TTC14 dysfunction contributing to microcephaly and lissencephaly spectrum features through protein mislocalization...

Congenital microcephaly and lissencephaly spectrum disorders are characterized by disrupted neuronal proliferation and migration, often driven by underlying genetic variants. Here, we identified and characterized of a novel gene (Tetratricopeptide Repeat Domain 14, TTC14) and its homozygous missense variant (c.89 A > G; p.His30Arg (p.H30R)) in a female proband presenting with microcephaly, epileptic spasms, global developmental delay, and neuroimaging features of simplified gyral pattern, focal pachygyria, and corpus callosum thinning. Trio-based whole exome sequencing revealed this variant to be rare and autosomal recessively inherited from both asymptomatic parents. Structural modeling demonstrated that H30 lies at the start of an α-helical region and is evolutionarily conserved. The p.His30Arg substitution caused significant steric clashes and disrupted local folding. Interaction network analysis and molecular dynamics simulations confirmed structural destabilization, increased conformational flexibility, and loss of stability in the mutant protein. While mRNA and protein levels remained unaltered, the TTC14-p.His30Arg protein mislocalized from the nucleus to the cytosol and formed aggregates. Functionally, proband fibroblasts exhibited increased cell death and altered cell cycle progression. TTC14 interacts with RNA splicing and mRNA processing proteins, and gene ontology analysis implicated it in RNA binding and spliceosomal complex assembly in key brain regions including the cerebral cortex, hippocampus, and white matter. These findings collectively suggest that TTC14 plays a crucial role in RNA metabolism during neurodevelopment, and that the p.His30Arg variant impairs its function, possibly leading to a neurodevelopmental disorder within the lissencephaly spectrum. This study identifies TTC14 as a likely pathogenic candidate gene in cortical malformation syndromes.