The Long Noncoding RNA Cardiac Mesoderm Enhancer-Associated Noncoding RNA (Carmn) Is a Critical Regulator of Gastrointestinal Smooth Muscle Contractile Function and Motility.

BACKGROUND & AIMS: Visceral smooth muscle cells (SMCs) are an integral component of the gastrointestinal (GI) tract that regulate GI motility. SMC contraction is regulated by posttranslational signaling and the state of differentiation. Impaired SMC contraction is associated with significant morbidity and mortality, but the mechanisms regulating SMC-specific contractile gene expression, including the role of long noncoding RNAs (lncRNAs), remain largely unexplored. Herein, we reveal a critical role of Carmn (cardiac mesoderm enhancer-associated noncoding RNA), an SMC-specific lncRNA, in regulating visceral SMC phenotype and contractility of the GI tract. METHODS: Genotype-Tissue Expression and publicly available single-cell RNA sequencing (scRNA-seq) data sets from embryonic, adult human, and mouse GI tissues were interrogated to identify SMC-specific lncRNAs. The functional role of Carmn was investigated using novel green fluorescent protein (GFP) knock-in (KI) reporter/knock-out (KO) mice. Bulk RNA-seq and single nucleus RNA sequencing (snRNA-seq) of colonic muscularis were used to investigate underlying mechanisms. RESULTS: Unbiased in silico analyses and GFP expression patterns in Carmn GFP KI mice revealed that Carmn is highly expressed in GI SMCs in humans and mice. Premature lethality was observed in global Carmn KO and inducible SMC-specific KO mice due to GI pseudo-obstruction and severe distension of the GI tract, with dysmotility in cecum and colon segments. Histology, GI transit, and muscle myography analysis revealed severe dilation, significantly delayed GI transit, and impaired GI contractility in Carmn KO vs control mice. Bulk RNA-seq of GI muscularis revealed that loss of Carmn promotes SMC phenotypic switching, as evidenced by up-regulation of extracellular matrix genes and down-regulation of SMC contractile genes, including Mylk, a key regulator of SMC contraction. snRNA-seq further revealed SMC Carmn KO not only compromised myogenic motility by reducing contractile gene expression but also impaired neurogenic motility by disrupting cell-cell connectivity in the colonic muscularis. These findings may have translational significance, because silencing CARMN in human colonic SMCs significantly attenuated contractile gene expression, including MYLK, and decreased SMC contractility. Luciferase reporter assays showed that CARMN enhances the transactivation activity of the master regulator of SMC contractile phenotype, myocardin, thereby maintaining the GI SMC myogenic program. CONCLUSIONS: Our data suggest that Carmn is indispensable for maintaining GI SMC contractile function in mice and that loss of function of CARMN may contribute to human visceral myopathy. To our knowledge this is the first study showing an essential role of lncRNA in the regulation of visceral SMC phenotype.

Histopathological, Ultrastructural, and Immunohistochemical Findings in MYH11-Variant Visceral Myopathy.

BACKGROUND: Pathogenic mutations in the smooth muscle myosin heavy chain gene, MYH11, cause megacystis megacolon intestinal hypoperistalsis syndrome and other forms of chronic intestinal pseudo-obstruction. Evaluation of intestinal tissues from affected patients is often performed before mutational analysis, but the pathological findings of MYH11-variant visceral myopathy have not been well defined. METHODS: Light microscopic, immunohistochemical, and ultrastructural findings from multiple intestinal samples from 2 patients with MYH11-variant visceral myopathy were reviewed, including MYH11-specific immunohistochemistry. The findings were compared with intestinal samples from patients with gamma-smooth muscle actin (ACTG2)-variant visceral myopathy and non-pseudo-obstruction controls. RESULTS: Apart from non-specific changes (e.g., muscle hypertrophy and distension-related muscularis propria necrosis), no alterations were identified by routine histopathological evaluation or electron microscopy. Immunohistochemistry with antibodies against a battery of smooth muscle proteins, including MYH11, revealed indistinguishable patterns of immunoreactivity in the muscularis propria of both patients and controls. CONCLUSIONS: Myopathic morphological or immunohistochemical changes may not be present in intestinal specimens from patients with MYH11-variant visceral myopathy. Molecular genetic studies should be considered for patients with chronic intestinal pseudo-obstruction and normal or non-specific pathology findings.

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.

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.

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.

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.

Visceral myopathy: Clinical and molecular survey of a cohort of seven new patients and state of the art of overlapping phenotypes.

Visceral motility dysfunction is a key feature of genetic disorders such as megacystis-microcolon-intestinal hypoperistalsis syndrome (MMIHS, MIM moved from 249210 to 155310), chronic intestinal pseudo-obstruction (CIPO, MIM609629), and multisystemic smooth muscle dysfunction syndrome (MSMDS, MIM613834). The genetic bases of these conditions recently begun to be clarified with the identification of pathogenic variants in ACTG2, ACTA2, and MYH11 in individuals with visceral motility dysfunction. The MMIHS was associated with the heterozygous variant in ACTG2 and homozygous variant in MYH11, while the heterozygous variant in ACTA2 was observed in patients with MSMDS. In this study, we describe the clinical data as well as the molecular investigation of seven individuals with visceral myopathy phenotypes. Five patients presented with MMIHS, including two siblings from consanguineous parents, one had CIPO, and the other had MSMDS. In three individuals with MMIHS and in one with CIPO we identified heterozygous variant in ACTG2, one being a novel variant (c.584C>T-p.Thr195Ile). In the individual with MSMDS we identified a heterozygous variant in ACTA2. We performed the whole-exome sequencing in one sibling with MMIHS and her parents; however, the pathogenic variant responsible for her phenotype could not be identified. These results reinforce the clinical and genetic heterogeneity of the visceral myopathies. Although many cases of MMIHS are associated with ACTG2 variants, we suggest that other genes, besides MYH11, could cause the MMIHS with autosomal recessive pattern. © 2016 Wiley Periodicals, Inc.

Surgical treatment of megaduodenum in familial visceral myopathy - report of a case and review of the literature.

INTRODUCTION: Familial visceral myopathy (VM) is a rare genetic disease that affects intestinal motility and results in pseudo-obstruction. Medical treatments can provide supportive measures but no curative treatment. CASE REPORT: A 20-year-old male with known diagnosis of VM was referred to our Unit in May 2013 with recurrent episodes of vomiting and hospital admissions not responding to medical treatment. Pre-operative imaging showed megaduodenum with marked delayed transit and normal small and large bowel transit. He underwent an elective Roux-en-Y duodeno-jejunostomy. The post-operative course was uneventful with complete resolution of the symptoms with a 2 years follow-up. DISCUSSION: Due to the early age of presentation, VM affects patient both psychologically and physically. Surgical treatment of megaduodenum in visceral myopathy in the absence of motility disorder of the small bowel seems to achieve satisfactory symptomatic relief and could be considered in this rare cohort of patients.

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.

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.

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.

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.

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.

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.

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.

Treating pediatric colorectal patients in low and middle income settings: Creative adaptation to the resources available.

Colorectal disease profiles for children in low- and middle-income settings (LMIC) are characterized by late presentation, increased complications and limited follow-up in many cases. There is a high prevalence of infectious conditions causing secondary colorectal disease such as Mycobacterium Tuberculosis(TB), Human Immunodeficiency Virus(HIV) and Human Papilloma Virus(HPV), which also impact the management of other primary colorectal conditions, such as wound-healing and intestinal anastomosis. Perineal trauma from sexual assault, motor vehicle or pedestrian accidents, burns, and traditional enemas are commonly encountered and may require adaptation of principles used in treatment of congenital anomalies such as Hirschsprung's disease and Anorectal Malformations for reconstruction. Endemic conditions in certain LMIC require further research to delineate underlying causes and optimize management, such as "African" degenerative visceral leiomyopathy, congenital pouch colon in the Indian subcontinent, and congenital H-type rectal fistulae prevalent in Asia. These unique disease profiles require creative adaptations of resources within poor healthcare infrastructure settings. These special challenges and pitfalls in colorectal care and complications of adverse socioeconomic conditions, are discussed.

Multimodality imaging findings of visceral myopathy in a child presenting with palpable abdominal mass.

Bayramoglu Z, Yilmaz R, Demir AA, Ataizi-Çelikel Ç, Kombak FE, Ikinci A, Yekeler E. Multimodality imaging findings of visceral myopathy in a child presenting with palpable abdominal mass. Turk J Pediatr 2019; 61: 120-125. Visceral myopathy is a rare cause of intestinal obstruction characterized by intestinal dysmotility and constipation. Patients often present with recurrent abdominal pain, vomiting and abdominal distension. We report a rare case of visceral myopathy in a child presenting with intraabdominal mass. We aimed to describe ultrasound, computed tomography and magnetic resonance enterography findings of this rare disease that has not been demonstrated before. Differential diagnosis of mural thickening with distinguishable layers in addition to intestinal dilatation in the absence of mesenteric inflammation includes visceral myopathy.

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.

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.