Neonatal enteropathies: defining the causes of protracted diarrhea of infancy

Approach to Congenital Diarrhea and Enteropathies (CODEs)

Congenital diarrhea and enteropathies (CODEs) constitute a group of rare genetic disorders characterized by severe diarrhea and malabsorption in the neonatal period or early infancy. Timely diagnosis and treatment is essential to prevent life-threatening complications, including dehydration, electrolyte imbalance, and malnutrition. This review offers a simplified approach to the diagnosis of CODEs, with a specific focus on microvillus inclusion disease (MVID), congenital tufting enteropathy (CTE), congenital chloride diarrhea (CLD), and congenital sodium diarrhea (CSD). Patients with CODEs typically present with severe watery or occasionally bloody diarrhea, steatorrhea, dehydration, poor growth, and developmental delay. Therefore, it is crucial to thoroughly evaluate infants with diarrhea to rule out infectious, allergic, or anatomical causes before considering CODEs as the underlying etiology. Diagnostic investigations for CODEs encompass various modalities, including stool tests, blood tests, immunological studies, endoscopy and biopsies for histology and electron microscopy, and next-generation sequencing (NGS). NGS plays a pivotal role in identifying the genetic mutations responsible for CODEs. Treatment options for CODEs are limited, often relying on total parenteral nutrition for hydration and nutritional support. In severe cases, intestinal transplantation may be considered. The long-term prognosis varies among specific CODEs, with some patients experiencing ongoing intestinal failure and associated complications. In conclusion, the early recognition and accurate diagnosis of CODEs are of paramount importance for implementing appropriate management strategies. Further research and advancements in genetic testing hold promise for enhancing diagnostic accuracy and exploring potential targeted therapies for these rare genetic disorders.

Homozygous Missense Epithelial Cell Adhesion Molecule Variant in a Patient with Congenital Tufting Enteropathy and Literature Review

Congenital diarrheal disorders (CDDs) with genetic etiology are uncommon hereditary intestinal diseases characterized by chronic, life-threatening, intractable watery diarrhea that starts in infancy. CDDs can be mechanistically divided into osmotic and secretory diarrhea. Congenital tufting enteropathy (CTE), also known as intestinal epithelial dysplasia, is a type of secretory CDD. CTE is a rare autosomal recessive enteropathy that presents with intractable neonatal-onset diarrhea, intestinal failure, severe malnutrition, and parenteral nutrition dependence. Villous atrophy of the intestinal epithelium, crypt hyperplasia, and irregularity of surface enterocytes are the specific pathological findings of CTE. The small intestine and occasionally the colonic mucosa include focal epithelial tufts. In 2008, Sivagnanam et al. discovered that mutations in the epithelial cell adhesion molecule (EpCAM, MIM# 185535) were the genetic cause of CTE (MIM# 613217). More than a hundred mutations have been reported to date. Furthermore, mutations in the serine peptidase inhibitor Kunitz type 2 (SPINT2, MIM# 605124) have been linked to syndromic CTE. In this study, we report the case of a 17-month-old male infant with congenital diarrhea. Despite extensive etiological workup, no etiology could be established before admission to our center. The patient died 15 hours after being admitted to our center in a metabolically decompensated state, probably due to a delay in admission and diagnosis. Molecular autopsy with exome sequencing revealed a previously reported homozygous missense variant, c.757G>A, in EpCAM, which was confirmed by histopathological examination.

Severe congenital diarrhea secondary to tufting enteropathy. Case report

Introduction: Tufting enteropathy is a rare cause of congenital diarrhea in neonates. It is characterized by the abnormal distribution of epithelial adhesion molecules, which causes enterocytes to shed into the lumen, forming the characteristic tufts. Case presentation: A 15-day-old female neonate was taken by her parents to the emergency department of a tertiary care hospital due to diarrheal stools she had been experiencing since birth. The patient presented with dehydration, abnormal weight loss, metabolic acidosis, and acute kidney failure. She received treatment with alizapride, loperamide, zinc sulfate, and probiotics, but after 75 days of treatment she was still symptomatic. An upper tract endoscopy and colonoscopy were performed, finding flattening of the villi and lymphoid cells in the lamina propria. However, the symptoms persisted, and she died at the age of ten months. A post-mortem exome sequencing reported tufting enteropathy. Conclusions. When congenital diarrhea is present, tufting enteropathy should be considered. An early molecular study would allow to evaluate the possibility of performing an intestinal transplant or modifying the treatment to meet the patient’s palliative care needs.

EPCAM and TROP2 share role in claudin stabilization and development of intestinal and extraintestinal epithelia in mice

EPCAM (Epithelial Cell Adhesion Molecule) is a transmembrane glycoprotein expressed on the surface of most epithelial and epithelium-derived tumor cells and reported to regulate stability of epithelial tight junction proteins, claudins. Despite its widespread expression, loss of EPCAM function has so far only been reported to prominently affect intestinal development, resulting in severe early onset enteropathy associated with impaired growth and decreased survival in both humans and mice. In this study, we show that the critical role of EPCAM is not limited to intestinal tissues and that it shares its essential function with its only known homolog, TROP2 (Trophoblast cell surface antigen 2). EPCAM-deficient mice show significant growth retardation and die within four weeks after birth. In addition to changes in small and large intestines, loss of EPCAM results in hyperkeratosis in skin and forestomach, hair follicle atrophy leading to alopecia, nephron hypoplasia in kidney, proteinuria, and altered production of digestive enzymes by pancreas. Expression of TROP2 partially, but not completely, overlaps with EPCAM in a number developing epithelia. Although loss of TROP2 had no gross impact on mouse development and survival, TROP2 deficiency generally compounded developmental defects observed in EPCAM-deficient mice, led to about 60% decrease in embryonic viability, and further shortened postnatal lifespan of born pups. Importantly, TROP2 was able to compensate for the loss of EPCAM in stabilizing claudin-7 expression and cell membrane localization in tissues that co-express both proteins. These findings identify overlapping functions of EPCAM and TROP2 as regulators of epithelial development in both intestinal and extraintestinal tissues.

Management of pediatric intestinal failure related to short bowel syndrome

Intestinal failure (IF) secondary to short bowel syndrome is a challenging and complex medical condition with significant risk for surgical and medical complications. Significant advancements in the care of this patient population have led to improved survival rates. Due to their intensive medical needs children with IF are at risk for long-term complications that require comprehensive management and close monitoring. The purpose of this paper is to review the available literature emphasizing the surgical aspects of care for children with IF secondary to short bowel syndrome. A key priority in the surgical care of this patient population includes strategies to preserve available bowel and maximize its function. Utilization of novel surgical techniques and autologous bowel reconstruction can have a significant impact on children with IF secondary to short bowel syndrome related to the function of their bowel and ability to achieve enteral autonomy. It is also important to understand the potential long-term complications to ensure strategies are put in place to mitigate risk with early detection to improve long-term outcomes.

SPI2 T3SS effectors facilitate enterocyte apical to basolateral transmigration of Salmonella-containing vacuoles in vivo

Salmonella pathogenicity island (SPI) 2 type three secretion system (T3SS)-mediated effector molecules facilitate bacterial survival in phagocytes but their role in the intestinal epithelium in vivo remains ill-defined. Using our neonatal murine infection model in combination with SPI2 reporter technology and RNA-Seq of sorted primary enterocytes, we demonstrate expression of SPI2 effector molecules by intraepithelial Salmonella Typhimurium (S. Typhimurium). Contrary to expectation, immunostaining revealed that infection with SPI2 T3SS-mutants resulted in significantly enlarged intraepithelial Salmonella-containing vacuoles (SCV) with altered cellular positioning, suggesting impaired apical to basolateral transmigration. Also, infection with isogenic tagged S. Typhimurium strains revealed a reduced spread of intraepithelial SPI2 T3SS mutant S. Typhimurium to systemic body sites. These results suggest that SPI2 T3SS effector molecules contribute to enterocyte apical to basolateral transmigration of the SCV during the early stage of the infection.

Diurnal changes in the murine small intestine are disrupted by obesogenic Western Diet feeding and microbial dysbiosis

Intestinal functions demonstrate circadian rhythms thought to be entrained, in part, by an organisms’ intrinsic feeding and fasting periods as well as by the intestinal microbiome. Circadian disruption as a result of ill-timed nutrient exposure and obesogenic feeding poses an increased risk to disease. As such, the aim of this study was to assess the relationships between dietary timing, composition, and the microbiome with regard to rhythmic small intestinal structure and mucosal immunity. Rodent chow (RC)-mice exhibited time-dependent increases in small intestinal weight, villus height, and crypt depth as well as an increased proportion of CD8αα⁺ cells and concomitant decrease in CD8αβ+ cells at the onset of the feeding period (p < 0.05–0.001). Western diet (WD)-animals displayed disrupted time-dependent patterns in intestinal structure and lymphocyte populations (p < 0.05–0.01). Antibiotic-induced microbial depletion abrogated the time- and diet-dependent patterns in both RC- and WD-mice (p < 0.05–0.001). However, although germ-free-mice displayed altered rhythms, fecal microbial transfer from RC-mice was generally unsuccessful in restoring structural and immune changes in these animals. This study shows that adaptive changes in the small intestine at the onset of the feeding and fasting periods are disrupted by WD-feeding, and that these changes are dependent, in part, on the intestinal microbiome.

Targeted HAI-2 deletion causes excessive proteolysis with prolonged active prostasin and depletion of HAI-1 monomer in intestinal but not epidermal epithelial cells

Mutations of SPINT2, the gene encoding the integral membrane, Kunitz-type serine inhibitor HAI-2, primarily affect the intestine, while sparing many other HAI-2-expressing tissues, causing sodium loss in patients with syndromic congenital sodium diarrhea. The membrane-bound serine protease prostasin was previously identified as a HAI-2 target protease in intestinal tissues but not in the skin. In both tissues, the highly related inhibitor HAI-1 is, however, the default inhibitor for prostasin and the type 2 transmembrane serine protease matriptase. This cell-type selective functional linkage may contribute to the organ-selective damage associated with SPINT 2 mutations. To this end, the impact of HAI-2 deletion on matriptase and prostasin proteolysis was, here, compared using Caco-2 human colorectal adenocarcinoma cells and HaCaT human keratinocytes. Greatly enhanced prostasin proteolytic activity with a prolonged half-life and significant depletion of HAI-1 monomer were observed with HAI-2 loss in Caco-2 cells but not HaCaT cells. The constitutive, high level prostasin zymogen activation observed in Caco-2 cells, but not in HaCaT cells, also contributes to the excessive prostasin proteolytic activity caused by HAI-2 loss. HAI-2 deletion also caused increased matriptase zymogen activation, likely as an indirect result of increased prostasin proteolysis. This increase in activated matriptase, however, only had a negligible role in depletion of HAI-1 monomer. Our study suggests that the constitutive, high level of prostasin zymogen activation and the cell-type selective functional relationship between HAI-2 and prostasin renders Caco-2 cells more susceptible than HaCaT cells to the loss of HAI-2, causing a severe imbalance favoring prostasin proteolysis.

Advanced Microscopy for Liver and Gut Ultrastructural Pathology in Patients with MVID and PFIC Caused by MYO5B Mutations

Mutations in the actin motor protein myosinVb (myo5b) cause aberrant apical cargo transport and the congenital enteropathy microvillus inclusion disease (MVID). Recently, missense mutations in myo5b were also associated with progressive familial intrahepatic cholestasis (MYO5B-PFIC). Here, we thoroughly characterized the ultrastructural and immuno-cytochemical phenotype of hepatocytes and duodenal enterocytes from a unique case of an adult MYO5B-PFIC patient who showed constant hepatopathy but only periodic enteric symptoms. Selected data from two other patients supported the findings. Advanced methods such as cryo-fixation, freeze-substitution, immuno-gold labeling, electron tomography and immuno-fluorescence microscopy complemented the standard procedures. Liver biopsies showed mislocalization of Rab11 and bile canalicular membrane proteins. Rab11-positive vesicles clustered around bile canaliculi and resembled subapical clusters of aberrant recycling endosomes in enterocytes from MVID patients. The adult patient studied in detail showed a severe, MVID-specific enterocyte phenotype, despite only a mild clinical intestinal presentation. This included mislocalization of numerous proteins essential for apical cargo transport and morphological alterations. We characterized the heterogeneous population of large catabolic organelles regarding their complex ultrastructure and differential distribution of autophagic and lysosomal marker proteins. Finally, we generated duodenal organoids/enteroids from biopsies that recapitulated all MVID hallmarks, demonstrating the potential of this disease model for personalized medicine.

EpCAM is essential for maintenance of the small intestinal epithelium architecture via regulation of the expression and localization of proteins that compose adherens junctions

Epithelial cell adhesion molecule (EpCAM) is highly expressed in mammalian intestines, and is essential for maintaining the homeostasis of the intestinal epithelium. EpCAM protein is localized at tight junctions and the basolateral membrane of the intestinal epithelium, where it interacts with many cell adhesion molecules. To explore the molecular functions of EpCAM in regulating adherens junctions in the intestinal epithelium, EpCAM knockout embryos and newborn pups were analyzed. Hematoxylin and eosin staining was used to assess the histology of the duodenum, jejunum, ileum and colon from wild-type and EpCAM^−/− mice at E18.5, P0 and P3. The expression and localization of adherens junction-associated genes and genes that encode the proteins that participate in the assembly of adherens junctions were measured at the mRNA and protein levels using qPCR, western blot analysis and immunofluorescence staining. The results showed that although there was no significant damage to the intestines of EpCAM^−/− mice at E18.5 and P0, they were significantly damaged at P3 in mutant mice. The expression of adherens junction-associated genes in EpCAM mutant mice was normal at the mRNA level from E18.5 to P3, but their protein levels were gradually reduced and mislocalized from E18.5 to P3. The expression of nectin 1, which can regulate the assembly and adhesion activity of E-cadherin, was also gradually reduced at both the mRNA and protein levels in the intestinal epithelium of EpCAM mutant mice from E18.5 to P3. In summary, the loss of EpCAM may cause the reduction and mislocalization of proteins that compose adherens junctions partly via the downregulation of nectin 1 in the intestines.

Intestinal Morphogenesis in Development, Regeneration, and Disease: The Potential Utility of Intestinal Organoids for Studying Compartmentalization of the Crypt-Villus Structure

The morphology and structure of the intestinal epithelium are rearranged dynamically during development, tissue regeneration, and disease progression. The most important characteristic of intestinal epithelial morphogenesis is the repetitive compartmentalized structures of crypt-villus units, which are crucial for maintaining intestinal homeostasis and functions. Abnormal structures are known to be closely associated with disease development and progression. Therefore, understanding how intestinal crypt-villus structures are formed and grown is essential for elucidating the physiological and pathophysiological roles of the intestinal epithelium. However, a critical knowledge gap in understanding the compartmentalization of the crypt-villus axis remains when using animal models, due to obvious inter-species differences and difficulty in real-time monitoring. Recently, emerging technologies such as organoid culture, lineage tracing, and single cell sequencing have enabled the assessment of the intrinsic mechanisms of intestinal epithelial morphogenesis. In this review, we discuss the latest research on the regulatory factors and signaling pathways that play a central role in the formation, maintenance, and regeneration of crypt-villus structures in the intestinal epithelium. Furthermore, we discuss how these factors and pathways play a role in development, tissue regeneration, and disease. We further explore how the current technology of three-dimensional intestinal organoids has contributed to the understanding of crypt-villus compartmentalization, highlighting new findings related to the self-organizing-process-driven initiation and propagation of crypt-villus structures. We also discuss intestinal diseases featuring abnormalities of the crypt-villus structure to provide insights for the development of novel therapeutic strategies targeting intestinal morphogenesis and crypt-villus formation.

Tufting Enteropathy: A Review of Clinical and Histological Presentation, Etiology, Management, and Outcome

Congenital tufting enteropathy (CTE), also named intestinal epithelial dysplasia, is a rare, autosomal recessive enteropathy with persistent and life-threatening intractable diarrhea early in life. Intractable diarrhea is present independent of breast or formula feeding. Most CTE patients require total parenteral nutrition (TPN), and in severe cases, small bowel transplantation is needed. In the last decade, we have seen remarkable progress in certain aspects, such as the pathogenesis and diagnostic methods of the disease. Rapidly developing molecular analysis techniques have improved the diagnostic methods for CTE and reduced invasive and expensive procedures. Mutations in the gene encoding human epithelial cell adhesion molecule (EpCAM) were identified in the typical form of CTE, which usually exhibits isolated refractory diarrhea. Moreover, the syndromic form of CTE features anal and choanal atresias as well as ophthalmologic signs, which are associated with mutations in the gene encoding Serine Peptidase Inhibitor Kunitz Type 2 (SPINT2). This article reviews CTE disease based on its clinical and histological presentation, etiology and pathogenesis, and management and outcome.

Challenges of Microvillus Inclusion Disease in the NICU

Mutations in the myosin 5β, syntaxin-binding protein 2, and syntaxin 3 genes lead to microvillus inclusion disease (MVID), an autosomal recessive congenital enteropathy. This rare disease is characterized by lack of microvilli on the surface of enterocytes in the small intestine, the presence of pathognomonic intracellular microvillus inclusions, and vesicular bodies within these enterocytes. This pathology leads to the characteristic intractable, life-threatening, watery diarrhea. In the more common early-onset form, affected patients present in the first few days after birth, whereas in the late-onset form, clinical manifestations appear at approximately 2 to 3 months of age. Genetic testing can confirm the diagnosis, but the infant's medical history, clinical presentation, and small intestinal biopsy results are strongly suggestive of the diagnosis. The prevalence of MVID is thought to be higher in countries with a high degree of consanguinity. Patients with MVID cannot tolerate feedings and require continuous total parenteral nutrition. Mortality is extremely high in the early-onset type with reports of survival in patients treated with small intestinal transplantation. Medical counseling for parents of infants with MVID needs to reflect our current understanding of the various genetic forms of this disease, the feasible management, and anticipated outcomes.

Comprehensive Targeted Sequencing Identifies Monogenic Disorders in Patients With Early-onset Refractory Diarrhea

OBJECTIVES

Causes of early-onset refractory diarrhea include exudative diarrhea associated with very early-onset inflammatory bowel diseases, osmotic or secretory diarrhea, and protein-losing enteropathy. Monogenic disorders are included in these diseases, yet a comprehensive genetic analysis has not been fully established.

METHODS

We established targeted gene panels covering all responsible genes for early-onset diarrhea. In total, 108 patients from 15 institutions were enrolled in this study. We collected clinical data from all patients. Seventy-three patients with exudative diarrhea, 4 with osmotic or secretory diarrhea and 8 with protein-losing enteropathy were subjected to genetic analysis.

RESULTS

A total of 15 out of the 108 enrolled patients (13.9%) were identified as monogenic. We identified 1 patient with RELA, 2 with TNFAIP3, 1 with CTLA4, 1 with SLCO2A1, 4 with XIAP, 3 with IL10RA, 1 with HPS1, 1 with FOXP3, and 1 with CYBB gene mutations. We also identified 1 patient with NFKB2 and 1 with TERT mutations from the gene panel for primary immunodeficiency syndromes. The patient with refractory diarrhea caused by heterozygous truncated RelA protein expression is the first case identified worldwide, and functional analysis revealed that the mutation affected nuclear factor kappa B signaling. Genotypes were significantly associated with the clinical and pathological findings in each patient.

CONCLUSIONS

We identified variable monogenic diseases in the patients and found that genes responsible for primary immunodeficiency diseases were frequently involved in molecular pathogenesis. Comprehensive genetic analysis was useful for accurate molecular diagnosis, understanding of underlying pathogenesis, and selecting the optimal treatment for patients with early-onset refractory diarrhea.An infographic for this article is available at: http://links.lww.com/MPG/B853.

Congenital Diarrheal Diseases

Early diagnosis of diarrhea is critical to prevent disease progression. Diarrhea in newborns can be congenital or acquired; acquired diarrheas are the major cause in infants. Congenital diarrheal diseases are rare and include defects in digestion, absorption, and transport of nutrients, and electrolytes; disorders of enterocyte differentiation and polarization; defects of enteroendocrine cell differentiation; dysregulation of the intestinal immune response; and dysfunction of the immune system. This review discusses the clinical approach that may help in early identification and management of different congenital diarrheal diseases.

Recent advances in understanding and managing malabsorption: focus on microvillus inclusion disease

Microvillus inclusion disease (MVID) is a rare congenital severe malabsorptive and secretory diarrheal disease characterized by blunted or absent microvilli with accumulation of secretory granules and inclusion bodies in enterocytes. The typical clinical presentation of the disease is severe chronic diarrhea that rapidly leads to dehydration and metabolic acidosis. Despite significant advances in our understanding of the causative factors, to date, no curative therapy for MVID and associated diarrhea exists. Prognosis mainly relies on life-long total parenteral nutrition (TPN) and eventual small bowel and/or liver transplantation. Both TPN and intestinal transplantation are challenging and present with many side effects. A breakthrough in the understanding of MVID emanated from seminal findings revealing mutations in MYO5B as a cause for MVID. During the last decade, many studies have thus utilized cell lines and animal models with knockdown of MYO5B to closely recapitulate the human disease and investigate potential therapeutic options in disease management. We will review the most recent advances made in the research pertaining to MVID. We will also highlight the tools and models developed that can be utilized for basic and applied research to increase our understanding of MVID and develop novel and effective targeted therapies.

Glucocorticoids and myosin5b loss of function induce heightened PKA signaling in addition to membrane traffic defects

Loss-of-function mutations in the nonconventional myosin Vb (Myo5b) result in microvillus inclusion disease (MVID) and massive secretory diarrhea that often begins at birth. Myo5b mutations disrupt the apical recycling endosome (ARE) and membrane traffic, resulting in reduced surface expression of apical membrane proteins. ARE disruption also results in constitutive phosphoinositide-dependent kinase 1 gain of function. In MVID, decreased surface expression of apical anion channels involved in Cl^- extrusion, such as cystic fibrosis transmembrane conductance regulator (CFTR), should reduce fluid secretion into the intestinal lumen. But the opposite phenotype is observed. To explain this contradiction and the onset of diarrhea, we hypothesized that signaling effects downstream from Myo5b loss of function synergize with higher levels of glucocorticoids to activate PKA and CFTR. Data from intestinal cell lines, human MVID, and Myo5b KO mouse intestine revealed changes in the subcellular redistribution of PKA activity to the apical pole, increased CFTR phosphorylation, and establishment of apical cAMP gradients in Myo5b-defective cells exposed to physiological levels of glucocorticoids. These cells also displayed net secretory fluid fluxes and transepithelial currents mainly from PKA-dependent Cl^- secretion. We conclude that Myo5b defects result in PKA stimulation that activates residual channels on the surface when intestinal epithelia are exposed to glucocorticoids at birth.

Autoimmune Enteropathy: An Updated Review with Special Focus on Stem Cell Transplant Therapy

Autoimmune enteropathy (AIE) is a complex disease affecting both children and adults. Although associated with significant morbidity and mortality, the pathophysiology of the disease and its treatment have not been well characterized. This study aims to review the medical literature available on this rare but clinically significant ailment, to help establish a better understanding of its pathophysiology and enumerate the available diagnostic and treatment modalities. A literature search was conducted on PubMed using key terms related to autoimmune enteropathy and intractable diarrhea, with no restrictions on the date of publication or language. We found a total of 98 reports of AIE published in the form of case reports and case series. The evidence reviewed suggests that AIE is a multifaceted disorder that requires a high index of suspicion in the appropriate clinical setting to be able to make an early diagnosis. Current evidence supports the use of supportive care to correct nutritional and metabolic deficiencies, and immunosuppressives and immunomodulators as directed therapies. Hematopoietic stem cell transplant is an aggressive, but successful curative modality for patients with AIE as part of immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome. Cumulative clinical experience with management of AIE has allowed improved outcomes in transplanted and non-transplanted AIE patients even though morbidity and mortality with are still high in patients with this condition. More research is needed to further define the role of new therapies for AIE, and a central registry with participation of multiple institutions might help share and standardize care of patients with this rare but serious condition.

EPCAM mutation update: Variants associated with congenital tufting enteropathy and Lynch syndrome

The epithelial cell adhesion molecule gene (EPCAM, previously known as TACSTD1 or TROP1) encodes a membrane‐bound protein that is localized to the basolateral membrane of epithelial cells and is overexpressed in some tumors. Biallelic mutations in EPCAM cause congenital tufting enteropathy (CTE), which is a rare chronic diarrheal disorder presenting in infancy. Monoallelic deletions of the 3′ end of EPCAM that silence the downstream gene, MSH2, cause a form of Lynch syndrome, which is a cancer predisposition syndrome associated with loss of DNA mismatch repair. Here, we report 13 novel EPCAM mutations from 17 CTE patients from two separate centers, review EPCAM mutations associated with CTE and Lynch syndrome, and structurally model pathogenic missense mutations. Statistical analyses indicate that the c.499dupC (previously reported as c.498insC) frameshift mutation was associated with more severe treatment regimens and greater mortality in CTE, whereas the c.556‐14A>G and c.491+1G>A splice site mutations were not correlated with treatments or outcomes significantly different than random simulation. These findings suggest that genotype–phenotype correlations may be useful in contributing to management decisions of CTE patients. Depending on the type and nature of EPCAM mutation, one of two unrelated diseases may occur, CTE or Lynch syndrome.

Regulation of actin-based apical structures on epithelial cells

Cells of transporting epithelia are characterized by the presence of abundant F-actin-based microvilli on their apical surfaces. Likewise, auditory hair cells have highly reproducible rows of apical stereocilia (giant microvilli) that convert mechanical sound into an electrical signal. Analysis of mutations in deaf patients has highlighted the critical components of tip links between stereocilia, and related structures that contribute to the organization of microvilli on epithelial cells have been found. Ezrin/radixin/moesin (ERM) proteins, which are activated by phosphorylation, provide a critical link between the plasma membrane and underlying actin cytoskeleton in surface structures. Here, we outline recent insights into how microvilli and stereocilia are built, and the roles of tip links. Furthermore, we highlight how ezrin is locally regulated by phosphorylation, and that this is necessary to maintain polarity. Localized phosphorylation is achieved through an intricate coincidence detection mechanism that requires the membrane lipid phosphatidylinositol 4,5-bisphosphate [PI(4,5)P₂] and the apically localized ezrin kinase, lymphocyte-oriented kinase (LOK, also known as STK10) or Ste20-like kinase (SLK). We also discuss how ezrin-binding scaffolding proteins regulate microvilli and how, despite these significant advances, it remains to be discovered how the cell polarity program ultimately interfaces with these processes.

Functions of EpCAM in physiological processes and diseases (Review)

EpCAM (epithelial cell adhesion molecule) is a type I transmembrane glycoprotein, which was originally identified as a tumor-associated antigen due to its high expression level in rapidly growing epithelial tumors. Germ line mutations of the human EpCAM gene have been indicated as the cause of congenital tufting enteropathy. Previous studies based on cell models have revealed that EpCAM contributes to various biological processes including cell adhesion, signaling, migration and proliferation. Due to the previous lack of genetic animal models, the in vivo functions of EpCAM remain largely unknown. However, EpCAM genetic animal models have recently been generated, and are useful for understanding the functions of EpCAM. The authors here briefly review the functions and mechanisms of EpCAM in physiological processes and different diseases.

Advances in Evaluation of Chronic Diarrhea in Infants

Diarrhea is common in infants (children less than 2 years of age), usually acute, and, if chronic, commonly caused by allergies and occasionally by infectious agents. Congenital diarrheas and enteropathies (CODEs) are rare causes of devastating chronic diarrhea in infants. Evaluation of CODEs is a lengthy process and infrequently leads to a clear diagnosis. However, genomic analyses and the development of model systems have increased our understanding of CODE pathogenesis. With these advances, a new diagnostic approach is needed. We propose a revised approach to determine causes of diarrhea in infants, including CODEs, based on stool analysis, histologic features, responses to dietary modifications, and genetic tests. After exclusion of common causes of diarrhea in infants, the evaluation proceeds through analyses of stool characteristics (watery, fatty, or bloody) and histologic features, such as the villus to crypt ratio in intestinal biopsies. Infants with CODEs resulting from defects in digestion, absorption, transport of nutrients and electrolytes, or enteroendocrine cell development or function have normal villi to crypt ratios; defects in enterocyte structure or immune-mediated conditions result in an abnormal villus to crypt ratios and morphology. Whole-exome and genome sequencing in the early stages of evaluation can reduce the time required for a definitive diagnosis of CODEs, or lead to identification of new variants associated with these enteropathies. The functional effects of gene mutations can be analyzed in model systems such as enteroids or induced pluripotent stem cells and are facilitated by recent advances in gene editing procedures. Characterization and investigation of new CODE disorders will improve management of patients and advance our understanding of epithelial cells and other cells in the intestinal mucosa.

Magnolol and Honokiol Attenuate Apoptosis of Enterotoxigenic Escherichia Coli-Induced Intestinal Epithelium by Maintaining Secretion and Absorption Homeostasis and Protecting Mucosal Integrity

BACKGROUND The cortex of Magnolia officinalis has long been used as an element of traditional Chinese medicine for the treatment of anxiety, chronic bronchitis, and gastrointestinal dysfunction. This study aimed to elucidate the underlying mechanism of its functional ingredients (magnolol and honokiol) in modifying the secretion and absorption homeostasis and protecting mucosal integrity in an Enterotoxigenic Escherichia coli (ETEC)-induced diarrhea mouse model. MATERIAL AND METHODS This study established a diarrhea mouse model infected by ETEC at a dosage of 0.02 ml/g live body weight (BW) in vivo. Magnolol or honokiol was followed by an intraperitoneal administration at dosages of 100, 300, and 500 mg/kg BW according to a 3×3 factorial arrangement. The useful biomarkers for evaluating the integrity of intestinal tract and histologic injury were analyzed and morphological development (including villus height, crypt depth, and ratio of villus height to crypt depth) and the expressions of inflammatory cytokines were determined by real-time PCR. RESULTS The results showed that magnolol and honokiol (500 mg/kg BW) reduced the concentrations of NO, DAO, and DLA, and iNOS activity, and the mRNA expressions of the interferon gamma (IFN-γ) and interleukin 10 (IL-10), and inhibited intestinal epithelial cell apoptosis. Magnolol and honokiol (300 mg/kg BW) elongated the villus height and crypt depth and decreased the number of goblet cells and the ratio of villus height to crypt depth. CONCLUSIONS The current results indicate that magnolol and honokiol enhance the intestinal anti-inflammatory capacities, elongate the villus height and crypt depth, and reduce goblet cell numbers to inhibit the intestinal epithelium apoptosis and effectively protect the intestinal mucosa. These results show that magnolol and honokiol protect the intestinal mucosal integrity and regulate gastrointestinal dysfunction.

Prenatal Bowel Findings in Male Siblings With a Confirmed FOXP3 Mutation

There are multiple etiologies for fetal dilated bowel loops on ultrasonography (US), and we present a unique case of male siblings with a forkhead box P3 (FOXP3) mutation. Both children presented with fetal bowel anomalies on prenatal US. Family histories of cystic fibrosis and immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome were reported. Amniocentesis in both pregnancies identified a normal male karyotype and the familial mutation associated with IPEX syndrome. IPEX syndrome is one of a group of conditions known as congenital diarrhea disorders. Other congenital diarrhea disorder cases have presented with similar prenatal US findings. As a result of these associations, we suggest considering IPEX syndrome as a potential cause of fetal bowel anomalies, particularly with a known family history. However, continued research into the phenotypic and genotypic correlations for IPEX syndrome is likely needed to better understand this possible prenatal presentation.

Intestinal epithelial cell polarity defects in disease: lessons from microvillus inclusion disease

The intestinal epithelium is a highly organized tissue. The establishment of epithelial cell polarity, with distinct apical and basolateral plasma membrane domains, is pivotal for both barrier formation and for the uptake and vectorial transport of nutrients. The establishment of cell polarity requires a specialized subcellular machinery to transport and recycle proteins to their appropriate location. In order to understand and treat polarity-associated diseases, it is necessary to understand epithelial cell-specific trafficking mechanisms. In this Review, we focus on cell polarity in the adult mammalian intestine. We discuss how intestinal epithelial polarity is established and maintained, and how disturbances in the trafficking machinery can lead to a polarity-associated disorder, microvillus inclusion disease (MVID). Furthermore, we discuss the recent developments in studying MVID, including the creation of genetically manipulated cell lines, mouse models and intestinal organoids, and their uses in basic and applied research.

Summary: Microvillus inclusion disease serves as a useful model to enhance our understanding of the intestinal trafficking and polarity machinery in health and disease.

Microvillus Inclusion Disease Variant in an Infant with Intractable Diarrhea

Microvillus inclusion disease (MVID) is a rare autosomal recessive congenital enteropathy characterized by intractable secretory diarrhea. We report a case of MVID variant with a homozygous gene mutation in syntaxin 3 (STX3). The patient is a male Saudi infant who presented shortly after birth with severe vomiting, metabolic acidosis, and mild diarrhea. Electron microscopy study for small intestinal biopsy was consistent with MVID. MYO5B gene mutation was excluded; subsequently, whole exome sequencing (WES) was performed, which revealed homozygous gene mutation in STX3. Using WES in clinical environment can be a useful tool for diagnosing difficult and rare inherited congenital enteropathies.

A Case Study of Intractable Diarrhea Due to Neonatal Microvillous Inclusion Disease

BACKGROUND

Microvillous inclusion disease (MVID) is one of the most severe congenital diarrhea disorders, caused by a genetic defect in enterocyte differentiation and polarization.

CASE REPORT

We describe a neonate who presented with severe weight loss, hypernatremic dehydration and metabolic acidosis due to intractable diarrhea due to MVID, confirmed by electron microscopy.

CONCLUSION

MVID can present with severe weight loss, hypernatremic dehydration and metabolic acidosis that is life threatening. The diagnosis is made by typical findings on light microscopy and electron microscope of small bowel biopsies. The only therapeutic options at this time are total parenteral nutrition and bowel rest and intestinal transplantation.

Newcomers in paediatric GI pathology: childhood enteropathies including very early onset monogenic IBD

Childhood enteropathies are a group of diseases causing severe chronic (>2-3 weeks) diarrhoea often starting in the first week of life with the potential for fatal complications for the affected infant. Early identification and accurate classification of childhood enteropathies are, therefore, crucial for making treatment decisions to prevent life-threatening complications. Childhood enteropathies are classified into four groups based on the underlying pathology: (i) conditions related to defective digestion, absorption and transport of nutrients and electrolytes; (ii) disorders related to enterocyte differentiation and polarization; (iii) defects of enteroendocrine cell differentiation; and (iv) disorders associated with defective modulation of intestinal immune response. While the intestinal mucosa is usually normal in enteropathies related to congenital transport or enzyme deficiencies, the intestinal biopsy in other disorders may reveal a wide range of abnormalities varying from normal villous architecture to villous atrophy and/or inflammation, or features specific to the underlying disorder including epithelial abnormalities, lipid vacuolization in the enterocytes, absence of plasma cells, lymphangiectasia, microorganisms, and mucosal eosinophilic or histiocytic infiltration. This review intends to provide an update on small intestinal biopsy findings in childhood enteropathies, the "newcomers", including very early onset monogenic inflammatory bowel disease (IBD), in particular, for the practicing pathologist.

Microvillus inclusion disease: a subtotal enterectomy as a bridge to transplantation

BACKGROUND

Microvillus inclusion disease (MVID) is a known congenital cause of intractable diarrhea resulting in permanent intestinal failure. There is need for a lifelong total parenteral nutrition (TPN) from diagnosis and the prognosis is poor. Most patients die by the second decade of life as a result of complications of parenteral alimentation including liver failure or sepsis. The only available treatment at this moment is a small bowel transplantation. But before that moment, the patients often suffer from a persistent failure to thrive and electrolyte disturbances despite continuous TPN.

METHODS AND RESULTS

We report what we believe is a first case of an extensive small bowel resection in a 5-month-old boy with proven MVID to act as a bridge to (liver-) intestinal transplantation to treat failure to thrive and intractable diarrhea.

CONCLUSIONS

An extensive small bowel resection can be done to enhance the chance of survival leading up to the transplantation by managing fluid and electrolyte imbalance. It facilitates medical management of these patients and makes a bowel transplantation possible at a later stage.

Identification of intestinal ion transport defects in microvillus inclusion disease

Loss of function mutations in the actin motor myosin Vb (Myo5b) lead to microvillus inclusion disease (MVID) and death in newborns and children. MVID results in secretory diarrhea, brush border (BB) defects, villus atrophy, and microvillus inclusions (MVIs) in enterocytes. How loss of Myo5b results in increased stool loss of chloride (Cl(-)) and sodium (Na(+)) is unknown. The present study used Myo5b loss-of-function human MVID intestine, polarized intestinal cell models of secretory crypt (T84) and villus resembling (CaCo2BBe, C2BBe) enterocytes lacking Myo5b in conjunction with immunofluorescence confocal stimulated emission depletion (gSTED) imaging, immunohistochemical staining, transmission electron microscopy, shRNA silencing, immunoblots, and electrophysiological approaches to examine the distribution, expression, and function of the major BB ion transporters NHE3 (Na(+)), CFTR (Cl(-)), and SLC26A3 (DRA) (Cl(-)/HCO3 (-)) that control intestinal fluid transport. We hypothesized that enterocyte maturation defects lead villus atrophy with immature secretory cryptlike enterocytes in the MVID epithelium. We investigated the role of Myo5b in enterocyte maturation. NHE3 and DRA localization and function were markedly reduced on the BB membrane of human MVID enterocytes and Myo5bKD C2BBe cells, while CFTR localization was preserved. Forskolin-stimulated CFTR ion transport in Myo5bKD T84 cells resembled that of control. Loss of Myo5b led to YAP1 nuclear retention, retarded enterocyte maturation, and a cryptlike phenotype. We conclude that preservation of functional CFTR in immature enterocytes, reduced functional expression of NHE3, and DRA contribute to Cl(-) and Na(+) stool loss in MVID diarrhea.

Detection of parasites in children with chronic diarrhea

The aim of this study was to investigate the frequency of intestinal parasites in patients with chronic diarrhea and clarify the importance of these parasitic pathogens in such cases. A total of 60 pediatric patients with chronic diarrhea between June 2012 and October 2014 were enrolled in the study. Out of 60 stool samples, five were positive for Giardia lamblia, two, Dientamoeba fragilis, and one, Blastocystis hominis. One stool sample was positive for Entamoeba hartmanni and B. hominis, another one was positive for G. lamblia and B. hominis, another, G. lamblia and E. hartmanni and one sample was positive for Enterobius vermicularis, D. fragilis and B. hominis together. Parasitic infection, which decreases quality of life and increases susceptibility to other infections, should not be neglected, particularly in patients with chronic diarrhea. Accurate diagnosis decreases morbidity and mortality in patients with parasite infection.

Novel approaches: Tissue engineering and stem cells--In vitro modelling of the gut

In many intestinal diseases, the function of the epithelial lining is impaired. In this review, we describe the recent developments of in vitro intestinal stem cell cultures. When these stem cells are grown in 3D structures (organoids), they provide a model of the intestinal epithelium, which is closely similar to the growth and development of the in vivo gut. This model provides a new tool to study various diseases of malabsorption in functional detail and therapeutic applications, which could not be achieved with traditional cell lines. First, we describe the organization and function of the healthy small intestinal epithelium. Then, we discuss the establishment of organoid cultures and how these structures represent the healthy epithelium. Finally, we discuss organoid cultures as a tool for studying intrinsic properties of the epithelium, as a model for intestinal disease, and as a possible source for stem cell transplantations.

Villin immunohistochemistry is a reliable method for diagnosing microvillus inclusion disease

Microvillus inclusion disease (MVID) is a rare congenital disorder that manifests early in infancy as intractable watery diarrhea. The entity is characterized morphologically by a deficient brush border and apical cytoplasmic inclusions within absorptive cells (enterocytes) due to misplaced assembly of brush border proteins. The diagnosis is based upon histopathology, special stains, immunohistochemistry (IHC), and ultimately upon electron microscopy. Currently, the periodic acid-Schiff stain (PAS) and CD10 IHC are commonly used as adjuncts, but in addition to brush border structures, they stain a variety of apical cytoplasmic inclusions and organelles, thereby interfering with recognition of microvillus inclusions. Villin is a protein that specifically binds to the actin core bundle of microvilli. We utilized villin IHC in formalin-fixed paraffin-embedded gastrointestinal biopsies from 6 patients with MVID, 5 with celiac disease, and 17 children with normal intestinal biopsies and compared the results with those obtained with CD10 IHC and PAS staining. All MVID cases had confirmatory electron microscopy at the time of diagnosis. Villin immunoreactivity was restricted to the brush border in the control groups. In MVID, villin IHC showed attenuation or loss of the surface brush border and also highlighted the cytoplasmic microvillus inclusions with clarity. In MVID, CD10 IHC and the PAS stain also showed attenuation or loss of the surface brush border, but staining of a variety of cytoplasmic structures largely obscured the microvillus inclusions. In sum, villin IHC is a reliable and superior adjunct in the diagnosis of MVID. Study of additional cases will determine whether villin IHC would obviate the need for electron microscopic confirmation.

Features of gastric and colonic mucosa in congenital enteropathies: a study in histology and immunohistochemistry

Congenital enteropathies comprise a constellation of rare clinicopathologic diagnoses characterized by intractable watery diarrhea and failure to thrive in infants. These diagnoses include, but are not limited to, tufting enteropathy (TE), microvillous inclusion disease (MID), and enteroendocrine cell dysgenesis (EED). Commonly, the diagnosis is based on identification of their characteristic histologic and/or ultrastructural features in small intestinal mucosa. In cases in which the changes in the small intestine are inconclusive or a small intestine biopsy is not performed, the diagnosis can be hampered or significantly delayed. We describe the histologic features and immunohistochemical staining patterns of gastric and colonic mucosa in patients with confirmed TE (3), MID (2), and EED (1). Specifically, focal epithelial tufts were found in the gastric mucosa of one TE patient and multifocally in the colonic mucosa of another. All TE patients showed complete loss of membranous epithelial EpCAM expression in gastric and colonic mucosa, characteristic of the diagnosis. Gastric biopsies were available in 1 patient with MID; this showed focal disruption of the gastric glandular architecture. Three colon biopsies and 1 resection from 2 patients with MID showed characteristic cytoplasmic vacuoles and periodic acid-Schiff/villin-positive cytoplasmic inclusions. Chromogranin stains showed complete absence of enteroendocrine cells within the colon and a normal distribution in the gastric mucosa of the EED patient. On the basis of our findings, we conclude that the characteristic histologic and immunohistochemical features associated with the small intestine can be confirmed within the gastric and/or colonic mucosa by careful histologic examination and immunohistochemistry.

Mutation of EpCAM leads to intestinal barrier and ion transport dysfunction

Congenital tufting enteropathy (CTE) is a devastating diarrheal disease seen in infancy that is typically associated with villous changes and the appearance of epithelial tufts. We previously found mutations in epithelial cell adhesion molecule (EpCAM) to be causative in CTE. We developed a knock-down cell model of CTE through transfection of an EpCAM shRNA construct into T84 colonic epithelial cells to elucidate the in vitro role of EpCAM in barrier function and ion transport. Cells with EpCAM deficiency exhibited decreased electrical resistance, increased permeability, and decreased ion transport. Based on mutations in CTE patients, an in vivo mouse model was developed, with tamoxifen-inducible deletion of exon 4 in Epcam resulting in mutant protein with decreased expression. Tamoxifen treatment of Epcam (Δ4/Δ4) mice resulted in pathological features of villous atrophy and epithelial tufts, similar to those in human CTE patients, within 4 days post induction. Epcam (Δ4/Δ4) mice also showed decreased expression of tight junctional proteins, increased permeability, and decreased ion transport in the intestines. Taken together, these findings reveal mechanisms that may underlie disease in CTE.

KEY MESSAGES

Knock-down EpCAM cell model of congenital tufting enteropathy was developed. In vivo inducible mouse model was developed resulting in mutant EpCAM protein. Cells with EpCAM deficiency demonstrated barrier and ion transport dysfunction. Tamoxifen-treated Epcam (Δ4/Δ4) mice demonstrated pathological features. Epcam (Δ4/Δ4) mice showed improper barrier function and ion transport.

Evaluation of intestinal biopsies for pediatric enteropathy: a proposed immunohistochemical panel approach

Congenital enteropathies are rare disorders with significant clinical consequences; however, definitive diagnosis based on morphologic assessment of duodenal biopsies with routine stains alone is often impossible. To determine the role of immunohistochemistry (IHC) in the evaluation for microvillous inclusion disease, congenital tufting enteropathy (intestinal epithelial dysplasia), and enteroendocrine cell dysgenesis, a series of duodenal biopsies from 26 pediatric patients with chronic/intractable diarrhea was retrospectively reviewed. IHC stains for CD10, EpCAM, chromogranin, and villin were performed on all biopsies, and the results were correlated with hematoxylin and eosin and ultrastructural findings using electron microscopy, when available. Biopsies from 2 patients diagnosed with microvillous inclusion disease at the time of original biopsy demonstrated diffuse CD10-positive cytoplasmic inclusions within enterocytes and normal expression of EpCAM and chromogranin. Biopsies from 3 patients, including 2 siblings with confirmed EPCAM mutations, demonstrated complete loss of EpCAM expression and normal expression of CD10 and chromogranin; electron microscopic evaluation revealed characteristic ultrastructural findings of tufting enteropathy. Biopsies from 1 patient with a confirmed NEUROG3 mutation demonstrated an absence of intestinal enteroendocrine cells by chromogranin staining, consistent with enteroendocrine cell dysgenesis. Four patients' biopsies displayed nonspecific staining patterns for CD10 and/or EpCAM with normal expression of chromogranin, and 16 patients' biopsies exhibited normal expression for all 3 markers. Villin stains demonstrated heterogenous brush border labeling with nonspecific cytoplasmic reactivity, a pattern variably present throughout the biopsy series. In conclusion, the routine use of an IHC panel of CD10, EpCAM, and chromogranin is warranted in patients meeting specific age and/or clinical criteria, as the morphologic findings of congenital enteropathies may be subtle, focal, or inapparent on routine stains.

A case of Protracted Diarrhea in a Newborn: a Diagnostic Challenge

Congenital diarrhea comprises a broad range of pathologies and often requires a thorough workup and immediate treatment. Although rare, microvillous inclusion disease (MVID) should be included in differential diagnosis of this presentation in the neonate. We report the case of a 36-week newborn who developed signs of severe dehydration and lethargy, requiring fluid resuscitation and total parenteral nutrition. MVID was diagnosed by recognition of profuse secretory diarrhea after an exhaustive etiological investigation, confirmed by DNA analysis.

Loss of syntaxin 3 causes variant microvillus inclusion disease

Microvillus inclusion disease (MVID) is a disorder of intestinal epithelial differentiation characterized by life-threatening intractable diarrhea. MVID can be diagnosed based on loss of microvilli, microvillus inclusions, and accumulation of subapical vesicles. Most patients with MVID have mutations in myosin Vb that cause defects in recycling of apical vesicles. Whole-exome sequencing of DNA from patients with variant MVID showed homozygous truncating mutations in syntaxin 3 (STX3). STX3 is an apical receptor involved in membrane fusion of apical vesicles in enterocytes. Patient-derived organoid cultures and overexpression of truncated STX3 in Caco-2 cells recapitulated most characteristics of variant MVID. We conclude that loss of STX3 function causes variant MVID.

Tufting enteropathy revisited: the utility of MOC31 (EpCAM) immunohistochemistry in diagnosis

Tufting enteropathy (TE) is an uncommon disease causing intractable diarrheas starting in early childhood and resulting in failure to thrive, dependence on total parenteral nutrition, and eventually requiring transplantation for treatment. The diagnosis has been based on histology showing the presence of epithelial "tufts" in the small bowel and colonic mucosa and variable villus alterations with mild to no inflammatory changes and preserved brush border. The gene for TE has been identified to be the EpCAM gene on chromosome 2p21. With Institutional Review Board approval, all cases of intractable diarrhea in children in whom TE was suspected or diagnosed were retrieved from the pathology files (17 patients). Other cases of infantile, neonatal, and childhood diarrhea were also retrieved to serve as controls for the staining studies (total 37 patients). EpCAM/MOC31 antibody staining was performed on all cases. The study cohort comprised 17 patients (13 boys, 4 girls) with a diagnosis of TE ranging in age at diagnosis from 3 months to 9 years, all presenting with protracted diarrhea and/or failure to thrive, usually since birth. Staining with MOC31 was carried out in all but 2 patients (both consults) and was completely negative in the epithelium irrespective of the site of biopsy or resection. In contrast, MOC31 was positive in all other cases tested, giving a sensitivity and specificity of 100% for loss of staining. MOC31 is a diagnostic stain for TE and should be included in the panel in any case of prolonged diarrhea in children to exclude this possibility.

Functional consequences of EpCam mutation in mice and men

Congenital tufting enteropathy (CTE) is a severe diarrheal disease of infancy characterized by villous changes and epithelial tufts. We previously identified mutations in epithelial cell adhesion molecule (EpCAM) as the cause of CTE. We developed an in vivo mouse model of CTE based on EpCAM mutations found in patients with the aim to further elucidate the in vivo role of EpCAM and allow for a direct comparison to human CTE. Using Cre-LoxP recombination technology, we generated a construct lacking exon 4 in Epcam. Epcam(Δ4/Δ4) mice and CTE patient intestinal tissue integrity was analyzed by histology using both light immunohistochemistry and electron microscopy. Epcam(Δ4/Δ4) mice demonstrate neonatal lethality and growth retardation with pathological features, including epithelial tufts, enterocyte crowding, altered desmosomes, and intercellular gaps, similar to human CTE patients. Mutant EpCAM protein is present at low levels and is mislocalized in the intestine of Epcam(Δ4/Δ4) mice and CTE patients. Deletion of exon 4 was found to decrease expression of both EpCAM and claudin-7 causing a loss of colocalization, functionally disrupting the EpCAM/claudin-7 complex, a finding for the first time confirmed in CTE patients. Furthermore, compared with unaffected mice, mutation of Epcam leads to enhanced permeability and intestinal cell migration, uncovering underlying disease mechanisms.

A novel nonsense mutation in the EpCAM gene in a patient with congenital tufting enteropathy

OBJECTIVES

Tufting enteropathy (TE) is a classical congenital disorder of the intestinal mucosa causing protracted diarrhea in infancy as a result of a dysfunctional epithelial cell barrier, which is mainly caused by mutations in the EpCAM gene and expression of a nonfunctional epithelial cell adhesion molecule in the intestine. We report here a novel nonsense mutation in a patient suspected of having TE, resulting in a complete absence of EpCAM in duodenal enterocytes.

METHODS

A patient presenting with congenital diarrhea and suspected of having TE was screened for EpCAM mutations, and duodenal biopsies were stained for EpCAM using immunohistochemistry analysis.

RESULTS

We identified a novel homozygous nonsense mutation in the EpCAM gene in a patient suspected of having TE, causing a complete loss of EpCAM expression in duodenal enterocytes.

CONCLUSIONS

With screening analysis for EpCAM mutations and immunohistochemistry for EpCAM expression in duodenal enterocytes, we found a novel homozygous mutation in a patient with classical protracted diarrhea in infancy finally diagnosed as TE, which results in a complete absence of EpCAM and in dysfunctional barrier formation in duodenal enterocytes.

Bitterness of glucose/galactose: novel mutations in the SLC5A1 gene

Glucose galactose malabsorption (GGM) is a rare autosomal recessive disorder characterized by life-threatening osmotic diarrhea at infancy. When the intake of the offending sugars (namely, glucose, galactose and lactose) is ceased, the diarrhea promptly stops. Mutations in the SLC5A1 gene, encoding the sodium-glucose co-transporter located in the brush border of enterocytes, have been shown to cause the disease. More than 300 subjects of diverse origin have been reported worldwide, most of whom are a result of a consanguineous union. We examined 6 patients from 4 families presenting with complaints consistent with GGM and responsive to the appropriate fructose-based diet. Genomic DNA of the patients was polymerase chain reaction amplified for each of the 15 exons of the SLC5A1 gene and analyzed by nucleotide sequencing. The analysis lead to the identification of 2 novel mutations: a 1915 del C mutation, a frameshift mutation leading to a premature stop at codon 645; and a substitution missense mutation of T to C on nucleotide 947 (exon 9) causing a L316P substitution. In addition, G426R and C255W mutations previously described were identified; in both cases, the patients were shown to be homozygous and their parents heterozygous for the mutation. Of note, additional patients who underwent a similar evaluation at our center for suspected GGM did not show mutations in the SLC5A1 gene. Because the latter did not previously undergo a diagnostic algorithm in full, for instance, one that may consist of a glucose breath hydrogen test and an empiric attempt of a dietary switch to galactomin, we suggest that molecular genotyping of such patients should only follow such appropriate clinical evaluation.

Microvillus inclusion disease: loss of Myosin vb disrupts intracellular traffic and cell polarity

Microvillus inclusion disease (MVID) is a congenital enteropathy characterized by loss of apical microvilli and formation of cytoplasmic inclusions lined by microvilli in enterocytes. MVID is caused by mutations in the MYO5B gene, coding for the myosin Vb motor protein. Although myosin Vb is implicated in the organization of intracellular transport and cell surface polarity in epithelial cells, its precise role in the pathogenesis of MVID is unknown. We performed correlative immunohistochemistry analyses of sections from duodenal biopsies of a MVID patient, compound heterozygous for two novel MYO5B mutations, predicting loss of function of myosin Vb in duodenal enterocytes together with a stable MYO5B CaCo2 RNAi cell system. Our findings show that myosin Vb-deficient enterocytes display disruption of cell polarity as reflected by mislocalized apical and basolateral transporter proteins, altered distribution of certain endosomal/lysosomal constituents including Rab GTPases. Together, this severe disturbance of epithelial cell function could shed light on the pathology and symptoms of MVID.

An overview and online registry of microvillus inclusion disease patients and their MYO5B mutations

Microvillus inclusion disease (MVID) is one of the most severe congenital intestinal disorders and is characterized by neonatal secretory diarrhea and the inability to absorb nutrients from the intestinal lumen. MVID is associated with patient-, family-, and ancestry-unique mutations in the MYO5B gene, encoding the actin-based motor protein myosin Vb. Here, we review the MYO5B gene and all currently known MYO5B mutations and for the first time methodologically categorize these with regard to functional protein domains and recurrence in MYO7A associated with Usher syndrome and other myosins. We also review animal models for MVID and the latest data on functional studies related to the myosin Vb protein. To congregate existing and future information on MVID geno-/phenotypes and facilitate its quick and easy sharing among clinicians and researchers, we have constructed an online MOLGENIS-based international patient registry (www.MVID-central.org). This easily accessible database currently contains detailed information of 137 MVID patients together with reported clinical/phenotypic details and 41 unique MYO5B mutations, of which several unpublished. The future expansion and prospective nature of this registry is expected to improve disease diagnosis, prognosis, and genetic counseling.

Diarrheal Illness in the Pediatric Population: A Review of Neonatal Enteropathies and Childhood Idiopathic Inflammatory Bowel Disease

In the clinical context of pediatric diarrheal illness, the interpretation of endoscopic mucosal biopsies varies significantly from that in adults. This review outlines these differences by first describing a host of diarrheal illnesses that are nearly exclusive to the pediatric age group. The final portion of this article describes salient pathologic differences between adult and pediatric idiopathic inflammatory bowel disease. The goal of this review is to provide a brief description of each disease process and focus on practical aspects of diagnosis that are applicable for pathologists working in general practice settings.

Immune dysregulation, polyendocrinopathy, enteropathy, x-linked syndrome: a paradigm of immunodeficiency with autoimmunity

Immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome is a rare monogenic primary immunodeficiency (PID) due to mutations of FOXP3, a key transcription factor for naturally occurring (n) regulatory T (Treg) cells. The dysfunction of Treg cells is the main pathogenic event leading to the multi-organ autoimmunity that characterizes IPEX syndrome, a paradigm of genetically determined PID with autoimmunity. IPEX has a severe early onset and can become rapidly fatal within the first year of life regardless of the type and site of the mutation. The initial presenting symptoms are severe enteritis and/or type-1 diabetes mellitus, alone or in combination with eczema and elevated serum IgE. Other autoimmune symptoms, such as hypothyroidism, cytopenia, hepatitis, nephropathy, arthritis, and alopecia can develop in patients who survive the initial acute phase. The current therapeutic options for IPEX patients are limited. Supportive and replacement therapies combined with pharmacological immunosuppression are required to control symptoms at onset. However, these procedures can allow only a reduction of the clinical manifestations without a permanent control of the disease. The only known effective cure for IPEX syndrome is hematopoietic stem cell transplantation, but it is always limited by the availability of a suitable donor and the lack of specific guidelines for bone marrow transplant in the context of this disease. This review aims to summarize the clinical histories and genomic mutations of the IPEX patients described in the literature to date. We will focus on the clinical and immunological features that allow differential diagnosis of IPEX syndrome and distinguish it from other PID with autoimmunity. The efficacy of the current therapies will be reviewed, and possible innovative approaches, based on the latest highlights of the pathogenesis to treat this severe primary autoimmune disease of childhood, will be discussed.