ACTG2 variants impair actin polymerization in sporadic Megacystis Microcolon Intestinal Hypoperistalsis Syndrome

Actin Gamma Smooth Muscle 2 Promotes Epithelial Ovarian Cancer Cell Proliferation via the AKT1/NF-κB Signaling Pathway

Epithelial ovarian cancer (EOC) is associated with high mortality rates worldwide and is characterized as the most lethal gynecological cancer. The study aimed to investigate the functional role and underlying molecular mechanism of actin gamma smooth muscle 2 (ACTG2) in the progression of EOC. Data mining from The Cancer Genome Atlas (TCGA) databases showed the expression of ACTG2 was significantly upregulated in EOC and negatively associated with longer overall survival and better prognosis of patients. By using of gain-of-function and loss-of-function experiments in vitro and in vivo, we found that ACTG2 promoted EOC cell proliferation and suppressed cell apoptosis. Mechanistic study revealed that ACTG2 regulates EOC cell proliferation by activating the AKT serine/threonine kinase 1 (AKT1)/nuclear factor-κB (NF-κB) signaling pathway. Importantly, p65 plays a crucial role in this newly identified regulatory mechanism. Our findings demonstrate that ACTG2 may play an oncogenic role in EOC, suggesting its potential as a therapeutic target.

Shared Lineage, Distinct Outcomes: Yap and Taz Loss Differentially Impact Schwann and Olfactory Ensheathing Cell Development Without Disrupting GnRH-1 Migration

Olfactory Ensheathing Cells (OECs) are glial cells originating from the neural crest, critical for bundling olfactory axons to the brain. Their development is crucial for the migration of Gonadotropin-Releasing Hormone-1 (GnRH-1) neurons, which are essential for puberty and fertility. OECs have garnered interest as potential therapeutic targets for central nervous system lesions, although their development is not fully understood. Our single-cell RNA sequencing of mouse embryonic nasal tissues suggests that OECs and Schwann cells share a common origin from Schwann cell precursors yet exhibit significant genetic differences. The transcription factors Yap and Taz have previously been shown to play a crucial role in Schwann cell development. We used Sox10 -Cre mice to conditionally ablate Yap and Taz in migrating the neural crest and its derivatives. Our analyses showed reduced Sox10+ glial cells along nerves in the nasal region, altered gene expression of SCs, melanocytes, and OECs, and a significant reduction in olfactory sensory neurons and vascularization in the vomeronasal organ. However, despite these changes, GnRH-1 neuronal migration remained unaffected. Our findings highlight the importance of the Hippo pathway in OEC development and how changes in cranial neural crest derivatives indirectly impact the development of olfactory epithelia.

Multi-omics profiling combined with molecular docking reveals immune-inflammatory proteins as potential drug targets in colorectal cancer

Colorectal cancer is globally ranked as the third most common malignant tumor. Its development involves a complex biological process driven by various genetic and epigenetic alterations. To elucidate the biological significance of the extensive omics data, we conducted comparative multi-omics studies on colorectal cancer patients at different clinical stages. Bioinformatics methods were applied to analyze multi-omics datasets and explore the molecular landscape. Drug prediction and molecular docking also were conducted to assess potential therapeutic interventions. In vitro experiments were used to validate the inhibitory effect on the migration and proliferation of cell lines. The results indicate up-regulated proteins involved in immune-inflammatory related pathways, while biomarkers related to muscular contraction and cell adhesion are significantly down-regulated. Drug prediction, coupled with in vitro experiments, suggests that AZ-628 may act as a potential drug to inhibit the proliferation and migration of CRC cell lines HCT-116 and HT-29 by regulating the aforementioned key biological pathways or proteins. Complementing these findings, metabolomics analysis unveiled a down-regulation of key carbon metabolism pathways, alongside an up-regulation in amino acid metabolism, particularly proline metabolism. This metabolic shift may reflect an adaptive response in cancer cells, favoring specific amino acids to support their growth. Together, these integrated results provide valuable insights into the intricate landscape of tumor development, highlighting the crossroads of immune regulation, cellular structure, and metabolic reprogramming in the tumorigenic process and providing valuable insights into cancer pathology.

Exploring the complexities of megacystis-microcolon-intestinal hypoperistalsis syndrome: insights from genetic studies

Megacystis microcolon intestinal hypoperistalsis syndrome (MMIHS) is an uncommon genetic disorder inherited in an autosomal recessive pattern that affects the muscles that line the bladder and intestines. The most common genes associated with MMIHS mutations are ACTG2, LMOD1, MYH11, MYL9, MYLK, and PDCL3. However, the complete genetic landscape of MMIHS still needs to be fully understood. The diagnosis of MMIHS can be challenging. However, advances in prenatal and diagnostic techniques, such as ultrasound and fetal urine analysis, have improved the ability to detect the syndrome early. Targeted next-generation sequencing (NGS) and other diagnostic tests can also diagnose MMIHS. The management of MMIHS involves addressing severe intestinal dysmotility, which often necessitates total parenteral nutrition (TPN), which can lead to complications such as hepatotoxicity and nutritional deficiencies. Multivisceral and intestinal transplantation has emerged as therapeutic options, offering the potential for improved outcomes and enteral autonomy. Understanding the genetic underpinnings of MMIHS is crucial for personalized care. While the prognosis varies, timely interventions and careful monitoring enhance patient outcomes. Genetic studies have given us valuable insights into the molecular mechanisms of MMIHS. These studies have identified mutations in genes involved in the development and function of smooth muscle cells. They have also shown that MMIHS is associated with defects in the signaling pathways that control muscle contraction. Continued research in the genetics of MMIHS holds promise for unraveling the complexities of MMIHS and improving the lives of affected individuals.

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.

Genome-wide analysis identifies MYH11 compound heterozygous variants leading to visceral myopathy corresponding to late-onset form of megacystis-microcolon-intestinal hypoperistalsis syndrome

Megacystis-microcolon-hypoperistalsis-syndrome (MMIHS) is a rare and early-onset congenital disease characterized by massive abdominal distension due to a large non-obstructive bladder, a microcolon and decreased or absent intestinal peristalsis. While in most cases inheritance is autosomal dominant and associated with heterozygous variant in ACTG2 gene, an autosomal recessive transmission has also been described including pathogenic bialellic loss-of-function variants in MYH11. We report here a novel family with visceral myopathy related to MYH11 gene, confirmed by whole genome sequencing (WGS). WGS was performed in two siblings with unusual presentation of MMIHS and their two healthy parents. The 38 years-old brother had severe bladder dysfunction and intestinal obstruction, whereas the 30 years-old sister suffered from end-stage kidney disease with neurogenic bladder and recurrent sigmoid volvulus. WGS was completed by retrospective digestive pathological analyses. Compound heterozygous variants of MYH11 gene were identified, associating a deletion of 1.2 Mb encompassing MYH11 inherited from the father and an in-frame variant c.2578_2580del, p.Glu860del inherited from the mother. Pathology analyses of the colon and the rectum revealed structural changes which significance of which is discussed. Cardiac and vascular assessment of the mother was normal. This is the second report of a visceral myopathy corresponding to late-onset form of MMIHS related to compound heterozygosity in MYH11; with complete gene deletion and a hypomorphic allele in trans. The hypomorphic allele harbored by the mother raised the question of the risk of aortic disease in adults. This case shows the interest of WGS in deciphering complex phenotypes, allowing adapted diagnosis and genetic counselling.

Megacystis microcolon intestinal hypoperistalsis syndrome (MMIHS): challenges in diagnosis and management

Megacystis microcolon intestinal hypoperistalsis syndrome (MMIHS) is a rare, congenital functional intestinal obstruction, characterised by megacystis (bladder distention in the absence of mechanical obstruction), microcolon and intestinal hypoperistalsis (dysmotility).We are reporting a case of a female child with normal antenatal course who presented with recurrent episodes of abdominal distension since the second day of life and underwent negative exploratory laparotomy on multiple occasions. She also had urinary retention with a grossly distended bladder, requiring drainage by clean intermittent catheterisation. Surgical procedures for bowel decompression, including gastrostomy and ileostomy, were carried out without success. Genetic analysis revealed a mutation in the human smooth muscle (enteric) gamma-actin gene (ACTG2 gene), clinching the diagnosis of MMIHS. The patient was managed with parenteral nutrition and prokinetic medications and tolerated jejunostomy feeds for a brief period before she succumbed to the illness.Female neonates or infants presenting with abdominal distension and dilated urinary tract should be investigated for MMIHS early on. A timely diagnosis will enable the early involvement of a multidisciplinary team to provide the best options available for management.

ATP5PO levels regulate enteric nervous system development in zebrafish, linking Hirschsprung disease to Down Syndrome

Hirschsprung disease (HSCR) is a complex genetic disorder characterized by the absence of enteric nervous system (ENS) in the distal region of the intestine. Down Syndrome (DS) patients have a >50-fold higher risk of developing HSCR than the general population, suggesting that overexpression of human chromosome 21 (Hsa21) genes contribute to HSCR etiology. However, identification of responsible genes remains challenging. Here, we describe a genetic screening of potential candidate genes located on Hsa21, using the zebrafish. Candidate genes were located in the DS-HSCR susceptibility region, expressed in the human intestine, were known potential biomarkers for DS prenatal diagnosis, and were present in the zebrafish genome. With this approach, four genes were selected: RCAN1, ITSN1, ATP5PO and SUMO3. However, only overexpression of ATP5PO, coding for a component of the mitochondrial ATPase, led to significant reduction of ENS cells. Paradoxically, in vitro studies showed that overexpression of ATP5PO led to a reduction of ATP5PO protein levels. Impaired neuronal differentiation and reduced mitochondrial ATP production, were also detected in vitro, after overexpression of ATP5PO in a neuroblastoma cell line. Finally, epistasis was observed between ATP5PO and ret, the most important HSCR gene. Taken together, our results identify ATP5PO as the gene responsible for the increased risk of HSCR in DS patients in particular if RET variants are also present, and show that a balanced expression of ATP5PO is required for normal ENS development.

Syndromic and single gene disorders associated with fetal megacystis (I): Megacystis-microcolon-intestinal hypoperistalsis syndrome (MMIHS)

Fetal megacystis has been reported to be associated with chromosomal abnormalities, megacystis-microcolon-intestinal hypoperistalsis syndrome (MMIHS), obstructive uropathy, prune belly syndrome, cloacal anomalies, limb-body wall complex, amniotic band syndrome, anorectal malformations, VACTERL association (vertebral anomalies, anal atresia, cardiac malformations, tracheo-esophageal fistula, renal anomalies and limb abnormalities) and fetal overgrowth syndrome such as Bechwith-Wiedemann syndrome and Sotos syndrome. This review provides an overview of syndromic and single gene disorders associated with fetal megacystis which is useful for genetic counseling at prenatal diagnosis of fetal megacystis.

Actin polymerization and depolymerization in developing vertebrates

Development is a complex process that occurs throughout the life cycle. F-actin, a major component of the cytoskeleton, is essential for the morphogenesis of tissues and organs during development. F-actin is formed by the polymerization of G-actin, and the dynamic balance of polymerization and depolymerization ensures proper cellular function. Disruption of this balance results in various abnormalities and defects or even embryonic lethality. Here, we reviewed recent findings on the structure of G-actin and F-actin and the polymerization of G-actin to F-actin. We also focused on the functions of actin isoforms and the underlying mechanisms of actin polymerization/depolymerization in cellular and organic morphogenesis during development. This information will extend our understanding of the role of actin polymerization in the physiologic or pathologic processes during development and may open new avenues for developing therapeutics for embryonic developmental abnormalities or tissue regeneration.

Single-cell sequencing analysis reveals development and differentiation trajectory of Schwann cells manipulated by M. leprae

BACKGROUND

M. leprae preferentially infects Schwann cells (SCs) in the peripheral nerves leading to nerve damage and irreversible disability. Knowledge of how M. leprae infects and interacts with host SCs is essential for understanding mechanisms of nerve damage and revealing potential new therapeutic strategies.

METHODOLOGY/PRINCIPAL FINDINGS

We performed a time-course single-cell sequencing analysis of SCs infected with M. leprae at different time points, further analyzed the heterogeneity of SCs, subpopulations associated with M. leprae infection, developmental trajectory of SCs and validated by Western blot or flow cytometry. Different subpopulations of SCs exhibiting distinct genetic features and functional enrichments were present. We observed two subpopulations associated with M. leprae infection, a stem cell-like cell subpopulation increased significantly at 24 h but declined by 72 h after M. leprae infection, and an adipocyte-like cell subpopulation, emerged at 72 h post-infection. The results were validated and confirmed that a stem cell-like cell subpopulation was in the early stage of differentiation and could differentiate into an adipocyte-like cell subpopulation.

CONCLUSIONS/SIGNIFICANCE

Our results present a systematic time-course analysis of SC heterogeneity after infection by M. leprae at single-cell resolution, provide valuable information to understand the critical biological processes underlying reprogramming and lipid metabolism during M. leprae infection of SCs, and increase understanding of the disease-causing mechanisms at play in leprosy patients as well as revealing potential new therapeutic strategies.

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.

Single-cell RNA sequencing reveals the developmental program underlying proximal-distal patterning of the human lung at the embryonic stage

The lung is the primary respiratory organ in human, in which the proximal airway and the distal alveoli are responsible for air conduction and gas exchange, respectively. However, the regulation of proximal-distal patterning at the embryonic stage of human lung development is largely unknown. Here we investigated the early lung development of human embryos at weeks 4-8 post fertilization (Carnegie stages 12-21) using single-cell RNA sequencing, and obtained a transcriptomic atlas of 169,686 cells. We observed discernible gene expression patterns of proximal and distal epithelia at week 4, upon the initiation of lung organogenesis. Moreover, we identified novel transcriptional regulators of the patterning of proximal (e.g., THRB and EGR3) and distal (e.g., ETV1 and SOX6) epithelia. Further dissection revealed various stromal cell populations, including an early-embryonic BDNF⁺ population, providing a proximal-distal patterning niche with spatial specificity. In addition, we elucidated the cell fate bifurcation and maturation of airway and vascular smooth muscle progenitor cells at the early stage of lung development. Together, our study expands the scope of human lung developmental biology at early embryonic stages. The discovery of intrinsic transcriptional regulators and novel niche providers deepens the understanding of epithelial proximal-distal patterning in human lung development, opening up new avenues for regenerative medicine.

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.

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.

Five New Cases of Megacystis-Microcolon-Intestinal Hypoperistalsis Syndrome (MMIHS), with One Case Showing a Novel Mutation

BACKGROUND

Megacystis-microcolon-intestinal hypoperistalsis syndrome (MMIHS) is a lethal congenital disorder characterized by a large, non-obstructed bladder, microcolon, and lack of proper peristalsis.

MATERIALS AND METHODS

Five cases of MMIHS were identified, confirmed histologically and were predominantly female (F:M, 4:1). DNA sequencing was also performed.

RESULTS

Four cases showed mutations in the α3 and β4 nicotinic acetylcholine receptor (ηAChR) subunits (CHRNA3 and CHRNB4, respectively) on chromosome 15q24. The 5th case had a delayed clinical presentation of intussusception at 11 months and showed a novel missense mutation in ATP2B4 on Chromosome 1q32.

CONCLUSION

The first four patients showed a previously identified mutation. The 5th patient shows a novel mutation in ATP2B4. This novel gene was associated with a less severe presentation and increases success of multiorgan transplant than the other four patients. This highlights how identifying various mutations may impact prognosis and clinical treatment plans for MMIHS patients.

The long Filamin-A isoform is required for intestinal development and motility: implications for chronic intestinal pseudo-obstruction

Filamin A (FLNA) is a cytoplasmic actin binding protein, recently shown to be expressed as a long and short isoform. Mutations in FLNA are associated with a wide spectrum of disorders, including an X-linked form of chronic intestinal pseudo-obstruction (CIPO). However, the role of FLNA in intestinal development and function is largely unknown. In this study, we show that FLNA is expressed in the muscle layer of the small intestine from early human fetal stages. Expression of FLNA variants associated with CIPO, blocked expression of the long flna isoform and led to an overall reduction of RNA and protein levels. As a consequence, contractility of human intestinal smooth muscle cells was affected. Lastly, our transgenic zebrafish line showed that the flna long isoform is required for intestinal elongation and peristalsis. Histological analysis revealed structural and architectural changes in the intestinal smooth muscle of homozygous fish, likely triggered by the abnormal expression of intestinal smooth muscle markers. No defect in the localization or numbers of enteric neurons was observed. Taken together, our study demonstrates that the long FLNA isoform contributes to intestinal development and function. Since loss of the long FLNA isoform does not seem to affect the enteric nervous system, it likely results in a myopathic form of CIPO, bringing new insights to disease pathogenesis.

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.

TFAP2B Haploinsufficiency Impacts Gastrointestinal Function and Leads to Pediatric Intestinal Pseudo-obstruction

Background: Pediatric Intestinal Pseudo-obstruction (PIPO) is a congenital enteric disorder characterized by severe gastrointestinal (GI) dysmotility, without mechanical obstruction. Although several genes have been described to cause this disease, most patients do not receive a genetic diagnosis. Here, we aim to identify the genetic cause of PIPO in a patient diagnosed with severe intestinal dysmotility shortly after birth.

Methods: Whole exome sequencing (WES) was performed in the patient and unaffected parents, in a diagnostic setting. After identification of the potential disease-causing variant, its functional consequences were determined in vitro and in vivo. For this, expression constructs with and without the causing variant, were overexpressed in HEK293 cells. To investigate the role of the candidate gene in GI development and function, a zebrafish model was generated where its expression was disrupted using CRISPR/Cas9 editing.

Results: WES analysis identified a de novo heterozygous deletion in TFAP2B (NM_003221.4:c.602-5_606delTCTAGTTCCA), classified as a variant of unknown significance. In vitro studies showed that this deletion affects RNA splicing and results in loss of exon 4, leading to the appearance of a premature stop codon and absence of TFAP2B protein. Disruption of tfap2b in zebrafish led to decreased enteric neuronal numbers and delayed transit time. However, no defects in neuronal differentiation were detected. tfap2b crispants also showed decreased levels of ednrbb mRNA, a downstream target of tfap2b.

Conclusion: We showed that TFAP2B haploinsufficiency leads to reduced neuronal numbers and GI dysmotility, suggesting for the first time, that this gene is involved in PIPO pathogenesis.

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.

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.

The remodelling of actin composition as a hallmark of cancer

Actin is a key structural protein that makes up the cytoskeleton of cells, and plays a role in functions such as division, migration, and vesicle trafficking. It comprises six different cell-type specific isoforms: ACTA1, ACTA2, ACTB, ACTC1, ACTG1, and ACTG2. Abnormal actin isoform expression has been reported in many cancers, which led us to hypothesize that it may serve as an early biomarker of cancer. We show an overview of the different actin isoforms and highlight mechanisms by which they may contribute to tumorigenicity. Furthermore, we suggest how the aberrant expression of actin subunits can confer cells with greater proliferation ability, increased migratory capability, and chemoresistance through incorporation into the normal cellular F-actin network and altered actin binding protein interaction. Studying this fundamental change that takes place within cancer cells can further our understanding of neoplastic transformation in multiple tissue types, which can ultimately aid in the early-detection, diagnosis and treatment of cancer.

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.

Megacystis Microcolon Intestinal Hypoperistalsis Syndrome: A Case Series With Long-term Follow-up and Prolonged Survival

OBJECTIVES

Describe clinical characteristics, management, and outcome in a cohort of megacystis microcolon intestinal hypoperistalsis syndrome (MMIHS) patients.

METHODS

We conducted a retrospective chart review of MMIHS patients followed at a large transplant and intestinal rehabilitation center over a period of 17 years.

RESULTS

We identified 25 patients with MMIHS (68% girls, 13 transplanted). One transplanted and 1 nontransplanted patient were lost to follow-up. We estimated 100, 100, and 86% for 5-, 10-, and 20-year survival, respectively, with only 1 death. Of the 22 patients alive at the time of study (11 transplanted, 11 nontransplanted), median age was 9.2 years (range 2.7-22.9 years). Longest posttransplant follow-up was 16 years. Seventeen patients had available prenatal imaging reports; all showed distended bladder. Eight had genetic testing (5, ACTG2; 2, MYH11; 1, MYL9). Almost all patients had normal growth with median weight z-score -0.77 (interquartile range -1.39 to 0.26), height z score -1.2 (-2.04 to -0.48) and body mass index z-score 0.23 (-0.37 to 0.93) with no statistical difference between transplanted and nontransplanted patients. All nontransplanted patients were on parenteral nutrition with minimal/no feeds, and all except 1 of the transplanted patients were on full enteral feeds. Recent average bilirubin, INR, albumin, and creatinine fell within the reference ranges.

CONCLUSIONS

This is the largest single-center case series with the longest duration of follow-up for MMIHS patients. In the current era of improved intestinal rehabilitation and transplantation, MMIHS patients have excellent outcomes in survival, growth, and liver function. This observation contradicts previous reports and should alter counselling and management decisions in these patients at diagnosis.

Megacystis-Microcolon-Intestinal Hypoperistalsis Syndrome (MMIHS): Series of 4 Cases Caused by Mutation of ACTG2 (Actin Gamma 2, Smooth Muscle) Gene

MMIHS, also known as Berdon's syndrome, is a rare disease that belongs to primary causes of CIPOS (chronic intestinal pseudoobstruction syndrome). Clinical characteristics of MMIHS are differential, but we come across the following classic symptoms: disorders of intestinal peristalsis, microcolon, and megacystis. In this article, we present a series of 4 patients with Berdon's syndrome, in whom we managed to identify the genetic causes of MMIHS. All infants showed clinical features of bowel obstruction and dysfunction of the urinary system after birth. Two of them also manifested disorders from other systems. The prognosis for these patients is poor, but a constant betterment of management in MMIHS, in which the leading role plays TPN (total parental nutrition), causes improvement of patients' survival.

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.

DOCK8 is essential for LFA-1-dependent positioning of T follicular helper cells in germinal centers

T follicular helper (Tfh) cell migration into germinal centers (GCs) is essential for the generation of GC B cells and antibody responses to T cell-dependent (TD) antigens. This process requires interactions between lymphocyte function-associated antigen 1 (LFA-1) on Tfh cells and ICAMs on B cells. The mechanisms underlying defective antibody responses to TD antigens in DOCK8 deficiency are incompletely understood. We show that mice selectively lacking DOCK8 in T cells had impaired IgG antibody responses to TD antigens, decreased GC size, and reduced numbers of GC B cells. However, they developed normal numbers of Tfh cells with intact capacity for driving B cell differentiation into a GC phenotype in vitro. Notably, migration of DOCK8-deficient T cells into GCs was defective. Following T cell receptor (TCR)/CD3 ligation, DOCK8-deficient T cells had impaired LFA-1 activation and reduced binding to ICAM-1. Our results therefore indicate that DOCK8 is important for LFA-1-dependent positioning of Tfh cells in GCs, and thereby the generation of GC B cells and IgG antibody responses to TD antigen.

Fetal megacystis-microcolon: Genetic mutational spectrum and identification of PDCL3 as a novel candidate gene

Megacystis-microcolon-intestinal-hypoperistalsis syndrome (MMIHS) is a severe congenital visceral myopathy characterized by an abdominal distension due to a large non-obstructed urinary bladder, a microcolon and intestinal hypo- or aperistalsis. Most of the patients described to date carry a sporadic heterozygous variant in ACTG2. More recently, recessive forms have been reported and mutations in MYH11, LMOD1, MYLK and MYL9 have been described at the molecular level. In the present report, we describe five patients carrying a recurrent heterozygous variant in ACTG2. Exome sequencing performed in four families allowed us to identify the genetic cause in three. In two families, we identified variants in MMIHS causal genes, respectively a nonsense homozygous variant in MYH11 and a previously described homozygous deletion in MYL9. Finally, we identified compound heterozygous variants in a novel candidate gene, PDCL3, c.[143_144del];[380G>A], p.[(Tyr48Ter)];[(Cys127Tyr)]. After cDNA analysis, a complete absence of PDLC3 expression was observed in affected individuals, indicating that both mutated transcripts were unstable and prone to mediated mRNA decay. PDCL3 encodes a protein involved in the folding of actin, a key step in thin filament formation. Presumably, loss-of-function of this protein affects the contractility of smooth muscle tissues, making PDCL3 an excellent candidate gene for autosomal recessive forms of MMIHS.

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.

Is Hirschsprung disease a purely neurological condition? A study of the Actin G2 smooth muscle gene in Hirschsprung disease

BACKGROUND

Hirschsprung disease is a functional obstruction of the gastrointestinal tract due to the congenital absence of ganglion cells in the intermyenteric plexuses of the distal bowel. Gastrointestinal motility requires intact muscular layers as well as neural network connection to function properly. The Actin G2 gene is the main gene encoding actin gamma 2; a smooth muscle actin found in enteric tissues.

AIM

This study of the Actin G2 gene in patients with Hirschsprung disease explores a possible molecular basis abnormal muscle function and post-surgical pseudo-obstruction in a group of patients. As far as the authors are aware, this is the first report confirming structural muscle deficits in Hirschsprung disease.

PATIENTS AND METHODS

Ethical permission and informed consent were obtained. DNA was extracted from whole blood samples in 10 patients with histologically proven HSCR patients. PCR amplification of the ACTG2 gene, were subjected to semi-automated bi-directional sequencing analysis. Sequencing results were analyzed using FinchTV Sequence Alignment Software (http:/en.biosoft.net) to read chromatogram files. Further predicting bioinformatic investigation was obtained by PolyPhen 2 software to evaluate the significance of the observed amino acid changes.

RESULTS

Ten new patients with similar HSCR phenotypes were prospectively investigated for variation in the Actin G2 gamma gene (ACTG2) variations. The results of ACTG2 gene analysis showing variation in exons 5, 8 and 10 of the ACTG2 gene in 7 of them (64%). The c.109C > G S345 L was the most frequent occurring in 6 of the 10 patients (54%), the c.171 A > A K119E in 2 and the significant c.108 T > G W357G variation in exon 10 (1 patient) Four patients had a combination of different variants in different exons which were less significant. Allele frequency on a control sample of the South African population showed no comparable pathology link scores (http://gnomad.broadinstitute.org/). Bioinformatic in silico modeling showed that the residue replacements in both variants (Lys to Glu and Trp to Gly) are highly non-conservative and variation can alter interactions within the protein conformation.

CONCLUSIONS

The Actin smooth muscle gene showed variation in 64% of samples, indicating a reason for abnormal functioning muscle in many HSCR patients. Hirschsprung disease is part of a complex spectrum which also includes smooth muscle.

LEVEL OF EVIDENCE

VI.

Identification of a dominant MYH11 causal variant in chronic intestinal pseudo-obstruction: Results of whole-exome sequencing

Chronic Intestinal Pseudo-Obstruction (CIPO) is a rare gastrointestinal disorder, which affects the smooth muscle contractions of the gastrointestinal tract. Dominant mutations in the smooth muscle actin gene, ACTG2, accounts for 44%-50% of CIPO patients. Other recessive or X-linked genes, including MYLK, LMOD1, RAD21, MYH11, MYL9, and FLNA were reported in single cases. In this study, we used Whole-Exome Sequencing (WES) to study 23 independent CIPO families including one extended family with 13 affected members. A dominantly inherited rare mutation, c.5819delC (p.Pro1940HisfsTer91), in the smooth muscle myosin gene, MYH11, was found in the extended family, shared by 7 affected family members but not by 3 unaffected family members with available DNA, suggesting a high probability of genetic linkage. Gene burden analysis indicates that additional genes, COL4A1, FBLN1 and HK2, may be associated with the disease. This study expanded our understanding of CIPO etiology and provided additional genetic evidence to physicians and genetic counselors for CIPO diagnosis.

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.

Newly described recessive MYH11 disorder with clinical overlap of Multisystemic smooth muscle dysfunction and Megacystis microcolon hypoperistalsis syndromes

We describe a neonatal patient with fixed dilated pupils and pulmonary, bladder, and bowel dysfunction suspicious for the presence of ACTA2 R179 mediated multisystemic smooth muscle dysfunction syndrome. Whole exome sequencing revealed compound heterozygous mutations in MYH11 after ACTA2 specific testing revealed no abnormalities. The child lived until 18 months of age and represents the only reported case of an MYH11 compound heterozygote with widespread smooth muscle dysfunction.

Consanguinity and its relevance for the incidence of megacystis microcolon intestinal hypoperistalsis syndrome (MMIHS): systematic review

BACKGROUND/PURPOSE

Megacystis microcolon intestinal hypoperistalsis syndrome (MMIHS) is a rare congenital and generally fatal cause of functional intestinal obstruction in the newborn. The cause of this syndrome is unknown. Familial occurrence and reports of consanguinity in MMIHS implies that genetic factors may have an important role in the pathogenesis of this syndrome. The aim of the study was to determine the consequence of consanguinity for the incidence of MMIHS.

METHODS

A literature search was performed using the keywords "megacystis microcolon intestinal hypoperistalsis" for studies published between 1976 and 2018. Retrieved articles, including additional studies from reference lists, were reviewed for consanguinity between parents and recurrence of MMIHS between siblings. Data were extracted for cases where familial MMIHS was present.

RESULTS

A total of 450 patients with the diagnosis of MMIHS have been reported in the literature. There were 56 (12%) cases in which familial MMIHS was confirmed, 25 families with multiple siblings and 3 families with single affected infant. Of the 25 families with multiple siblings, 22 families had 2 siblings with confirmed MMIHS and 3 families had 3 children each with MMIHS. Consanguinity between parents was confirmed in 30 cases (18 siblings and 12 individual cases). Female-to-male ratio in the 30 patients was 4.4:1.

CONCLUSION

The occurrence of MMIHS in the offspring of consanguineous parents and recurrence in siblings of healthy parents suggest that MMIHS is an autosomal recessive disorder. Pre-marital and pre-conception counselling of consanguineous populations is recommended to prevent harmful consequences.

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.

Identification of Variants in RET and IHH Pathway Members in a Large Family With History of Hirschsprung Disease

BACKGROUND & AIMS

Hirschsprung disease (HSCR) is an inherited congenital disorder characterized by absence of enteric ganglia in the distal part of the gut. Variants in ret proto-oncogene (RET) have been associated with up to 50% of familial and 35% of sporadic cases. We searched for variants that affect disease risk in a large, multigenerational family with history of HSCR in a linkage region previously associated with the disease (4q31.3-q32.3) and exome wide.

METHODS

We performed exome sequencing analyses of a family in the Netherlands with 5 members diagnosed with HSCR and 2 members diagnosed with functional constipation. We initially focused on variants in genes located in 4q31.3-q32.3; however, we also performed an exome-wide analysis in which known HSCR or HSCR-associated gene variants predicted to be deleterious were prioritized for further analysis. Candidate genes were expressed in HEK293, COS-7, and Neuro-2a cells and analyzed by luciferase and immunoblot assays. Morpholinos were designed to target exons of candidate genes and injected into 1-cell stage zebrafish embryos. Embryos were allowed to develop and stained for enteric neurons.

RESULTS

Within the linkage region, we identified 1 putative splice variant in the lipopolysaccharide responsive beige-like anchor protein gene (LRBA). Functional assays could not confirm its predicted effect on messenger RNA splicing or on expression of the mab-21 like 2 gene (MAB21L2), which is embedded in LRBA. Zebrafish that developed following injection of the lrba morpholino had a shortened body axis and subtle gut morphological defects, but no significant reduction in number of enteric neurons compared with controls. Outside the linkage region, members of 1 branch of the family carried a previously unidentified RET variant or an in-frame deletion in the glial cell line derived neurotrophic factor gene (GDNF), which encodes a ligand of RET. This deletion was located 6 base pairs before the last codon. We also found variants in the Indian hedgehog gene (IHH) and its mediator, the transcription factor GLI family zinc finger 3 (GLI3). When expressed in cells, the RET-P399L variant disrupted protein glycosylation and had altered phosphorylation following activation by GDNF. The deletion in GDNF prevented secretion of its gene product, reducing RET activation, and the IHH-Q51K variant reduced expression of the transcription factor GLI1. Injection of morpholinos that target ihh reduced the number of enteric neurons to 13% ± 1.4% of control zebrafish.

CONCLUSIONS

In a study of a large family with history of HSCR, we identified variants in LRBA, RET, the gene encoding the RET ligand (GDNF), IHH, and a gene encoding a mediator of IHH signaling (GLI3). These variants altered functions of the gene products when expressed in cells and knockout of ihh reduced the number of enteric neurons in the zebrafish gut.

Prenatal diagnosis of megacystis microcolon intestinal hypoperistalsis syndrome by biochemical analysis of fetal urine

OBJECTIVES

The objective of the study is to determine a model of fetal urine biochemical markers to differentiate megacystis microcolon intestinal hypoperistalsis syndrome (MMIHS) from other megacystis.

METHOD

This is a retrospective study of biochemical analysis of fetal urine in patients who presented prenatally with megacystis. We studied β2-microglobulin, sodium, calcium, and phosphorus. Twenty-six patients subsequently diagnosed with MMIHS were compared with 2 control groups: one of end-stage renal failure (64 fetuses) and the second of "good" postnatal renal function (control group, 64 fetuses).

RESULTS

Mean fetal urine β2-microglobulin was significantly higher (P < .001) in end-stage renal failure (15.7 mg/L) than in MMIHS (2.2 mg/L) and the control group (3.2 mg/L). Fetal urine profiles differed significantly (P < .001) between MMIHS and the control group: median sodium 46.5 and 51 mmol/L, median calcium 1.12 and 0.73 mmol/L, and median phosphorus 0.03 and 0.15 mmol/L respectively. Fetal urinary ionic index [ratio: calcium / (phosphorus × sodium)] gave an area under the ROC curve of 0.86, at 54% sensitivity and 97% specificity, with correct classification in 84% of cases. We defined a nomogram to obtain a probability for MMIHS.

CONCLUSION

Fetal urinalysis can be helpful in prenatal differentiation of MMIHS from posterior urethral valves with good postnatal renal function.

Megacystis Microcolon Intestinal Hypoperistalsis Syndrome in Which a Different De Novo Actg2 Gene Mutation was Detected: A Case Report

INTRODUCTION

Megacystis microcolon intestinal hypoperistalsis syndrome (MMIHS) is characterized by bladder distension without urinary tract obstruction, decreased or absent intestinal peristalsis and microcolon. Although the definitive cause remains unknown, changes in the ACTG2 gene are thought to be responsible for the intestinal and bladder hypoperistalsis.

CASE REPORT

This female newborn with MMIHS had a c.532C>A /p.Arg178Ser heterozygous de novo mutation detected in the ACTG2 gene. Normal immature ganglion cells, normal calretinin punctate positivity, maintence of smooth muscle actin immunoreactivity, and decreased numbers of interstitial cells of Cajal(ICCs) were detected.

CONCLUSION

This previously unreported c.532C>A /p.Arg178Ser heterozygous de novo mutation in the ACTG2 gene may lead to a severe form of MMIHS.

Homozygous deletion in MYL9 expands the molecular basis of megacystis-microcolon-intestinal hypoperistalsis syndrome

Megacystis-microcolon-intestinal hypoperistalsis syndrome (MMIHS) is a severe disease characterized by functional obstruction in the urinary and gastrointestinal tract. The molecular basis of this condition started to be defined recently, and the genes related to the syndrome (ACTG2-heterozygous variant in sporadic cases; and MYH11 (myosin heavy chain 11), LMOD1 (leiomodin 1) and MYLK (myosin light chain (MLC) kinase)-autosomal recessive inheritance), encode proteins involved in the smooth muscle contraction, supporting a myopathic basis for the disease. In the present article, we described a family with two affected siblings with MMIHS born to consanguineous parents and the molecular investigation performed to define the genetic etiology. Previous whole exome sequencing of the affected child and parents did not identify a candidate gene for the disease in this family, but now we present a reanalysis of the data that led to the identification of a homozygous deletion encompassing the last exon of MYL9 (myosin regulatory light chain 9) in the affected individual. MYL9 gene encodes a regulatory myosin MLC and the phosphorylation of this protein is a crucial step in the contraction process of smooth muscle cell. Despite the absence of human or animal phenotype related to MYL9, a cause-effect relationship between MYL9 and the MMIHS seems biologically plausible. The present study reveals a strong candidate gene for autosomal recessive forms of MMIHS, expanding the molecular basis of this disease and reinforces the myopathic basis of this condition.

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.