A de novo variant in calponin2 causes intestinal pseudo-obstruction: Evidence from patient and mouse model

Pediatric intestinal pseudo-obstruction (PIPO) is a severe gastrointestinal motility disorder with considerable genetic heterogeneity. Nevertheless, genetic etiology in a substantial proportion of the patients remains unknown. This study aimed to identify the underlying genetic cause in a child with unexplained PIPO and to establish a novel disease gene associated with this condition.

Whole-exome sequencing was performed in a PIPO pedigree negative for mutations in known causative genes. The effects of the variant identified on protein expression were evaluated by Western blotting. A knock-in mouse model bearing the patient-specific variant was generated using CRISPR/Cas9. Intestinal motility was evaluated by carmine red transit assay. The contractile function of primary mouse intestinal smooth muscle cells (MISMCs) was assessed by collagen gel contraction assays.

We identified an extremely rare, evolutionarily conserved de novo missense variant (c.20A > G, p.N7S) in the patient's CNN2 gene. This gene encodes a protein belonging to the calponin (CaP) family, which plays a critical regulatory role in smooth muscle contraction. Cnn2^N7S/N7S mice exhibited significantly prolonged gastrointestinal transit time, recapitulating the intestinal dysmotility phenotype. Functional analyses revealed that the variant significantly impaired MISMC contractile function in a gene dosage-dependent manner.

Our study revealed that a variant in CNN2 causes intestinal dysmotility in a PIPO patient and mouse model, establishing CNN2 as a novel disease gene. These findings provide a molecular diagnosis for the affected patient, expands the genetic spectrum of PIPO, and reveals an essential role of calponin 2 in the regulation of intestinal motility.