Many Patients With Irritable Bowel Syndrome Have Atypical Food Allergies Not Associated With Immunoglobulin E.

BACKGROUND & AIMS: Confocal laser endomicroscopy (CLE) is a technique that permits real-time detection and quantification of changes in intestinal tissues and cells, including increases in intraepithelial lymphocytes and fluid extravasation through epithelial leaks. Using CLE analysis of patients with irritable bowel syndrome (IBS), we found that more than half have responses to specific food components. Exclusion of the defined food led to long-term symptom relief. We used the results of CLE to detect reactions to food in a larger patient population and analyzed duodenal biopsy samples and fluid from patients to investigate mechanisms of these reactions. METHODS: In a prospective study, 155 patients with IBS received 4 challenges with each of 4 common food components via the endoscope, followed by CLE, at a tertiary medical center. Classical food allergies were excluded by negative results from immunoglobulin E serology analysis and skin tests for common food antigens. Duodenal biopsy samples and fluid were collected 2 weeks before and immediately after CLE and were analyzed by histology, immunohistochemistry, reverse transcription polymerase chain reaction, and immunoblots. Results from patients who had a response to food during CLE (CLE+) were compared with results from patients who did not have a reaction during CLE (CLE-) or healthy individuals (controls). RESULTS: Of the 108 patients who completed the study, 76 were CLE+ (70%), and 46 of these (61%) reacted to wheat. CLE+ patients had a 4-fold increase in prevalence of atopic disorders compared with controls (P = .001). Numbers of intraepithelial lymphocytes were significantly higher in duodenal biopsy samples from CLE+ vs CLE- patients or controls (P = .001). Expression of claudin-2 increased from crypt to villus tip (P < .001) and was up-regulated in CLE+ patients compared with CLE- patients or controls (P = .023). Levels of occludin were lower in duodenal biopsy samples from CLE+ patients vs controls (P = .022) and were lowest in villus tips (P < .001). Levels of messenger RNAs encoding inflammatory cytokines were unchanged in duodenal tissues after CLE challenge, but eosinophil degranulation increased, and levels of eosinophilic cationic protein were higher in duodenal fluid from CLE+ patients than controls (P = .03). CONCLUSIONS: In a CLE analysis of patients with IBS, we found that more than 50% of patients could have nonclassical food allergy, with immediate disruption of the intestinal barrier upon exposure to food antigens. Duodenal tissues from patients with responses to food components during CLE had immediate increases in expression of claudin-2 and decreases in occludin. CLE+ patients also had increased eosinophil degranulation, indicating an atypical food allergy characterized by eosinophil activation.

Chapter 2. ESPGHAN: 50 Years Memories-The Early Years.

Thirty-six founding members from Europe were present in 1968, when the European Society of Paediatric Gastroenterology (ESGA) had its first meeting in Paris. The aim was to create a forum for presentations and discussions of research activities in paediatric gastroenterology in Europe. At the second meeting of ESGA 1969 in Interlaken, an important landmark was set for all gastroenterologists in the world. In this conference, the first ever criteria for "the Diagnosis of Coeliac Disease" (CD) were established. In 1990, the revised criteria for the diagnosis of CD were published. After the introduction of new noninvasive techniques, like tissue transglutaminase 2-antibodies and the HLADQ2/HLADQ8 determinations in blood, "new" criteria for the diagnosis of CD were published in 2012 by the European society of Paediatric Gastroenterology, Hepatology and Nutrition (ESPGHAN). Close collaboration of ESPGHAN and the North American Society of Paediatric Gastroenterology, Hepatology and Nutrition led to mutual meetings. The first combined meeting was 1978 in Paris, followed by meetings in New York, Amsterdam, Houston, and last in Toulouse. The first World Congress of Paediatric Gastroenterology took place in Boston 2000 followed by congresses in Paris, Iguazu, Taipeh, and Toronto. The creation of specialised committees (Nutrition Committees, GI-Committee, and Hepatology-Committee) enabled the society to elaborate numerous guidelines for standards in the diagnosis and treatment of diseases within the subspecialties. The Journal of Paediatric Gastroenterology and Nutrition, as organ of ESPGHAN and the North American Society of Paediatric Gastroenterology, Hepatology and Nutrition since 1991, serves as the voice for these worldwide accepted guidelines. Growing educational activities with summer schools, the Young Investigator Forum and the creation of working groups have distributed our current knowledge among the younger generation and led to fruitful reports, guidelines, and syllabus. In 1992, ESPGHAN was 1 of the founding 7 members of the United European Gastroenterology Federation (UEGF), which developed into a successful organisation for gastroenterology in Europe. This year we celebrate the 50th anniversary of ESPGHAN at our annual Meeting in Geneva.

Chapter 8. 50 Years of the European Society for Paediatric Gastroenterology, Hepatology and Nutrition (ESPGHAN): Captivating Witness Reports of a Success Story.

Since the conception of an idea of a few paediatric gastroenterologists in Europe to create a society for Paediatric Gastroenterology in 1967, and its foundation in 1968, half a century has passed. The European Society for Paediatric Gastroenterology, Hepatology and Nutrition (ESPGHAN) now celebrates its 50th anniversary and its utmost success in combining clinical and scientific expertise in the fields of paediatric gastroenterology, haepatology, and nutrition. To describe this success story 14 of the still living presidents of ESPGHAN recount their impressions of the steady growth of ESPGHAN with all the historical facets from their own points of view. This historical view of ESPGHAN over the last 5 decades provides personal accounts of the development of all activities and creations of this great European Society. The Society started as a small family of experts in the field into a global working open society involved in a large variety of activities within the subspecialties, becoming a leading organisation in Europe and beyond. This unique view gives also a wonderful insight into the famous clinicians and researchers from all over Europe who have helped in the growth and development of ESPGHAN. By describing all these activities and collaborations it becomes clear that this astonishing pan-European enterprise was achieved by people who put considerable effort and time into the development of this society. Their statements serve as a historical source and reference for future evaluation of the first 50 years of ESPGHAN. In depicting different time episodes, and by assembling all the historical pieces of a puzzle together, the statements help to illustrate how a highly structured society such as ESPGHAN has evolved over the last 50 years, for what it stands for today and what is to be expected in the future.

Confocal endomicroscopy shows food-associated changes in the intestinal mucosa of patients with irritable bowel syndrome.

BACKGROUND & AIMS: We investigated suspected food intolerances in patients with irritable bowel syndrome (IBS) using confocal laser endomicroscopy (CLE) for real-time visualization of structural/functional changes in the intestinal mucosa after food challenge. Patients with functional changes after food challenge (CLE+) were placed on personalized exclusion diets and followed up for long-term symptom relief. METHODS: Thirty-six IBS patients with suspected food intolerance and 10 patients with Barrett's esophagus (controls) without IBS symptoms were examined by CLE at University Hospital Schleswig-Holstein (Kiel, Germany). Diluted food antigens were administered directly to the duodenal mucosa through the working channel of the endoscope. Epithelial breaks, intervillous spaces, and the number of intraepithelial lymphocytes (IEL) were measured before and after the food challenge. CLE+ patients were placed on exclusion diets, given symptom score questionnaires, and followed up for 1 year; controls resumed their previous diet. RESULTS: CLE showed a real-time response to food antigens in 22 of 36 patients; no responses were observed in 14 of 36 patients (CLE-) or any of the controls. Baseline IELs were significantly higher in CLE+ than CLE- subjects (P = .004); numbers increased significantly after food challenge (P = .0008). Within 5 minutes of exposure of CLE+ patients to food antigens, IELs increased, epithelial leaks/gaps formed, and intervillous spaces widened. Epithelial leaks and intervillous spaces also increased significantly in CLE+ vs baseline (both P < .001). The concordance of IELs measured by CLE and conventional histology was 70.6%; they did not correlate (P = .89; r(2) = 0.027). Symptom scores improved more than 50% in CLE+ patients after a 4-week exclusion diet and increased to 74% at 12 months; symptoms continued in CLE- patients. CONCLUSIONS: Based on CLE analysis of IBS patients with a suspected food intolerance, exposure to candidate food antigens caused immediate breaks, increased intervillous spaces, and increased IELs in the intestinal mucosa. These changes are associated with patient responses to exclusion diets. Registered at clinicaltrials.gov (registration number: NCT01692613).

The London Classification of gastrointestinal neuromuscular pathology: report on behalf of the Gastro 2009 International Working Group.

OBJECTIVE: Guidelines on histopathological techniques and reporting for adult and paediatric gastrointestinal neuromuscular pathology have been produced recently by an international working group (IWG). These addressed the important but relatively neglected areas of histopathological practice of the general pathologist, including suction rectal biopsy and full-thickness intestinal tissue. Recommendations were presented for the indications, safe acquisition of tissue, histological techniques, reporting and referral of such histological material. DESIGN: Consensual processes undertaken by the IWG and following established guideline decision group methodologies. RESULTS AND CONCLUSION: This report presents a contemporary and structured classification of gastrointestinal neuromuscular pathology based on defined histopathological criteria derived from the existing guidelines. In recognition of its origins and first presentation in London at the World Congress of Gastroenterology 2009, this has been named 'The London Classification'. The implementation of this classification should allow some diagnostic standardisation, but should necessarily be viewed as a starting point for future modification as new data become available.

Lymphocytic leiomyositis and myenteric ganglionitis are intrinsic features of cystic fibrosis: studies in distal intestinal obstruction syndrome and meconium ileus.

BACKGROUND: Cystic fibrosis (CF) is a multisystem disorder intrinsically associated with inflammation of mucosal surfaces. Because inflammation can result in enteric neuromuscular dysfunction we hypothesized that terminal ileitis in patients with CF may predispose to distal ileal obstruction syndrome (DIOS). METHODS AND PATIENTS: Full-thickness terminal ileal tissues from 6 children with CF and severe DIOS, 6 infants with complicated meconium ileus (MI), and 6 children with non-CF intestinal atresia were studied. RESULTS: Lymphocyte-predominant mucosal and transmural ileal inflammation was present in 6 of 6 patients with DIOS. Lymphocytic ganglionitis was present in 4 of 6 although numbers of myenteric neurons were not decreased (5/5). Myocyte proteins were preserved (6/6). Mild submucosal fibrosis was common in DIOS (5/6) and transformation of submucosal fibroblasts to a myofibroblastic phenotype was noted in 4 of 6. Inflammatory changes were distinct from those described in fibrosing colonopathy. Antroduodenal manometry in an individual who had experienced MI/DIOS was consistent with a neuropathic pseudo-obstructive process. Submucosal or transmural lymphocyte predominant inflammation was also present in 6 of 6 infants with complicated MI, which, when coupled with submucosal myofibroblast proliferation (5/6), appeared highly predictive of CF rather than non-CF atresia. Histological findings at birth were similar, although milder, than those seen in DIOS, suggesting that these changes are a primary abnormality in CF. CONCLUSIONS: Submucosal or transmural inflammation of the ileum is common in newborns with CF and MI and older children with DIOS. Severe recurrent DIOS should be investigated with seromuscular and mucosal biopsy of the ileum to seek a transmural ileitis potentially amenable to anti-inflammatory therapies.

Gastrointestinal neuromuscular pathology: guidelines for histological techniques and reporting on behalf of the Gastro 2009 International Working Group.

The term gastrointestinal neuromuscular disease describes a clinically heterogeneous group of disorders of children and adults in which symptoms are presumed or proven to arise as a result of neuromuscular, including interstitial cell of Cajal, dysfunction. Such disorders commonly have impaired motor activity, i.e. slowed or obstructed transit with radiological evidence of transient or persistent visceral dilatation. Whilst sensorimotor abnormalities have been demonstrated by a variety of methods in these conditions, standards for histopathological reporting remain relatively neglected. Significant differences in methodologies and expertise continue to confound the reliable delineation of normality and specificity of particular pathological changes for disease. Such issues require urgent clarification to standardize acquisition and handling of tissue specimens, interpretation of findings and make informed decisions on risk-benefit of full-thickness tissue biopsy of bowel or other diagnostic procedures. Such information will also allow increased certainty of diagnosis, facilitating factual discussion between patients and caregivers, as well as giving prognostic and therapeutic information. The following report, produced by an international working group, using established consensus methodology, presents proposed guidelines on histological techniques and reporting for adult and paediatric gastrointestinal neuromuscular pathology. The report addresses the main areas of histopathological practice as confronted by the pathologist, including suction rectal biopsy and full-thickness tissue obtained with diagnostic or therapeutic intent. For each, indications, safe acquisition of tissue, histological techniques, reporting and referral recommendations are presented.

Advances in understanding colonic function.

The colon is an organ of conservation that salvages water, electrolytes, and energy. The organization of colonic function is determined by the roles played by the luminal flora, the function of the different mucosal epithelial cell types, immunocompetent cells, and the neuromusculature. These different components of the colon interact with one another and with the colonic flora, and different areas of the colon serve different functions. In the normal adult during the course of a day the colon absorbs approximately 1.5 L of fluid, but under the influence of aldosterone increases up to 5 to 6 L. Diarrhoea occurs when secretion exceeds absorptive processes by either small intestinal secretion overwhelming colonic salvage or salvage being impaired by reduced colonic absorption or increased colonic secretion.

Mast cell-nerve interactions in children with functional dyspepsia.

BACKGROUND AND AIMS: Functional dyspepsia in childhood is commonly triggered by food allergen in sensitised individuals. We investigated the topography of eosinophils and mast cells in gastric antral lamina propria, the interaction of mast cell products with mucosal nerve fibres, and changes in gastric antral muscle slow wave activity in children with atopy and non-atopy-related functional dyspepsia. PATIENTS AND METHODS: Open label study of gastric mucosal cow's milk challenge in 10 atopic and 6 nonatopic children (ages 2-12 years) investigated consecutively with gastroscopy for functional dyspepsia. Simultaneous surface electrogastrography and milk challenge were undertaken and laser scanning fluorescence microscopy used to examine the association of mast cell tryptase with mucosal nerves in the gastric mucosa before and after challenge. RESULTS: Eosinophils and mast cells within the lamina propria were increased in number in children with atopic functional dyspepsia and degranulated rapidly after cow's milk challenge in the atopic group. For degranulating eosinophils, median = 13.0% (interquartile range = 3.7-31.0) premilk versus 32.0% (12.0-42.0) after milk biopsies (P < 0.05); for degranulating mast cells, 5.35% (2.7-10.9) premilk biopsies versus 18.75% (12.9-22.1) after milk biopsies (P < 0.05). No such differences were seen in nonatopic patients. Mast cells were closely associated with mucosal nerve fibres and released tryptase, which colocalised with proteinase-activated receptors on mucosal nerve fibres. The gastric antral slow wave became abnormal within 2 minutes of antigen challenge in atopics with an increase in dominant frequency instability coefficient (P < 0.005), decrease in 3 cycles per minute myoelectrical activity (P < 0.01), and increase in bradygastria (P < 0.01). CONCLUSIONS: Early-onset neuroimmune interactions induced by cow's milk in the gastric mucosa of atopic children are associated with rapid disturbance of gastric myoelectrical activity and dyspeptic symptoms.

Treatment of intractable ulcerating enterocolitis of infancy by allogeneic bone marrow transplantation.

BACKGROUND & AIMS: Intractable ulcerating enterocolitis of infancy (IE) is an uncommon, autosomal-recessive, and devastating inflammatory bowel disorder that arises as a consequence of a poorly defined underlying immunologic disorder. Infants with IE suffer from recurrent severe oro-anal disease and an enterocolitis that is unresponsive to conventional immunosuppressive therapy and requires early pancolectomy to control the severity of the disease. Despite such aggressive treatment these individuals remain at high risk of Epstein-Barr virus-driven lymphomatous proliferations, including non-Hodgkin's lymphoma. The underlying genetic basis for this disease remains undefined. This report aims to describe the use of bone marrow transplantation as a treatment for this condition. METHODS: This was a case series report. RESULTS: We describe the successful treatment of IE by allogeneic bone marrow transplantation in 2 brothers, now aged 7 and 11 years, one of whom had developed an Epstein-Barr virus-related monomorphous B-lymphocyte lymphoproliferative disorder. This treatment has resulted in prolonged clinical remission in both boys and abrogated the need for aggressive immunosuppression. CONCLUSIONS: Bone marrow transplantation can be used for the treatment of intractable ulcerating enterocolitis of infancy, which may support a role in other intractable inflammatory bowel conditions in the pediatric population.

Filamin A is mutated in X-linked chronic idiopathic intestinal pseudo-obstruction with central nervous system involvement.

We have previously reported that an X-linked recessive form of chronic idiopathic intestinal pseudo-obstruction (CIIPX) maps to Xq28. To select candidate genes for the disease, we analyzed the expression in murine fetal brain and intestine of 56 genes from the critical region. We selected and sequenced seven genes and found that one affected male from a large CIIPX-affected kindred bears a 2-bp deletion in exon 2 of the FLNA gene that is present at the heterozygous state in the carrier females of the family. The frameshift mutation is located between two close methionines at the filamin N terminus and is predicted to produce a protein truncated shortly after the first predicted methionine. Loss-of-function FLNA mutations have been associated with X-linked dominant nodular ventricular heterotopia (PVNH), a central nervous system (CNS) migration defect that presents with seizures in females and lethality in males. Notably, the affected male bearing the FLNA deletion had signs of CNS involvement and potentially has PVNH. To understand how the severe frameshift mutation we found can explain the CIIPX phenotype and its X-linked recessive inheritance, we transiently expressed both the wild- type and mutant filamin in cell culture and found that filamin translation can start from either of the two initial methionines in these conditions. Therefore, translation of a normal shorter filamin can occur in vitro from the second methionine downstream of the 2-bp insertion we found. We confirmed this, demonstrating that the filamin protein is present in the patient's lymphoblastoid cell line that shows abnormal cytoskeletal actin organization compared with normal lymphoblasts. We conclude that the filamin N terminal region between the initial two methionines is crucial for proper enteric neuron development.

Transition from parenteral to enteral nutrition.

Children are unique as their food intake must provide sufficient nutrients not only for the maintenance of body tissues but also for growth. Improvements in techniques for nutritional support has resulted in very long term parenteral nutrition being available for those with chronic intestinal failure in addition to those who require short term parenteral feeding either following surgery or whilst treatment for an underlying enteric disease becomes effective. Parenteral nutrition is required whenever insufficient nutrients cannot be provided enterally to prevent or correct malnutrition or to sustain appropriate growth. Somatic growth is fastest in infancy and puberty but other organs such as the brain may only grow and differentiate at one particular time. When a period of more liberal feeding intervenes catch-up of growth and function occurs. In adolescence the risk is of not achieving growth potential. Timing and methods of weaning from parenteral to normal nutrition remain controversial. In infants and children it is essential to consider carefully whether gastrointestinal function is sufficient for enteral nutrition to adequately support them. Thus the time when the infant and child can be weaned from parenteral nutrition will depend both on the activity of the underlying disease and the age and size of the infant or child.

Childhood functional gastrointestinal disorders: neonate/toddler.

Recognizing the importance of childhood functional gastrointestinal disorders in understanding adult functional gastrointestinal disorders, and encouraging clinical and research interest, the Rome Coordinating Committee added a pediatric working team to Rome II in 1999. For Rome III, there was an increase from 1 to 2 pediatric working teams. This report summarizes the current consensus concerning functional disorders in infants and toddlers. Another report covers disorders diagnosed more often in school-aged children and adolescents. The symptoms from functional gastrointestinal disorders in children younger than 5 years depend on maturational factors in anatomy, gastrointestinal physiology, and intellectual and affective functioning. There has been little or no change for infant regurgitation, infant rumination syndrome, or infant dyschezia. Cyclic vomiting syndrome may be diagnosed after 2 rather than 3 episodes. The description of infant colic has been expanded, although there was consensus that infant colic does not reflect gastrointestinal malfunction. The greatest change was in functional constipation. Functional constipation and functional fecal retention in the 1999 report were merged into a single entity: functional constipation. Data-driven changes in diagnostic criteria for functional constipation appear to be less rigid and more inclusive than previous criteria.

Long-term outcome of intractable ulcerating enterocolitis of infancy.

BACKGROUND: Chronic enterocolitis is rare in infancy and accounts for less than 0.5% of all newly diagnosed inflammatory bowel disease (IBD) in the UK. Presentation at this young age is usually indicative of underlying immunodeficiency/immunodysregulation. A group of such infants suffer intractable ulcerating enterocolitis of infancy (IE) in which there is a pan-enteritis with marked oro-anal involvement and deep flask like mucosal ulcers throughout the colon. METHODS: Retrospective review of presenting features, treatment and long-term outcome in a series of 8 children with typical IE. RESULTS: The 8 children were aged between 1 and 4 weeks at onset (median 2 weeks, mean 2.3 weeks), of which 7 were followed up for 2-22 years (median 7.5 years, mean 11 years). All 8 children had an intractable disease course requiring a colectomy for control of symptoms. The median age at colectomy was 1.7 years (range 4 months-4 years). Three children developed a generalised lymphadenopathy due to uncontrolled EBV-related lymphoid proliferations (ages 4, 12, 18). These comprised a monomorphous B-lymphoycte lympho-proliferative disorder, a large pleomorphic follicular lymphoma, and a high grade pleomorphic B cell non-Hodgkin's lymphoma. CONCLUSIONS: Infants with IE have a high risk of developing lymphomatous proliferations that appears to be related to the underlying immunodysregulation. Use of aggressive immunosuppression and acquisition of EBV infection appears to accelerate this process; hence we advocate early colectomy in confirmed cases. In children with IE screening for EBV and vigilance for abnormal lymphoid proliferations is paramount.

Hepatic nervous system development.

During embryonic development, the liver emerges from the foregut as a thickening of the ventral endodermal epithelium. The embryonic liver then develops into a bud of cells that proliferates and differentiates to eventually form the largest gland of the body. Prior to birth, the primary function of the liver is hematopoietic, and the organ receives little innervation during early development. Postnatally, the role of the liver changes and many different nerve types modulate its function. Although the liver shares a common embryonic origin with other foregut derivatives, such as the gallbladder and the pancreas, the development of its innervation exhibits distinct characteristics. In this review, we summarize what is known about the development of the hepatic innervation, draw comparisons with the intrinsic innervation of the gastrointestinal tract and associated organs, and discuss the potential role of molecular signals in guiding the nerves that innervate the liver.

Programming of defective rat pancreatic beta-cell function in offspring from mothers fed a low-protein diet during gestation and the suckling periods.

Poor fetal and infant nutrition has been linked to impaired glucose tolerance in later life. We studied the effect of protein deficiency during gestation and the suckling period in a rat model and found that poor nutrition 'programmes' pancreatic beta-cell GK (glucokinase; known as the glucose sensor) and glucose-stimulated insulin secretion response in newborn, suckling and adult rat offspring. Pregnant female rats were divided into three groups: a control group was kept on a normal protein (20%) diet, another group was fed a low-protein (LP) (6%) diet during gestation and suckling periods (LP-G + S group) and another was fed a LP diet during gestation then a normal protein diet during the suckling period (LP-G group). The pulsatile glucose-stimulated insulin secretion response was acutely disrupted and the peak insulin secretion was markedly decreased in newborn and 3-week-old offspring of the LP-G + S group compared with the control group. Also, there was an altered pulsatile secretory response in adults of the LP-G + S and 3-week-old and adult offspring of the LP-G groups compared with the control group. GK protein levels, detected by Western blotting, were decreased in newborn and 3-week-old offspring of both LP-G + S and LP-G groups compared with the control groups. The Km and Vmax of GK were altered. The prenatal and postnatal LP diet appeared to have a permanent effect in increasing the affinity of GK for glucose (indicated by decreased Km values) and decreasing the Vmax. This showed that the critical period of programming of the function of GK was after birth and during the postnatal weaning period, since the adult offspring of the LP-G + S group when fed a normal protein diet showed no reversal in the Km values of the enzyme. Similar experiments in adult offspring of the LP-G group showed normalization of the Km values of GK at 3 weeks of age. In conclusion, fetal and infantile nutrition 'programmes' pancreatic beta-cell function; poor nutrition during this period caused irreversible effects on glucose homoeostatic mechanisms in the offspring, which may predispose the offspring to diabetes in later life.

Small-intestinal dysfunction accompanies the complex endocrinopathy of human proprotein convertase 1 deficiency.

We have previously described the only reported case of human proprotein convertase 1 (PC1) deficiency, in a female (Subject A) with obesity, hypogonadism, hypoadrenalism, and reactive hypoglycemia. We now report the second case of human PC1 deficiency (Subject B), also due to compound heterozygosity for novel missense and nonsense mutations. While both subjects shared the phenotypes of obesity, hypoadrenalism, reactive hypoglycemia, and elevated circulating levels of certain prohormones, the clinical presentation of Subject B was dominated by severe refractory neonatal diarrhea, malabsorptive in type. Subsequent investigation of Subject A revealed marked small-intestinal absorptive dysfunction, which was not previously clinically suspected. We postulate that PC1, presumably in the enteroendocrine cells, is essential for the normal absorptive function of the human small intestine. The differences in the nature and severity of presentation between the two cases cannot readily be explained on the basis of allelic heterogeneity, as the nonsense and missense mutations from both subjects had comparably severe effects on the catalytic activity of PC1. Despite Subject A's negligible PC1 activity, some mature ACTH and glucagon-like peptide 17-36(amide) were detectable in her plasma, suggesting that the production of these hormones, at least in humans, does not have an absolute dependence on PC1. The presence of severe obesity and the absence of growth retardation in both subjects contrast markedly with the phenotype of mice lacking PC1 and suggest that the precise physiological repertoire of this enzyme may vary between mammalian species.