Cellular and molecular basis of proximal small intestine disorders.

The proximal part of the small intestine, including duodenum and jejunum, is not only dedicated to nutrient digestion and absorption but is also a highly regulated immune site exposed to environmental factors. Host-protective responses against pathogens and tolerance to food antigens are essential functions in the small intestine. The cellular ecology and molecular pathways to maintain those functions are complex. Maladaptation is highlighted by common immune-mediated diseases such as coeliac disease, environmental enteric dysfunction or duodenal Crohn's disease. An expanding spectrum of more than 100 rare monogenic disorders inform on causative molecular mechanisms of nutrient absorption, epithelial homeostasis and barrier function, as well as inflammatory immune responses and immune regulation. Here, after summarizing the architectural and cellular traits that underlie the functions of the proximal intestine, we discuss how the integration of tissue immunopathology and molecular mechanisms can contribute towards our understanding of disease and guide diagnosis. We propose an integrated mechanism-based taxonomy and discuss the latest experimental approaches to gain new mechanistic insight into these disorders with large disease burden worldwide as well as implications for therapeutic interventions.

Familial recurrence of incontinentia pigmenti due to de novo pathogenic variants in the IKBKG gene.

Incontinentia pigmenti (IP, Bloch-Sulzberger syndrome) is a multisystem disorder which associates specific skin lesions that evolves in four stages, and occasionally, central nervous system, eye, hair, and teeth involvement. Familial (35%) and sporadic (65%) cases are caused by pathogenic variants in the IKBKG gene. Here we report an unusual family, where, in two half-sisters affected by typical IP, molecular genetic analysis identified a likely pathogenic non-sense variant in the IKBKG gene of one of the sisters, the other being not a carrier. The strong clinical conviction motivated further molecular genetic investigations, which led to the characterization of a second variant in this unique family. X chromosome inactivation studies demonstrated the paternal origin of these two de novo variants. For genes with frequent de novo mutations, the coexistence of different pathogenic mutations in the same family is a possibility, and constitutes a challenge for genetic counseling.

Insights into the expanding intestinal phenotypic spectrum of SOCS1 haploinsufficiency and therapeutic options.

PURPOSE: Hyper activation of the JAK-STAT signaling underlies the pathophysiology of many human immune-mediated diseases. Herein, the study of 2 adult patients with SOCS1 haploinsufficiency illustrates the severe and pleomorphic consequences of its impaired regulation in the intestinal tract. METHODS: Two unrelated adult patients presented with gastrointestinal manifestations, one with Crohn's disease-like ileo-colic inflammation refractory to anti-TNF and the other with lymphocytic leiomyositis causing severe chronic intestinal pseudo-occlusion. Next-generation sequencing was used to identify the underlying monogenic defect. One patient received anti-IL-12/IL-23 treatment while the other received the JAK1 inhibitor, ruxolitinib. Peripheral blood, intestinal tissues, and serum samples were analyzed before-and-after JAK1 inhibitor therapy using mass cytometry, histology, transcriptomic, and Olink assay. RESULTS: Novel germline loss-of-function variants in SOCS1 were identified in both patients. The patient with Crohn-like disease achieved clinical remission with anti-IL-12/IL-23 treatment. In the second patient with lymphocytic leiomyositis, ruxolitinib induced rapid resolution of the obstructive symptoms, significant decrease of the CD8+ T lymphocyte muscular infiltrate, and normalization of serum and intestinal cytokines. Decreased frequencies of circulating Treg cells, MAIT cells, and NK cells, with altered CD56bright:CD16lo:CD16hi NK subtype ratios were not modified by ruxolitinib. CONCLUSION: SOCS1 haploinsufficiency can result in a broad spectrum of intestinal manifestations and need to be considered as differential diagnosis in cases of severe treatment-refractory enteropathies, including the rare condition of lymphocytic leiomyositis. This provides the rationale for genetic screening and considering JAK inhibitors in such cases.

DOCK11 deficiency in patients with X-linked actinopathy and autoimmunity.

Dedicator of cytokinesis (DOCK) proteins play a central role in actin cytoskeleton regulation. This is highlighted by the DOCK2 and DOCK8 deficiencies leading to actinopathies and immune deficiencies. DOCK8 and DOCK11 activate CDC42, a Rho-guanosine triphosphate hydrolases involved in actin cytoskeleton dynamics, among many cellular functions. The role of DOCK11 in human immune disease has been long suspected but, to the best of our knowledge, has never been described to date. We studied 8 male patients, from 7 unrelated families, with hemizygous DOCK11 missense variants leading to reduced DOCK11 expression. The patients were presenting with early-onset autoimmunity, including cytopenia, systemic lupus erythematosus, skin, and digestive manifestations. Patients' platelets exhibited abnormal ultrastructural morphology and spreading as well as impaired CDC42 activity. In vitro activated T cells and B-lymphoblastoid cell lines from patients exhibited aberrant protrusions and abnormal migration speed in confined channels concomitant with altered actin polymerization during migration. Knock down of DOCK11 recapitulated these abnormal cellular phenotypes in monocytes-derived dendritic cells and primary activated T cells from healthy controls. Lastly, in line with the patients' autoimmune manifestations, we also observed abnormal regulatory T-cell (Treg) phenotype with profoundly reduced FOXP3 and IKZF2 expression. Moreover, we found reduced T-cell proliferation and impaired STAT5B phosphorylation upon interleukin-2 stimulation of the patients' lymphocytes. In conclusion, DOCK11 deficiency is a new X-linked immune-related actinopathy leading to impaired CDC42 activity and STAT5 activation, and is associated with abnormal actin cytoskeleton remodeling as well as Treg phenotype, culminating in immune dysregulation and severe early-onset autoimmunity.

Generation of induced pluripotent stem cells (iPSCs) from a microvillus inclusion disease patient with a homozygous missense mutation in UNC45A.

Mutations in UNC45A, a co-chaperone for myosins, were recently found causative of a syndrome combining cholestasis, diarrhea, loss of hearing and bone fragility. We generated induced pluripotent stem cells (iPSCs) from a patient with a homozygous missense mutation in UNC45A. Cells from this patient, which were reprogrammed using integration-free Sendaï virus, have normal karyotype, express pluripotency markers and are able to differentiate into the three germ cell layers.

Crohn-like Disease Affecting Small Bowel Due to Monogenic SLCO2A1 Mutations: First Cases of Chronic Enteropathy Associated with SLCO2A1 Gene [CEAS] in France.

INTRODUCTION: Multiple chronic ulcers of small intestine are mainly ascribed to Crohn's disease. Among possible differential diagnoses are chronic ulcers of small bowel caused by abnormal activation of the prostaglandin pathway either in the archetypal but uncommon non-steroidal anti-inflammatory drug [NSAID]-induced enteropathy, or in rare monogenic disorders due to PLA2G4A and SLCO2A1 mutations. SLCO2A1 variants are responsible for CEAS [chronic enteropathy associated with SLCO2A1], a syndrome which was exclusively reported in patients of Asian origin. Herein, we report the case of two French female siblings, P1 and P2, with CEAS. CASE REPORT: P1 underwent iterative bowel resections [removing 1 m of small bowel in total] for recurrent strictures and perforations. Her sister P2 had a tight duodenal stricture which required partial duodenectomy. Next-generation sequencing was performed on P1's DNA and identified two compound heterozygous variants in exon 12 in SLCO2A1, which were also present in P2. CONCLUSION: CEAS can be detected within the European population and raises the question of its incidence and recognition outside Asia. Presence of intractable recurrent ulcerations of the small intestine, mimicking Crohn's disease with concentric strictures, should motivate a genetic search for SLCO2A1 mutations, particularly in the context of family history or consanguinity.

Tubulin mutations in human neurodevelopmental disorders.

Mutations causing dysfunction of tubulins and microtubule-associated proteins, also known as tubulinopathies, are a group of recently described entities that lead to complex brain malformations. Anatomical and functional consequences of the disruption of tubulins include microcephaly, combined with abnormal corticogenesis due to impaired migration or lamination and abnormal growth cone dynamics of projecting and callosal axons. Key imaging features of tubulinopathies are characterized by three major patterns of malformations of cortical development (MCD): lissencephaly, microlissencephaly, and dysgyria. Additional distinctive MRI features include dysmorphism of the basal ganglia, midline commissural structure hypoplasia or agenesis, and cerebellar and brainstem hypoplasia. Tubulinopathies can be diagnosed as early as 21-24 gestational weeks using imaging and neuropathology, with possible extreme microlissencephaly with an extremely thin cortex, lissencephaly with either thick or thin/intermediate cortex, and dysgyria combined with cerebellar hypoplasia, pons hypoplasia and corpus callosum dysgenesis. More than 100 MCD-associated mutations have been reported in TUBA1A, TUBB2B, or TUBB3 genes, whereas fewer than ten are known in other genes such TUBB2A, TUBB or TUBG1. Although these mutations are scattered along the α- and ß-tubulin sequences, recurrent mutations are consistently associated with almost identical cortical dysgenesis. Much of the evidence supports that these mutations alter the dynamic properties and functions of microtubules in several fashions. These include diminishing the abundance of functional tubulin heterodimers, altering GTP binding, altering longitudinal and lateral protofilament interactions, and impairing microtubule interactions with kinesin and/or dynein motors or with MAPs. In this review we discuss the recent advances in our understanding of the effects of mutations of tubulins and microtubule-associated proteins on human brain development and the pathogenesis of malformations of cortical development.

Bothnian Palmoplantar Keratoderma: Further Delineation of the Associated Phenotype.

Bothnian palmoplantar keratoderma (PPKB, MIM600231) is an autosomal dominant form of diffuse non-epidermolytic PPK characterized by spontaneous yellowish-white PPK associated with a spongy appearance after water-immersion. It is due to AQP5 heterozygous mutations. We report four patients carrying a novel AQP5 heterozygous mutation (c.125T>A; p.(Ile42Asn)), and belonging to the same French family. Early palmoplantar swelling (before one year of age), pruritus and hyperhidrosis were constant. The PPK was finally characterized as transgrediens, non-progrediens, diffuse PPK with a clear delineation between normal and affected skin. The cutaneous modifications at water-immersion test, "hand-in-the-bucket sign", were significantly evident after 3 to 6 min of immersion in the children and father, respectively. AQP5 protein is expressed in eccrine sweat glands (ESG), salivary and airway submucosal glands. In PPKB, gain of function mutations seem to widen the channel diameter of ESG and increase water movement. Thus, swelling seems to be induced by hypotonicity with water entrance into cells, while hyperhidrosis is the result of an increased cytosolic calcium concentration.

UNC45A deficiency causes microvillus inclusion disease-like phenotype by impairing myosin VB-dependent apical trafficking.

Variants in the UNC45A cochaperone have been recently associated with a syndrome combining diarrhea, cholestasis, deafness, and bone fragility. Yet the mechanism underlying intestinal failure in UNC45A deficiency remains unclear. Here, biallelic variants in UNC45A were identified by next-generation sequencing in 6 patients with congenital diarrhea. Corroborating in silico prediction, variants either abolished UNC45A expression or altered protein conformation. Myosin VB was identified by mass spectrometry as client of the UNC45A chaperone and was found misfolded in UNC45AKO Caco-2 cells. In keeping with impaired myosin VB function, UNC45AKO Caco-2 cells showed abnormal epithelial morphogenesis that was restored by full-length UNC45A, but not by mutant alleles. Patients and UNC45AKO 3D organoids displayed altered luminal development and microvillus inclusions, while 2D cultures revealed Rab11 and apical transporter mislocalization as well as sparse and disorganized microvilli. All those features resembled the subcellular abnormalities observed in duodenal biopsies from patients with microvillus inclusion disease. Finally, microvillus inclusions and shortened microvilli were evidenced in enterocytes from unc45a-deficient zebrafish. Taken together, our results provide evidence that UNC45A plays an essential role in epithelial morphogenesis through its cochaperone function of myosin VB and that UNC45A loss causes a variant of microvillus inclusion disease.

Congenital enteropathies involving defects in enterocyte structure or differentiation.

Congenital enteropathies (CE) are a group of rare inherited diseases with a typical onset early in life. They involve defects in enterocyte structure or differentiation. They can cause a severe condition of intestinal failure (IF). The diagnostic approach is based first on clinical presentation (consanguinity, prenatal expression, polyhydramnios, early neonatal onset, aspect of stools, persistence at bowel rest, associated extra-digestive manifestations….) and histo-pathological analyses. These rare intestinal diseases cause protracted diarrhea that might resolve, for a few, with a dietetic approach. However, protracted or permanent IF may require long term parenteral nutrition and, in limited cases, intestinal transplantation. With the progresses in both clinical nutrition and genetics, many of these CE are nowadays associated with recognized gene mutations. It improved our knowledge and the understanding in the patho-physiology of these diseases, thus, leading potentially to therapeutic perspectives. These review cover most of the early onset CE and excludes the immune related diarrhea.

Systemic inflammatory syndrome in children with FARSA deficiency.

Variants in aminoacyl-tRNA synthetases (ARSs) genes are associated to a broad spectrum of human inherited diseases. Patients with defective PheRS, encoded by FARSA and FARSB, display brain abnormalities, interstitial lung disease and facial dysmorphism. We investigated four children from two unrelated consanguineous families carrying two missense homozygous variants in FARSA with significantly reduced PheRS-mediated aminoacylation activity. In addition to the core ARS-phenotype, all patients showed an inflammatory profile associated with autoimmunity and interferon score, a clinical feature not ascribed to PheRS-deficient patients to date. JAK inhibition improved lung disease in one patient. Our findings expand the genetic and clinical spectrum of FARSA-related disease.

Increased Use of Anti-Tumor Necrosis Factor Following the Implementation of the ECCO-ESPGHAN Guidelines and its Impact on the Outcome of Pediatric Crohn's Disease: A Retrospective Single-Center Study.

OBJECTIVES: The first ECCO-ESPGHAN guidelines for the medical management of pediatric Crohn disease (CD) were published in 2014. Whether their implementation, and the consequent increased use of an upfront anti-tumor necrosis factor therapy, have changed the course of the disease has not been investigated yet. We aimed at comparing the evolution of pediatric CD patients diagnosed and treated before and after 2014. METHODS: Single-center retrospective study including all children diagnosed with CD from January 2010 to December 2018. Patients diagnosed between 2010 and 2014 (group 1) were compared to those diagnosed after 2014 (group 2). For each patient, at baseline and every 6-month, number of relapses, the occurrence of complication, therapy received and biological parameters were noted, as well as any endoscopic or radiologic evaluation. RESULTS: One hundred and fifty-four patients were included in the analysis, 78 (51%) diagnosed after 2014. The cumulative probability of a relapse-free and surgery-free course was significantly higher for patients treated according to the guidelines (log rank hazard ratio [HR] = 1,818, P = 0.003 and HR = 3,15, 95% confidence interval, P = 0.04, respectively). Mucosal healing rate was significantly higher among patients of group 2 at 1 and 2 years (P = 0.04 and P = 0.05, respectively), while no significant difference was observed for transmural healing rates, as well as for the risk of complications. CONCLUSIONS: The implementation of the 2014 CD guidelines appears to have a significant impact on disease outcomes, with a significantly lower risk for relapse and surgery, while no effect could be observed on the risk of developing complications.

Mevalonate Kinase Deficiency: A Cause of Severe Very-Early-Onset Inflammatory Bowel Disease.

Mevalonate kinase deficiency should be considered in patients with severe very-early-onset inflammatory bowel disease (IBD), especially in patients with a history of recurrent or chronic fever, peritoneal adhesions, and atypical IBD pathology. Anti-interleukin-1 therapy may be efficacious in these patients with monogenic very-early-onset IBD.

Duplication of the IL2RA locus causes excessive IL-2 signaling and may predispose to very early onset colitis.

Single genetic mutations predispose to very early onset inflammatory bowel disease (VEO-IBD). Here, we identify a de novo duplication of the 10p15.1 chromosomal region, including the IL2RA locus, in a 2-year-old girl with treatment-resistant pancolitis that was brought into remission by colectomy. Strikingly, after colectomy while the patient was in clinical remission and without medication, the peripheral blood CD4:CD8 ratio was constitutively high and CD25 expression was increased on circulating effector memory, Foxp3+, and Foxp3neg CD4+ T cells compared to healthy controls. This high CD25 expression increased IL-2 signaling, potentiating CD4+ T-cell-derived IFNγ secretion after T-cell receptor (TCR) stimulation. Restoring CD25 expression using the JAK1/3-inhibitor tofacitinib controlled TCR-induced IFNγ secretion in vitro. As diseased colonic tissue, but not the unaffected duodenum, contained mainly CD4+ T cells with a prominent IFNγ-signature, we hypothesize that local microbial stimulation may have initiated colonic disease. Overall, we identify that duplication of the IL2RA locus can associate with VEO-IBD and suggest that increased IL-2 signaling predisposes to colonic intestinal inflammation.

Bi-allelic variants in IPO8 cause a connective tissue disorder associated with cardiovascular defects, skeletal abnormalities, and immune dysregulation.

Dysregulated transforming growth factor TGF-ß signaling underlies the pathogenesis of genetic disorders affecting the connective tissue such as Loeys-Dietz syndrome. Here, we report 12 individuals with bi-allelic loss-of-function variants in IPO8 who presented with a syndromic association characterized by cardio-vascular anomalies, joint hyperlaxity, and various degree of dysmorphic features and developmental delay as well as immune dysregulation; the individuals were from nine unrelated families. Importin 8 belongs to the karyopherin family of nuclear transport receptors and was previously shown to mediate TGF-ß-dependent SMADs trafficking to the nucleus in vitro. The important in vivo role of IPO8 in pSMAD nuclear translocation was demonstrated by CRISPR/Cas9-mediated inactivation in zebrafish. Consistent with IPO8's role in BMP/TGF-ß signaling, ipo8-/- zebrafish presented mild to severe dorso-ventral patterning defects during early embryonic development. Moreover, ipo8-/- zebrafish displayed severe cardiovascular and skeletal defects that mirrored the human phenotype. Our work thus provides evidence that IPO8 plays a critical and non-redundant role in TGF-ß signaling during development and reinforces the existing link between TGF-ß signaling and connective tissue defects.

Intestinal immunoregulation: lessons from human mendelian diseases.

The mechanisms that maintain intestinal homeostasis despite constant exposure of the gut surface to multiple environmental antigens and to billions of microbes have been scrutinized over the past 20 years with the goals to gain basic knowledge, but also to elucidate the pathogenesis of inflammatory bowel diseases (IBD) and to identify therapeutic targets for these severe diseases. Considerable insight has been obtained from studies based on gene inactivation in mice as well as from genome wide screens for genetic variants predisposing to human IBD. These studies are, however, not sufficient to delineate which pathways play key nonredundant role in the human intestinal barrier and to hierarchize their respective contribution. Here, we intend to illustrate how such insight can be derived from the study of human Mendelian diseases, in which severe intestinal pathology results from single gene defects that impair epithelial and or hematopoietic immune cell functions. We suggest that these diseases offer the unique opportunity to study in depth the pathogenic mechanisms leading to perturbation of intestinal homeostasis in humans. Furthermore, molecular dissection of monogenic intestinal diseases highlights key pathways that might be druggable and therapeutically targeted in common forms of IBD.