A novel nutritional approach to infants and children with congenital diarrhea due to homozygous DGAT1 mutations.

OBJECTIVES: Diacylglycerol acyltransferase (DGAT) catalyzes the final step in triglyceride synthesis. DGAT1 is expressed in human enterocytes and is essential for fat absorption. Homozygous DGAT1 deficiency often presents with severe diarrhea and protein-losing enteropathy (PLE) in the 1st weeks of life. Because severe restriction of fat intake controls diarrhea and decreases PLE, total parenteral nutrition (TPN) was the initial standard therapy in infants and children. We present tertiary center experience managing infants and children with DGAT1 deficiency resulting in the development of a nutritional approach that minimizes the use of TPN. METHODS: From 2014 to 2020, 12 infants with DGAT1 deficiency were treated. Stool output, growth, and development, as well as essential fatty acid status, were monitored. This retrospective experience formed the basis for treatment recommendations, which include an ultralow fat formula with intermittent peripheral intravenous lipid infusions during the 1st year of life. RESULTS: All patients with prolonged intestinal fat exposure had PLE, which resolved when treated with the nutrition protocol. Essential fatty acid status as measured by triene:tetraene ratios normalized in all treated patients. Over time, early genetic diagnosis and prompt initiation of an ultralow fat diet with peripheral intravenous lipid infusions replaced the need for TPN. CONCLUSIONS: Children with DGAT1 deficiency respond to dietary restriction of lipids. Management with a novel nutritional approach provides effective treatment for infants with DGAT1 deficiency, treats diarrhea and PLE, promotes growth and development, avoids TPN dependency, and decreases the potential for essential fatty acid deficiency.

Lymphoma in Pediatric-Onset Inflammatory Bowel Disease Treated with Infliximab Monotherapy: A Case Series.

BACKGROUND: Inflammatory bowel diseases (IBD) are often treated with anti-tumor necrosis factor alpha (anti-TNFα) medications. Concomitant treatment of IBD with anti-TNFα agents and immunomodulators appears to be associated with an increased risk for lymphoma. METHODS: Patients who developed lymphoma while on monotherapy with an anti-TNFα agent were identified at three centers. Institutional Review Board approval was obtained. RESULTS: Five adolescents and young adult patients with pediatric-onset IBD who were treated with infliximab (IFX) without exposure to thiopurines were subsequently diagnosed with lymphoma. Three of the five patients had bone involvement at presentation. Epstein-Barr virus was positive in 2 cases. Median time from diagnosis of IBD and exposure to IFX prior to diagnosis of lymphoma was 5 and 4.3 years, respectively. CONCLUSIONS: This case series reports long-term follow-up for young patients with IBD who were treated with IFX monotherapy and developed lymphoma. Three of the five patients had bone involvement. In general, the risk of lymphoma following exposure to anti-TNFα medications alone remains low, but the incidence of primary bone lymphomas in IBD has not been reported. Studies examining longer exposure times may be needed to determine the true lymphoma risk in patients treated with IFX monotherapy.

Interactions between the intestinal microbiota and epigenome in individuals with autism spectrum disorder.

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by variable impairment of cognitive function and interpersonal relationships. Furthermore, some individuals with ASD have gastrointestinal disorders that have been correlated with impairments in intestinal microbiota. Gut microbiota are important not only for intestinal health, but also for many other functions including food digestion, energy production, immune system regulation, and, according to current data, behavior. Disruption of the indigenous microbiota, microbial dysbiosis (imbalance between microorganisms present in the gut), overgrowth of potentially pathogenic microorganisms, a less diverse microbiome, or lower levels of beneficial bacteria in children with ASD can affect behavior. Metabolome analysis in children with ASD has identified perturbations in multiple metabolic pathways that might be associated with cognitive functions. Recent studies have shown that the intestinal microbiome provides environmental signals that can modify host response to stimuli by modifying the host epigenome, which affects DNA methylation, histone modification, and non-coding RNAs. The most studied microbiota-produced epigenetic modifiers are short-chain fatty acids, although other products of intestinal microbiota might also cause epigenetic modifications in the host's DNA. Here we review evidence suggesting that epigenetic alterations caused by modification of gene expression play an important role in understanding ASD.

Importance of early detection of infantile inflammatory bowel disease with defective IL-10 pathway: A case report.

RATIONALE: Infantile inflammatory bowel disease (IBD) is an extremely rare subgroup of IBD that includes patients whose age of onset is younger than 2 years old. These patients can have more surgical interventions, and a severe and refractory disease course with higher rates of conventional treatment failure. Monogenic defects play an important role in this subgroup of IBD, and identification of the underlying defect can guide the therapeutic approach. PATIENT CONCERNS: In 2007, a 4-month-old girl from a nonconsanguineous family presenting with anal fistula, chronic diarrhea, and failure to thrive. She underwent multiple surgical repairs but continued to have persistent colitis and perianal fistulas. DIAGNOSIS: Crohn's disease was confirmed by endoscopic and histologic finding. INTERVENTION: Conventional pediatric IBD therapy including multiple surgical interventions and antitumor necrosis factor alpha agents were applied. OUTCOMES: The patient did not respond to conventional pediatric IBD therapy. Interleukin-10 (IL-10) receptor mutation was discovered by whole-exome sequencing and defective IL-10 signaling was proved by functional test of IL-10 signaling pathway by the age of 12. The patient is currently awaiting hematopoietic stem cell transplantation. LESSONS: Early detection of underlying genetic causes of patients with infantile-IBD is crucial, since it may prevent patients from undergoing unnecessary surgeries and adverse effects from ineffective medical therapies. Moreover, infantile-IBD patients with complex perianal disease, intractable early onset enterocolitis and extraintestinal manifestations including oral ulcers and skin folliculitis, should undergo genetic and functional testing for IL-10 pathway defect.

Bacterial dysbiosis predicts the diagnosis of Crohn's disease in Saudi children.

BACKGROUND: Studies have reached different conclusions regarding the accuracy of dysbiosis in predicting the diagnosis of Crohn's disease (CD). The aim of this report is to assess the utility of mucosal and fecal microbial dysbiosis as predictors in the diagnosis of this condition in Saudi children. METHODS: Tissue and fecal samples were collected prospectively from children with final diagnosis of CD and from controls. Bacterial DNA was extracted and sequenced using Illumina MiSeq chemistry. The abundance and diversity of bacteria in tissue and fecal samples were determined in relation to controls. Sparse logistic regression was calculated to predict the diagnosis of CD based on subject's microbiota profile. RESULTS: There were 17 children with CD and 18 controls. All children were Saudis. The median age was 13.9 and 16.3 years for children with CD and controls respectively. Sex distribution showed that 11/17 (65%) of the CD and 12/18 (67%) of the control subjects were boys. The mean area under the curve (AUC) was significantly higher in stool (AUC = 0.97 ± 0.029) than in tissue samples (AUC = 0.83 ±0.055) (P < 0.001). CONCLUSIONS: We found high AUC in mucosal and fecal samples. The higher AUC for fecal samples suggests higher accuracy in predicting the diagnosis of CD.

Gut Microbiota and Gender in Autism Spectrum Disorders.

Gender dimorphism in autism spectrum disorders (ASD) is well known; however, the reasons for gender differences in autism are poorly understood. There are several hypotheses that might explain male prevalence in ASD, including increased levels of androgens, "extreme male brain," and a combination of elevated levels of prenatal testosterone in conjunction with prenatal stress. In this comprehensive review, differences in the gut microbiome and metabolome in humans and animals are described to explain gender differences in individuals with ASD, effects on behavior and social interactions and the impact of antibiotics, probiotics and fecal transplants. The bidirectional relationship between sex hormones and intestinal microbiota could also be relevant. Such interactions have been described in autoimmune diseases, but thus far, are not implicated in ASD. Since intestinal microbiota may affect behavior, it is possible that the prevalence of ASD in boys may be associated with more significant changes in the intestinal microbiome than in affected girls.

Outcomes Following Pouch Formation in Paediatric Ulcerative Colitis: A Study From the Porto Group of ESPGHAN.

INTRODUCTION: Contemporary pediatric data on pouch outcomes are sparse, especially in the era of laparoscopic surgeries. We aimed to assess outcomes and predictors in children with ulcerative colitis/inflammatory bowel disease (IBD)-unclassified who underwent colectomy and ileal pouch-anal anastomosis. METHODS: This was a multicenter retrospective cohort study from 17 IBD centers affiliated with the pediatric IBD Porto group of ESPGHAN. An electronic REDcap system was used to collate baseline characteristics, demographic, clinical, management and surgical data, short- and long-term outcomes, and to identify potential predictors of pouch outcome. RESULTS: Of the 129 patients included, 86 (67%) developed pouchitis during follow-up of median 40 months (interquartile range 26-72), of whom 33 (26%) with chronic pouchitis. Patients operated on by surgeons performing <10 pouch surgeries/year had a higher rate of chronic pouchitis (11/27 [41%] vs 8/54 [15%], P = 0.013) on both univariable and multivariable analyses and also associated with time to pouchitis (P = 0.018) and chronic pouchitis (P = 0.020). At last follow-up, overall pouch performance was rated good/excellent in 86 (74%) patients. Time from colectomy to pouch formation was not associated with pouch outcomes. Despite higher rate of nonsevere surgical complications among children undergoing colectomy at <10 years of age (7/16 [44%] vs 10/92 [11%], P = 0.003), functional outcome and pouchitis rate did not differ. CONCLUSIONS: Pouchitis rate in children with ulcerative colitis/IBD unclassified is high. Surgeon experience is the major modifiable risk factor for pouch outcome. Our analyses suggest that pouch surgery can also be performed successfully in young children.

Additional Intestinal Mucosal Biopsy Sampling for Research Is Safe During Pediatric Endoscopic Procedures.

Advancing the understanding of inflammatory bowel disease (IBD) pathogenesis has been facilitated by mechanistic studies that require human intestinal tissue. Enrolling pediatric subjects into these studies improves our knowledge of IBD in this underserved population. Given the additional research protections granted to children, institutional review boards (IRBs) must weigh the benefit of obtaining research biopsies against perceived risks. Although obtaining clinical biopsies from children is generally considered safe, there are only limited data on the safety of obtaining research biopsies in children.1-6.

Long-term Outcomes of Paediatric Patients Admitted With Acute Severe Colitis- A Multicentre Study From the Paediatric IBD Porto Group of ESPGHAN.

BACKGROUND AND AIM: Acute severe colitis [ASC] is associated with significant morbidity in paediatric patients with ulcerative colitis [UC]. Most outcome studies in ASC since tumour necrosis factor alpha [TNFα] antagonists became available have focused on the first year after admission. The aim of this study was to characterise the longer-term outcomes of paediatric patients admitted with ASC. METHODS: This retrospective study was conducted in 25 centres across Europe and North America. Data on patients with UC aged <18 years, admitted with ASC (defined as paediatric ulcerative colitis activity index [PUCAI] score ≥65) between 2009 and 2011, were collected at discharge and 1, 3 and 5 years after admission. The primary outcome was colectomy-free rates at each time point. RESULTS: Of the 141 patients admitted with ASC, 137 [97.1%] were treated with intravenous corticosteroids. Thirty-one [22.6%] patients were escalated to second-line therapy, mainly to infliximab. Sixteen patients [11.3%] underwent colectomy before discharge. Long-term follow-up showed colectomy-free rates were 71.3%, 66.4% and 63.6% at 1, 3 and 5 years after initial ASC admission, respectively, and were similar across different age groups. Sub-analysis of colectomy rates in patients with new-onset disease [42.5% of the cohort] yielded similar results. In a multivariate analysis, use of oral steroids in the 3 months before admission, erythrocyte sedimentation rate >70 mm/h, and albumin <2.5 g/dL, were significantly associated with 5-year colectomy risk. CONCLUSIONS: High colectomy rates were demonstrated in paediatric UC patients admitted with ASC. Additional studies are required to determine whether intensification of anti-TNFα treatment, close therapeutic drug monitoring, and use of new drugs alter this outcome.

Performance of Surveillance MR Enterography (MRE) in Asymptomatic Children and Adolescents With Crohn's Disease.

BACKGROUND: MR enterography (MRE) is the primary modality for evaluating small bowel disease in pediatric Crohn's patients. Standard clinical practice includes imaging patients at diagnosis and during symptomatic recurrence. The role for MRE in surveillance of asymptomatic Crohn's patients has not yet been established. PURPOSE: To determine whether MRE imaging features are associated with clinical recurrence. STUDY TYPE: Retrospective. POPULATIONS: Pediatric Crohn's patients who underwent MRE while asymptomatic, defined by pediatric gastroenterologists using a physician global assessment; 35 MREs were identified. FIELD STRENGTH/SEQUENCE: 1.5T including T2 -weighted single-shot fast spin echo, balanced steady-state free precession, diffusion-weighted, and contrast-enhanced multiphase T1 -weighted gradient recalled echo sequences. ASSESSMENT: MREs were reviewed by three radiologists independently for mural thickening, T2 -weighted hyperintensity, diffusion restriction, hyperenhancement, vasa recta engorgement, and overall assessment of disease activity. Two pediatric gastroenterologists reviewed patient medical records for 6 months following MRE to evaluate for recurrence, defined as Crohn's-related treatment escalation, surgery, or hospitalization. STATISTICAL TESTS: Fisher's exact test, Wald chi-square test, and model selection by Akaike information criterion minimization were used to assess statistical significance of MRE imaging features. RESULTS: Of 35 MREs identified, seven cases demonstrated clinical recurrence at 6 months (20%); 28 cases remained in remission (80%). Imaging features of active disease were present in 86% of patients with recurrence compared to 29% of patients in remission (P = 0.01). Wall thickening, T2 -weighted hyperintensity, hyperenhancement, and diffusion restriction were significantly associated with recurrence. Multivariate regression analysis determined diffusion restriction to be the best predictor of recurrence within 6 months (P = 0.001, area under the curve 0.786). DATA CONCLUSION: MRE performed on young asymptomatic Crohn's patients can identify patients who have a high probability of developing clinical recurrence in a 6-month period, indicating a potential role for surveillance imaging to assess for subclinical active disease. LEVEL OF EVIDENCE: 3 Technical Efficacy Stage 5 J. Magn. Reson. Imaging 2019;50:1955-1963.

Multi-omics of the gut microbial ecosystem in inflammatory bowel diseases.

Inflammatory bowel diseases, which include Crohn's disease and ulcerative colitis, affect several million individuals worldwide. Crohn's disease and ulcerative colitis are complex diseases that are heterogeneous at the clinical, immunological, molecular, genetic, and microbial levels. Individual contributing factors have been the focus of extensive research. As part of the Integrative Human Microbiome Project (HMP2 or iHMP), we followed 132 subjects for one year each to generate integrated longitudinal molecular profiles of host and microbial activity during disease (up to 24 time points each; in total 2,965 stool, biopsy, and blood specimens). Here we present the results, which provide a comprehensive view of functional dysbiosis in the gut microbiome during inflammatory bowel disease activity. We demonstrate a characteristic increase in facultative anaerobes at the expense of obligate anaerobes, as well as molecular disruptions in microbial transcription (for example, among clostridia), metabolite pools (acylcarnitines, bile acids, and short-chain fatty acids), and levels of antibodies in host serum. Periods of disease activity were also marked by increases in temporal variability, with characteristic taxonomic, functional, and biochemical shifts. Finally, integrative analysis identified microbial, biochemical, and host factors central to this dysregulation. The study's infrastructure resources, results, and data, which are available through the Inflammatory Bowel Disease Multi'omics Database ( http://ibdmdb.org ), provide the most comprehensive description to date of host and microbial activities in inflammatory bowel diseases.

Development of a Brief Parent-Report Screen for Common Gastrointestinal Disorders in Autism Spectrum Disorder.

Gastrointestinal dysfunction in children with autism spectrum disorder (ASD) is common and associated with problem behaviors. This study describes the development of a brief, parent-report screen that relies minimally upon the child's ability to report or localize pain for identifying children with ASD at risk for one of three common gastrointestinal disorders (functional constipation, functional diarrhea, and gastroesophageal reflux disease). In a clinical sample of children with ASD, this 17-item screen identified children having one or more of these disorders with a sensitivity of 84%, specificity of 43%, and a positive predictive value of 67%. If found to be valid in an independent sample of children with ASD, the screen will be useful in both clinical practice and research.

Microbiota profile in new-onset pediatric Crohn's disease: data from a non-Western population.

BACKGROUND: The role of microbiota in Crohn's disease (CD) is increasingly recognized. However, most of the reports are from Western populations. Considering the possible variation from other populations, the aim of this study was to describe the microbiota profile in children with CD in Saudi Arabia, a non-Western developing country population. RESULTS: Significantly more abundant genera in children with CD included Fusobacterium, Peptostreptococcus, Psychrobacter, and Acinetobacter; whereas the most significantly-depleted genera included Roseburia, Clostridium, Ruminococcus, Ruminoclostridium, Intestinibacter, Mitsuokella, Megasphaera, Streptococcus, Lactobacillus, Turicibacter, and Paludibacter. Alpha diversity was significantly reduced in stool (p = 0.03) but not in mucosa (p = 0.31). Beta diversity showed significant difference in community composition between control and CD samples (p = 0.03). CONCLUSION: In this developing country, we found a pattern of microbiota in children with CD similar to Western literature, suggesting a role of recent dietary lifestyle changes in this population on microbiota structure.

Fungal dysbiosis predicts the diagnosis of pediatric Crohn's disease.

AIM: To investigate the accuracy of fungal dysbiosis in mucosa and stool for predicting the diagnosis of Crohn's disease (CD). METHODS: Children were prospectively enrolled in two medical centers: one university hospital and one private gastroenterology clinic in the city of Riyadh, Kingdom of Saudi Arabia. The children with confirmed diagnosis of CD by standard guidelines were considered cases, and the others were considered non-inflammatory bowel disease controls. Mucosal and stool samples were sequenced utilizing Illumina MiSeq chemistry following the manufacturer's protocols, and abundance and diversity of fungal taxa in mucosa and stool were analyzed. Sparse logistic regression was used to predict the diagnosis of CD. The accuracy of the classifier was tested by computing the receiver operating characteristic curves with 5-fold stratified cross-validation under 100 permutations of the training data partition and the mean area under the curve (AUC) was calculated. RESULTS: All the children were Saudi nationals. There were 15 children with CD and 20 controls. The mean age was 13.9 (range: 6.7-17.8) years for CD children and 13.9 (3.25-18.6) years for controls, and 10/15 (67%) of the CD and 13/20 (65%) of the control subjects were boys. CD locations at diagnosis were ileal (L1) in 4 and colonic (L3) in 11 children, while CD behavior was non-stricturing and non-penetrating (B1) in 12 and stricturing (B2) in 3 children. The mean AUC for the fungal dysbiosis classifier was significantly higher in stools (AUC = 0.85 ± 0.057) than in mucosa (AUC = 0.71 ± 0.067) (P < 0.001). Most fungal species were significantly more depleted in stools than mucosal samples, except for Saccharomyces cerevisiae and S. bayanus, which were significantly more abundant. Diversity was significantly more reduced in stools than in mucosa. CONCLUSION: We found high AUC of fungal dysbiosis in fecal samples of children with CD, suggesting high accuracy in predicting diagnosis of CD.

Colonic Inhibition of Phosphatase and Tensin Homolog Increases Colitogenic Bacteria, Causing Development of Colitis in Il10-/- Mice.

Background: Phosphatase and tensin homolog (Pten) is capable of mediating microbe-induced immune responses in the gut. Thus, Pten deficiency in the intestine accelerates colitis development in Il10-/- mice. As some ambient pollutants inhibit Pten function and exposure to ambient pollutants may increase inflammatory bowel disease (IBD) incidence, it is of interest to examine how Pten inhibition could affect colitis development in genetically susceptible hosts. Methods: With human colonic mucosa biopsies from pediatric ulcerative colitis and non-IBD control subjects, we assessed the mRNA levels of the PTEN gene and the gene involved in IL10 responses. The data from the human tissues were corroborated by treating Il10-/-, Il10rb-/-, and wild-type C57BL/6 mice with Pten-specific inhibitor VO-OHpic. We evaluated the severity of mouse colitis by investigating the tissue histology and cytokine production. The gut microbiome was investigated by analyzing the 16S ribosomal RNA gene sequence with mouse fecal samples. Results: PTEN and IL10RB mRNA levels were reduced in the human colonic mucosa of pediatric ulcerative colitis compared with non-IBD subjects. Intracolonic treatment of the Pten inhibitor induced colitis in Il10-/- mice, characterized by reduced body weight, marked colonic damage, and increased production of inflammatory cytokines, whereas Il10rb-/- and wild-type C57BL/6 mice treated with the inhibitor did not develop colitis. Pten inhibitor treatment changed the fecal microbiome, with increased abundance of colitogenic bacteria Bacteroides and Akkermansia in Il10-/- mice. Conclusions: Loss of Pten function increases the levels of colitogenic bacteria in the gut, thereby inducing deleterious colitis in an Il10-deficient condition.

Genetic Variation Affects C-Reactive Protein Elevations in Crohn's Disease.

BACKGROUND: C-reactive protein (CRP) is a serum marker that is used to measure disease activity in Crohn's disease (CD). However, a subset of CD patients have normal CRP during flares. In rheumatoid arthritis and lupus, genetic variants can restrict CRP elevations during flares. This study sought to determine if common CRP genetic variants affect CRP values during active CD. METHODS: Subjects with CD who participated in the Partners HealthCare BioBank were genotyped for 5 common CRP genetic variants (rs2794520, rs3122012, rs3093077, rs2808635, and rs1800947). Medical records were reviewed to determine disease activity and the highest CRP value during active CD. CRP values during active infection or malignancy at the time of the test were excluded. CRP values were compared by genotype using the Mann-Whitney test. RESULTS: The study included 199 subjects with active CD (21 to 86 years of age). Subjects with the rs2794520 TT genotype had a lower CRP than subjects with the CC genotype (58.3 mg/L vs 28.4 mg/L, P = 0.008). Subjects with the rs1800947 CG genotype had a lower CRP than those with the CC genotype (54.3 mg/L vs 22.4 mg/L, P < 0.0001); 41.6% of TT subjects had a normal CRP compared with 24.1% of CT subjects and 16.5% of CC subjects (P = 0.041). CONCLUSIONS: This study demonstrates that rs2794520 and rs1800947 are associated with a restriction of CRP elevations during active CD. While CRP is typically a reliable biomarker in CD, there is a subset of CD patients with a genetically determined restriction of CRP in whom other disease markers should be utilized.

Genetic variants in cellular transport do not affect mesalamine response in ulcerative colitis.

BACKGROUND AND AIMS: Mesalamine is commonly used to treat ulcerative colitis (UC). Although mesalamine acts topically, in vitro data suggest that intracellular transport is required for its beneficial effect. Genetic variants in mucosal transport proteins may affect this uptake, but the clinical relevance of these variants has not been studied. The aim of this study was to determine whether variants in genes involved in cellular transport affect the response to mesalamine in UC. METHODS: Subjects with UC from a 6-week clinical trial using multiple doses of mesalamine were genotyped using a genome-wide array that included common exome variants. Analysis focused on cellular transport gene variants with a minor allele frequency >5%. Mesalamine response was defined as improvement in Week 6 Physician's Global Assessment (PGA) and non-response as a lack of improvement in Week 6 PGA. Quality control thresholds included an individual genotyping rate of >90%, SNP genotyping rate of >98%, and exclusion for subjects with cryptic relatedness. All included variants met Hardy-Weinberg equilibrium (p>0.001). RESULTS: 457 adults with UC were included with 280 responders and 177 non-responders. There were no common variants in transporter genes that were associated with response to mesalamine. The genetic risk score of responders was similar to that of non-responders (p = 0.18). Genome-wide variants demonstrating a trend towards mesalamine response included ST8SIA5 (p = 1x10-5). CONCLUSIONS: Common transporter gene variants did not affect response to mesalamine in adult UC. The response to mesalamine may be due to rare genetic events or environmental factors such as the intestinal microbiome.

Identification and characterization of a novel DGAT1 missense mutation associated with congenital diarrhea.

Acyl-CoA:diacylglycerol acyltransferase (DGAT)1 and DGAT2 catalyze triglyceride (TG) biosynthesis in humans. Biallelic loss-of-function mutations in human DGAT1 result in severe congenital diarrhea and protein-losing enteropathy. Additionally, pharmacologic inhibition of DGAT1 led to dose-related diarrhea in human clinical trials. Here we identify a previously unknown DGAT1 mutation in identical twins of South Asian descent. These male patients developed watery diarrhea shortly after birth, with protein-losing enteropathy and failure to thrive. Exome sequencing revealed a homozygous recessive mutation in DGAT1, c.314T>C, p.L105P. We show here that the p.L105P DGAT1 enzyme produced from the mutant allele is less abundant, resulting in partial loss of TG synthesis activity and decreased formation of lipid droplets in patient-derived primary dermal fibroblasts. Thus, in contrast with complete loss-of-function alleles of DGAT1, the p.L105P missense allele partially reduces TG synthesis activity and causes a less severe clinical phenotype. Our findings add to the growing recognition of DGAT1 deficiency as a cause of congenital diarrhea with protein-losing enteropathy and indicate that DGAT1 mutations result in a spectrum of diseases.