De Novo variants in EEF2 cause a neurodevelopmental disorder with benign external hydrocephalus

Abstract

Eukaryotic translation elongation factor 2 (eEF2) is a key regulatory factor in gene expression that catalyzes the elongation stage of translation. A functionally impaired eEF2, due to a heterozygous missense variant in the EEF2 gene, was previously reported in one family with spinocerebellar ataxia-26 (SCA26), an autosomal dominant adult-onset pure cerebellar ataxia. Clinical exome sequencing identified de novo EEF2 variants in three unrelated children presenting with a neurodevelopmental disorder. Individuals shared a mild phenotype comprising motor delay and relative macrocephaly associated with ventriculomegaly. Populational data and bioinformatic analysis underscored the pathogenicity of all de novo missense variants. eEF2 yeast model strains demonstrated that patient-derived variants affect cellular growth, sensitivity to translation inhibitors and translational fidelity. Consequently, we propose that pathogenic variants in the EEF2 gene, so far exclusively associated with late-onset SCA26, can cause a broader spectrum of neurologic disorders, including childhood-onset neurodevelopmental disorders and benign external hydrocephalus.

eEF2 in the prefrontal cortex promotes excitatory synaptic transmission and social novelty behavior

“…Eukaryotic elongation factor 2 (eEF2), a unique factor that regulates the phase of mRNA translation elongation, catalyzes the GTP‐dependent translocation of peptidyl tRNA from the A site to the P site of ribosome, thus making ribosome to shift along the reading frame of mRNA with polypeptide elongation. Missense variations of EEF2 or defective post‐translation modification of the protein have been found causatively linked with neurodevelopmental disorders and spinocerebellar ataxia (Hekman et al , 2012; Hawer et al , 2020; Nabais Sá et al , 2021). The best studied molecular regulation of eEF2 activity is through inhibitory phosphorylation at Thr56 (pT56) by eEF2 kinase (eEF2K), also known as Ca 2+ /calmodulin‐dependent protein kinases III (CaMKIII).…”

Deep mutational analysis of elongation factor eEF2 residues implicated in human disease to identify functionally important contacts with the ribosome

“…Anisomycin binds the peptidyltransferase center in the A site of the LSU ( Fig. 3 A ), where it destabilizes aa-tRNA binding and inhibits peptidyl transfer ( 27 , 28 ). Cycloheximide binds to the LSU E site ( Fig.…”

“…The effects of the mutants on programmed translational recoding were measured using dual luciferase assays of HIV-1–mediated −1 PRF and Ty 1 -driven +1 PRF as previously described ( 27 ). Briefly, production of the downstream firefly luciferase enzymes is reliant on successful ribosomal frameshifting, while upstream Renilla luciferase functions as an internal control for any effects on general translation conferred by the mutants.…”

“…The cost of DNA sequencing has decreased to a level where it is becoming an effective tool for diagnosis of rare genetic disorders. Accordingly, missense mutations of eEF2 are emerging as the underlying causes of an increasing number of neurodevelopmental pathologies ( 17 , 23 , 27 ). Importantly, many of these have all mapped to the three sites where eEF2 physically interacts with functionally important rRNA-based structural features of the ribosome: The SRL (H98), H69, and the H43 of the GTPase-associated center.…”

“…Additional patients harboring novel eEF2 mutations have been identified ( 27 ). In contrast to P596H, these eEF2 mutations including V28M, C372Y, and H769Y were associated with neurodevelopmental delays and cranial abnormalities, indicating that eEF2 mutations have wider-reaching pathologies than SCA26.…”