Segregation of a missense variant in enteric smooth muscle actin γ-2 with autosomal dominant familial visceral myopathy

Structural and functional mechanisms of actin isoforms

Actin is a highly conserved and fundamental protein in eukaryotes and participates in a broad spectrum of cellular functions. Cells maintain a conserved ratio of actin isoforms, with muscle and non-muscle actins representing the main actin isoforms in muscle and non-muscle cells, respectively. Actin isoforms have specific and redundant functional roles and display different biochemistries, cellular localization, and interactions with myosins and actin-binding proteins. Understanding the specific roles of actin isoforms from the structural and functional perspective is crucial for elucidating the intricacies of cytoskeletal dynamics and regulation and their implications in health and disease. Here, we review how the structure contributes to the functional mechanisms of actin isoforms with a special emphasis on the questions of how post-translational modifications and disease-linked mutations affect actin isoforms biochemistry, function, and interaction with actin-binding proteins and myosin motors.

Cutting-edge regenerative therapy for Hirschsprung disease and its allied disorders

Hirschsprung disease (HSCR) and its associated disorders (AD-HSCR) often result in severe hypoperistalsis caused by enteric neuropathy, mesenchymopathy, and myopathy. Notably, HSCR involving the small intestine, isolated hypoganglionosis, chronic idiopathic intestinal pseudo-obstruction, and megacystis-microcolon-intestinal hypoperistalsis syndrome carry a poor prognosis. Ultimately, small-bowel transplantation (SBTx) is necessary for refractory cases, but it is highly invasive and outcomes are less than optimal, despite advances in surgical techniques and management. Thus, regenerative therapy has come to light as a potential form of treatment involving regeneration of the enteric nervous system, mesenchyme, and smooth muscle in affected areas. We review the cutting-edge regenerative therapeutic approaches for managing HSCR and AD-HSCR, including the use of enteric nervous system progenitor cells, embryonic stem cells, induced pluripotent stem cells, and mesenchymal stem cells as cell sources, the recipient intestine's microenvironment, and transplantation methods. Perspectives on the future of these treatments are also discussed.

HEARTSVG: a fast and accurate method for identifying spatially variable genes in large-scale spatial transcriptomics

Identifying spatially variable genes (SVGs) is crucial for understanding the spatiotemporal characteristics of diseases and tissue structures, posing a distinctive challenge in spatial transcriptomics research. We propose HEARTSVG, a distribution-free, test-based method for fast and accurately identifying spatially variable genes in large-scale spatial transcriptomic data. Extensive simulations demonstrate that HEARTSVG outperforms state-of-the-art methods with higherF 1 scores (averageF 1 Score=0.948), improved computational efficiency, scalability, and reduced false positives (FPs). Through analysis of twelve real datasets from various spatial transcriptomic technologies, HEARTSVG identifies a greater number of biologically significant SVGs (average AUC = 0.792) than other comparative methods without prespecifying spatial patterns. Furthermore, by clustering SVGs, we uncover two distinct tumor spatial domains characterized by unique spatial expression patterns, spatial-temporal locations, and biological functions in human colorectal cancer data, unraveling the complexity of tumors.

Molecular mechanisms linking missense ACTG2 mutations to visceral myopathy

Visceral myopathy is a life-threatening disease characterized by muscle weakness in the bowel, bladder, and uterus. Mutations in smooth muscle γ-actin (ACTG2) are the most common cause of the disease, but the mechanisms by which the mutations alter muscle function are unknown. Here, we examined four prevalent ACTG2 mutations (R40C, R148C, R178C, and R257C) that cause different disease severity and are spread throughout the actin fold. R178C displayed premature degradation, R148C disrupted interactions with actin-binding proteins, R40C inhibited polymerization, and R257C destabilized filaments. Because these mutations are heterozygous, we also analyzed 50/50 mixtures with wild-type (WT) ACTG2. The WT/R40C mixture impaired filament nucleation by leiomodin 1, and WT/R257C produced filaments that were easily fragmented by smooth muscle myosin. Smooth muscle tropomyosin isoform Tpm1.4 partially rescued the defects of R40C and R257C. Cryo-electron microscopy structures of filaments formed by R40C and R257C revealed disrupted intersubunit contacts. The biochemical and structural properties of the mutants correlate with their genotype-specific disease severity.

Chronic intestinal pseudo-obstruction in adults: A practical guide to identify patient subgroups that are suitable for more specific treatments

Chronic intestinal pseudo-obstruction is a rare and heterogeneous syndrome characterized by recurrent symptoms of intestinal obstruction with radiological features of dilated small or large intestine with air/fluid levels in the absence of any mechanical occlusive lesion. Several diseases may be associated with chronic intestinal pseudo-obstruction and in these cases, the prognosis and treatment are related to the underlying disease. Also, in its "primary or idiopathic" form, two subgroups of patients should be determined as they require a more specific therapeutic approach: patients whose chronic intestinal pseudo-obstruction is due to sporadic autoimmune/inflammatory mechanisms and patients whose neuromuscular changes are genetically determined. In a context of a widely heterogeneous adult population presenting chronic intestinal pseudo-obstruction, this review aims to summarize a practical diagnostic workup for identifying definite subgroups of patients who might benefit from more specific treatments, based on the etiology of their underlying condition.

Pediatric Intestinal Pseudo-Obstruction: An International Survey on Diagnostic and Management Strategies in the European Reference Network for Rare Inherited and Congenital Anomalies Intestinal Failure Teams

OBJECTIVES

Pediatric intestinal pseudo-obstruction (PIPO) management is based on nutritional, medical, and surgical care while available evidence is scarce. The aim of this study was to outline the current diagnostic and management strategies in intestinal failure (IF) teams of the European Reference Network for rare Inherited and Congenital Anomalies (ERNICA) and to compare these practices to the latest PIPO international guidelines.

METHODS

An online survey on institutional diagnostic and management strategies of PIPO was conducted among the ERNICA IF teams.

RESULTS

In total, 11 of 21 ERNICA IF centers from 8 countries participated. On average, 64% of teams had ≥6 and 36% had 1-5 PIPO patients under active follow-up. In total, 80 of 102 PIPO patients were parenteral nutrition (PN) dependent while each IF team had median 4 (range 0-19) PN dependent PIPO patients under follow-up. On average, each center received 1-2 new PIPO patients per year. Diagnostics mostly followed current guidelines while medical and surgical management strategies were diverse.

CONCLUSIONS

Numbers of PIPO patients are low and management strategies are diverse among ERNICA IF teams. To improve PIPO patient care, regional reference centers with specialized multidisciplinary IF teams and continuous collaboration across centers are needed.

Use of whole genome sequencing to determine the genetic basis of visceral myopathies including Prune Belly syndrome

Objectives/aims

The visceral myopathies (VM) are a group of disorders characterised by poorly contractile or acontractile smooth muscle. They manifest in both the GI and GU tracts, ranging from megacystis to Prune Belly syndrome. We aimed to apply a bespoke virtual genetic panel and describe novel variants associated with this condition using whole genome sequencing data within the Genomics England 100,000 Genomes Project.

Methods

We screened the Genomics England 100,000 Genomes Project rare diseases database for patients with VM-related phenotypes. These patients were screened for sequence variants and copy number variants (CNV) in ACTG2, ACTA2, MYH11, MYLK, LMOD1, CHRM3, MYL9, FLNA and KNCMA1 by analysing whole genome sequencing data. The identified variants were analysed using variant effect predictor online tool, and any possible segregation in other family members and novel missense mutations was modelled using in silico tools. The VM cohort was also used to perform a genome-wide variant burden test in order to identify confirm gene associations in this cohort.

Results

We identified 76 patients with phenotypes consistent with a diagnosis of VM. The range of presentations included megacystis/microcolon hypoperistalsis syndrome, Prune Belly syndrome and chronic intestinal pseudo-obstruction. Of the patients in whom we identified heterozygous ACTG2 variants, 7 had likely pathogenic variants including 1 novel likely pathogenic allele. There were 4 patients in whom we identified a heterozygous MYH11 variant of uncertain significance which leads to a frameshift and a predicted protein elongation. We identified one family in whom we found a heterozygous variant of uncertain significance in KCNMA1 which in silico models predicted to be disease causing and may explain the VM phenotype seen. We did not find any CNV changes in known genes leading to VM-related disease phenotypes. In this phenotype selected cohort, ACTG2 is the largest monogenic cause of VM-related disease accounting for 9% of the cohort, supported by a variant burden test approach, which identified ACTG2 variants as the largest contributor to VM-related phenotypes.

Conclusions

VM are a group of disorders that are not easily classified and may be given different diagnostic labels depending on their phenotype. Molecular genetic analysis of these patients is valuable as it allows precise diagnosis and aids understanding of the underlying disease manifestations. We identified ACTG2 as the most frequent genetic cause of VM. We recommend a nomenclature change to 'autosomal dominant ACTG2 visceral myopathy' for patients with pathogenic variants in ACTG2 and associated VM phenotypes.

Supplementary Information

The online version contains supplementary material available at 10.1007/s44162-023-00012-z.

Patient's dermal fibroblasts as disease markers for visceral myopathy

Visceral myopathy (VSCM) is a rare genetic disease, orphan of pharmacological therapy. VSCM diagnosis is not always straightforward due to symptomatology similarities with mitochondrial or neuronal forms of intestinal pseudo-obstruction. The most prevalent form of VSCM is associates with variants in the gene ACTG2, encoding the protein gamma-2 actin. Overall, VSCM is a mechano-biological disorder, in which different genetic variants lead to similar alterations to the contractile phenotype of enteric smooth muscles, resulting in the emergence of life-threatening symptoms. In this work we analyzed the morpho-mechanical phenotype of human dermal fibroblasts from patients affected with VSCM, demonstrating that they retain a clear signature of the disease when compared with different controls. We evaluated several biophysical traits of fibroblasts, and we show that a measure of cellular traction forces can be used as a non-specific biomarker of the disease. We propose that a simple assay based on traction forces could be designed to provide a valuable support for clinical decision or pre-clinical research.

Heterozygous Actg2R257C mice mimic the phenotype of megacystis microcolon intestinal hypoperistalsis syndrome

BACKGROUND

Megacystis microcolon intestinal hypoperistalsis syndrome (MMIHS) is a rare and serious congenital disorder with poor outcomes, where a heterozygous missense mutation is present in the ACTG2 gene. Here, we aimed to investigate the pathogenesis of ACTG2 in MMIHS.

METHODS

A cohort with 20 patients with MMIHS was screened. Actg2^R257C heterozygous mutant mice were generated using the CRISPR/Cas9 system. Gastrointestinal (GI) motility, voluntary urination, collagen gel contraction, and G-actin/F-actin analysis were performed.

KEY RESULTS

The R257C variant of ACTG2 most frequently occurred in patients with MMIHS and demonstrated the typical symptoms of MMIHS. Actg2^R257C heterozygous mutant mice had dilated intestines and bladders. The functional assay showed a prolonged total time of GI transit and decreased urine spot area. Collagen gel contraction assay and G-actin/F-actin analysis indicated that mutant mice showed reduced area of contraction of smooth muscle cells (SMCs) and impaired actin polymerization.

CONCLUSIONS & INFERENCES

A mouse model demonstrating MMIHS-like symptoms was generated. The Actg2^R257C heterozygous variant impairs SMCs contraction by interfering with actin polymerization, leading to GI motility disorders.

Enteric Neuromyopathies: Highlights on Genetic Mechanisms Underlying Chronic Intestinal Pseudo-Obstruction

Severe gut motility disorders are characterized by the ineffective propulsion of intestinal contents. As a result, the patients develop disabling/distressful symptoms, such as nausea and vomiting along with altered bowel habits up to radiologically demonstrable intestinal sub-obstructive episodes. Chronic intestinal pseudo-obstruction (CIPO) is a typical clinical phenotype of severe gut dysmotility. This syndrome occurs due to changes altering the morpho-functional integrity of the intrinsic (enteric) innervation and extrinsic nerve supply (hence neuropathy), the interstitial cells of Cajal (ICC) (mesenchymopathy), and smooth muscle cells (myopathy). In the last years, several genes have been identified in different subsets of CIPO patients. The focus of this review is to cover the most recent update on enteric dysmotility related to CIPO, highlighting (a) forms with predominant underlying neuropathy, (b) forms with predominant myopathy, and (c) mitochondrial disorders with a clear gut dysfunction as part of their clinical phenotype. We will provide a thorough description of the genes that have been proven through recent evidence to cause neuro-(ICC)-myopathies leading to abnormal gut contractility patterns in CIPO. The discovery of susceptibility genes for this severe condition may pave the way for developing target therapies for enteric neuro-(ICC)-myopathies underlying CIPO and other forms of gut dysmotility.

Intestinal Pathology in Patients With Pathogenic ACTG2-Variant Visceral Myopathy: 16 Patients From 12 Families and Review of the Literature

BACKGROUND

Dominant gamma-smooth muscle actin gene (ACTG2) variants cause clinically diverse forms of visceral myopathy. Many patients undergo intestinal resection or biopsy before identification of their genetic defect. The pathology of ACTG2-variant visceral myopathy has not been evaluated systematically.

METHODS

Glass slides, ultrastructural images, molecular genetic reports, and clinical records from 16 patients with pathogenic (15) or likely pathogenic (1) ACTG2 variants were reviewed and compared with surgical specimens from controls (no evidence of a primary myopathy or pseudo-obstruction due to Hirschsprung disease) and published descriptions.

RESULTS

The variable clinical manifestations in our cohort matched those in the literature. Only non-specific light and electron microscopic findings observed in non-myopathic controls were encountered in 13 of 16 patients. The remaining 3 patients harbored hyalinized cytoplasmic inclusions in smooth muscle cells and 1 of them had polyglucosan bodies in the muscularis propria.

CONCLUSIONS

Apart from hyalinized inclusions, which were only observed in 3/16 patients, intestinal pathology in the majority of patients with ACTG2 variants is not indicative of an underlying visceral myopathy. Molecular testing should be considered even when no diagnostic intestinal pathology is identified.

Autosomal Recessive ACTG2-Related Visceral Myopathy in Brothers

Pediatric intestinal pseudo-obstruction (PIPO) is a heterogeneous condition characterized by impaired gastrointestinal propulsion, a broad clinical spectrum, and variable severity. Several molecular bases underlying primary PIPO have been identified, of which autosomal dominant ACTG2-related visceral myopathy is the most common in both familial or sporadic primary PIPO cases. We present a family with autosomal recessive ACTG2-related disease in which both parents have mild gastrointestinal symptoms and sons have severe PIPO and bladder dysfunction.

Methods

Clinical genome sequencing was performed on the patients and the mother. Immunohistochemistry was performed on intestinal tissue from the patients to show expression levels of the ACTG2.

Results

Genome sequencing identified a 6.8 kb 2p13.1 loss that includes the ACTG2 gene and a maternally inherited missense variant p.Val10Met in the ACTG2 gene.

Discussion

This case demonstrates that monoallelic hypomorphic ACTG2 variants may underly mild primary gastrointestinal symptoms, while biallelic mild variants can cause severe diseases. The Deletions of the noncoding ACTG2 exon can be an under-recognized cause of mild gastrointestinal symptoms unidentifiable by exome sequencing, explaining some instances of interfamilial variability with an apparent autosomal dominant inheritance. Genome sequencing is recommended as a genetic work-up for primary or idiopathic PIPO because of genetic heterogeneity.

Structure of the myenteric plexus in normal and diseased human ileum analyzed by X-ray virtual histology slices

BACKGROUND

The enteric nervous system (ENS) is situated along the entire gastrointestinal tract and is divided into myenteric and submucosal plexuses in the small and large intestines. The ENS consists of neurons, glial cells, and nerves assembled into ganglia, surrounded by telocytes, interstitial cells of Cajal, and connective tissue. Owing to the complex spatial organization of several interconnections with nerve fascicles, the ENS is difficult to examine in conventional histological sections of 3-5 μm.

AIM

To examine human ileum full-thickness biopsies using X-ray phase-contrast nanotomography without prior staining to visualize the ENS.

METHODS

Six patients were diagnosed with gastrointestinal dysmotility and neuropathy based on routine clinical and histopathological examinations. As controls, full-thickness biopsies were collected from healthy resection ileal regions after hemicolectomy for right colon malignancy. From the paraffin blocks, 4-µm thick sections were prepared and stained with hematoxylin and eosin for localization of the myenteric ganglia under a light microscope. A 1-mm punch biopsy (up to 1 cm in length) centered on the myenteric plexus was taken and placed into a Kapton^® tube for mounting in the subsequent investigation. X-ray phase-contrast tomography was performed using two custom-designed laboratory setups with micrometer resolution for overview scanning. Subsequently, selected regions of interest were scanned at a synchrotron-based end-station, and high-resolution slices were reported. In total, more than 6000 virtual slices were analyzed from nine samples.

RESULTS

In the overview scans, the general architecture and quality of the samples were studied, and the myenteric plexus was localized. High-resolution scans revealed details, including the ganglia, interganglional nerve fascicles, and surrounding tissue. The ganglia were irregular in shape and contained neurons and glial cells. Spindle-shaped cells with very thin cellular projections could be observed on the surface of the ganglia, which appeared to build a network. In the patients, there were no alterations in the general architecture of the myenteric ganglia. Nevertheless, several pathological changes were observed, including vacuolar degeneration, autophagic activity, the appearance of sequestosomes, chromatolysis, and apoptosis. Furthermore, possible expulsion of pyknotic neurons and defects in the covering cellular network could be observed in serial slices. These changes partly corresponded to previous light microscopy findings.

CONCLUSION

The analysis of serial virtual slices could provide new information that cannot be obtained by classical light microscopy. The advantages, disadvantages, and future possibilities of this method are also discussed.

The Diverse Phenotype of Intestinal Dysmotility Secondary to ACTG2-related Disorders

BACKGROUND AND AIMS

The initial description of a heterozygous dominant ACTG2 variant in familial visceral myopathy was followed by the identification of additional variants in other forms of intestinal dysmotility disorders. we aimed to describe the diverse phenotype of this newly reported and rare disease.

METHODS

Report of 4 new patients, and a systematic review of ACTG2-related disorders. we analyzed the population frequency and used in silico gene damaging predictions. Genotype-phenotype correlations were explored.

RESULTS

One hundred three patients (52% girls), from 14 publications, were included. Twenty-eight unique variants were analyzed, all exceedingly rare, and 27 predicted to be highly damaging. The median Combined Annotation Dependent Depletion (CADD) score was 29.2 (Interquartile range 26.3-29.4). Most patients underwent abdominal surgery (66%), about half required intermittent bladder catheterization (48.5%), and more than half were parenteral nutrition (PN)-dependent (53%). One-quarter of the patients died (25.7%), and 6 required transplant (5.8%). Girls had a higher rate of microcolon (P  = 0.009), PN dependency (P = 0.003), and death/transplant (P = 0.029) compared with boys, and early disease onset (<2 years of age) was associated with megacystis-microcolon-intestinal hypoperistalsis syndrome (MMIHS) features. There was no statistical association between disease characteristics and CADD scores.

CONCLUSIONS

Damaging ACTG2 variants are rare, often associated with MMIHS phenotype, and overall have a wide phenotypic variation. Symptoms usually present in the perinatal period but can also appear at a later age. The course of the disease is marked by frequent need for surgical interventions, PN support, and mortality. Poor outcomes are more common among girls with ACTG2 variants.

Loss-of-function variants within LMOD1 actin-binding site 2 cause pediatric intestinal pseudo-obstruction by impairing protein stability and actin nucleation

The leiomodin1 (LMOD1) gene, encoding a potent actin nucleator, was recently reported as a potential pathogenic gene of megacystis-microcolon-intestinal hypoperistalsis syndrome (MMIHS, OMIM 619362). However, only a single patient has been reported to have LMOD1 mutations, and the underlying pathogenic mechanism remains unknown. Here, we described a male infant with LMOD1 mutations presenting typical symptoms of pediatric intestinal pseudo-obstruction (PIPO) but without megacystis and microcolon. Two compound heterozygous missense variants (c.1106C>T, p.T369M; c.1262G>A, p.R421H) were identified, both affecting highly conserved amino acid residues within the second actin-binding site (ABS2) domain of LMOD1. Expression analysis showed that both variants resulted in significantly reduced protein amounts, especially for p.T369M, which was almost undetectable. The reduction was only partially rescued by the proteasome inhibitor MG-132, indicating that there might be proteasome-independent pathways involved in the degradation of the mutant proteins. Molecular modeling showed that variant p.T369M impaired the local protein conformation of the ABS2 domain, while variant p.R421H directly impaired the intermolecular interaction between ABS2 and actin. Accordingly, both variants significantly damaged LMOD1-mediated actin nucleation. These findings provide further human genetic evidence supporting LMOD1 as a pathogenic gene underlying visceral myopathy including PIPO and MMIHS, strengthen the critical role of ABS2 domain in LMOD1-mediated actin nucleation, and moreover, reveal an unrecognized role of ABS2 in protein stability.

ACTG2 Variants in Pediatric Chronic Intestinal Pseudo-obstruction With Megacystis

Background/Aims

Chronic intestinal pseudo-obstruction (CIPO) is a clinically heterogeneous syndrome characterized by compromised peristalsis and intestinal obstruction. Variants of actin gamma 2 (ACTG2), a protein crucial for correct enteric muscle contraction, have been found in CIPO patients. The aim of this study is to examine the clinical features and ACTG2 variants in Korean patients with CIPO.

Methods

From January 1995 to August 2020, 12 patients diagnosed with CIPO were included and genetic analysis testing of ACTG2 was performed.

Results

Heterozygous ACTG2 missense variants were found in 6 patients (50.0%). The p.Arg257Cys variant was found in 3 patients, and p.Arg63Gln and p.Arg178His variants were found in 1 patient each. A novel variant, p.Ile193Phe, was found in 1 patient. Three patients were diagnosed at birth, 2 at the age of 1 year, and 1 at 3 years of age. Abnormal prenatal genitourinary ultrasonographic findings were found in all 6 patients; microcolon was found in 4 patients (66.7%), and megacystis in all 6 patients. The pathology showed abnormal ganglion cells as well as myopathic findings. All patients are dependent on total parenteral nutrition and are to date alive.

Conclusions

ACTG2 variants are commonly found in Korean patients with CIPO. In CIPO patients with megacystis and abnormal prenatal ultrasonography, genetic testing of ACTG2 should be considered. Molecular diagnosis of CIPO is more important than pathologic diagnosis.

Clinical and Pathological Features of Severe Gut Dysmotility

Severe gut motility disorders are characterized by ineffective propulsion of intestinal contents. As a result, patients often develop extremely uncomfortable symptoms, ranging from nausea and vomiting along with alterations of bowel habits, up to radiologically confirmed subobstructive episodes. Chronic intestinal pseudo-obstruction (CIPO) is a typical clinical phenotype of severe gut dysmotility due to morphological and functional alterations of the intrinsic (enteric) innervation and extrinsic nerve supply (hence neuropathy), interstitial cells of Cajal (ICCs) (mesenchymopathy), and smooth muscle cells (myopathy). In this chapter, we highlight some molecular mechanisms of CIPO and review the clinical phenotypes and the genetics of the different types of CIPO. Specifically, we will detail the role of some of the most representative genetic mutations involving RAD21, LIG3, and ACTG2 to provide a better understanding of CIPO and related underlying neuropathic or myopathic histopathological abnormalities. This knowledge may unveil targeted strategies to better manage patients with such severe disease.

NAA80 bi-allelic missense variants result in high-frequency hearing loss, muscle weakness and developmental delay

The recent identification of NAA80/NAT6 as the enzyme that acetylates actins generated new insight into the process of post-translational actin modifications; however, the role of NAA80 in human physiology and pathology has not been clarified yet. We report two individuals from a single family harbouring a homozygous c.389T>C, p.(Leu130Pro) NAA80 genetic variant. Both individuals show progressive high-frequency sensorineural hearing loss, craniofacial dysmorphisms, developmental delay and mild proximal and axial muscle weakness. Based on the molecular structure, we predicted and confirmed the NAA80 c.389T>C, p.(Leu130Pro) variant to result in protein destabilization, causing severely decreased NAA80 protein availability. Concurrently, individuals exhibited a ∼50% decrease of actin acetylation. NAA80 individual derived fibroblasts and peripheral blood mononuclear cells showed increased migration, increased filopodia counts and increased levels of polymerized actin, in agreement with previous observations in NAA80 knock-out cells. Furthermore, the significant clinical overlap between NAA80 individuals and individuals with pathogenic variants in several actin subtypes reflects the general importance of controlled actin dynamics for the inner ear, brain and muscle. Taken together, we describe a new syndrome, caused by NAA80 genetic variants leading to decreased actin acetylation and disrupted associated molecular functions. Our work suggests a crucial role for NAA80-mediated actin dynamics in neuronal health, muscle health and hearing.

Hollow Visceral Myopathy, a Rare Gastrointestinal Disorder: A Case Report and Short Review

Hollow visceral myopathy (HVM) is described as impaired intestinal function and motility in the absence of mechanical obstruction. In this case report, we describe a unique case of an 18-year-old female who presented to the hospital with complaints of persistent nausea, vomiting, inability to tolerate oral feeds, and substantial weight loss for 2 months. After appropriate investigations, a diagnosis of gastroparesis was established. The patient was started on metoclopramide, which led to significant symptomatic improvement, and she was eventually discharged home. One month after discharge, she presented to the hospital with symptoms similar to her initial presentation. After further laboratory and radiological investigation, she was diagnosed with severe gastroparesis and chronic intestinal pseudo-obstruction. Over the next month, the patient was given an extensive trial of multiple prokinetic agents such as mirtazapine, ondansetron, pyridostigmine, octreotide, and promethazine, but she failed to show clinical improvement. Due to failure of medical therapy, a nasojejunal feeding tube was placed for enteral nutrition. However, the patient reported worsening of her symptoms despite slow feeding rates; hence, a decision was made to start the patient on total parenteral nutrition and transfer her to a larger tertiary center for higher level of care. At the tertiary hospital, the patient was continued on total parenteral nutrition and underwent extensive evaluation. Ultimately, she was diagnosed with HVM after a laparoscopic full-thickness intestinal biopsy showed histopathological evidence of the disease. She underwent isolated small intestine transplant, which led to significant improvement of her symptoms and was eventually discharged home. The patient continues to be symptom-free and follows up with Gastroenterology and Transplant Surgery regularly. This case report highlights a rare clinical condition, HVM, as a potential diagnosis in patients with clinical features of intestinal obstruction without mechanical obstruction.

Expanding the genotypic spectrum of ACTG2-related visceral myopathy

Visceral myopathies (VMs) encompass a spectrum of disorders characterized by chronic disruption of gastrointestinal function, with or without urinary system involvement. Pathogenic missense variation in smooth muscle γ-actin gene (ACTG2) is associated with autosomal dominant VM. Whole-genome sequencing of an infant presenting with chronic intestinal pseudo-obstruction revealed a homozygous 187 bp (c.589_613 + 163del188) deletion spanning the exon 6–intron 6 boundary within ACTG2. The patient's clinical course was marked by prolonged hospitalizations, multiple surgeries, and intermittent total parenteral nutrition dependence. This case supports the emerging understanding of allelic heterogeneity in ACTG2-related VM, in which both biallelic and monoallelic variants in ACTG2 are associated with gastrointestinal dysfunction of similar severity and overlapped clinical presentation. Moreover, it illustrates the clinical utility of rapid whole-genome sequencing, which can comprehensively and precisely detect different types of genomic variants including small deletions, leading to guidance of clinical care decisions.

Visceral myopathy: clinical syndromes, genetics, pathophysiology, and fall of the cytoskeleton

Visceral smooth muscle is a crucial component of the walls of hollow organs like the gut, bladder, and uterus. This specialized smooth muscle has unique properties that distinguish it from other muscle types and facilitate robust dilation and contraction. Visceral myopathies are diseases where severe visceral smooth muscle dysfunction prevents efficient movement of air and nutrients through the bowel, impairs bladder emptying, and affects normal uterine contraction and relaxation, particularly during pregnancy. Disease severity exists along a spectrum. The most debilitating defects cause highly dysfunctional bowel, reduced intrauterine colon growth (microcolon), and bladder-emptying defects requiring catheterization, a condition called megacystis-microcolon-intestinal hypoperistalsis syndrome (MMIHS). People with MMIHS often die early in childhood. When the bowel is the main organ affected and microcolon is absent, the condition is known as myopathic chronic intestinal pseudo-obstruction (CIPO). Visceral myopathies like MMIHS and myopathic CIPO are most commonly caused by mutations in contractile apparatus cytoskeletal proteins. Here, we review visceral myopathy-causing mutations and normal functions of these disease-associated proteins. We propose molecular, cellular, and tissue-level models that may explain clinical and histopathological features of visceral myopathy and hope these observations prompt new mechanistic studies.

Dysregulation of the NRG1/ERBB pathway causes a developmental disorder with gastrointestinal dysmotility in humans

Hirschsprung disease (HSCR) is the most frequent developmental anomaly of the enteric nervous system, with an incidence of 1 in 5000 live births. Chronic intestinal pseudo-obstruction (CIPO) is less frequent and classified as neurogenic or myogenic. Isolated HSCR has an oligogenic inheritance with RET as the major disease-causing gene, while CIPO is genetically heterogeneous, caused by mutations in smooth muscle-specific genes. Here, we describe a series of patients with developmental disorders including gastrointestinal dysmotility, and investigate the underlying molecular bases. Trio-exome sequencing led to the identification of biallelic variants in ERBB3 and ERBB2 in 8 individuals variably associating HSCR, CIPO, peripheral neuropathy, and arthrogryposis. Thorough gut histology revealed aganglionosis, hypoganglionosis, and intestinal smooth muscle abnormalities. The cell type-specific ErbB3 and ErbB2 function was further analyzed in mouse single-cell RNA sequencing data and in a conditional ErbB3-deficient mouse model, revealing a primary role for ERBB3 in enteric progenitors. The consequences of the identified variants were evaluated using quantitative real-time PCR (RT-qPCR) on patient-derived fibroblasts or immunoblot assays on Neuro-2a cells overexpressing WT or mutant proteins, revealing either decreased expression or altered phosphorylation of the mutant receptors. Our results demonstrate that dysregulation of ERBB3 or ERBB2 leads to a broad spectrum of developmental anomalies, including intestinal dysmotility.

Phenotypic switch of smooth muscle cells in paediatric chronic intestinal pseudo-obstruction syndrome

Smooth Muscle Cells (SMC) are unique amongst all muscle cells in their capacity to modulate their phenotype. Indeed, SMCs do not terminally differentiate but instead harbour a remarkable capacity to dedifferentiate, switching between a quiescent contractile state and a highly proliferative and migratory phenotype, a quality often associated to SMC dysfunction. However, phenotypic plasticity remains poorly examined in the field of gastroenterology in particular in pathologies in which gut motor activity is impaired. Here, we assessed SMC status in biopsies of infants with chronic intestinal pseudo-obstruction (CIPO) syndrome, a life-threatening intestinal motility disorder. We showed that CIPO-SMCs harbour a decreased level of contractile markers. This phenotype is accompanied by an increase in Platelet-Derived Growth Factor Receptor-alpha (PDGFRA) expression. We showed that this modulation occurs without origin-related differences in CIPO circular and longitudinal-derived SMCs. As we characterized PDGFRA as a marker of digestive mesenchymal progenitors during embryogenesis, our results suggest a phenotypic switch of the CIPO-SMC towards an undifferentiated stage. The development of CIPO-SMC culture and the characterization of SMC phenotypic switch should enable us to design therapeutic approaches to promote SMC differentiation in CIPO.

Visceral myopathy diagnosed by a de novo ACTG2 mutation in a patient with chronic intestinal pseudo-obstruction-a case report

Visceral myopathy is a rare genetic disorder that commonly affects the digestive and renal systems. Manifestations include a clinical spectrum covering chronic intestinal pseudo-obstruction (CIPO) and megacystis-microcolon-intestinal hypoperistalsis syndrome (MMIHS). The smooth muscle actin γ-2 gene (ACTG2) is one of the most common disease-causing genes. Here, we present a case of pediatric intestinal pseudo-obstruction associated with a novel missense ACTG2 mutation, c.588G>C/p.E196D. His parents had no this mutation, which suggested the possibility of spontaneous mutation. Amino acid conservation analysis of γ-2 actin showed replacement of glutamate at position 196 by aspartate. The patient suffered from recurrent episodes of abdominal bloating, undergone repeated gastrointestinal surgery, had feeding difficulties, and required long-term parenteral nutrition support. The patient had no other specific symptoms or underlying diseases. X-ray of the abdomen showed dilation of the intestine as well as an air-fluid pattern. The manifestations of biopsy were various. All biochemical tests were normal, and the possibility of secondary intestinal pseudo-obstruction was excluded. The mutation site of ACTG2 in the present study has not been previously described in patients with visceral myopathy, and thus, our study reveals a novel mutation of ACTG2-associated visceral myopathy in a patient with CIPO. This report can serve as a reference for future research and further expands the map of genetic variation for visceral myopathy.

Variants in the Enteric Smooth Muscle Actin γ-2 Cause Pediatric Intestinal Pseudo-obstruction in Chinese Patients

OBJECTIVES

Pediatric intestinal pseudo-obstruction (PIPO) is a severe gastrointestinal disorder occurring in children, leading to failure to thrive, malnutrition, and long-term parenteral nutrition dependence. Enteric smooth muscle actin γ-2 (ACTG2) variants have been reported to be related to the pathogenesis of PIPO. This study aimed to determine the presence of ACTG2 variants in Chinese PIPO patients.

METHODS

Whole-exome sequencing was performed using samples from 39 recruited patients, whereas whole ACTG2 Sanger sequencing was performed using samples from 2 patients. Published data was reviewed to determine the number of pathogenic variants and the genotype related to ACTG2 variants in the Chinese population.

RESULTS

A total of 21 Chinese probands were found to carry heterozygous missense variants of ACTG2, among which 20 were de novo. Fifteen probands had p.Arg257 variants (c.770G>A and c.769C>T), and the other 2 probands had c.533G>A (p.Arg178His) and c.443G>T (p.Arg148Leu) variants. Four probands had novel variants c.337C>T (p.Pro113Ser), c.588G>C (p.Glu196Asp), c.734A>G (p.Asp245Gly), and c.553G>T (p.Asp185Tyr).

CONCLUSIONS

Variants affecting codon 257 of ACTG2 protein sequence appeared to be frequent in both Chinese and Caucasian PIPO patients, whereas p.Arg178 variants were less common in Chinese patients compared with Caucasian patients. The 4 novel variants in ACTG2 were also found to be related to Chinese PIPO.

Novel ACTG2 variants disclose allelic heterogeneity and bi-allelic inheritance in pediatric chronic intestinal pseudo-obstruction

Variants in the ACTG2 gene, encoding a protein crucial for correct enteric muscle contraction, have been found in patients affected with chronic intestinal pseudo-obstruction, either congenital or late-onset visceral myopathy, and megacystis-microcolon-intestinal hypoperistalsis syndrome. Here we report about ten pediatric and one adult patients, from nine families, carrying ACTG2 variants: four show novel still unpublished missense variants, including one that is apparently transmitted according to a recessive mode of inheritance. Four of the remaining five probands carry variants affecting arginine residues, that have already been associated with a severe phenotype. A de novo occurrence of the variants could be confirmed in six of these families. Since a genotype-phenotype correlation is affected by extrinsic factors, such as, diagnosis delay, quality of clinical management, and intra-familial variability, we have undertaken 3D molecular modeling to get further insights into the effects of the variants here described. The present findings and further ACTG2 testing of patients presenting with intestinal pseudo-obstruction, will improve our understanding of visceral myopathies, including implications in the prognosis and genetic counseling of this set of severe disorders.

Pseudo-obstruction-inducing ACTG2R257C alters actin organization and function

Actin γ 2, smooth muscle (ACTG2) R257C mutation is the most common genetic cause of visceral myopathy. Individuals with ACTG2 mutations endure prolonged hospitalizations and surgical interventions, become dependent on intravenous nutrition and bladder catheterization, and often die in childhood. Currently, we understand little about how ACTG2 mutations cause disease, and there are no mechanism-based treatments. Our goal was to characterize the effects of ACTG2R257C on actin organization and function in visceral smooth muscle cells. We overexpressed ACTG2WT or ACTG2R257C in primary human intestinal smooth muscle cells (HISMCs) and performed detailed quantitative analyses to examine effects of ACTG2R257C on (a) actin filament formation and subcellular localization, (b) actin-dependent HISMC functions, and (c) smooth muscle contractile gene expression. ACTG2R257C resulted in 41% fewer, 13% thinner, 33% shorter, and 40% less branched ACTG2 filament bundles compared with ACTG2WT. Curiously, total F-actin probed by phalloidin and a pan-actin antibody was unchanged between ACTG2WT- and ACTG2R257C-expressing HISMCs, as was ultrastructural F-actin organization. ACTG2R257C-expressing HISMCs contracted collagen gels similar to ACTG2WT-expressing HISMCs but spread 21% more and were 11% more migratory. In conclusion, ACTG2R257C profoundly affects ACTG2 filament bundle structure, without altering global actin cytoskeleton in HISMCs.

Massive atonic bleeding during cesarean delivery in a patient with chronic idiopathic intestinal pseudo-obstruction: A case report and literature review

A 35-year-old primigravid woman with chronic idiopathic intestinal pseudo-obstruction presented to our institution. Except for an enlarged fetal bladder, her pregnancy was almost uneventful until she developed pre-eclampsia requiring emergent cesarean section at 34 weeks gestation. After delivery, intractable uterine atony developed with blood loss reaching 3500 mL within 15 min. Following a B-Lynch suture, the bleeding attenuated but uterine atony persisted; lochia persisted for 3 months post-partum. The infant was diagnosed with megacystis microcolon intestinal hypoperistalsis syndrome after birth. The mother's clinical course and previous reports suggested that atonic bleeding was associated with the pathology of chronic idiopathic intestinal pseudo-obstruction; the infant's disease was considered to be maternal-related disease. Clinicians should be vigilant in pregnant patients with chronic idiopathic intestinal pseudo-obstruction especially with these complications.

Barrett Esophagus and Intestinal Metaplasia of the Gastroesophageal Junction in Children: A Clinicopathologic Study

OBJECTIVES

Barrett esophagus (BE) and intestinal metaplasia of gastroesophageal junction (IMGEJ) are rare in the pediatric population. This multi-institutional retrospective study evaluated the clinicopathologic characteristics and natural history of BE and IMGEJ in children.

METHODS

Data from 20 BE patients (70% boys, mean age: 14.9 years) and 17 IMGEJ patients (71% boys, mean age: 14 years) were retrospectively obtained from chart review. Endoscopic and pathologic findings from index and follow-up endoscopies were analyzed.

RESULTS

Most patients (70% BE and 59% IMGEJ) had underlying conditions which put them at risk for gastroesophageal reflux disease. Increased body mass index (BMI) was observed in patients without underlying conditions (BE: 30.1 ± 9.8; IMGEJ: 23.9 ± 6.3) compared with those with underlying conditions (BE: 19.6 ± 7.8; IMGEJ: 16.4 ± 2.1) (BE, P = 0.02; IMGEJ, P = 0.01). Incomplete intestinal metaplasia (IM) was the predominant histology seen in BE (80%) and IMGEJ patients (75%). Dysplasia and malignancy were not identified in the initial and follow-up biopsies. Concurrent gastric biopsies showed various findings (79% BE and 40% IMGEJ were normal), with 1 IMGEJ patient showing coexisting gastric IM (7%). Follow-up in 12 BE patients (mean follow-up time 51.6 months) showed 100% persistent endoscopic disease and 58% persistent IM histologically. Three of 6 IMGEJ patients (mean follow-up time 24 months) demonstrated endoscopic and histologic features consistent with BE on subsequent procedures. Moreover, a subset of BE (57%) and IMGEJ patients (67%) who underwent endoscopy before initial diagnosis showed nongoblet columnar mucosa above the anatomic gastroesophageal junction.

CONCLUSIONS

Increased BMI may be a risk factor for BE and IMGEJ in pediatric patients without underlying conditions. Nongoblet columnar metaplasia and IMGEJ might represent incomplete forms of BE. Our data suggest that these patients should be closely monitored.

Recurrent arginine substitutions in the ACTG2 gene are the primary driver of disease burden and severity in visceral myopathy

Visceral myopathy with abnormal intestinal and bladder peristalsis includes a clinical spectrum with megacystis-microcolon intestinal hypoperistalsis syndrome and chronic intestinal pseudo-obstruction. The vast majority of cases are caused by dominant variants in ACTG2; however, the overall genetic architecture of visceral myopathy has not been well-characterized. We ascertained 53 families, with visceral myopathy based on megacystis, functional bladder/gastrointestinal obstruction, or microcolon. A combination of targeted ACTG2 sequencing and exome sequencing was used. We report a molecular diagnostic rate of 64% (34/53), of which 97% (33/34) is attributed to ACTG2. Strikingly, missense mutations in five conserved arginine residues involving CpG dinucleotides accounted for 49% (26/53) of disease in the cohort. As a group, the ACTG2-negative cases had a more favorable clinical outcome and more restricted disease. Within the ACTG2-positive group, poor outcomes (characterized by total parenteral nutrition dependence, death, or transplantation) were invariably due to one of the arginine missense alleles. Analysis of specific residues suggests a severity spectrum of p.Arg178>p.Arg257>p.Arg40 along with other less-frequently reported sites p.Arg63 and p.Arg211. These results provide genotype-phenotype correlation for ACTG2-related disease and demonstrate the importance of arginine missense changes in visceral myopathy.

Familial intestinal degenerative neuropathy with chronic intestinal pseudo-obstruction linked to a gene locus with duplication in chromosome 9

Background: Intestinal degenerative neuropathy without extra-intestinal involvement occurs as familial forms (FIDN) but the genetics behind is unknown. We studied a Swedish family with autosomal dominant disease and several cases of chronic intestinal pseudo-obstruction (CIP).Methods: We included 33 members of a family sharing a male ancestor. Chronic intestinal symptoms including diarrhoea occurred in 11, four had severe CIP. DNA was analysed with SNP-microarray (Affymetrix), linkage (Allegro Software) and gene dosage (CNAG 3.0).Results: Genetic linkage was found to the short arm of Ch9 to a 9.7 Mb region with 45 protein-coding genes, 22 of which were duplicated (1.2 Mb duplication) (dup(9)(p21.3) with breaking point in the FOCAD-gene. Lod score for the region was 3.4. Fourteen subjects were duplication carriers including all 11 subjects having severe chronic symptoms/CIP. Nineteen subjects had no duplication. The occurrence of gastrointestinal symptoms in the family was strongly linked to duplication carrier-ship (p = .0005). The two branches of the family had separate maternal ancestors (A and B). Including the previous generation, severe disease (overt CIP and/or death from intestinal failure) was assessed to occur in 100% (5/5) of duplication carriers in branch A and in 21% (3/14) in branch B (p = .005). In branch B the onset of symptoms was later (median 38 vs. 24 yrs) and three duplication carriers were symptom-free.Conclusions: In this family with autosomal dominant hereditary intestinal neuropathy, the disorder is linked to a 9.7 Mb region in Ch9 including a 1.2 Mb duplication. There is a significant difference in disease expressivity between family branches, seemingly related to separate maternal ancestors.

Waardenburg Syndrome Type IV De Novo SOX10 Variant Causing Chronic Intestinal Pseudo-Obstruction

Waardenburg syndrome (WS) type IV is characterized by pigmentary abnormalities, deafness and Hirschsprung's disease. This syndrome can be triggered by dysregulation of the SOX10 gene, which belongs to the SOX (SRY-related high-mobility group-box) family of genes. We discuss the first known case of a SOX10 frameshift mutation variant defined as c.895delC causing WS type IV without Hirschsprung's disease. This female patient of unrelated Kuwaiti parents, who tested negative for cystic fibrosis and Hirschsprung's disease, was born with meconium ileus and malrotation and had multiple surgical complications likely due to chronic intestinal pseudo-obstruction. These complications included small intestinal necrosis requiring resection, development of a spontaneous fistula between the duodenum and jejunum after being left in discontinuity, and short gut syndrome. This case and previously reported cases demonstrate that SOX10 gene sequencing is a consideration in WS patients without aganglionosis but with intestinal dysfunction.

Pseudo-obstruction, enteric dysmotility and irritable bowel syndrome

New diagnostic techniques have advanced our knowledge about the irritable bowel syndrome. The majority of patients that we believed to have a psychosomatic disorder have received other diagnoses explaining their symptoms. Endoscopy makes it possible to diagnose celiac disease before it leads to malnutrition and allows the detection of microscopic colitis as a cause of watery diarrhea. At the severe end of the symptom spectrum enteric dysmotility marks the border at which IBS ceases to be a functional disorder and becomes a genuine motility disorder. Joint hypermobility or Ehlers-Danlos syndrome is present in a substantial proportion of patients with enteric dysmotility. Chronic intestinal pseudo-obstruction is the end-stage of a large number of very rare disorders in which failed peristalsis is the common denominator. Nutritional needs and symptom control are essential in the management of pseudo-obstruction. Home parenteral nutrition is life saving in more than half of patients with chronic intestinal pseudo-obstruction.

Recurrent ACTG2 gene variation in African degenerative visceral leiomyopathy

INTRODUCTION

Visceral myopathies remain difficult and frustrating clinical entities, a distinctive form of acquired degenerative visceral myopathy, African degenerative leiomyopathy, a myogenic functional intestinal obstruction without aganglionosis which affects smooth muscle of the intestine, in young indigenous African children. The Actin G2 gene is the main gene encoding smooth muscle actin found in enteric tissues. Recent research has identified Actin G2 alpha gene variation as an important causative biomarker in visceral myopathies and megacystis microcolon. This study of the Actin G2 gene (ACTG2) in an African population explores a possible molecular basis abnormal muscle function in a visceral myopathy.

PATIENTS AND METHODS

Following ethical permission and informed consent, DNA was extracted from whole blood samples in five patients with histologically proven African degenerative leiomyopathy. PCR amplification of ACTG2 alpha gene products by semi-automated bi-directional sequencing analysis. Results were analysed using FinchTV Sequence Alignment Software and predicting bioinformatic investigation by PolyPhen 2 software.

RESULTS

Five new patients with the ADL phenotypes were prospectively investigated for variation in the Actin G2 gamma gene (ACTG2). ACTG2 gene variation occurred in exon 5 (c.463 A>G K119R), in three (60%). In addition, intronic variation t > c-IVS3 was identified in three with the K119 mutation plus further g >  c -IVS12 and t > c + IVS16(2), suggesting a possible haplotype. Bioinformatic modelling showed that these ACTG2 gene variations are highly non-conservative altering protein expression.

CONCLUSIONS

Recurrent Actin G2 smooth muscle gene variation in African degenerative visceral leiomyopathy is associated with abnormal muscle actin development.

Molecular Signature of CAID Syndrome: Noncanonical Roles of SGO1 in Regulation of TGF-β Signaling and Epigenomics

BACKGROUND & AIMS

A generalized human pacemaking syndrome, chronic atrial and intestinal dysrhythmia (CAID) (OMIM 616201), is caused by a homozygous SGO1 mutation (K23E), leading to chronic intestinal pseudo-obstruction and arrhythmias. Because CAID patients do not show phenotypes consistent with perturbation of known roles of SGO1, we hypothesized that noncanonical roles of SGO1 drive the clinical manifestations observed.

METHODS

To identify a molecular signature for CAID syndrome, we achieved unbiased screens in cell lines and gut tissues from CAID patients vs wild-type controls. We performed RNA sequencing along with stable isotope labeling with amino acids in cell culture. In addition, we determined the genome-wide DNA methylation and chromatin accessibility signatures using reduced representative bisulfite sequencing and assay for transposase-accessible chromatin with high-throughput sequencing. Functional studies included patch-clamp, quantitation of transforming growth factor-β (TGF-β) signaling, and immunohistochemistry in CAID patient gut biopsy specimens.

RESULTS

Proteome and transcriptome studies converge on cell-cycle regulation, cardiac conduction, and smooth muscle regulation as drivers of CAID syndrome. Specifically, the inward rectifier current, an important regulator of cellular function, was disrupted. Immunohistochemistry confirmed overexpression of Budding Uninhibited By Benzimidazoles 1 (BUB1) in patients, implicating the TGF-β pathway in CAID pathogenesis. Canonical TGF-β signaling was up-regulated and uncoupled from noncanonical signaling in CAID patients. Reduced representative bisulfite sequencing and assay for transposase-accessible chromatin with high-throughput sequencing experiments showed significant changes of chromatin states in CAID, pointing to epigenetic regulation as a possible pathologic mechanism.

CONCLUSIONS

Our findings point to impaired inward rectifier potassium current, dysregulation of canonical TGF-β signaling, and epigenetic regulation as potential drivers of intestinal and cardiac manifestations of CAID syndrome. Transcript profiling and genomics data are as follows: repository URL: https://www.ncbi.nlm.nih.gov/geo; SuperSeries GSE110612 was composed of the following subseries: GSE110309, GSE110576, and GSE110601.

Variants in ACTG2 underlie a substantial number of Australasian patients with primary chronic intestinal pseudo-obstruction

BACKGROUND

Primary chronic intestinal pseudo-obstruction (CIPO) is a rare, potentially life-threatening disorder characterized by severely impaired gastrointestinal motility. The objective of this study was to examine the contribution of ACTG2, LMOD1, MYH11, and MYLK mutations in an Australasian cohort of patients with a diagnosis of primary CIPO associated with visceral myopathy.

METHODS

Pediatric and adult patients with primary CIPO and suspected visceral myopathy were recruited from across Australia and New Zealand. Sanger sequencing of the genes encoding enteric gamma-actin (ACTG2) and smooth muscle leiomodin (LMOD1) was performed on DNA from patients, and their relatives, where available. MYH11 and MYLK were screened by next-generation sequencing.

KEY RESULTS

We identified heterozygous missense variants in ACTG2 in 7 of 17 families (~41%) diagnosed with CIPO and its associated conditions. We also identified a previously unpublished missense mutation (c.443C>T, p.Arg148Leu) in one family. One case presented with megacystis-microcolon-intestinal hypoperistalsis syndrome in utero with subsequent termination of pregnancy at 28 weeks' gestation. All of the substitutions identified occurred at arginine residues. No likely pathogenic variants in LMOD1, MYH11, or MYLK were identified within our cohort.

CONCLUSIONS AND INFERENCES

ACTG2 mutations represent a significant underlying cause of primary CIPO with visceral myopathy and associated phenotypes in Australasian patients. Thus, ACTG2 sequencing should be considered in cases presenting with hypoperistalsis phenotypes with suspected visceral myopathy. It is likely that variants in other genes encoding enteric smooth muscle contractile proteins will contribute further to the genetic heterogeneity of hypoperistalsis phenotypes.

ACTG2-Associated Visceral Myopathy With Chronic Intestinal Pseudoobstruction, Intestinal Malrotation, Hypertrophic Pyloric Stenosis, Choledochal Cyst, and a Novel Missense Mutation

Primary visceral myopathy caused by a pathogenic mutation in the gene encoding the enteric smooth muscle actin gamma 2 ( ACTG2) affects gastrointestinal and genitourinary tracts and often presents as chronic intestinal pseudoobstruction. We present a case of pediatric onset chronic intestinal pseudoobstruction associated with a novel missense ACTG2 mutation c.439G>T/p.G147C. In addition to the known disease manifestations of feeding intolerance and intestinal malrotation, our patient had a late-onset hypertrophic pyloric stenosis and a late-onset choledochal cyst, the former of which has not previously been described in patients with ACTG2-associated visceral myopathy.

Severe allograft rejection in an intestinal transplant patient following oral immunoglobulin treatment for chronic norovirus infection: a case report

In an intestinal transplant patient under triple immunosuppression therapy with tacrolimus levels >10 ng/L, a 2-day oral immunoglobulin therapy given as treatment for chronic norovirus infection was temporally closely associated with the development of severe steroid-resistant acute graft rejection, thus suggesting that oral immunoglobulin might be able to promote a rejection response.

Paediatric Intestinal Pseudo-obstruction: Evidence and Consensus-based Recommendations From an ESPGHAN-Led Expert Group

OBJECTIVES

Chronic intestinal pseudo-obstructive (CIPO) conditions are considered the most severe disorders of gut motility. They continue to present significant challenges in clinical care despite considerable recent progress in our understanding of pathophysiology, resulting in unacceptable levels of morbidity and mortality. Major contributors to the disappointing lack of progress in paediatric CIPO include a dearth of clarity and uniformity across all aspects of clinical care from definition and diagnosis to management. In order to assist medical care providers in identifying, evaluating, and managing children with CIPO, experts in this condition within the European Society for Pediatric Gastroenterology, Hepatology, and Nutrition as well as selected external experts, were charged with the task of developing a uniform document of evidence- and consensus-based recommendations.

METHODS

Ten clinically relevant questions addressing terminology, diagnostic, therapeutic, and prognostic topics were formulated. A systematic literature search was performed from inception to June 2017 using a number of established electronic databases as well as repositories. The approach of the Grading of Recommendations Assessment, Development and Evaluation (GRADE) was applied to evaluate outcome measures for the research questions. Levels of evidence and quality of evidence were assessed using the classification system of the Oxford Centre for Evidence-Based Medicine (diagnosis) and the GRADE system (treatment). Each of the recommendations were discussed, finalized, and voted upon using the nominal voting technique to obtain consensus.

RESULTS

This evidence- and consensus-based position paper provides recommendations specifically for chronic intestinal pseudo-obstruction in infants and children. It proposes these be termed paediatric intestinal pseudo-obstructive (PIPO) disorders to distinguish them from adult onset CIPO. The manuscript provides guidance on the diagnosis, evaluation, and treatment of children with PIPO in an effort to standardise the quality of clinical care and improve short- and long-term outcomes. Key recommendations include the development of specific diagnostic criteria for PIPO, red flags to alert clinicians to the diagnosis and guidance on the use of available investigative modalities. The group advocates early collaboration with expert centres where structured diagnosis and management is guided by a multi-disciplinary team, and include targeted nutritional, medical, and surgical interventions as well as transition to adult services.

CONCLUSIONS

This document is intended to be used in daily practice from the time of first presentation and definitive diagnosis PIPO through to the complex management and treatment interventions such as intestinal transplantation. Significant challenges remain to be addressed through collaborative clinical and research interactions.

Diagnostic Criteria of Pediatric Intestinal Myopathies

The authors aim to identify criteria for the diagnosis of intestinal visceral myopathy (IVM); results were compared with ultrastructural studies. Six IVM patients and 7 pediatric control cases (without gastrointestinal diseases) were studied. One case was a typical megacystis-microcolon-intestinal hypoperistalsis syndrome. The diagnostic path included: rectal suction biopsy, one-trocar transumbilical laparoscopic intestinal full-thickness biopsy technique. Pathological analysis included anti-alpha smooth muscle actin staining, and US study of intestinal biopsies. IVM histological examination demonstrated thinning of longitudinal muscle layer. The ratio of circular/longitudinal thickness was evaluated in all samples; in cases, this ratio presented as a mean value of 2.91, and in controls, a mean value of 1.472 (P = 0.0002). Ultrastructural diagnosis revealed variable myofibrils density in smooth muscle cells, irregularity of sarcolemma membranes, interstitial fibrosis, and myofiber disarray. The authors concluded that in IVM, circular/longitudinal thickness ratio and alpha smooth muscle actin staining can be used as significant tools to address the diagnosis.

Misato underlies visceral myopathy in Drosophila

Genetic mechanisms for the pathogenesis of visceral myopathy (VM) have been rarely demonstrated. Here we report the visceral role of misato (mst) in Drosophila and its implications for the pathogenesis of VM. Depletion of mst using three independent RNAi lines expressed by a pan-muscular driver elicited characteristic symptoms of VM, such as abnormal dilation of intestinal tracts, reduced gut motility, feeding defects, and decreased life span. By contrast, exaggerated expression of mst reduced intestine diameters, but increased intestinal motilities along with thickened muscle fibers, demonstrating a critical role of mst in the visceral muscle. Mst expression was detected in the adult intestine with its prominent localization to actin filaments and was required for maintenance of intestinal tubulin and actomyosin structures. Consistent with the subcellular localization of Mst, the intestinal defects induced by mst depletion were dramatically rescued by exogenous expression of an actin member. Upon ageing the intestinal defects were deteriorative with marked increase of apoptotic responses in the visceral muscle. Taken together, we propose the impairment of actomyosin structures induced by mst depletion in the visceral muscle as a pathogenic mechanism for VM.

Diagnosis of Chronic Intestinal Pseudo-obstruction and Megacystis by Sequencing the ACTG2 Gene

OBJECTIVES

The diagnosis of chronic intestinal pseudo-obstruction has depended on clinical features, manometry, and imaging. This report aimed to determine the efficacy of sequencing the actin γ-2 (ACTG2) gene for diagnosis. In addition, the goal was to determine how often a mutation would be found in our randomly collected cohort of probands and those probands published previously.

METHODS

Whole exome sequencing was performed in 4 probands with chronic intestinal pseudo-obstruction. Subsequently, only the ACTG2 gene was sequenced in another 24 probands (total 28). We analyzed published data of 83 probands and our 28 (total 111) and determined how many had pathogenic variants and the precise genotype.

RESULTS

Whole exome and Sanger sequencing revealed a pathogenic variant in the ACTG2 gene in 4 out of 28 of our probands and in 45 out of 83 published probands (49/111 [44.1%]). Moreover, a mutational hotspot in the ACTG2 gene was recognized. Genetic heterogeneity is evident.

CONCLUSIONS

Pooled gene sequencing results from 1 individual in each of 111 families enabled a precise diagnosis of an ACTG2 mutation in 49 (44%). The benefit to patients and families of early confirmation of a motility disorder not only helps avoid unnecessary intervention, but also enables institution of appropriate treatments and avoidance of secondary disorders such as malnutrition and poor growth. Knowledge of a pathogenic variant in a parent, with a 50% risk of recurrence, provides an opportunity for genetic counseling.