP dietary restriction may have undiagnosed disaccharidase deficiency and may benefit from testing. Diagnostic testing methods are limited to duodenal biopsies, which is the gold standard, and breath testing. Dietary restriction and enzyme replacement therapy have been shown to be effective treatments in these patients. Disaccharidase deficiency is an underdiagnosed condition in adults with chronic GI symptoms. Patients who do not respond to traditional treatment strategies for DBGI may benefit from testing for disaccharidase deficiency. Further studies delineating the distinctions between disaccharidase deficient patients and those with other motility disorders are needed.

13C-sucrose breath test for the non-invasive assessment of environmental enteropathy in Zambian adults

Objectives

Environmental enteropathy (EE) is a subclinical disorder highly prevalent in tropical and disadvantaged populations and is thought to play a role in growth faltering in children, poor responses to oral vaccines, and micronutrient deficiencies. This study aims to evaluate the potential of a non-invasive breath test based on stable isotopes for evaluation of impaired digestion and absorption of sucrose in EE.

Methods

We optimized a ¹³C-sucrose breath test (¹³C-SBT) in 19 young adults in Glasgow, United Kingdom. In a further experiment (in 18 adults) we validated the ¹³C-SBT using Reducose, an intestinal glucosidase inhibitor. We then compared the ¹³C-SBT to intestinal mucosal morphometry, immunostaining for sucrose-isomaltase (SI) expression, and SI activity in 24 Zambian adults with EE.

Results

Fully labeled sucrose (0.3 mg/kg) provided clear breath enrichment signals over 2–3 h in both British and Zambian adults, more than fivefold higher than naturally enriched sucrose. Reducose dramatically impaired ¹³C-sucrose digestion, reducing 4 h ¹³CO₂ breath recovery by > 50%. Duodenal biopsies in Zambian adults confirmed the presence of EE, and SI immunostaining was present in 16/24 adults. The kinetics of ¹³CO₂ evolution were consistently faster in participants with detectable SI immunostaining. Although sucrase activity was strongly correlated with villus height (r = 0.72; P < 0.05) after adjustment for age, sex and body mass index, there were no correlations between ¹³C-SBT and villus height or measured sucrase activity in pinch biopsies.

Conclusion

A ¹³C-SBT was developed which was easy to perform, generated clear enrichment of ¹³CO₂ in breath samples, and clearly reports sucrase activity. Further work is needed to validate it and understand its applications in evaluating EE.

Carbohydrate Maldigestion and Intolerance

This review summarizes dietary carbohydrate intolerance conditions and recent advances on the possible role of carbohydrate maldigestion and dietary outcomes in patients with functional bowel disease. When malabsorbed carbohydrates reach the colon, they are fermented by colonic bacteria, with the production of short-chain fatty acids and gas lowering colonic pH. The appearance of diarrhoea or symptoms of flatulence depends in part on the balance between the production and elimination of these fermentation products. Different studies have shown that there are no differences in the frequency of sugar malabsorption between patients with irritable bowel disease (IBS) and healthy controls; however, the severity of symptoms after a sugar challenge is higher in patients than in controls. A diet low in 'Fermentable, Oligo-Di- and Monosaccharides and Polyols' (FODMAPs) is an effective treatment for global symptoms and abdominal pain in IBS, but its implementation should be supervised by a trained dietitian. A 'bottom-up' approach to the low-FODMAP diet has been suggested to avoid an alteration of gut microbiota and nutritional status. Two approaches have been suggested in this regard: starting with only certain subgroups of the low-FODMAP diet based on dietary history or with a gluten-free diet.

Making a Confident Diagnosis of Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is among the most common diagnoses made by medical providers and its symptoms are common causes for health care consultation. IBS is characterized by abdominal pain associated with abnormal stool consistency and/or frequency and is widely considered a diagnosis of exclusion, despite abundant evidence contradicting such an approach. A positive diagnosis is achieved through application of symptom-based clinical criteria, careful history and physical examination, evaluation for alarm sign/symptoms, and judicious use of diagnostic testing. This article reviews the symptom-based criteria for IBS and utility of diagnostic tests commonly included in the evaluation of IBS symptoms.

European guideline on indications, performance and clinical impact of 13 C-breath tests in adult and pediatric patients: An EAGEN, ESNM, and ESPGHAN consensus, supported by EPC

Introduction

¹³C‐breath tests are valuable, noninvasive diagnostic tests that can be widely applied for the assessment of gastroenterological symptoms and diseases. Currently, the potential of these tests is compromised by a lack of standardization regarding performance and interpretation among expert centers.

Methods

This consensus‐based clinical practice guideline defines the clinical indications, performance, and interpretation of ¹³C‐breath tests in adult and pediatric patients. A balance between scientific evidence and clinical experience was achieved by a Delphi consensus that involved 43 experts from 18 European countries. Consensus on individual statements and recommendations was established if ≥ 80% of reviewers agreed and <10% disagreed.

Results

The guideline gives an overview over general methodology of ¹³C‐breath testing and provides recommendations for the use of ¹³C‐breath tests to diagnose Helicobacter pylori infection, measure gastric emptying time, and monitor pancreatic exocrine and liver function in adult and pediatric patients. Other potential applications of ¹³C‐breath testing are summarized briefly. The recommendations specifically detail when and how individual ¹³C‐breath tests should be performed including examples for well‐established test protocols, patient preparation, and reporting of test results.

Conclusion

This clinical practice guideline should improve pan‐European harmonization of diagnostic approaches to symptoms and disorders, which are very common in specialist and primary care gastroenterology practice, both in adult and pediatric patients. In addition, this guideline identifies areas of future clinical research involving the use of ¹³C‐breath tests.

Sucrase-Isomaltase Deficiency Causing Persistent Bloating and Diarrhea in an Adult Female

Congenital sucrase isomaltase deficiency (CSID) is an autosomal recessive disorder which leads to chronic intestinal malabsorption of nutrients from ingested starch and sucrose. Symptoms usually present after consumption of fruits, juices, grains, and starches, leading to failure to thrive and malnutrition. Diagnosis is suspected on detailed patient history and confirmed by a disaccharidase assay using small intestinal biopsies or sucrose hydrogen breath test. Treatment of CSID consists of limiting sucrose in diet and replacement therapy with sacrosidase. Due to its nonspecific symptoms, CSID may be undiagnosed in many patients for several years. We present a case of a 50-year-old woman with persistent symptoms of bloating in spite of extensive evaluation and treatment.

The patient journey to diagnosis and treatment of congenital sucrase-isomaltase deficiency

Purpose

Congenital sucrase-isomaltase deficiency (CSID) is a rare genetic disorder characterized by a deficiency of the sucrase-isomaltase (SI) enzyme complex within the brush border membrane of the small intestine. Mutations in the SI gene result in abnormal synthesis and/or incorrect transport of the SI enzyme. Patients with CSID generally have reduced sucrase activity, but levels of isomaltase activity range from absent to almost normal. This study sought to better understand the experience of patients with CSID prior to, during, and after their diagnosis and its subsequent treatment with sacrosidase.

Methods

This was a cross-sectional interview study conducted in conjunction with a longitudinal, observational study of US patients prescribed and taking sacrosidase for at least three consecutive months as treatment for CSID. The observational study included both children and adults.

Results

This qualitative interview study explored the experiences of 43 adult and pediatric patients (n = 8 adults and n = 35 children/adolescents) with CSID pre-, during, and post-diagnosis. Findings suggest that a CSID diagnosis is particularly problematic given the disparate range of more commonly understood gastrointestinal (GI) disorders. After diagnosis and treatment with sacrosidase, participants reported considerable improvement in symptoms and health-related quality of life (HRQL), yet symptoms persist that continue to affect daily life, indicating areas of potential unmet need.

Conclusion

Educating clinicians about CSID may help improve the overall diagnosis experience. As this research is the first of its kind in CSID, additional research, qualitative and quantitative, will be important to furthering the understanding of HRQL impact and unmet need experienced by this population and identifying ways to best meet those needs.

Overview of Breath Testing in Clinical Practice in North America

Human breath is an easily, noninvasively obtained substance. It offers insight into metabolism and is used to diagnose disaccharide malabsorption, infection, small bowel bacterial over growth, and transit times. Herein, we discuss the readily available clinical breath tests, how they function, how they are administered and interpreted and some pitfalls in their use.

13C-Labeled-Starch Breath Test in Congenital Sucrase-isomaltase Deficiency

BACKGROUND AND HYPOTHESES

Human starch digestion is a multienzyme process involving 6 different enzymes: salivary and pancreatic α-amylase; sucrase and isomaltase (from sucrose-isomaltase [SI]), and maltase and glucoamylase (from maltase-glucoamylase [MGAM]). Together these enzymes cleave starch to smaller molecules ultimately resulting in the absorbable monosaccharide glucose. Approximately 80% of all mucosal maltase activity is accounted for by SI and the reminder by MGAM. Clinical studies suggest that starch may be poorly digested in those with congenital sucrase-isomaltase deficiency (CSID). Poor starch digestion occurs in individuals with CSID and can be documented using a noninvasive C-breath test (BT).

METHODS

C-Labled starch was used as a test BT substrate in children with CSID. Sucrase deficiency was previously documented in study subjects by both duodenal biopsy enzyme assays and C-sucrose BT. Breath CO2 was quantitated at intervals before and after serial C-substrate loads (glucose followed 75 minutes later by starch). Variations in metabolism were normalized against C-glucose BT (coefficient of glucose absorption). Control subjects consisted of healthy family members and a group of children with functional abdominal pain with biopsy-proven sucrase sufficiency.

RESULTS

Children with CSID had a significant reduction of C-starch digestion mirroring that of their duodenal sucrase and maltase activity and C-sucrase BT.

CONCLUSIONS

In children with CSID, starch digestion may be impaired. In children with CSID, starch digestion correlates well with measures of sucrase activity.

Variable Use of Disaccharidase Assays When Evaluating Abdominal Pain

Background and Aims: Patients with a disaccharidase deficiency typically present with abdominal discomfort and often with diarrhea. However, disaccharidase deficiency is often overlooked as a cause of these complaints. Therefore, we sought to determine the prevalence of lactase and sucrase deficiencies in a pediatric population undergoing diagnostic esophagogastroduodenoscopy (EGD) and to describe disaccharidase testing practices among pediatric gastroenterologists. Methods: Endoscopic records from patients undergoing diagnostic EGD and disaccharidase analysis (DA) were retrospectively reviewed. Diagnostic EGDs performed over a 5-year period (2010 through 2014) at a freestanding endoscopy center serving 13 pediatric gastroenterologists were assessed. Demographic and clinical data on patients were collected and grouped; patients with primary sucrase-isomaltase deficiency (SID) were the main focus. The data were stratified by the physician performing the procedures. Results: Over the 5-year study period, 5368 EGDs were performed, with abdominal pain as the primary indication in 3235 cases (60.2%). DAs were performed on 963 patients (17.9% of the total cohort; 29.8% of those with abdominal pain). Lactase deficiencies, sucrase deficiencies, and primary SID were found in 44.7%, 7.6%, and 3.5% of DAs, respectively. The number of DAs performed varied widely among physicians, ranging from 1.6% to 64.5% of EGDs evaluating patients with abdominal pain. Univariate regression analysis revealed significant correlations between the number of DAs performed and the number of SID and lactase deficiencies found (P<.001 for both). Conclusion: Rates of DAs vary widely among pediatric gastroenterologists performing diagnostic EGDs in children with abdominal pain. Physician education and clinical practice guidelines regarding the use of DAs are warranted.

Improved Starch Digestion of Sucrase-deficient Shrews Treated With Oral Glucoamylase Enzyme Supplements

BACKGROUND AND OBJECTIVE

Although named because of its sucrose hydrolytic activity, this mucosal enzyme plays a leading role in starch digestion because of its maltase and glucoamylase activities. Sucrase-deficient mutant shrews, Suncus murinus, were used as a model to investigate starch digestion in patients with congenital sucrase-isomaltase deficiency.Starch digestion is much more complex than sucrose digestion. Six enzyme activities, 2 α-amylases (Amy), and 4 mucosal α-glucosidases (maltases), including maltase-glucoamylase (Mgam) and sucrase-isomaltase (Si) subunit activities, are needed to digest starch to absorbable free glucose. Amy breaks down insoluble starch to soluble dextrins; mucosal Mgam and Si can either directly digest starch to glucose or convert the post-α-amylolytic dextrins to glucose. Starch digestion is reduced because of sucrase deficiency and oral glucoamylase enzyme supplement can correct the starch maldigestion. The aim of the present study was to measure glucogenesis in suc/suc shrews after feeding of starch and improvement of glucogenesis by oral glucoamylase supplements.

METHODS

Sucrase mutant (suc/suc) and heterozygous (+/suc) shrews were fed with C-enriched starch diets. Glucogenesis derived from starch was measured as blood C-glucose enrichment and oral recombinant C-terminal Mgam glucoamylase (M20) was supplemented to improve starch digestion.

RESULTS

After feedings, suc/suc and +/suc shrews had different starch digestions as shown by blood glucose enrichment and the suc/suc had lower total glucose concentrations. Oral supplements of glucoamylase increased suc/suc total blood glucose and quantitative starch digestion to glucose.

CONCLUSIONS

Sucrase deficiency, in this model of congenital sucrase-isomaltase deficiency, reduces blood glucose response to starch feeding. Supplementing the diet with oral recombinant glucoamylase significantly improved starch digestion in the sucrase-deficient shrew.

蔗糖酶-异麦芽糖酶缺乏与腹泻的研究进展

蔗糖酶-异麦芽糖酶(sucrase-isomaltase, SI)是蔗糖酶在肠道内最主要的存在形式, 是最丰富的肠道二糖酶, 其包含了所有的蔗糖酶活性, 大部分的异麦芽糖酶活性及60%-80%的麦芽糖酶活性. 蔗糖酶-异麦芽糖酶缺乏症(sucrase-isomaltase deficiency, SID)是由于该二糖酶缺乏导致二糖吸收不良, 肠道正常生理功能受损, 机体营养不良, 生长发育落后, 甚至产生危及生命的胃肠道症状. 其最主要的临床表现是腹泻. 临床上通过调整肠道SI活性来治疗腹泻, 并将SI活性用于临床诊断. 本文主要阐述SID与腹泻的关系、研究进程以及诊疗手段, 促进SI在药理方面的研究.

Structure-function analysis of human sucrase-isomaltase identifies key residues required for catalytic activity

Sucrase-isomaltase (SI) is an intestinal membrane-associated α-glucosidase that breaks down di- and oligosaccharides to absorbable monosaccharides. SI has two homologous functional subunits (sucrase and isomaltase) that both belong to the glycoside hydrolase family 31 (GH31) and differ in substrate specificity. All GH31 enzymes share a consensus sequence harboring an aspartic acid residue as a catalytic nucleophile. Moreover, crystallographic structural analysis of isomaltase predicts that another aspartic acid residue functions as a proton donor in hydrolysis. Here, we mutagenized the predicted proton donor residues and the nucleophilic catalyst residues in each SI subunit. We expressed these SI variants in COS-1 cells and analyzed their structural, transport, and functional characteristics. All of the mutants revealed expression levels and maturation rates comparable with those of the wild-type species and the corresponding nonmutated subunits were functionally active. Thereby we determined rate and substrate specificity for each single subunit without influence from the other subunit. This approach provides a model for functional analysis of the single subunits within a multidomain protein, achieved without the necessity to express the individual subunits separately. Of note, we also found that glucose product inhibition regulates the activities of both SI subunits. We experimentally confirmed the catalytic function of the predicted proton donor residues, and sequence analysis suggested that these residues are located in a consensus region in many GH31 family members. In summary, these findings reveal the kinetic features specific for each human SI subunit and demonstrate that the activities of these subunits are regulated via product inhibition.

Use of the Biphasic (13)C-Sucrose/Glucose Breath Test to Assess Sucrose Maldigestion in Adults with Functional Bowel Disorders

Sucrase insufficiency has been observed in children with of functional bowel disorders (FBD) and symptoms of dietary carbohydrate intolerance may be indistinguishable from those of FBD. A two-phase (13)C-sucrose/(13)C-glucose breath test ((13)C-S/GBT) was used to assess sucrase activity because disaccharidase assays are seldom performed in adults. When (13)C-sucrose is hydrolyzed to liberate monosaccharides, oxidation to (13)CO2 is a proportional indicator of sucrase activity. Subsequently, (13)C-glucose oxidation rate was determined after a secondary substrate ingestion (superdose) to adjust for individual habitus effects (Phase II). (13)CO2 enrichment recovery ratio from (13)C-sucrose and secondary (13)C-glucose loads reflect the individualized sucrase activity [Coefficient of Glucose Oxidation for Sucrose (CGO-S)]. To determine if sucrase insufficiency could be a factor in FBD, (13)C-S/GBT was validated using subjects with known sucrase gene mutation status by comparing (13)CO2-breath enrichment with plasma (13)C-glucose enrichment. (13)C-S/GBT was used to assess sucrose digestion in FBD patients and asymptomatic controls. (13)CO2-breath enrichment correlated with the appearance of (13)C-sucrose-derived glucose in plasma (r (2) = 0.80). Mean, control group CGO-S-enrichment outcomes were 1.01 at 60', 0.92 at 75', and 0.96 at mean 60'-75' with normal CGO-S defined as >0.85 (95% C.I.). In contrast, FBD patients demonstrated lower CGO-S values of 0.77 at 60', 0.77 at 75', and 0.76 at mean 60'-75' (Chi Square: 6.55; p < 0.01), which points to sucrose maldigestion as a cause of FBD.

Diagnosing and Treating Intolerance to Carbohydrates in Children

Intolerance to carbohydrates is relatively common in childhood, but still poorly recognized and managed. Over recent years it has come to the forefront because of progresses in our knowledge on the mechanisms and treatment of these conditions. Children with intolerance to carbohydrates often present with unexplained signs and symptoms. Here, we examine the most up-to-date research on these intolerances, discuss controversies relating to the diagnostic approach, including the role of molecular analysis, and provide new insights into modern management in the pediatric age, including the most recent evidence for correct dietary treatment.

The clinical consequences of sucrase-isomaltase deficiency

Primary sucrase-isomaltase deficiency, originally thought to be a homozygous recessive disorder, has been found to have numerous genetic variants that alone or in combination (compound heterozygosity) express varying degrees of clinical illness, most commonly causing chronic diarrhea, abdominal pain, and bloating. These symptoms are also present with secondary sucrase-isomaltase deficiency. Recent investigations are providing evidence that sucrase-isomaltase deficiency is more prevalent and of greater clinical significance than previously suspected. Further research is required to correlate the specific genotypes and phenotypes with their clinical expressions and to determine the most appropriate treatment algorithm for these patients.

Congenital sucrase-isomaltase deficiency: diagnostic challenges and response to enzyme replacement therapy

Congenital sucrase-isomaltase (SI) deficiency is a rare genetic condition characterised by a deficiency in the brush-border SI enzyme, resulting in an inability to metabolise sucrose and starches. Six cases of congenital SI deficiency treated with Sucraid (sacrosidase, a yeast-derived enzyme that facilitates sucrose digestion) are described. Typical presenting symptoms were watery diarrhoea, abdominal pain and bloating, sometimes noticeably worse after ingestion of fruit. Diagnosis is challenging since conventional hydrogen breath testing after an oral sucrose load is impractical in young children, and many laboratories no longer look for maldigested sucrose using faecal sugar chromatography. Confirmation is by disaccharidase assay of duodenal or jejunal mucosa obtained endoscopically. All six patients showed little improvement following advice regarding dietary management, but experienced a marked reduction in symptoms with sacrosidase administration; no adverse events were reported. Sacrosidase is an effective and well-tolerated treatment for patients with congenital SI deficiency. Gene testing and clinical trial of sacrosidase may become an alternative to endoscopic biopsies for diagnosis.

Glucose absorption in small intestinal diseases

Recent developments in the field of diabetes and obesity management have established the central role of the gut in glucose homeostasis; not only is the gut the primary absorptive site, but it also triggers neurohumoral feedback responses that regulate the pre- and post-absorptive phases of glucose metabolism. Structural and/or functional disorders of the intestine have the capacity to enhance (e.g.: diabetes) or inhibit (e.g.: short-gut syndrome, critical illness) glucose absorption, with potentially detrimental outcomes. In this review, we first describe the normal physiology of glucose absorption and outline the methods by which it can be quantified. Then we focus on the structural and functional changes in the small intestine associated with obesity, critical illness, short gut syndrome and other malabsorptive states, and particularly Type 2 diabetes, which can impact upon carbohydrate absorption and overall glucose homeostasis.

Congenital sucrase-isomaltase deficiency: an under-diagnosed disease in Chinese children

Background

Congenital sucrase-isomaltase deficiency (CSID) is a rare genetic disorder. The prevalence of CSID in Chinese population is unknown and no single case has been reported.

Methods

Sucrose tolerance tests were performed in three children suspected of CSID. Glucose tolerance tests were performed to exclude glucose malabsorption. Blood glucose was measured at fasting and at 30 min, 60 min, 120 min, and 180 min of the study. Gastrointestinal symptoms were recorded up to 4 hours after the study.

Results

From December 2008 to June 2011, three children, ranging from 16 to 19 months old, were referred to our tertiary children’s hospital due to chronic watery diarrhea and failure to thrive. Laboratory investigations including complete blood counts, ESR, CRP, and serum immunoglobulins were normal. Routine stool culture for bacteria and exam for parasites were negative. Upper endoscopy, colonoscopy and histology were unremarkable. All children failed lactose-free and amino acid-based formulas. All three children had flat sucrose tolerance tests and began to have watery stool 2–4 hours after feeding sucrose test solution. The glucose tolerance tests were normal and no children developed watery stools up to 4 hours after feeding glucose test solution.

Conclusions

This is the first case series of CSID in Chinese children. The diagnosis of CSID can be made based on clinical suspicion and sucrose tolerance test. CSID is probably an under-diagnosed or misdiagnosed disease in Chinese children and should be considered in children with chronic watery diarrhea.

An apparent homozygous deletion in maltase-glucoamylase, a lesson in the evolution of SNP arrays

Single nucleotide polymorphism (SNP) arrays possess clinical potential due to their high throughput capacity, sensitivity and versatility. We used such an array to perform a genome-wide SNP analysis of a patient with a multi-system undiagnosed disease involving peripheral neuropathies and food intolerances. The patient had a homozygous deletion within the gene encoding maltase-glucoamylase (MGAM), an intestinal starch digestion enzyme, predicting absence of enzyme activity and potential starch indigestion. We then performed validation testing using a functional MGAM analysis that involved starch ingestion followed by measuring blood glucose and insulin levels as well as hydrogen breath levels. Gastrointestinal tissue was also obtained via endoscopy and immunohistochemical staining for intestinal MGAM was performed. Our results strongly suggest the presence and functioning of MGAM which disproved deficiency predictions based on SNP array analysis findings, classifying the deletion as a functional polymorphism. This study highlights a current clinical limitation of SNP arrays, i.e., distinguishing deleterious genomic alterations from misleading functional polymorphisms. We conclude that novel findings from SNP arrays should be clinically validated and published.