De novo ACTG2 mutations cause congenital distended bladder, microcolon, and intestinal hypoperistalsis

Prenatal Diagnosis of ACTG2-Related Megacystis-Microcolon-Intestinal Hypoperistalsis Syndrome-Case Report and Systematic Review

Background/Objectives: Megacystis-microcolon-intestinal hypoperistalsis syndrome (MMIHS) is characterized by smooth muscle dysfunction and results in severe bladder dilatation and intestinal dysmotility. Prenatal diagnosis is challenging due to the non-specific nature of ultrasound findings and the limitations of current genetic testing. We present a case of persistent fetal megacystis, with genetic testing confirming MMIHS, and a systematic review of prenatally diagnosed cases. Methods: An electronic search of the PubMed, Medline, Web of Science and CORE databases was conducted to identify reports of genetic prenatal diagnoses of MMIHS. The inclusion criteria were cases of prenatally suspected MMIHS with a genetic diagnosis based on prenatal samples. Reports that described neonatal or paediatric cases or lacked clinical details or genetic testing results were excluded, and the clinical details for the included cases were collected. Results: We identified six publications describing 17 cases of MMIHS confirmed on genetic testing. Including our case, 18 cases are described in this manuscript. Most cases (72.2%) presented in the second or third trimester of pregnancy; the majority (55.6%) were due to ACTG2 mutations. All cases had fetal megacystis detected on ultrasound. Five cases (27.8%) also had a known family history of MMIHS. The majority of the cases (77.8%) resulted in the termination of pregnancy. Conclusions: MMIHS is a rare condition with significant morbidity and mortality and prenatal diagnosis remains challenging. ACTG2 mutations are described in over half of these cases. These data contribute to the limited literature on its prenatal presentation and the evolving role of prenatal molecular genetic testing.

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.

When parenteral nutrition is the answer: The case of pediatric intestinal rehabilitation

In pediatric patients with intestinal failure, parenteral nutrition is lifesaving but also has several associated risks. The goals of intestinal rehabilitation include promoting growth, minimizing complications associated with intestinal failure, and reaching enteral autonomy, if possible. Pediatric intestinal rehabilitation programs are interdisciplinary teams that strive to provide optimal care for children dependent on parenteral nutrition. The provision of parenteral nutrition requires close monitoring of patients' growth, nutrition concerns, clinical status, and laboratory parameters. Recent advances in the field of intestinal rehabilitation include new lipid emulsions, considerations regarding enteral feeding, advances in micronutrient provision, and central venous catheter preservation techniques. Challenges in the field remain, including improving overall quality of life with home parenteral nutrition administration and preventing recently recognized complications such as chronic intestinal inflammation.

Heat Stress Induces Alterations in Gene Expression of Actin Cytoskeleton and Filament of Cellular Components Causing Gut Disruption in Growing-Finishing Pigs

We aimed to investigate the impact of heat stress (HS) on the expression of tight junction (TJ) proteins and the interaction between genes affecting intestinal barrier function using transcriptomics in the porcine jejunum. Twenty-four barrows (crossbred Yorkshire × Landrace × Duroc; average initial body weight, 56.71 ± 1.74 kg) were placed in different temperatures (normal temperature [NT]; HS) and reared for 56 days. At the end of the experiment, jejunal samples were collected from three pigs per treatment for transcriptome and reverse-transcription quantitative polymerase chain reaction (RT-qPCR) analyses. We identified 43 differentially expressed genes, involving five Kyoto Encyclopedia of Genes and Genomes pathways, eight molecular functions, seven cellular components (CCs), and nine biological processes, using gene ontology enrichment analysis. Genes associated with the actin cytoskeleton, filament-binding pathways, and TJ proteins were selected and analyzed by RT-qPCR. Significant differences in relative mRNA expression showed that downregulated genes in the HS group included ZO1, CLDN1, OCLN, PCK1, and PCK2, whereas ACTG2, DES, MYL9, MYLK, TPM1, TPM2, CNN1, PDLIM3, and PCP4 were upregulated by HS (p < 0.05). These findings indicate that HS in growing-finishing pigs induces depression in gut integrity, which may be related to genes involved in the actin cytoskeleton and filaments of CC.

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: A Case Report of an Uncommon Condition

The megacystis-microcolon-intestinal hypoperistalsis syndrome (MMIHS), also known as Berdon syndrome, is a rare congenital condition that falls within the spectrum of visceral myopathies. It is characterized by the presence of megacystis, microcolon, and hypoperistalsis, which are secondary to gastrointestinal and urinary system dysmotility. It is frequently associated with other alterations in the gastrointestinal and genitourinary tracts. Although it is possible to make the diagnosis in the prenatal period, most cases are diagnosed after birth through genetic and imaging studies. Advances in treatment have led to a progressive increase in survival rates. We present the case of a newborn with congenital alterations described prenatally and with imaging findings characteristic of the syndrome.

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.

Multi-disciplinary Insights from the First European Forum on Visceral Myopathy 2022 Meeting

Visceral myopathy is a rare, life-threatening disease linked to identified genetic mutations in 60% of cases. Mostly due to the dearth of knowledge regarding its pathogenesis, effective treatments are lacking. The disease is most commonly diagnosed in children with recurrent or persistent disabling episodes of functional intestinal obstruction, which can be life threatening, often requiring long-term parenteral or specialized enteral nutritional support. Although these interventions are undisputedly life-saving as they allow affected individuals to avoid malnutrition and related complications, they also seriously compromise their quality of life and can carry the risk of sepsis and thrombosis. Animal models for visceral myopathy, which could be crucial for advancing the scientific knowledge of this condition, are scarce. Clearly, a collaborative network is needed to develop research plans to clarify genotype-phenotype correlations and unravel molecular mechanisms to provide targeted therapeutic strategies. This paper represents a summary report of the first 'European Forum on Visceral Myopathy'. This forum was attended by an international interdisciplinary working group that met to better understand visceral myopathy and foster interaction among scientists actively involved in the field and clinicians who specialize in care of people with visceral myopathy.

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.

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

Objectives/aims

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

Methods

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

Results

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

Conclusions

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

Supplementary Information

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

Patient's dermal fibroblasts as disease markers for visceral myopathy

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

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

BACKGROUND

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

METHODS

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

KEY RESULTS

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

CONCLUSIONS & INFERENCES

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

Rumen Epithelial Development- and Metabolism-Related Genes Regulate Their Micromorphology and VFAs Mediating Plateau Adaptability at Different Ages in Tibetan Sheep

The rumen is an important hallmark organ of ruminants and plays an important role in the metabolism and immune barrier of Tibetan sheep on the Plateau. However, there are few studies on rumen development and metabolism regulation in Tibetan sheep at different ages. Here, we comprehensively analyzed the immune function, fermentation function, rumen epithelial micromorphology and transcriptome profile of Tibetan sheep at different ages. The results showed that the concentration of IgG decreased and the concentration of IgM increased with age (p < 0.05), and the highest concentration of IgA was observed at 1.5 and 3.5 years of age. In terms of rumen fermentation characteristics, VFAs of 4-month-old lambs were the highest, followed by VFAs and NH3-N of Tibetan sheep at 3.5 years of age. Hematoxylin-eosin staining and transmission electron microscopy section examination of rumen epithelial tissue showed that the rumen papilla width increased with age (p < 0.001), the thickness of the stratum corneum decreased, the cells in the stratum corneum showed accelerated migration and the thickness of the rumen muscle layer increased (p < 0.001). Desmosomal junctions between the layers of rumen epithelium increased at 1.5 and 3.5 years old, forming a compact barrier structure, and the basal layer had more mitochondria involved in the regulation of energy metabolism. RNA-seq analysis revealed that a total of 1006 differentially expressed genes (DEGs) were identified at four ages. The DEGs of Tibetan sheep aged 4 months and 6 years were mainly enriched in the oxidation−reduction process and ISG15-protein conjugation pathway. The 1.5 and 3.5-year-olds were mainly enriched in skeletal muscle thin filament assembly, mesenchyme migration and the tight junction pathway. WGCNA showed that DEGs related to rumen microbiota metabolite VFAs and epithelial morphology were enriched in “Metabolism of xenobiotics by cytochrome P450, PPAR signaling pathway, Butanoate metabolism pathways” and participated in the regulation of rumen epithelial immune and fermentation metabolism functions of Tibetan sheep at different ages. This study systematically revealed the regulatory mechanism of rumen epithelial development and metabolism in the plateau adaptation of Tibetan sheep, providing a new approach for the study of plateau adaptation.

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.

Disease mechanisms of monogenic congenital anomalies of the kidney and urinary tract American Journal of Medical Genetics Part C

Congenital Anomalies of the Kidney and Urinary Tract (CAKUT) is a developmental disorder of the kidney and/or genito-urinary tract that results in end stage kidney disease (ESKD) in up to 50% of children. Despite the congenital nature of the disease, CAKUT accounts for almost 10% of adult onset ESKD. Multiple lines of evidence suggest that CAKUT is a Mendelian disorder, including the observation of familial clustering of CAKUT. Pathogenesis in CAKUT is embryonic in origin, with disturbances of kidney and urinary tract development resulting in a heterogeneous range of disease phenotypes. Despite polygenic and environmental factors being implicated, a significant proportion of CAKUT is monogenic in origin, with studies demonstrating single gene defects in 10%-20% of patients with CAKUT. Here, we review monogenic disease causation with emphasis on the etiological role of gene developmental pathways in CAKUT.

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.

MYL9 deficiency is neonatal lethal in mice due to abnormalities in the lung and the muscularis propria of the bladder and intestine

Class II myosin complexes are responsible for muscle contraction as well as other non-sarcomeric contractile functions in cells. Myosin heavy chain molecules form the core of these structures, while light chain molecules regulate their stability and function. MYL9 is a light chain isoform that is thought to regulate non-sarcomeric myosin. However, whether this in only in specific cell types or in all cells remains unclear. To address this, we generated MYL9 deficient mice. These mice die soon after birth with abnormalities in multiple organs. All mice exhibited a distended bladder, shortening of the small intestine and alveolar overdistension in the lung. The Myl9 allele in these mice included a LacZ reporter knockin that allowed for mapping of Myl9 gene expression. Using this reporter, we show that MYL9 expression is restricted to the muscularis propria of the small intestine and bladder, as well as in the smooth muscle layer of the bronchi in the lung and major bladder vessels in all organs. This suggests that MYL9 is important for the function of smooth muscle cells in these organs. Smooth muscle dysfunction is therefore likely to be the cause of the abnormalities observed in the intestine, bladder and lung of MYL9 deficient mice and the resulting neonatal lethality.

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

BACKGROUND AND AIMS

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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

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

ACTG2 Variants in Pediatric Chronic Intestinal Pseudo-obstruction With Megacystis

Background/Aims

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

Methods

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

Results

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

Conclusions

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

Expanding the genotypic spectrum of ACTG2-related visceral myopathy

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

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

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

The enteric nervous system in gastrointestinal disease etiology

A highly conserved but convoluted network of neurons and glial cells, the enteric nervous system (ENS), is positioned along the wall of the gut to coordinate digestive processes and gastrointestinal homeostasis. Because ENS components are in charge of the autonomous regulation of gut function, it is inevitable that their dysfunction is central to the pathophysiology and symptom generation of gastrointestinal disease. While for neurodevelopmental disorders such as Hirschsprung, ENS pathogenesis appears to be clear-cut, the role for impaired ENS activity in the etiology of other gastrointestinal disorders is less established and is often deemed secondary to other insults like intestinal inflammation. However, mounting experimental evidence in recent years indicates that gastrointestinal homeostasis hinges on multifaceted connections between the ENS, and other cellular networks such as the intestinal epithelium, the immune system, and the intestinal microbiome. Derangement of these interactions could underlie gastrointestinal disease onset and elicit variable degrees of abnormal gut function, pinpointing, perhaps unexpectedly, the ENS as a diligent participant in idiopathic but also in inflammatory and cancerous diseases of the gut. In this review, we discuss the latest evidence on the role of the ENS in the pathogenesis of enteric neuropathies, disorders of gut-brain interaction, inflammatory bowel diseases, and colorectal cancer.

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.

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.

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.

Latest developments in chronic intestinal pseudo-obstruction

Chronic intestinal pseudo-obstruction (CIPO) is a type of intestinal dysfunction presenting as symptoms of intestinal obstruction but without actual mechanical obstruction. An extremely low incidence, non-specific clinical symptoms, strong heterogeneity, and no definitive cause in some patients make CIPO very difficult to diagnose correctly. Imaging and gastrointestinal manometry are commonly used. Most patients have progressive worsening of their symptoms and require intervention, and nutritional assessment and treatment are very important to determine the prognosis. With improvements in surgical techniques, small bowel transplantation is a feasible treatment option for patients with advanced CIPO; however, the long-term prognosis for CIPO patients remains unsatisfactory. Generally, the disease is rare and difficult to diagnose, which leads to clinicians' lack of understanding of the disease and results in a high rate of misdiagnosis. This review describes the characteristics of CIPO and the latest developments in diagnosis and treatment, in detail. The goal of our review is to improve clinicians' understanding of CIPO so that the disease is identified quickly and accurately, and treated as early as possible to improve patients' quality of life.

Compound heterozygous loss of function variants in MYL9 in a child with megacystis-microcolon-intestinal hypoperistalsis syndrome

Megacystis–microcolon–intestinal hypoperistalsis syndrome (MMIHS), or “visceral myopathy,” is a severe early onset disorder characterized by impaired muscle contractility in the bladder and intestines. Five genes are linked to MMIHS: primarily ACTG2, but also LMOD1, MYH11, MYLK, and MYL9. Here we describe a three‐year‐old girl with bilateral hydronephrosis diagnosed at 20 weeks gestation and congenital mydriasis (both of which have been previously observed among individuals with MMIHS). A clinical diagnosis of MMIHS was made based upon the presence of megacystis, lack of urinary bladder peristalsis, and intestinal pseudo‐obstruction. After initial testing of ACTG2 was negative, further sequencing and deletion/duplication testing was performed on the LMOD1, MYH11,MYLK, and MYL9 genes. We identified two heterozygous loss of function variants in MYL9: an exon 4 deletion and a nine base pair deletion that removes the canonical splicing donor site at exon 2 (NM_006097.5:c.184+2_184+10del). Parental testing confirmed these variants to be in trans in our proband. To our knowledge, only one other individual with MMIHS has biallelic mutations in MYL9 (a homozygous deletion encompassing exon 4). We suggest MYL9 be targeted on genetic testing panels for MMIHS, smooth muscle myopathies, and cardiovascular phenotypes.

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.

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.

Kindlin-2 deficiency induces fatal intestinal obstruction in mice

Rationale: Smooth muscle-motility disorders are mainly characterized by impaired contractility and functional intestinal obstruction. Some of these cases are caused by genetic mutations of smooth muscle genes ACTA2, ACTG2, MYH11, MYLK and LMOD1. Still the etiology is complex and multifactorial and the underlying pathology is poorly understood. Integrin interaction protein Kindlin-2 is widely expressed in striated and smooth muscle cells (SMC). However, the function of Kindlin-2 in the smooth muscle remains elusive.

Methods: We generated two mouse models using different cre promoter transgenic mice, Kindlin-2^fl/fl SM22α-cre+ (cKO mice) and Kindlin-2^fl/fl; MYH-cre+ (iKO mice). Embryos and adult tissues were prepared for hematoxylin and eosin (H&E) staining, immunohistochemistry (IHC) and terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) apoptosis assay. We investigated ultrastructure changes of mouse smooth muscle using transmission electron microscopy (TEM) and measured smooth muscle contractile force in mounting aortic and intestinal rings using the multiwire myograph system (DMT 620M). In addition, cell traction force microscopy (CTFM) was applied to observe the functional change of primary SMC after Kindlin-2 depletion by RNAi.

Results: Depletion of Kindlin-2 encoding gene Fermt2 in embryonic smooth muscles leads to apoptosis, downregulates the key components of SMC, impairs smooth muscle development, and finally causes embryonic death at E14.5. Tamoxifen-induced Kindlin-2-specific knockout in adult mouse smooth muscle showed decreased blood pressure, intestinal hypoperistalsis, and eventually died of intestinal obstruction. Kindlin-2 depletion also leads to downregulated Myh11, α-SMA, and CNN, shortened myofilament, broken myofibrils, and impaired contractility of the smooth muscles in iKO mice. Mechanistically, loss of Kindlin-2 decreases Ca2⁺ influx in primary vascular smooth muscle cells (PVSMC) by downregulating the expression of calcium-binding protein S100A14 and STIM1.

Conclusion: We demonstrated that Kindlin-2 is essential for maintaining the normal structure and function of smooth muscles. Loss of Kindlin-2 impairs smooth muscle formation during embryonic development by inducing apoptosis and jeopardizes the contraction of adult smooth muscle by blocking Ca²⁺ influx that leads to intestinal obstruction. Mice with Kindlin-2 depletion in adult smooth muscle could be a potent animal model of intestinal obstruction for disease research, drug treatment and prognosis.

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.

Protein-elongating mutations in MYH11 are implicated in a dominantly inherited smooth muscle dysmotility syndrome with severe esophageal, gastric, and intestinal disease

Gastrointestinal motility disorders include a spectrum of mild to severe clinical phenotypes that are caused by smooth muscle dysfunction. We investigated the genetic etiology of severe esophageal, gastric, and colonic dysmotility in two unrelated families with autosomal dominant disease presentation. Using exome sequencing, we identified a 2 base pair insertion at the end of the myosin heavy chain 11 (MYH11) gene in all affected members of Family 1 [NM_001040113:c.5819_5820insCA(p.Gln1941Asnfs*91)] and a 1 base pair deletion at the same genetic locus in Proband 2 [NM_001040113:c.5819del(p.Pro1940Hisfs*91)]. Both variants are predicted to result in a similarly elongated protein product. Heterozygous dominant negative MYH11 pathogenic variants have been associated with thoracic aortic aneurysm and dissection while biallelic null alleles have been associated with megacystis microcolon intestinal hypoperistalsis syndrome. This report highlights heterozygous protein-elongating MYH11 variants affecting the SM2 isoforms of MYH11 as a cause for severe gastrointestinal dysmotility, and we hypothesize that the mechanistic pathogenesis of this disease, dominant hypercontractile loss-of-function, is distinct from those implicated in other diseases involving MYH11 dysfunction.

A homozygous missense variant in CHRM3 associated with familial urinary bladder disease

CHRM3 codes for the M3 muscarinic acetylcholine receptor that is located on the surface of smooth muscle cells of the detrusor, the muscle that effects urinary voiding. Previously, we reported brothers in a family affected by a congenital prune belly‐like syndrome with mydriasis due to homozygous CHRM3 frameshift variants. In this study, we describe two sisters with bladders that failed to empty completely and pupils that failed to constrict fully in response to light, who are homozygous for the missense CHRM3 variant c.352G > A; p.(Gly118Arg). Samples were not available for genotyping from their brother, who had a history of multiple urinary tract infections and underwent surgical bladder draining in the first year of life. He died at the age of 6 years. This is the first independent report of biallelic variants in CHRM3 in a family with a rare serious bladder disorder associated with mydriasis and provides important evidence of this association.

Compound heterozygous variants in MYH11 underlie autosomal recessive megacystis-microcolon-intestinal hypoperistalsis syndrome in a Chinese family

Megacystis-microcolon-intestinal-hypoperistalsis syndrome (MMIHS) is a rare and severe disorder characterized by functional obstruction in the urinary and gastrointestinal tract. The molecular basis of this condition has been defined recently. Heterozygous variants in ACTG2, homozygous mutations in LMOD1, MYLK, and MYH9 were related to the pathogenesis of the syndrome, which encodes proteins involved in the process of smooth muscle contraction, supporting a myopathic basis for the disease. Recent studies have identified homozygous or compound heterozygous variants in MYH11 as a candidate gene of MMIHS. In this report, we described a nonconsanguineous Chinese family with three male fetuses affected with megacystis. Trio-targeted exome sequencing identified compound heterozygous variants, c.2051 G > A (p.R684H) and c.3540_3541delinsTT (p.(E1180D, Q1181Ter)), in MYH11 (NM_001040114). The variants were inherited from the parents, respectively. Western blotting showed a marked decrease in MYH11 protein in the proband's umbilical cord tissue compared with the control sample. The study's results confirmed that MYH11 is a candidate gene for MMIHS with autosomal recessive (AR) inheritance and expanded the mutation spectrum for this clinical condition. Combining clinical phenotype with molecular diagnosis may enable the identification of candidate genes for potential monogenic diseases and facilitate accurate genetic counseling, informed decision-making, and prenatal diagnosis.

Central and Peripheral Changes in FOS Expression in Schizophrenia Based on Genome-Wide Gene Expression

Schizophrenia is a chronic, debilitating neuropsychiatric disorder. Multiple transcriptomic gene expression profiling analysis has been used to identify schizophrenia-associated genes, unravel disease-associated biomarkers, and predict clinical outcomes. We aimed to identify gene expression regulation, underlying pathways, and their roles in schizophrenia pathogenesis. We searched the Gene Expression Omnibus (GEO) database for microarray studies of fibroblasts, lymphoblasts, and post-mortem brains of schizophrenia patients. Our analysis demonstrated high FOS expression in non-neural peripheral samples and low FOS expression in brain tissues of schizophrenia patients compared with healthy controls. FOS exhibited predictive value for schizophrenia patients in these datasets. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis revealed that “amphetamine addiction” was among the top 10 significantly enriched KEGG pathways. FOS and FOSB, which are implicated in the amphetamine addiction pathway, were up-regulated in schizophrenia fibroblast samples. Protein–protein interaction (PPI) network analysis revealed that proteins closely interacting with FOS-encoded protein were also involved in the amphetamine addiction pathway. Pearson correlation test indicated that FOS showed positive correlation with genes in the amphetamine pathway. The results revealed that FOS was acceptable as a biomarker for schizophrenia and may be involved in schizophrenia pathogenesis.

Familial chronic megacolon presenting in childhood or adulthood: Seeking the presumed gene association

OBJECTIVE

We identified a pedigree over five generations with 49 members, some of whom had chronic megacolon presenting in adolescence or adulthood. We aimed to assess the genetic cause of chronic megacolon through clinical and DNA studies.

DESIGN

After ethical approval and informed consent, family members provided answers to standard bowel disease questionnaires, radiological or surgical records, and DNA (buccal mucosal scraping). Exome DNA sequencing of colon tissue or blood DNA from seven family members with colon or duodenal dilatation, or no megacolon (n = 1) was carried out. Sanger sequencing was performed in 22 additional family members to further evaluate candidate variants. The study focused on genes of potential relevance to enteric nerve (ENS) maturation and Hirschsprung's disease or megacolon, based on the literature (GFRA1, NKX2-1, KIF26A, TPM3, ACTG2, SCN10A, and C17orf107 [CHRNE]) and other genetic variants that co-segregated with megacolon in the six affected family members.

RESULTS

Information was available in all except five members alive at time of study; among 30 members who provided DNA, six had definite megacolon, one megaduodenum, seven significant constipation without bowel dilatation, and 16 normal bowel function by questionnaire. Among genes studied, SEMA3F (g.3:50225360A>G; c1873A>G) was found in 6/6 family members with megacolon. The SEMA3F gene variant was assessed as potentially pathogenic, based on M-CAP in silico prediction. SEMA3F function is associated with genes (KIT and PDGFRB) that impact intestinal pacemaker function.

CONCLUSION

Familial chronic megacolon appears to be associated with SEMA3F, which is associated with genes impacting enteric nerve or pacemaker function.

Lrig2 and Hpse2, mutated in urofacial syndrome, pattern nerves in the urinary bladder

Mutations in leucine-rich-repeats and immunoglobulin-like-domains 2 (LRIG2) or in heparanase 2 (HPSE2) cause urofacial syndrome, a devastating autosomal recessive disease of functional bladder outlet obstruction. It has been speculated that urofacial syndrome has a neural basis, but it is unknown whether defects in urinary bladder innervation are present. We hypothesized that urofacial syndrome features a peripheral neuropathy of the bladder. Mice with homozygous targeted Lrig2 mutations had urinary defects resembling those found in urofacial syndrome. There was no anatomical blockage of the outflow tract, consistent with a functional bladder outlet obstruction. Transcriptome analysis revealed differential expression of 12 known transcripts in addition to Lrig2, including 8 with established roles in neurobiology. Mice with homozygous mutations in either Lrig2 or Hpse2 had increased nerve density within the body of the urinary bladder and decreased nerve density around the urinary outflow tract. In a sample of 155 children with chronic kidney disease and urinary symptoms, we discovered novel homozygous missense LRIG2 variants that were predicted to be pathogenic in 2 individuals with non-syndromic bladder outlet obstruction. These observations provide evidence that a peripheral neuropathy is central to the pathobiology of functional bladder outlet obstruction in urofacial syndrome, and emphasize the importance of LRIG2 and heparanase 2 for nerve patterning in the urinary tract.

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.

Congenital Disorders of the Human Urinary Tract: Recent Insights From Genetic and Molecular Studies

The urinary tract comprises the renal pelvis, the ureter, the urinary bladder, and the urethra. The tract acts as a functional unit, first propelling urine from the kidney to the bladder, then storing it at low pressure inside the bladder which intermittently and completely voids urine through the urethra. Congenital diseases of these structures can lead to a range of diseases sometimes associated with fetal losses or kidney failure in childhood and later in life. In some of these disorders, parts of the urinary tract are severely malformed. In other cases, the organs appear grossly intact yet they have functional deficits that compromise health. Human studies are beginning to indicate monogenic causes for some of these diseases. Here, the implicated genes can encode smooth muscle, neural or urothelial molecules, or transcription factors that regulate their expression. Furthermore, certain animal models are informative about how such molecules control the development and functional differentiation of the urinary tract. In future, novel therapies, including those based on gene transfer and stem cell technologies, may be used to treat these diseases to complement conventional pharmacological and surgical clinical therapies.

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.

Causes and prognosis of chronic intestinal pseudo-obstruction in 48 subjects: A 10-year retrospective case series

The aim of the study was to evaluate the prognosis and survival of pediatric subjects with chronic intestinal pseudo-obstruction (CIPO) and investigate the independent risk factors affecting their prognosis.This was a retrospective case series of all pediatric subjects suffering from CIPO and treated at the Pediatric Surgical ward of Xinhua Hospital between January 2006 and January 2016.The overall mortality was 19/48 (39.6%). Because of delayed CIPO diagnosis, many subjects underwent a variety of surgical procedures. The rate of additional surgical procedures was high (35/48, 72.9%), but the number of surgical procedures, parenteral nutrition, and megacystis did not affect mortality. Mycotic infection was significantly associated with mortality, while onset at <1 year and hypoganglionosis showed a tendency to be associated with mortality.Mycotic infection was associated with mortality of children with CIPO. Despite improving treatment approaches, the overall prognosis of CIPO remains poor. The choice of the surgical intervention could be based on standard criteria.