Variants in STXBP3 are Associated with Very Early Onset Inflammatory Bowel Disease, Bilateral Sensorineural Hearing Loss and Immune Dysregulation.

BACKGROUND AND AIMS: Very early onset inflammatory bowel disease [VEOIBD] is characterized by intestinal inflammation affecting infants and children less than 6 years of age. To date, over 60 monogenic aetiologies of VEOIBD have been identified, many characterized by highly penetrant recessive or dominant variants in underlying immune and/or epithelial pathways. We sought to identify the genetic cause of VEOIBD in a subset of patients with a unique clinical presentation. METHODS: Whole exome sequencing was performed on five families with ten patients who presented with a similar constellation of symptoms including medically refractory infantile-onset IBD, bilateral sensorineural hearing loss and, in the majority, recurrent infections. Genetic aetiologies of VEOIBD were assessed and Sanger sequencing was performed to confirm novel genetic findings. Western analysis on peripheral blood mononuclear cells and functional studies with epithelial cell lines were employed. RESULTS: In each of the ten patients, we identified damaging heterozygous or biallelic variants in the Syntaxin-Binding Protein 3 gene [STXBP3], a protein known to regulate intracellular vesicular trafficking in the syntaxin-binding protein family of molecules, but not associated to date with either VEOIBD or sensorineural hearing loss. These mutations interfere with either intron splicing or protein stability and lead to reduced STXBP3 protein expression. Knock-down of STXBP3 in CaCo2 cells resulted in defects in cell polarity. CONCLUSION: Overall, we describe a novel genetic syndrome and identify a critical role for STXBP3 in VEOIBD, sensorineural hearing loss and immune dysregulation.

Mucosal Gene Expression in Pediatric and Adult Patients With Ulcerative Colitis Permits Modeling of Ideal Biopsy Collection Strategy for Transcriptomic Analysis.

Background: Transcriptional profiling has been performed on biopsies from ulcerative colitis patients. Limitations in prior studies include the variability introduced by inflammation, anatomic site of biopsy, extent of disease, and medications. We sought to more globally understand the variability of gene expression from patients with ulcerative colitis to advance our understanding of its pathogenesis and to guide clinical study design. Methods: We performed transcriptional profiling on 13 subjects, including pediatric and adult patients from 2 hospital sites. For each patient, we collected 6 biopsies from macroscopically inflamed tissue and 4 biopsies from macroscopically healthy-appearing tissue. Isolated RNA was used for microarray gene expression analysis utilizing Affymetrix Human Primeview microarrays. Ingenuity pathway analysis was used to assess over-representation of gene ontology and biological pathways. RNAseq was also performed, and differential analysis was assessed to compare affected vs unaffected samples. Finally, we modeled the minimum number of biopsies required to reliably detect gene expression across different subject numbers. Results: Transcriptional profiles co-clustered independently of the hospital collection site, patient age, sex, and colonic location, which parallels prior gene expression findings. A small set of genes not previously described was identified. Our modeling analysis reveals the number of biopsies and patients per cohort to yield reliable results in clinical studies. Conclusions: Key findings include concordance, including some expansion, of previously published gene expression studies and similarity among different age groups. We also established a reliable statistical model for biopsy collection for future clinical studies.

The Impact of Combination Therapy on Infliximab Levels and Antibodies in Children and Young Adults With Inflammatory Bowel Disease.

Goal: The aim of this study was to evaluate the effect of combination therapy with methotrexate or 6-mercaptopurine on infliximab levels (IFXL) and antibodies to infliximab (ATI). Background: Infliximab (IFX) is a highly effective therapy for inflammatory bowel disease (IBD). Unfortunately, 25%-50% of patients will lose response to IFX. Loss of response is correlated with low IFXL and ATI formation which accelerates drug clearance. Combination therapy is thought to decrease ATI formation. Methods: We performed a cross-sectional analysis of 223 pediatric and young adult patients with IBD on IFX. IFXL and ATI were measured and compared between subjects on current combination therapy, prior combination therapy, and IFX monotherapy. Results: Eighty-four (37.7%) patients were on combination therapy and 139 (62.3%) were on IFX monotherapy. Within the current monotherapy group, 112 (80.6%) had previously been on combination therapy, while 27 (19.4%) had never been on a concomitant immunomodulator. Patients currently on combination therapy had a higher IFXL (17.00 ± 1.33 µg/mL) than those currently on IFX monotherapy (13.18 ± 1.26 µg/mL), P < 0.01. IFXL was lowest in patients who had never been on combination therapy (11.53 ± 2.05 µg/mL) and highest in patients currently on combination therapy (17.00 ± 1.33 µg/mL). Patients currently on combination therapy had a lower rate of detectable ATI (9.5%) compared with those on monotherapy (20.0%) in multivariate analysis (odds ratio [OR]: 0.3; 95% confidence interval (CI), 0.1-0.7, P < 0.01). Conclusions: Current or prior combination therapy is associated with higher IFXL and lower rates of ATI formation.