A novel DPH5-related diphthamide-deficiency syndrome causing embryonic lethality or profound neurodevelopmental disorder

Functional Integrity of Radical SAM Enzyme Dph1•Dph2 Requires Non-Canonical Cofactor Motifs with Tandem Cysteines

“…Intriguingly, clinically relevant human DPH1•DPH2 variants include a Tyr replacement in DPH2Cys-342, which in yeast corresponds to Dph2Cys-362 and was identified to be inactive upon Tyr substitution [21,22], likely through Fe-S cluster loss and enhanced protein instability. Thus, insights into the consequences of Cys-based cofactor motif substitutions as reported can further address the critical roles diphthamide modification on eEF2 plays for accurate mRNA translation and protein synthesis in eukaryotes [55][56][57][58] and, importantly, help understand the molecular causes of pathogenic mutants for the diagnosis of patients with DDS symptoms [18][19][20][21][22]. Our identification of functionally and structurally important Dph1•Dph2 cysteines can directly be linked to diphthamide synthesis on eEF2 and thus is likely to impact on mRNA-translation elongation and cellular physiology with clinical relevance.…”

“…Thus, residual diphthamide levels produced from each mutant background may be sufficient enough to generate the observed pools of ADPR-eEF2. Such a scenario is not unheard of and was reported before with regard to a subset of pathogenic and clinically important variants of DPH1•DPH2 from human DDS patients [10,[19][20][21].…”

“…Diphthamide is formed via a dedicated synthesis network (i.e., Dph1-Dph8) on a conserved histidine of eEF2 in eukaryotes (His-699 in budding yeast Saccharomyces cerevisiae and His-715 in Homo sapiens) and EF2 in some archaea [14][15][16][17]. Importantly, human patients deficient in diphthamide-modified eEF2 display symptoms of a neurodevelopmental disorder known as diphthamide deficiency syndrome (DDS) [18][19][20][21][22] and diphtheria toxin (DT) from Corynebacterium diphtheriae attacks the diphthamide décor on eEF2 by ADP-ribosylation to block mRNA translation in infected host cells [23]. Yeast diphthamide mutants (i.e., dph1∆-dph8∆) are resistant to growth inhibition by DT, which is why the toxin is a valuable molecular tool to tell diphthamide proficiency from deficiency in vivo [17,24].…”

DPH1 and DPH2 variants that confer susceptibility to diphthamide deficiency syndrome in human cells and yeast models

“…Diphthamide deficiency syndrome is a rare autosomal-recessive disease that severely affects child development, mostly accompanied by intellectual disability (central nervous system malformations), short stature, craniofacial and additional morphological features (hand/foot anomalies), and additional clinical symptoms ( Hawer et al, 2020 ; Shankar et al, 2022 ; Urreizti et al, 2020 ). The molecular cause of the syndrome is reduced activity of diphthamide-synthesizing enzymes, which compromises the placement of diphthamide on translation elongation factor 2 (eEF2).…”

Biallelic variants in RBM42 cause a multisystem disorder with neurological, facial, cardiac, and musculoskeletal involvement

“…Common NDDs include intellectual disability, attention deficit/hyperactivity disorder, autism spectrum disorder, and schizophrenia with a prevalence of ~3% worldwide ( Parenti et al, 2020 ). Many NDDs are syndromic disorders which have multisystem involvement in addition to the neurological symptoms ( Shankar et al, 2022 ). NDDs are genetically heterogeneous with more than 1,000 underlying loci identified ( Soden et al,.…”