Novel KIF26A variants associated with pediatric intestinal pseudo-obstruction (PIPO) and brain developmental defects

Abstract

Pediatric intestinal pseudo-obstruction (PIPO) is a rare congenital disorder of the enteric nervous system with distal colon aganglionosis potentially leading to intestinal obstruction. Recently, biallelic variants in KIF26A, encoding a crucial motor protein for the migration and differentiation of enteric neural crest cells, have been associated with a neurodevelopmental condition featuring cortical defects and PIPO-like features, though in absence of aganglionosis. So far, only 10 patients have been reported. In this study, we investigated three subjects with congenital hydrocephalus, neurodevelopmental impairment, and intestinal obstruction megacolon syndrome. Brain MRI revealed malformations within cortical dysplasia spectrum, including polymicrogyria and heterotopia. Pathology study of the intestine revealed aganglionosis and elevated acetylcholinesterase activity in parasympathetic nerve fibers. Through trio-exome sequencing (ES), we detected four novel biallelic KIF26A variants, including two missense changes (#1) and two distinct homozygous truncating variants in (#2 and #3). All variants are rare and predicted to be deleterious according to in silico tools. To characterize the impact of the missense variants, we performed 3D protein modeling using Alphafold3 and YASARA. Mutants exhibited increased energy scores compared to wild-type protein, supporting a significant structural destabilization of the protein. Our study expands the genotype and phenotype spectrum of the emerging KIF26A-related disorder.

Keywords: KIF26A; brain malformations; congenital megacolon; exome sequencing; kinesin; neurodevelopmental disorder.

FIGURE 1

Clinical and genetic features of KIF26 patient. (A) Facial dysmorphism includes sparse eyebrows, almond‐shaped eyes, flat nasal bridge, thin lips, left mandibular hypoplasia with retrognathia, left‐sided helix hypoplasia, and bilateral lobe hypoplasia. (B) Brain MRI of the patient 1# performed at 6.5 years of age; (Bi–ii) Sagittal T1‐weighted images demonstrate cerebral aqueduct stenosis (curved arrow) associated with a small anterior commissure (dashed arrow) and hypothalamic adhesion (full arrowhead). There are several nodules of gray matter heterotopia extending from the parieto‐occipital cortex to the ventricle (thick black arrows). Note the caudal displacement of the cerebellar tonsils (empty arrowhead). (Biii) Axial T2‐weighted image shows bilateral incomplete hippocampal rotation. Note that the cortex overlying the nodular heterotopias is abnormal, showing a focal area of polymicrogyria (empty white arrows). (Biv) coronal T2‐weighted image depict enlargement of the lateral ventricles associated with focal fenestration of the septum pellucidum (thin black arrow). There is an additional area of polymicrogyria in the left insula (thick white arrow). (C) Brain MRI in patient #2: Hydrocephalus with obliterated aqueduct, hypoplasia of corpus callosum, agenesis of septum pellucidum. (Ci) x‐say: Intestinal dilatation due to distal obstruction. (Cii) Brain MRI: Dilatation of lateral. (D) Pedigree of the families showing the segregation of KIF26A variants in the proband and healthy parents. (E) Localization of previously reported (black) and novel (red) KIF26 variant in the protein.

FIGURE 2

Histopathological examination. Patient 1# (A) Acetylcholinesterase: Initial biopsy comprising rectal mucosa and submucosa where an increase in acetylcholinesterase activity is recognized in the parasympathetic nerve fibers, ganglion cells are not recognizable. (B) Hematoxylin Eosin: Intestinal resection demonstrating a segment with aganglionosis at the level of the myenteric plexus. (C) Hematoxylin Eosin: Intestinal resection demonstrating a segment with aganglionosis at the level of the submucosal plexus. Patient 2#. (D) Elastica‐van‐Gieson staining: Biopsies of the small and large intestine showing ganglia, indicative of hypoganglionosis. (E) S100‐staining: Second biopsy confirming the diagnosis of hypoganglionosis, characterized by increased distances between ganglia.