Congenital Diarrheal Disorders Research Articles

Congenital Sodium Diarrhea: Antenatal Diagnosis May Prevent Unnecessary Surgery in the Neonate

AbstractCongenital sodium diarrhea (CSD) is a rare, life-threatening condition characterized by intractable diarrhea, hyponatremia, and metabolic acidosis. It presents similarly to other congenital disorders and, therefore, is often misdiagnosed and mistreated.We present a case of CSD that presented with dilated loops of bowel and polyhydramnios at 18 weeks and was thought to be a congenital bowel obstruction. The patient was therefore managed surgically after birth with a diverting ileostomy, however was later found to have elevated stool sodium levels and metabolic derangements consistent with CSD.Our case demonstrates the need for high index of suspicion for congenital diarrheal disorders to prevent unnecessary surgery and a delay in appropriate medical management of this rare condition.

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.

Глюкозо-галактозная мальабсорбция: патогенез, диагностика, диетотерапия

Congenital glucose-galactose malabsorption is an orphan autosomal recessive life-threatening disease resulting from a selective defect in the intestinal glucose and galactose/sodium co-transport system in the brush border membrane of the enterocyte. In glucose-galactose malabsorption, glucose, galactose, as well as di- and polysaccharides: starch, dextrins, maltose, sucrose, lactose cannot be absorbed. The disease manifests itself in the neonatal period in the form of severe watery osmotic diarrhea, leading to rapid dehydration and metabolic acidosis. The only treatment is diet therapy with the exclusion of all carbohydrates except fructose. In infants with glucose-galactose malabsorption, diet therapy using specialized formulas with fructose as a carbohydrate component is vital. Subsequently, such infants need the introduction of low-carbohydrate complementary foods with primarily fructose content. The article presents a clinical example of the disease course and its successful dietary correction in an infant using a specialized formula and a specific diet. Key words: congenital diarrheal disorders, glucose-galactose malabsorption, infants, diet therapy, specialized milk formula based on fructose

Altered MYO5B Function Underlies Microvillus Inclusion Disease: Opportunities for Intervention at a Cellular Level.

Microvillus inclusion disease (MVID) is a congenital diarrheal disorder resulting in life-threatening secretory diarrhea in newborns. Inactivating and nonsense mutations in myosin Vb (MYO5B) have been identified in MVID patients. Work using patient tissues, cell lines, mice, and pigs has led to critical insights into the pathology of MVID and a better understanding of both apical trafficking in intestinal enterocytes and intestinal stem cell differentiation. These studies have demonstrated that loss of MYO5B or inactivating mutations lead to loss of apical sodium and water transporters, without loss of apical CFTR, accounting for the major pathology of the disease. In addition, loss of MYO5B expression induces the formation of microvillus inclusions through apical bulk endocytosis that utilizes dynamin and PACSIN2 and recruits tight junction proteins to the sites of bulk endosome formation. Importantly, formation of microvillus inclusions is not required for the induction of diarrhea. Recent investigations have demonstrated that administration of lysophosphatidic acid (LPA) can partially reestablish apical ion transporters in enterocytes of MYO5B KO mice. In addition, further studies have shown that MYO5B loss induces an imbalance in Wnt/Notch signaling pathways that can lead to alterations in enterocyte maturation and tuft cell lineage differentiation. Inhibition of Notch signaling leads to improvements in those cell differentiation deficits. These studies demonstrate that directed strategies through LPA receptor activation and Notch inhibition can bypass the inhibitory effects of MYO5B loss. Thus, effective strategies may be successful in MVID patients and other congenital diarrhea syndromes to reestablish proper apical membrane absorption of sodium and water in enterocytes and ameliorate life-threatening congenital diarrhea.

Congenital Diarrheal Disorders in Neonates: A Single-Center Experience

Congenital Diarrheal Disorders in Neonates: A Single-Center Experience

Cell differentiation is disrupted by MYO5B loss through Wnt/Notch imbalance.

Functional loss of myosin Vb (MYO5B) induces a variety of deficits in intestinal epithelial cell function and causes a congenital diarrheal disorder, microvillus inclusion disease (MVID). The impact of MYO5B loss on differentiated cell lineage choice has not been investigated. We quantified the populations of differentiated epithelial cells in tamoxifen-induced, epithelial cell–specific MYO5B-knockout (VilCreERT2 Myo5bfl/fl) mice utilizing digital image analysis. Consistent with our RNA-sequencing data, MYO5B loss induced a reduction in tuft cells in vivo and in organoid cultures. Paneth cells were significantly increased by MYO5B deficiency along with expansion of the progenitor cell zone. We further investigated the effect of lysophosphatidic acid (LPA) signaling on epithelial cell differentiation. Intraperitoneal LPA significantly increased tuft cell populations in both control and MYO5B-knockout mice. Transcripts for Wnt ligands were significantly downregulated by MYO5B loss in intestinal epithelial cells, whereas Notch signaling molecules were unchanged. Additionally, treatment with the Notch inhibitor dibenzazepine (DBZ) restored the populations of secretory cells, suggesting that the Notch pathway is maintained in MYO5B-deficient intestine. MYO5B loss likely impairs progenitor cell differentiation in the small intestine in vivo and in vitro, partially mediated by Wnt/Notch imbalance. Notch inhibition and/or LPA treatment may represent an effective therapeutic approach for treatment of MVID.

Early onset congenital diarrheas; single center experience

Congenital diarrheal disorders (CDDs) are a rare group of enteropathies that typically present in the early few months of life and pose a diagnostic challenge. We aimed to analyze the clinical findings and outcome of infants with CDDs and share experience about genetic testing. Demographic, clinical and genetic findings, and outcome of the patients (n=24) with CDDs were recorded from hospital files. The onset of diarrhea was within the neonatal period in 45.8% of the patients. The most frequent causes of CDDs were defects in digestion, absorption and transport of nutrients and electrolytes (DATN) (n=11, 45.8%) and defects in intestinal immune-related homeostasis (IIH) (n=6, 25%). Fat malabsorption (n=6) was the leading cause of defects in DATN. Extraintestinal manifestations including neurological involvement (25%) and renal involvement (20.8%) were common among the patients. Genetic analyses were performed for 16 patients (targeted gene analysis in 9, congenital diarrhea panel in 3, immune deficiency panel in 1 and whole-exome sequencing in 3 patients). Genetic diagnosis was achieved in 14 of 16 patients (87.5%) with therapeutic consequences in 8 of 16 patients (50%). During the follow-up, 6 patients (25%) died. The percentage of undefined etiology decreased, and treatment of the patients improved with the increased number of genetic testing in patients with CDDs.

Loss of Myosin Vb Results in Decreased Apical P‐Glycoprotein in vivo and in vitro

Background & Aims P-glycoprotein (p-gp), also known as multidrug resistance protein 1, is a xenobiotic efflux pump. In the small intestine, p-gp is localized to the apical membrane of enterocytes. Changes in p-gp expression is linked to inflammatory bowel diseases (IBD) and impairment of drug response in cancer. Regulating the trafficking of p-gp to the plasma membrane represents a plausible approach to improve therapy for cancer treatment. At present, the trafficking mechanism responsible for delivery of p-gp to the apical membrane of epithelial cells is unclear. Myosin Vb (Myo5b) is a molecular motor that is crucial for the proper transport of vesicles and proteins to the apical membrane of epithelial cells. Loss of functional Myo5b results in a congenital diarrheal disorder termed Microvillus Inclusion Disease (MVID). Individuals with MVID present with severe, unremitting diarrhea requiring parenteral nutrition and eventual small bowel transplantation. Studies using animal models of MVID and MVID patient tissue have revealed that loss of Myo5b results in a dramatic decrease in key transporters on the apical membrane of enterocytes. Therefore, we investigated whether proper localization of p-glycoprotein was impeded by loss of Myo5b. Methods Intestinal tissue was analyzed from neonatal control and germline Myo5b knockout (Myo5b KO) mice. Additionally, a tamoxifen inducible, intestinal specific mouse model of loss of Myo5b was also used (VillinCreERT2;Myo5bflox/flox). Adult Myo5bflox/flox mice treated with tamoxifen were used as controls for VillinCreERT2;Myo5bflox/flox mice. Intestinal organoids were generated from VillinCreERT2;Myo5bflox/flox mice and treated with either ethanol as a control or 4 hydroxy tamoxifen to induce loss of Myo5b. Results Immunostaining of gamma actin staining was performed to delineate the actin rich microvilli and identify the apical membrane. In control mice, p-gp was restricted to the apical membrane and co-localized with gamma actin as expected. In germline Myo5b KO mice, p-gp had increased immunofluorescence intensity and was observed below the apical membrane of small intestinal enterocytes. Lamp1 immunostaining also revealed that subapical p-gp was surrounded by lamp1 positive lysosomes in Myo5b KO mice. The association of lysosomes with p-gp suggests that improper localization of p-gp resulting from loss of Myo5b may promote lysosomal degradation of p-gp. Adult Myo5bflox/flox control mice treated with tamoxifen showed normal distribution of p-gp on the apical membrane of small intestinal enterocytes demonstrating co-localization with gamma actin. In contrast, tamoxifen induced VillinCreERT2;Myo5bflox/flox mice showed no p-gp at the apical brush border and no overlap with gamma actin immunostaining. Tamoxifen induced VillinCreERT2;Myo5bflox/flox mice displayed a large accumulation of p-gp below the apical membrane. Complementing our in vivo data, in vitro induction of Myo5b loss using 4 hydroxy tamoxifen resulted in a similar subapical localization of p-gp in induced VillinCreERT2;Myo5bflox/flox intestinal organoids compared to ethanol treated organoids. Conclusions Loss of Myo5b results in improper localization of p-gp. Collectively, these data suggest that Myo5b is necessary for the proper trafficking of p-gp to the apical membrane of intestinal cells.

A193 DGAT1 DEFICIENCY WITHOUT DIARRHEA

Abstract Background Acyl-CoA:diacylglycerol acyltransferase 1 (DGAT1) catalyzes the final step in triglyceride (TG) synthesis and is highly expressed in enterocytes (EC). DGAT1 deficiency (DGAT1D) is a rare autosomal recessive protein losing enteropathy (PLE) classified as a congenital diarrheal disorder (CDD). Presumably, fat ingestion causes accumulation of DGAT1 substrates within the EC causing lipotoxicity-induced EC dysfunction and death. Aims Report a presentation of DGAT1D atypical for a CDD. Methods We present an infant with DGAT1D with protracted emesis and failure to thrive (FTT) in the absence of diarrhea despite enteral nutrition with varied fat containing formulas (FCF). Results A male infant presented with emesis and FTT requiring multiple admissions. He was initially diagnosed with cow’s milk protein allergy due to concurrent bloody stools, which resolved with hypoallergenic formula. Reportedly watery stools when exclusively breastfed became formed following switch to formula at 2 weeks of age. Interestingly, he subsequently required intermittent suppositories. However, emesis and malnutrition progressed, refractory to omeprazole, baclofen, and varied hypo- and non-allergenic FCF (all containing >0.02g/ml fat, mixtures of medium and long chain FA). He had persistently low serum albumin, ceruloplasmin, and IgG, but SA1AT was normal. TGs were normal, although not measured on FCF. Low fecal elastase (FE) normalized after nutritional support but sweat chloride was intermediate. CFTR sequencing revealed CFTR mutations S466X and R1070 in cis. TPN was started for severe malnutrition at 2 months. Emesis resolved while fasted or receiving enteral electrolyte solution. Endoscopic biopsies on FCF showed increased lamina propria cellularity, no villous abnormalities in the duodenum, chronic inflammation in the gastric body, and normal colonic mucosa. Whole exome sequencing at 2 months showed homozygous c.838C>T (p.Arg280Ter) mutations in DGAT1, explaining his clinical presentation and biochemical features of PLE. After diagnosis, he was started on Tolerex® formula (fat = 0.017g/ml), which was tolerated. Conclusions DGAT1D is classified as a CDD, with vomiting often reported. This case describes a unique presentation of this rare condition, with emesis the predominant symptom, and notable constipation, demonstrating the variable phenotype of this condition. Fat malabsorption may contribute to constipation by altering viscosity of luminal contents or activating the ileal brake. Thus, DGAT1D should be considered on the differential for congenital PLE, even without diarrhea. This case also demonstrates the limitations of stool testing in DGAT1D as random SA1AT concentrations may not reflect A1AT clearance in the diagnosis of PLE. Low FE has been detected in children with malnutrition or dietary restriction and has been reported in DGAT1D, where it likely represents a physiologic consequence of FTT. Funding Agencies None

NGS Gene Panel Analysis Revealed Novel Mutations in Patients with Rare Congenital Diarrheal Disorders.

Congenital diarrheal disorders (CDDs) are early-onset enteropathies generally inherited as autosomal recessive traits. Most patients with CDDs require rapid diagnosis as they need immediate and specific therapy to avoid a poor prognosis, but their clinical picture is often overlapping with a myriad of nongenetic diarrheal diseases. We developed a next-generation sequencing (NGS) panel for the analysis of 92 CDD-related genes, by which we analyzed patients suspect for CDD, among which were (i) three patients with sucrose-isomaltase deficiency; (ii) four patients with microvillous inclusion disease; (iii) five patients with congenital tufting enteropathy; (iv) eight patients with glucose-galactose malabsorption; (v) five patients with congenital chloride diarrhea. In all cases, we identified the mutations in the disease-gene, among which were several novel mutations for which we defined pathogenicity using a combination of bioinformatic tools. Although CDDs are rare, all together, they have an incidence of about 1%. Considering that the clinical picture of these disorders is often confusing, a CDD-related multigene NGS panel contributes to unequivocal and rapid diagnosis, which also reduces the need for invasive procedures.

Long-Term Dietary Changes in Subjects with Glucose Galactose Malabsorption Secondary to Biallelic Mutations of SLC5A1

BackgroundGlucose galactose malabsorption (GGM) is a congenital diarrheal disorder of intestinal Na+/glucose cotransport (SGLT1/SLC5A1). The required glucose and galactose-restricted diet has been well described in infancy, but long-term nutrition follow-up is limited.AimTo perform a comprehensive nutritional assessment on a cohort of patients with GGM to gain insights into the consumption patterns within the population.MethodsA cross-sectional study examining dietary intake of a GGM cohort using prospective food records. The calories and nutrients of all foods, beverages, and condiments were analyzed with descriptive statistics and compared to intake patterns of age- and sex-matched NHANES groups.ResultsThe six patients were 0.7–26 years old. Whole foods and vegetable fats were major parts of the diet, while dairy and added sweeteners were restricted. Compared to typical US intakes, mean macronutrient distribution was 88th percentile from fat, 18th percentile from carbohydrates, and 78th percentile from protein. Fructose consumption, as a proportion of total sugar intake, decreased with age, from 86.1 to 50.4%. Meanwhile, glucose consumption increased with age, from 13.8 to 48.6% of sugar intake. However, the actual amount of glucose consumed remained low, equivalent to 4th percentile of US consumption level. Galactose intake was marginal throughout life.ConclusionsA GGM diet is a high-fat and high-protein/low-carbohydrate diet that is rich in fruits and vegetables but limited in dairy and added sugar. Relatively less fructose but more glucose is incorporated into the diet with age. Future studies should investigate the effects of the GGM diet on gut microbiome and long-term health.

Unequal Effects of Myosin 5B Mutations in Liver and Intestine Determine the Clinical Presentation of Low-Gamma-Glutamyltransferase Cholestasis.

Mutations in the MYO5B gene cause in some patients low gamma-glutamyltransferase (low-GGT) cholestatic liver disease (CLD) and in other patients microvillus inclusion disease (MVID, a congenital diarrheal and malabsorption disorder). Overlap of symptoms occurs but more MVID patients present cholestasis than CLD patients present diarrhea. Clinical observations indicate that MYO5B mutations can cause but also protect against CLD. This complicates family counseling and therapeutic decisions. Here we have reviewed the literature on MYO5B mutations in relation to CLD. It appears that variations in the clinical presentation of low-GGT CLD can be attributed to the coincident expression but unequal effects of MYO5B mutations in hepatocytes versus enterocytes, two cell types that jointly constitute the core of the enterohepatic circulation. Therefore, contrasting other low-GGT CLDs, those associated with MYO5B mutations should be viewed as a disease of the enterohepatic circulation rather than solely of the liver.

AP1S1 missense mutations cause a congenital enteropathy via an epithelial barrier defect

Congenital diarrheal disorders (CDD) comprise > 50 monogenic entities featuring chronic diarrhea of early-onset, including defects in nutrient and electrolyte absorption, enterocyte polarization, enteroendocrine cell differentiation, and epithelial integrity. Diarrhea is also a predominant symptom in many immunodeficiencies, congenital disorders of glycosylation, and in some defects of the vesicular sorting and transporting machinery. We set out to identify the etiology of an intractable diarrhea in 2 consanguineous families by whole-exome sequencing, and identified two novel AP1S1 mutations, c.269T>C (p.Leu90Pro) and c.346G>A (p.Glu116Lys). AP1S1 encodes the small subunit of the adaptor protein 1 complex (AP-1), which plays roles in clathrin coat-assembly and trafficking between trans-Golgi network, endosomes and the plasma membrane. An AP1S1 knock-out (KO) of a CaCo2 intestinal cell line was generated to characterize intestinal AP1S1 deficiency as well as identified mutations by stable expression in KO background. Morphology and prototype transporter protein distribution were comparable between parental and KO cells. We observed altered localization of tight-junction proteins ZO-1 and claudin 3, decreased transepithelial electrical resistance and an increased dextran permeability of the CaCo2-AP1S1-KO monolayer. In addition, lumen formation in 3D cultures of these cells was abnormal. Re-expression of wild-type AP1S1 in CaCo2-AP1S1-KO cells reverted these abnormalities, while expression of AP1S1 containing either missense mutation did not. Our data indicate that loss of AP1S1 function causes an intestinal epithelial barrier defect, and that AP1S1 mutations can cause a non-syndromic form of congenital diarrhea, whereas 2 reported truncating AP1S1 mutations caused MEDNIK syndrome, characterized by mental retardation, enteropathy, deafness, neuropathy, ichthyosis, and keratodermia.

Genetic variants in DGAT1 cause diverse clinical presentations of malnutrition through a specific molecular mechanism

BackgroundDGAT1, a gene encoding a protein involved in lipid metabolism, has been recently implicated in causing a rare nutritional and digestive disease presenting as Congenital Diarrheal Disorder (CDD). Genetic causes of malnutrition can be classified as metabolic disorders, caused by loss of a specific enzyme's function. However, disease driven by genetic variants in lipid metabolism genes is not well understood, and additional information is needed to better understand these effects. MethodsWe gathered a multi-institutional cohort of undiagnosed patients with a constellation of phenotypes presenting as malnutrition and metal ion dysregulation. Clinical Whole Exome Sequencing (WES) was performed on four patients and their unaffected parents. We prioritized genetic variants based on multiple criteria including population allele frequency and presumed inheritance pattern, and identified a candidate gene. Computational modeling was used to investigate if the altered amino acids are likely to result in a dysfunctional enzyme. ResultsWe identified a multi-institutional cohort of patients presenting with malnutrition-like symptoms and likely pathogenic genomic variants within DGAT1. Multiple approaches were used to profile the effect these variants have on protein structure and function. Laboratory and nutritional intervention studies showed rapid and robust patient responses. ConclusionsThis report adds on to the database for existing mutations known within DGAT1, a gene recently implicated with CDD, and also expands its clinical spectrum. Identification of these DGAT1 mutations by WES has allowed for changes in the patients’ nutritional rehabilitation, reversed growth failure and enabled them to be weaned off of total parenteral nutrition (TPN).

Lipid malabsorption from altered hormonal signaling changes early gut microbial responses.

Infants with congenital diarrheal disorders caused by enteroendocrine cell dysgenesis, or the loss of intestinal endocrine cells, causes severe malabsorptive diarrhea, though the mechanism is not fully understood. The transcription factor "aristaless-related homeobox" (Arx) is specifically expressed in intestinal endocrine cells. This study seeks to characterize the early malabsorptive phenotype of mice deficient for Arx using cell-type specific gene ablation in Villin-Cre; ArxloxP/Y ( Arxint) mice. In neonatal mice, the loss of intestinal Arx caused the loss of intestinal hormones, such as cholecystokinin, secretin, neurotensin, glucose-dependent insulinotropic peptide, glucagon-like peptide (GLP)-1 and GLP-2 but also upregulation of somatostatin. Arxint mice exhibited steatorrhea with the loss of lipid transport in duodenal enterocytes, upregulation of lysozyme-positive Paneth cells, and a secondary increase in antimicrobial peptides, specifically Reg3β. When the epithelium from Arxint mice was cultured ex vivo into enteroids, however, the Reg3β upregulation was lost under the sterile conditions. Thus, Arx is required for the appropriate lineage allocation of multiple enteroendocrine subtypes. We concluded that altered hormonal signaling caused by Arx deficiency results in lipid malabsorption, premature Paneth cell differentiation, and an inflammatory response, including neutrophilic infiltrates and a microbiota-triggered upregulation of Reg3β. NEW & NOTEWORTHY The enteroendocrine transcription factor aristaless-related homeobox (Arx) plays a key role in lineage specification. Changes in hormonal expression mediated by Arx lead to lipid malabsorption and premature Paneth cell development. Furthermore, global profiling of whole intestine from Arx-deficient mice revealed significant upregulation of antimicrobial peptides. This antimicrobial response in Arx-deficient animals is lost under sterile culture conditions of enteroids.

Intestinal Failure and Aberrant Lipid Metabolism in Patients With DGAT1 Deficiency

Background & AimsCongenital diarrheal disorders are rare inherited intestinal disorders characterized by intractable, sometimes life-threatening, diarrhea and nutrient malabsorption; some have been associated with mutations in diacylglycerol-acyltransferase 1 (DGAT1), which catalyzes formation of triacylglycerol from diacylglycerol and acyl-CoA. We investigated the mechanisms by which DGAT1 deficiency contributes to intestinal failure using patient-derived organoids.MethodsWe collected blood samples from 10 patients, from 6 unrelated pedigrees, who presented with early-onset severe diarrhea and/or vomiting, hypoalbuminemia, and/or (fatal) protein-losing enteropathy with intestinal failure; we performed next-generation sequencing analysis of DNA from 8 patients. Organoids were generated from duodenal biopsies from 3 patients and 3 healthy individuals (controls). Caco-2 cells and patient-derived dermal fibroblasts were transfected or transduced with vectors that express full-length or mutant forms of DGAT1 or full-length DGAT2. We performed CRISPR/Cas9-guided disruption of DGAT1 in control intestinal organoids. Cells and organoids were analyzed by immunoblot, immunofluorescence, flow cytometry, chromatography, quantitative real-time polymerase chain reaction, and for the activity of caspases 3 and 7.ResultsIn the 10 patients, we identified 5 bi-allelic loss-of-function mutations in DGAT1. In patient-derived fibroblasts and organoids, the mutations reduced expression of DGAT1 protein and altered triacylglycerol metabolism, resulting in decreased lipid droplet formation after oleic acid addition. Expression of full-length DGAT2 in patient-derived fibroblasts restored formation of lipid droplets. Organoids derived from patients with DGAT1 mutations were more susceptible to lipid-induced cell death than control organoids.ConclusionsWe identified a large cohort of patients with congenital diarrheal disorders with mutations in DGAT1 that reduced expression of its product; dermal fibroblasts and intestinal organoids derived from these patients had altered lipid metabolism and were susceptible to lipid-induced cell death. Expression of full-length wildtype DGAT1 or DGAT2 restored normal lipid metabolism in these cells. These findings indicate the importance of DGAT1 in fat metabolism and lipotoxicity in the intestinal epithelium. A fat-free diet might serve as the first line of therapy for patients with reduced DGAT1 expression. It is important to identify genetic variants associated with congenital diarrheal disorders for proper diagnosis and selection of treatment strategies.

MYO5B, STX3, and STXBP2 mutations reveal a common disease mechanism that unifies a subset of congenital diarrheal disorders: A mutation update.

Microvillus inclusion disease (MVID) is a rare but fatal autosomal recessive congenital diarrheal disorder caused by MYO5B mutations. In 2013, we launched an open‐access registry for MVID patients and their MYO5B mutations (www.mvid-central.org). Since then, additional unique MYO5B mutations have been identified in MVID patients, but also in non‐MVID patients. Animal models have been generated that formally prove the causality between MYO5B and MVID. Importantly, mutations in two other genes, STXBP2 and STX3, have since been associated with variants of MVID, shedding new light on the pathogenesis of this congenital diarrheal disorder. Here, we review these additional genes and their mutations. Furthermore, we discuss recent data from cell studies that indicate that the three genes are functionally linked and, therefore, may constitute a common disease mechanism that unifies a subset of phenotypically linked congenital diarrheal disorders. We present new data based on patient material to support this. To congregate existing and future information on MVID geno‐/phenotypes, we have updated and expanded the MVID registry to include all currently known MVID‐associated gene mutations, their demonstrated or predicted functional consequences, and associated clinical information.

New Insights and Perspectives in Congenital Diarrheal Disorders

We highlight new entities of congenital diarrheal disorders (CDDs) and progresses in understanding of functionally related genes, opening new diagnostic and therapeutic perspectives. The more significant advances have been made in field of pathogenesis, encouraging a better understanding not only of these rare diseases but also of more common pathogenetic mechanisms. CDDs represent an evolving group of rare chronic enteropathies with a typical onset early in the life. Usually, severe chronic diarrhea is the main clinical manifestation, but in other cases, diarrhea is only a component of a more complex systemic disease. The number of conditions has gradually increased, and many new genes have been indentified and functionally related to CDDs, opening new diagnostic and therapeutic perspectives. Advances in molecular analysis procedures have modified the diagnostic approach in CDDs, leading to a reduction in invasive and expensive procedures.

Molecular pathogenicity of novel sucrase-isomaltase mutations found in congenital sucrase-isomaltase deficiency patients

Background & aimsCongenital sucrase-isomaltase deficiency (CSID) is a genetic disorder associated with mutations in the sucrase-isomaltase (SI) gene. The diagnosis of congenital diarrheal disorders like CSID is difficult due to unspecific symptoms and usually requires invasive biopsy sampling of the intestine. Sequencing of the SI gene and molecular analysis of the resulting potentially pathogenic SI protein variants may facilitate a diagnosis in the future. This study aimed to categorize SI mutations based on their functional consequences. MethodscDNAs encoding 13 SI mutants were expressed in COS-1 cells. The molecular pathogenicity of the resulting SI mutants was defined by analyzing their biosynthesis, cellular localization, structure and enzymatic functions. ResultsThree biosynthetic phenotypes for the novel SI mutations were identified. The first biosynthetic phenotype was defined by mutants that are intracellularly transported in a fashion similar to wild type SI and with normal, but varying, levels of enzymatic activity. The second biosynthetic phenotype was defined by mutants with delayed maturation and trafficking kinetics and reduced activity. The third group of mutants is entirely transport incompetent and functionally inactive. ConclusionsThe current study unraveled CSID as a multifaceted malabsorption disorder that comprises three major classes of functional and trafficking mutants of SI and established a gradient of mild to severe functional deficits in the enzymatic functions of the enzyme. General significanceThis novel concept and the existence of mild consequences in a number of SI mutants strongly propose that CSID is an underdiagnosed and a more common intestinal disease than currently known.

Congenital Sodium Diarrhea: A Form of Intractable Diarrhea, With a Link to Inflammatory Bowel Disease.

Congenital diarrheal disorders (CDDs) represent a group of challenging clinical conditions for pediatricians because of the severity of the presentation and the broad range of possible differential diagnoses. CDDs arise from alterations in the transport of nutrients and electrolytes across the intestinal mucosa, from enterocyte and enteroendocrine cell differentiation and/or polarization defects, and from the modulation of the intestinal immune response. Advances were made recently in deciphering the etiology and pathophysiology of one of these disorders, congenital sodium diarrhea (CSD). CSD refers to an intractable diarrhea of intrauterine onset with high fecal sodium loss. CSD is clinically and genetically heterogeneous. A syndromic form of CSD features choanal and intestinal atresias as well as recurrent corneal erosions. Small bowel histology frequently detects an epithelial "tufting" dysplasia. It is autosomal recessively inherited, and caused by SPINT2 mutations. The nonsyndromic form of CSD can be caused by dominant activating mutations in GUCY2C, encoding intestinal receptor guanylate cyclase C (GC-C), and by autosomal recessive SLC9A3 loss-of-function mutations. SLC9A3 encodes Na/H antiporter 3, the major intestinal brush border Na/H exchanger, and a downstream target of GC-C. A number of patients with GUCY2C and SLC9A3 mutations developed inflammatory bowel disease. Both the number of recognized CDD forms as well as the number of underlying disease genes are gradually increasing. Knowledge of these CDD genes enables noninvasive, next-generation gene panel-based testing to facilitate an early diagnosis in CDD. Primary Na/H antiporter 3 and GC-C malfunction is implicated as a predisposition for inflammatory bowel disease in subset of patients.