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| Intellectual disability - microarray and sequencing v3.1561 | DPH5 |
Konstantinos Varvagiannis 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 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 |
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| Intellectual disability - microarray and sequencing v3.1104 | DPH1 | Arina Puzriakova Publications for gene: DPH1 were set to 29362492; 29410513; 26220823; 25558065 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Intellectual disability - microarray and sequencing v3.1103 | DPH1 | Arina Puzriakova Phenotypes for gene: DPH1 were changed from Developmental delay with short stature, dysmorphic features, and sparse hair, 616901 to Developmental delay with short stature, dysmorphic facial features, and sparse hair, OMIM:616901 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Intellectual disability - microarray and sequencing v3.694 | DPH2 |
Zornitza Stark gene: DPH2 was added gene: DPH2 was added to Intellectual disability. Sources: Literature Mode of inheritance for gene: DPH2 was set to BIALLELIC, autosomal or pseudoautosomal Publications for gene: DPH2 were set to 32576952; 27421267 Phenotypes for gene: DPH2 were set to Diphthamide-deficiency syndrome Review for gene: DPH2 was set to AMBER Added comment: One 19 month old reported (PMID:32576952) with biallelic (one missense, one nonsense) variants in DPH2, with phenotype similar to DPH1 deficiency (gross motor delay, not walking, fine motor and expressive language delays, macrocephaly) Another family (sibs) was previously reported with biallelic nonsense variants (PMID:27421267) with a comparable phenotype, this family also has biallelic variants in KALRN and the authors thought those variants more likely causative. Patients had ID and microcephaly (in contrast to the 19 month old above). In vitro functional assays support reduced diphthamide synthesis activity for the variants identified in PMID:32576952. Sources: Literature |
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| Intellectual disability - microarray and sequencing v2.978 | DPH1 |
Catherine Snow Source Expert Review Green was added to DPH1. Added phenotypes Developmental delay with short stature, dysmorphic features, and sparse hair, 616901 for gene: DPH1 Publications for gene DPH1 were changed from 25558065; 26220823; 29362492; 29410513 to 29362492; 29410513; 26220823; 25558065 Rating Changed from No List (delete) to Green List (high evidence) |
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| Intellectual disability - microarray and sequencing v2.556 | DPH1 |
Konstantinos Varvagiannis gene: DPH1 was added gene: DPH1 was added to Intellectual disability. Sources: Literature,Expert Review Mode of inheritance for gene: DPH1 was set to BIALLELIC, autosomal or pseudoautosomal Publications for gene: DPH1 were set to 25558065; 26220823; 29362492; 29410513 Phenotypes for gene: DPH1 were set to Developmental delay with short stature, dysmorphic features, and sparse hair, 616901 Penetrance for gene: DPH1 were set to Complete Review for gene: DPH1 was set to GREEN gene: DPH1 was marked as current diagnostic Added comment: Biallelic mutations in DPH1 cause Developmental delay with short stature, dysmorphic features, and sparse hair, MIM 616901. Overall 11 patients from 6 different families have probably been reported in detail. DD/ID is a universal feature. In PMID 25558065, Alazami et al. identified 1 patient from the same consanguineous Saudi Arabian family (of 8 total similarly affected individuals) homozygous for the Leu234Pro (NM_001383.3:c.701T>C) variant. This individual was part of a large cohort of patients with neurogenetic disorders from consanguineous families. The phenotype is not described in detail. In PMID 26220823 Louks et al. report on 4 patients from 3 families belonging to the same genetic isolate from North America and provide details on 4 of the individuals identified by Alazami et al. The individuals identified in this study were homozygous for Met6Lys which was however predicted to be benign and tolerated (by PolyPhen2 and SIFT respectively) in silico. DD/ID, unusual skull shape, ectodermal anomalies were universal (8/8) with additional features including short stature (7/8), renal (4/6) or cardiac anomalies (3/8). Some facial features appeared to be common, too. Functional studies were not performed. However Dph1 pathogenic variants in mice result in restricted growth, craniofacial and developmental defects similar to the human phenotypes (PMIDs 14744934 and 24895408 are cited). PMIDs 29362492 and 29410513 report on 3 further patients with similar (as well as some additional) features including DD/ID. The individual in the first article was compound heterozygous for a missense (Leu164Pro) and a frameshift variant (c.289delG) while 2 sibs born to consanguineous parents in the second article were homozygous for a frameshift variant (c.1227delG). The phenotype appears to be consistent among all the published patients. DPH1 is included in gene panels for intellectual disability offered by different diagnostic laboratories. As a result, this gene can be considered for inclusion in this panel as green. Sources: Literature, Expert Review |
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