Intellectual disability - microarray and sequencing
Gene: DPH5
The rating of this gene has been updated to Green following NHS Genomic Medicine Service approval.Created: 11 Oct 2023, 9:34 a.m. | Last Modified: 11 Oct 2023, 9:34 a.m.
Panel Version: 5.286
Mode of inheritance
BIALLELIC, autosomal or pseudoautosomal
Comment on list classification: There is enough evidence for this gene to be rated GREEN at the next major review.Created: 5 Oct 2022, 2:08 p.m. | Last Modified: 5 Oct 2022, 2:08 p.m.
Panel Version: 3.1737
Not associated with a phenotype in OMIM, but as moderate Gen2Phen gene for DPH5-related neurodevelopmental disorder. PMID: 35482014 reports four DPH5 variants in fives cases from three unrelated families. Biallelic NM_001077394.2:c.521dup (p.Asn174LysfsTer10) was identified in a consanguinous family (PMID: 35482014, family 3), the index case, an affected sibling and cousin all died in infancy. Affected members families 1 & 2 (PMID: 35482014) were seen in childhood, all had profound intellectual disability and seizures were seen in both families. A supportive mouse model was described, as were in vitro functonal studies (PMID: 35482014).Created: 5 Oct 2022, 2:07 p.m. | Last Modified: 5 Oct 2022, 2:07 p.m.
Panel Version: 3.1736
Comment on phenotypes: As described by Gen2Phen (https://www.ebi.ac.uk/gene2phenotype/gfd?dbID=4902).Created: 4 Oct 2022, 3:55 p.m. | Last Modified: 4 Oct 2022, 3:55 p.m.
Panel Version: 3.1736
Shankar et al (2022 - PMID: 35482014) present evidence for a diphthamide-deficiency syndrome due to biallelic DPH5 pathogenic variants.
As the authors summarize, DPH5 encodes a methyltransferase critical to the biosynthesis of diphthamide. Diphthamide is a post translationally modified histidine residue found in eukaryotic elongation factor 2 (eEF2). eEF2 is essential for mRNA translation and protein synthesis. The role of diphthamide is not clear, although it serves as a target for ADP-ribosylation, the latter resulting in inactivation of the eEF2 (inhibition of its translocation activity) and arrest of protein synthesis. Biosynthesis of diphthamide is complex involving multiple components (DPH1-DPH7) and the methylating co-factor S-adenosyl methionine, with 2 diphthamide-deficiency disorders due to biallelic DPH1 or DPH2 pathogenic variants and a NDD phenotype reported to date.
The authors describe a phenotypic spectrum associated with biallelic DPH5 variants ranging from a prenatally lethal presentation to profound neurodevelopmental disorder. Details are provided on 5 individuals from 3 unrelated families. While one subject died at the age of few days due to multisystem complications, the phenotype appeared to be relatively consistent with prenatal findings (decreased fetal movements in 2 from 2 families, polyhydramnios in 2 from 2 families), hypotonia, global DD and ID (4/4 from 2 families - profound in 3), seizures (3/5 from 2 families - abnormal EEG in 4/4), cardiovascular findings (5/5, MVP and regurgitation in 2 from Fam1 || aortic dilatation in 2 sibs from Fam2 || VSD, ASD and hypopl. PA, pericardial effusion in 5th), GI issues (5/5, poor feeding in 4), short stature (4/4). Ocular findings were reported in 3/4 (gray sclerae in 2, ocular melanocytosis in 2). The authors describe some common craniofacial findings incl. broad/prominent forehead (5/5), sparse eyebrows (4/5), downturned corners of mouth or triangular chin (each in 3/5).
WES/WGS revealed biallelic DPH5 variants in all affected individuals, namely: homozygosity for a missense variant in 2 sibs (NM_001077394.2:c.779A>G/p.His260Arg). Homozygosity for c.521dupA/p.Asn174LysTer10 for the individual deceased in the neonatal period (for this family there was significant history of spontaneous miscarriages/stillbirth/neonatal death). Two sibs born to non-consanguineous parents were compound htz for a stopgain and a missense SNV (c.619C>T/p.Arg207*, c.329A>G/p.Asn110Ser).
In silico modeling revealed that the pLoF variants, not predicted to lead to NMD, likely remove the domain for interaction with eEF2 while the missense ones also affected interaction with eEF2.
In recombinant MCF7 breast cancer cell line-derived DPH5-knockouts, transfected with recombinant expr. plasmids encoding wt or the 4 variants, the 2 truncating variants were shown to affect ADP-ribosylation of eEF2's diphthamide (total lack / minimal enzymatic activity for Arg207* and Asn174Lysfs respectively). Asn110Ser and His260Arg had residual activities which was thought to be explained by high expression levels compensating partial inactivation (given the multicopy plasmid-driven expression).
ADP-ribosylation assays in S. cerevisiae demonstrated loss of function for the 2 truncating variants. Although the 2 missense variants retained sufficient activity to produce diphthamide (assayed through toxin induced ADP-ribosylation of eEF2), more sensitive assays indicated that diphthamide synthesis was also partially compromised for both variants.
Generation of a knockin mouse model for His260Arg, appeared to recapitulate the human phenotypes with craniofacial, ophthalmologic, cardiac and visceral abnormalities and hmz mice being subviable. A single homozygous liveborn mouse had low birthweight, FTT, craniofacial dysmorphology, polydactyly, abnormal grooming behavior and early death. Few heterozygous embryos had craniofacial features, decreased body weight, reduced neuromuscular function without other abnormalities, either due to their inbred background or in the context of milder phenotype of heterozygosity in mice.
DPH5 is ubiquitously expressed in all human tissues. The gene has a pLI of 0 and LOEUF score of 0.77 (0.48-1.27) in gnomAD. The authors refer to unpublished data, noting that complete absence of DPH5 is incompatible with life with embryonic lethality of a Dph5(ko/ko) line.
The phenotype bears similarities to DPH1- and DPH2- related NDDs (both AR / green and amber respectively in ID panel) and appears to be more severe compared to the phenotype of de novo EEF2 variants (cited PMID: 33355653).
Please consider inclusion in the ID panel with amber (4 individuals from 2 families with ID) / green rating (rather consistent phenotype in 3 families probably representing a continuous spectrum, variant studies, mouse model, similarities with diphthamide-deficiency syndromes). Also consider amber rating in the epilepsy panel (3 individuals from 2 families reported). The gene may be also relevant in other gene panels e.g. for congenital heart disease, short stature, etc (not added).
Sources: LiteratureCreated: 1 May 2022, 10:19 a.m.
Mode of inheritance
BIALLELIC, autosomal or pseudoautosomal
Phenotypes
Abnormality of prenatal development or birth; Neonatal hypotonia; Global developmental delay; Intellectual disability; Seizures; Abnormality of the cardiovascular system; Abnormality of the globe; Feeding difficulties; Short stature; Abnormality of head or neck
Publications
Phenotypes for gene: DPH5 were changed from DPH5-related neurodevelopmental disorder to Neurodevelopmental disorder with short stature, prominent forehead, and feeding difficulties, OMIM:620070
Tag Q4_22_promote_green was removed from gene: DPH5.
Source NHS GMS was added to DPH5. Source Expert Review Green was added to DPH5. Rating Changed from Amber List (moderate evidence) to Green List (high evidence)
Tag Q4_22_rating was removed from gene: DPH5. Tag Q4_22_promote_green tag was added to gene: DPH5.
Tag Q4_22_rating tag was added to gene: DPH5.
Gene: dph5 has been classified as Amber List (Moderate Evidence).
Phenotypes for gene: DPH5 were changed from Abnormality of prenatal development or birth; Neonatal hypotonia; Global developmental delay; Intellectual disability; Seizures; Abnormality of the cardiovascular system; Abnormality of the globe; Feeding difficulties; Short stature; Abnormality of head or neck to DPH5-related neurodevelopmental disorder
gene: DPH5 was added gene: DPH5 was added to Intellectual disability. Sources: Literature Mode of inheritance for gene: DPH5 was set to BIALLELIC, autosomal or pseudoautosomal Publications for gene: DPH5 were set to 35482014 Phenotypes for gene: DPH5 were set to Abnormality of prenatal development or birth; Neonatal hypotonia; Global developmental delay; Intellectual disability; Seizures; Abnormality of the cardiovascular system; Abnormality of the globe; Feeding difficulties; Short stature; Abnormality of head or neck Penetrance for gene: DPH5 were set to unknown Review for gene: DPH5 was set to AMBER