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Early onset or syndromic epilepsy v2.518 DPH5 Konstantinos Varvagiannis gene: DPH5 was added
gene: DPH5 was added to Genetic epilepsy syndromes. 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
Added comment: 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: Literature
Early onset or syndromic epilepsy v2.122 HERC2 Konstantinos Varvagiannis gene: HERC2 was added
gene: HERC2 was added to Genetic epilepsy syndromes. Sources: Literature
Mode of inheritance for gene: HERC2 was set to BIALLELIC, autosomal or pseudoautosomal
Publications for gene: HERC2 were set to 23065719; 23243086; 30902390; 32571899; 27848944; 26077850; 27759030
Phenotypes for gene: HERC2 were set to Mental retardation, autosomal recessive 38 (MIM 615516)
Penetrance for gene: HERC2 were set to Complete
Review for gene: HERC2 was set to GREEN
Added comment: Biallelic pathogenic HERC2 variants cause Mental retardation, autosomal recessive 38 (MIM 615516).

The current review is based mostly on the information provided by Elpidorou et al (2020 - PMID: 32571899) summarizing the findings in several affected individuals as published in the literature. ID was a universal feature among them (27/27) and seizures were reported in some (9/27):
- 22 subjects from Amish/Mennonite families were homozygous for p.Pro594Leu [NM_004667.5(HERC2):c.1781C>T] (Puffenberger et al 2012 - PMID: 23065719, Harlalka et al 2013 - PMID: 23243086, Abraham et al - PMID: 30902390)
- 2 additional patients were homozygous for another missense SNV [NM_004667.5(HERC2):c.4625G>A - p.Arg1542His] (Abraham et al 2019 - PMID: 30902390)
- 3 sibs born to consanguineous parents, homozygous for NM_004667.5:c.13767_13770delTGAA - p.(Asn4589LysTer4598)] as described by Elpidorou et al.
- 1 male homozygous 286 kb deletion spanning several 5' exons of HERC2 as well as the first exons of OCA2 was described by Morice-Picard et al (2016 - PMID: 27759030). Despite a neurological presentation (axial hypotonia, peripheral hypertonia, extrapyramidal symptoms and uncoordinated movements) further information was not available.

Apart from the cases summarized by Elpidorou et al, there have been few additional ones e.g. :
- Trujillano et al (2017 - PMID: 27848944) reported briefly on a patient, homozygous for NM_004667.5:c.4676-1G>A displaying seizures, hypotonia, global DD, "Encephalopathy" and abnormality of the liver.
- Yavarna et al (2015 - PMID: 26077850) provided few details with on an individual with primarily 'neurocognitive' phenotype but rather atypical presentation (MRI abnormalities, TGA, VSD, renal anomaly, growth retardation, hearing loss) due to p.Q3164X variant (recessive inheritance was specified).

Several lines of evidence support an important role for the protein encoded (an E3 ubiquitin protein ligase, interacting also with UBE3A, involved in several cellular processes incl. cell cycle regulation, spindle formation during mitosis, mitochondrial functions, DNA damage responses by targeting proteins such as XPA) as well as the effect of the reported variants (mRNA studies, Western blot, detection of a fusion transcript in the case of the deletion, etc).

Individuals from the Amish families displayed Angelman-like features (in line with HERC2-UBE3A interaction) with - among others - gait instability. Mouse models recapitulate some of these features (e.g. the movement disorder) as extensively discussed by Abraham et al.

Overall this gene can be included in the ID and epilepsy panels with green rating.
Sources: Literature
Early onset or syndromic epilepsy v1.236 LYST Rebecca Foulger changed review comment from: Re-reviewed this gene when curating panel for GMS Clinical Indication R59 Early onset or syndromic epilepsy. Although the mouse model displays seizures (PMID:16518687), there is limited evidence of patients with seizures (no mention of seizures in PMID:9215679, and one 1990 report of Chédiak-Higashi syndrome with seizures from PMID:10450360). Therefore awaiting clinical opinion on whether LYST should be demoted on this panel.; to: Re-reviewed this gene when curating panel for GMS Clinical Indication R59 Early onset or syndromic epilepsy. In summary: although the mouse model displays seizures (PMID:16518687), there is limited evidence of patients with seizures (no mention of seizures in PMID:9215679, and one 1990 report of Chédiak-Higashi syndrome with seizures from PMID:10450360). Therefore consider demoting LYST.
Early onset or syndromic epilepsy v1.228 LYST Rebecca Foulger Marked gene: LYST as ready
Early onset or syndromic epilepsy v1.228 LYST Rebecca Foulger Gene: lyst has been classified as Amber List (Moderate Evidence).
Early onset or syndromic epilepsy v1.226 LYST Rebecca Foulger Classified gene: LYST as Amber List (moderate evidence)
Early onset or syndromic epilepsy v1.226 LYST Rebecca Foulger Gene: lyst has been classified as Amber List (Moderate Evidence).
Early onset or syndromic epilepsy v1.225 LYST Rebecca Foulger commented on gene: LYST: As discussed with members of the GMS Neurology Specialist Test Group on the Webex call Thursday 8th August 2019 for Clinical Indication R59 Early onset or syndromic epilepsy: Agreed that there is insufficient evidence to rate this gene Green, and an Amber rating is appropriate. Demoted from Green to Amber.
Early onset or syndromic epilepsy v1.225 LYST Rebecca Foulger commented on gene: LYST: Re-reviewed this gene when curating panel for GMS Clinical Indication R59 Early onset or syndromic epilepsy. Although the mouse model displays seizures (PMID:16518687), there is limited evidence of patients with seizures (no mention of seizures in PMID:9215679, and one 1990 report of Chédiak-Higashi syndrome with seizures from PMID:10450360). Therefore awaiting clinical opinion on whether LYST should be demoted on this panel.
Early onset or syndromic epilepsy v1.191 LYST Rebecca Foulger Source Wessex and West Midlands GLH was added to LYST.
Early onset or syndromic epilepsy v1.190 LYST Rebecca Foulger Source NHS GMS was added to LYST.
Early onset or syndromic epilepsy v1.189 LYST Rebecca Foulger reviewed gene: LYST: Rating: AMBER; Mode of pathogenicity: ; Publications: ; Phenotypes: ; Mode of inheritance:
Early onset or syndromic epilepsy v1.188 LYST Tracy Lester reviewed gene: LYST: Rating: AMBER; Mode of pathogenicity: ; Publications: 10648412; Phenotypes: Chediak-Higashi syndrome, 214500; Mode of inheritance: BIALLELIC, autosomal or pseudoautosomal
Early onset or syndromic epilepsy LYST Sarah Leigh classified LYST as Green List (high evidence)
Early onset or syndromic epilepsy LYST Sarah Leigh Added gene to panel