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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. Actg2R257C 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. Actg2R257C 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 Actg2R257C heterozygous variant impairs SMCs contraction by interfering with actin polymerization, leading to GI motility disorders. [ABSTRACT FROM AUTHOR]

Background: The breakpoint cluster region (BCR) is a protein that originally forms a fusion protein with c‐Abl tyrosine kinase and induces leukemia. Researchers have shown that BCR is enriched in the central nervous system and may contribute to neurological disorders. We aimed to investigate the physiological function of BCR in neural development in the gastrointestinal (GI) tract and brain. Methods: Whole‐exome sequencing was used to screen for mutations in the BCR. Bcr knockout mice (Bcr−/−, ΔExon 2–22) were generated using the CRISPR/Cas9 system. Transit of carmine red dye and glass bead expulsion assays were used to record total and proximal GI transit and distal colonic transit. Key Results: In an infant with pediatric intestinal pseudo‐obstruction, we found a heterozygous de novo mutation (NM_004327.3:c.3072+1G>A) in BCR. Bcr deficiency mice (Bcr−/−) exhibited growth retardation and impaired gastrointestinal motility. Bcr−/− mice had a prolonged average total GI transit time with increased distal colonic transit and proximal GI transit in isolation. Morphology analysis indicated that Bcr−/− mice had a less number of neurons in the submucosal plexus and myenteric plexus. Bcr−/− mice exhibited apparent structural defects in the brain, particularly in the cortex. Additionally, Bcr− depletion in the mouse cortex altered the expression of Ras homologous (Rho) family small GTPases. Conclusions and Inferences: BCR mutations are associated with intestinal obstruction in children. Loss of Bcr can cause intestinal dysmotility and brain developmental defects may via regulation of Rho GTPases. [ABSTRACT FROM AUTHOR]