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| Likely inborn error of metabolism - targeted testing not possible v2.1 | PCYT2 |
Sarah Leigh edited their review of gene: PCYT2: Added comment: Vaz et al. (2019 - PMID: 31637422 - DDD study among the co-authors) report on 5 individuals - from 4 families - with biallelic PCYT2 mutations. The phenotype corresponded to a complex hererditary paraplegia with global DD, regression (4/5), ID (mild in 3/5, severe in 2/5), spastic para-/tetraparesis, epilepsy (5/5 - variable onset 2-16 yrs - focal or tonic-clonic seizures) and progressive cerebral and cerebellar atrophy. Exome sequencing in all revealed biallelic PCYT2 variants, confirmed with Sanger s. in probands and their parents (NM_001184917.2 - corresponding to the canonical transcript used as Ref below): - P1 (Fam1) : 2 missense SNVs in trans configuration, c.730C>T or p.His244Tyr and c.920C>T or p.Pro307Leu - P2 (Fam2 - consanguineous of White British origin), P3 (Fam3 - Consanguineous of Turkish origin), P4,5 (Fam4 - consanguineous, unspecified origin) : homozygosity for c.1129C>T or p.Arg377Ter) affecting the last exon of 8/12 transcripts, including the canonical one. Individuals with the same genotype displayed variable degrees of ID (eg P3 - severe / P2, P4,5 - mild ID). For sibs in Fam4, homozygosity for a missense SACS variant led to consideration of the respective disorder (AR spastic ataxia of Charlevoix-Saguenay) though the variant was predicted to be tolerated in silico and notably the MRI images not suggestive. All variants were absent from / had extremely low AF in public databases, with no homozygotes. Posphatidylethanolamine (PE) is a membrane lipid, particularly enriched in human brain (45% of phospholypid fraction). PE is synthesized either via the CDP-ethanolamine pathway or by decarboxylation of phosphatidylserine in mitochondria. PCYT2 encodes CTP:phosophoethanolamine cytidyltransferase (ET) which is an ubiquitously expressed rate-limiting enzyme for PE biosynthesis in the former pathway. In silico, the 2 missense variants - localizing in the CTP catalytic domain 2 - were predicted to be damaging, as well as to affect protein stability. Fibroblasts of 3 patients (P1, P2, P3) representing all variants were studied: - Enzymatic activity was shown to be significantly reduced (though not absent) compared to controls. Abnormalities were noted upon Western Blot incl. absence in all 3 patients studied of one of the 2 bands normally found in controls (probably representing the longer isoform), reduced intensity in all 3 of another band probably corresponding to a shorter isoform, and presence of an additional band of intermediate molec. mass in patients with the truncating variant. - RT-PCR on mRNA from patient fibroblasts did not reveal (significant) reduction compared to controls. - Lipidomic profile of patient fibroblasts was compatible with the location of the block in the phospholipid biosynthesis pathway and different from controls. The lipidomic profile had similarities with what has been reported for EPT1 deficiency, the enzyme directly downstream of ET. The SELENO1-related phenotype (/EPT1 deficiency) is also highly overlapping. CRISPR-Cas9 was used to generate pcyt2 partial or complete knockout (ko) zebrafish, targeting either the final (ex13) or another exon (ex3) respectively. mRNA expression was shown to be moderately reduced in the first case and severely reduced/absent in the second, compared to wt. Similarly, complete-ko (ex3) led to significantly lower survival, with impaired though somewhat better survival of partial-ko (ex13) zebrafish. Complete knockout of Pcyt2 in mice is embryonically lethal (PMID cited: 17325045) while heterozygous mice develop features of metabolic syndrome (PMID cited: 22764088). Given lethality in knockout zebrafish / mice and the residual activity (15-20%) in patient fibroblasts, the variants reported were thought to be hypomorphic and complete loss of function possibly incompatible with life. PCYT2 is not associated with any phenotype in OMIM/G2P/SysID and not commonly included in gene panels for ID. As a result this gene could included in the ID / epilepsy panels with green (~/>3 indiv/fam/variants with the nonsense found in different populations, consistent phenotype, lipidomics, in silico/in vitro/in vivo evidence) or amber rating. [Please consider inclusion in other possibly relevant panels eg. for metabolic disorders, etc]. Sources: Literature Konstantinos Varvagiannis (Other), 11 Nov 2019; Changed rating: GREEN |
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| Likely inborn error of metabolism - targeted testing not possible v1.265 | PTS | Ivone Leong commented on gene: PTS: This gene was part of an initial gene list collated by Emma Ashton on behalf of the London North GLH, for GMS Metabolic Consensus Specialist Test Group. Additional information was not provided, such as mode of inheritance and phenotype. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Likely inborn error of metabolism - targeted testing not possible v1.264 | PTS | Ivone Leong Classified gene: PTS as Green List (high evidence) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Likely inborn error of metabolism - targeted testing not possible v1.264 | PTS | Ivone Leong Added comment: Comment on list classification: Promoted from Amber to Green. PTS is associated with an appropriate phenotype on OMIM and Gene2Phenotype. There are >3 unrelated cases listed on OMIM. Therefore, enough evidence for this gene to be promoted to Green status. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Likely inborn error of metabolism - targeted testing not possible v1.264 | PTS | Ivone Leong Gene: pts has been classified as Green List (High Evidence). | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Likely inborn error of metabolism - targeted testing not possible v1.263 | PTS | Ivone Leong Phenotypes for gene: PTS were changed from Intellectual disability; 6-Pyruvoyl-tetrahydropterin synthase deficiency (Disorders of pterin metabolism) to Intellectual disability; 6-Pyruvoyl-tetrahydropterin synthase deficiency (Disorders of pterin metabolism); Hyperphenylalaninemia, BH4-deficient, A 261640 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Likely inborn error of metabolism - targeted testing not possible v1.47 | PTS |
Ivone Leong Source NHS GMS was added to PTS. Source London North GLH was added to PTS. |
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| Likely inborn error of metabolism - targeted testing not possible v0.4 | PTS |
Ellen McDonagh gene: PTS was added gene: PTS was added to Inborn errors of metabolism. Sources: Expert Review Amber Mode of inheritance for gene: PTS was set to BIALLELIC, autosomal or pseudoautosomal Publications for gene: PTS were set to 27604308 Phenotypes for gene: PTS were set to Intellectual disability; 6-Pyruvoyl-tetrahydropterin synthase deficiency (Disorders of pterin metabolism) |
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