CDC123 variants associated with developmental abnormalities alter CDC123-eIF2 subunit interactions and impair protein synthesis

The translation initiation factor eIF2 is an essential regulator of cellular protein synthesis with direct links to human physiology and development. Composed of eIF2α, β, and γ subunits, eIF2 heterotrimer assembly requires the activity of its dedicated chaperone and the essential protein, CDC123. Accordingly, CDC123 is a key determinant of protein synthesis and cell growth. Previous research has demonstrated that variants in eIF2γ impair neurodevelopment, and CDC123 variants of uncertain significance have recently been reported for pediatric patients with neurologic findings. However, the potential pathogenicity, and cell and molecular impacts of these clinically relevant CDC123 variants remains entirely unexplored. In this work, we describe four unrelated families with pediatric patients that present with neurodevelopmental delays, hypotonia, and motor dysfunction. The probands are heterozygous for three novel CDC123 missense variants. The potential pathogenicity of the variants is comprehensively assessed through appraisal of CDC123 variant allele frequencies, protein conservational analyses, structural modeling, and functional assays in both humanized yeast and human cell-based model systems. Cellular and biochemical studies indicated that the variants are damaging to CDC123 activity, altering CDC123-eIF2 subunit interactions and leading to reduced cell growth. Furthermore, we demonstrate that the CDC123 variants display dominant-negative effects on yeast cell growth and protein synthesis, rather than causing haploinsufficiency. Together, our findings provide the first link between CDC123 missense variants and human disease and highlight that CDC123-mediated eIF2 heterotrimer formation is essential for human development.