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

When intestinal obstruction is not a surgical condition

We report the case of a middle-aged man who had undergone two diagnostic laparoscopies with no significant findings after he was attended at the emergency department with cramping pain, abdominal distention and vomiting, with radiological images simulating a small bowel obstruction. After multiple hospitalisations and an extensive set of tests, including a genetic study, he was diagnosed with chronic pseudo-obstruction, an uncommon, unrecognides syndrome with high morbidity. Being aware of this pathology can make it easier to diagnose, and thereby, we can avoid unnecessary surgical interventions, because its management and treatment are mainly based on pharmacological therapy. After a proper diagnosis our patient's progression was satisfactory due to the treatment introduced, with no further hospitalisations.

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.

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.

Smooth muscle motility disorder phenotypes: A systematic review of cases associated with seven pathogenic genes (ACTG2, MYH11, FLNA, MYLK, RAD21, MYL9 and LMOD1)

Smooth muscle disorders affecting both the intestine and the bladder have been known for a decade. However, the recent discovery of genes associated with these dysfunctions has led to the description of several clinical phenotypes. We performed a systematic review of all published cases involving seven genes with pathogenic variants, ACTG2, MYH11, FLNA, MYLK, RAD21, MYL9 and LMOD1, and included 28 articles describing 112 patients and 5 pregnancies terminated before birth. The most commonly described mutations involved ACTG2 (75/112, 67% of patients), MYH11 (14%) and FLNA (13%). Twenty-seven patients (28%) died at a median age of 14.5 months. Among the 76 patients for whom this information was available, 10 (13%) had isolated chronic intestinal pseudo-obstruction (CIPO), 17 (22%) had isolated megacystis, and 48 (63%) had combined CIPO and megacystis. The respective proportions of these phenotypes were 9%, 20% and 71% among the 56 patients with ACTG2 mutations, 20%, 20% and 60% among the 10 patients with MYH11 mutations and 50%, 50% and 0% among the 7 patients with FLNA mutations.

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.

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.

Chronic intestinal pseudoobstruction: difficulties in diagnosis and treatment. Case report

The article presents a clinical case of a 23-year-old patient with an extremely severe congenital form of chronic intestinal pseudoobstruction coupled with a neuromyopathy,colon malrotation, malabsorption, bacterial overgrowth syndrome, cholelithiasis and gastrostasis, which excluded bowel transplantation. Long-term treatment in the intensive care unit with combined, mainly parenteral nutrition for 6 months, using antibiotics, prokinetics, intestinal decompression allowed to achieve partial stabilization of the patients condition and transfer to home treatment with the continuation of adequate complex therapy.

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.

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.

Clinical Outcomes of Pediatric Chronic Intestinal Pseudo-Obstruction

Chronic intestinal pseudo-obstruction (CIPO) is an extremely rare condition with symptoms of recurrent intestinal obstruction without any lesions. The outcomes of pediatric CIPO and predictors for the outcomes have not yet been well established. We analyzed the clinical outcomes and associated factors for the outcomes of pediatric CIPO. We retrospectively reviewed 66 primary CIPO patients diagnosed between January 1985 and December 2017. We evaluated parenteral nutrition (PN) factors such as PN duration, PN use over 6 months, home PN, and mortality as outcomes. We selected onset age, presence of urologic symptoms, pathologic type, and involvement extent as predictors. The early-onset CIPO was found in 63.6%, and 21.2% of the patients presenting with urologic symptoms. Of the 66 patients, 47 and 11 had neuropathy and myopathy, respectively. The generalized involvement type accounted for 83.3% of the cases. At the last follow-up, 24.2% of the patients required home PN management. The mean duration of PN was 11.8 ± 21.0 months. The overall mortality rate of primary CIPO was 18.2%. PN factors were predicted by the urologic symptoms and extent of involvement. However, mortality was predicted by pathologic type. The onset age was not significantly associated with the outcomes. CIPO with urologic symptoms and generalized CIPO had poor PN outcomes. Myopathy is suggested as a predictor of mortality in children with primary CIPO.

Recurrent spontaneous small bowel perforations with a rare pathology: non-familial visceral myopathy

Visceral myopathy is a rare, often misdiagnosed disease characterised by abnormalities in the gastrointestinal smooth muscle layer. Its clinical presentation includes pseudo-obstruction, intestinal dysmotility and spontaneous perforation. We report an atypical case of a 51-year-old man with a history of recurrent small bowel perforations who presented with an acute abdomen. A laparotomy was performed with identification of a distal jejunal perforation. A small bowel resection with end-to-end anastomosis was done. Minimal adhesions were seen intraoperatively despite the patient's multiple prior surgeries. Pathology showed histiocytic inflammation and patchy loss of the muscle layer reflective of visceral myopathy. Genetic testing revealed a variant of uncertain significance in the myosin light chain kinase gene. It is difficult to make a conclusive diagnosis given the patient's clinical presentation closely mimicking other gastrointestinal disorders. However, it is crucial to consider visceral myopathy in patients with recurrent spontaneous intestinal perforations as a differential diagnosis.

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.

Actin Mutations and Their Role in Disease

Actin is a widely expressed protein found in almost all eukaryotic cells. In humans, there are six different genes, which encode specific actin isoforms. Disease-causing mutations have been described for each of these, most of which are missense. Analysis of the position of the resulting mutated residues in the protein reveals mutational hotspots. Many of these occur in regions important for actin polymerization. We briefly discuss the challenges in characterizing the effects of these actin mutations, with a focus on cardiac actin mutations.