M-9997-T-A

Position:

• chrM-9997-T-A

Variant summary

Our verdict is Likely pathogenic. Variant got 6 ACMG points: 6P and 0B. PM2 PP5_Strong

The ENST00000387429.1(MT-TG):​n.7T>A variant causes a non coding transcript exon change involving the alteration of a non-conserved nucleotide. Variant has been reported in ClinVar as Uncertain significance (★★★).

• Frequency: Mitomap GenBank: Absent
• Consequence: MT-TG ENST00000387429.1 non_coding_transcript_exon
• Scores: Mitotip Pathogenic 20
• Clinical Significance: Uncertain significance reviewed by expert panel P:1 U:1 Unspecified-patient-from-clinical-lab,MHCM
• Conservation: PhyloP100: 1.32

Genes affected

MT-TG (HGNC:7486): (mitochondrially encoded tRNA glycine)

TRNG (HGNC:):

MT-CO3 (HGNC:7422): (mitochondrially encoded cytochrome c oxidase III) Predicted to enable electron transfer activity and oxidoreduction-driven active transmembrane transporter activity. Involved in respiratory chain complex IV assembly. Part of respiratory chain complex IV. Implicated in MELAS syndrome. [provided by Alliance of Genome Resources, Apr 2022]

ACMG classification

Verdict is Likely_pathogenic. Variant got 6 ACMG points.

• PM2: No frequency data in Mitomap. Probably very rare.
• PP5: Variant M-9997-T-A is Pathogenic according to our data. Variant chrM-9997-T-A is described in ClinVar as [Uncertain_significance]. Clinvar id is 690090.Status of the report is reviewed_by_expert_panel, 3 stars. We mark this variant Likely_pathogenic, oryginal submissions are: {Likely_pathogenic=1, Uncertain_significance=1}.

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	Protein	UniProt
TRNG	TRNG.1	n.7T>A		non_coding_transcript_exon_variant	1/1
COX3	COX3.1			downstream_gene_variant			YP_003024032.1

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Protein	Appris	UniProt
MT-TG	ENST00000387429.1	n.7T>A		non_coding_transcript_exon_variant	1/1
MT-CO3	ENST00000362079.2			downstream_gene_variant				ENSP00000354982	P1

Frequencies

GnomAD4 exome Cov.: 0

We have no GnomAD4 genomes data on this position. Probably position not covered by the project.

Mitomap

Unspecified-patient-from-clinical-lab,MHCM

ClinVar

Significance: Uncertain significance

Submissions summary: Pathogenic:1 Uncertain:1

Revision: reviewed by expert panel

Submissions by phenotype

Juvenile myopathy, encephalopathy, lactic acidosis AND stroke Pathogenic:1

Likely pathogenic, criteria provided, single submitter

clinical testing

Wong Mito Lab, Molecular and Human Genetics, Baylor College of Medicine

Jul 12, 2019

The NC_012920.1:m.9997T>A variant in MT-TG gene is interpreted to be a Likely Pathogenic variant based on the modified ACMG guidelines (unpublished). This variant meets the following evidence codes reported in the guidelines: PM5, PM7, PM9, PM10 -

Mitochondrial disease Uncertain:1

Uncertain significance, reviewed by expert panel

curation

ClinGen Mitochondrial Disease Nuclear and Mitochondrial Variant Curation Expert Panel, ClinGen

Jul 22, 2024

The m.9997T>A variant in MT-TG has been reported in one individual to date, however clinical details were not provided (PMID: 31965079). Similarly, there is no available information on segregation in family members or de novo status. It is possible this individual was reported in a poster abstract submitted by Roggenbuck et al., 2016 (https://www.neurology.org/doi/10.1212/WNL.86.16_supplement.P5.016), but this has not been confirmed. The individual reported with this variant in this abstract was a man with exercise intolerance, myalgia, muscle weakness, ptosis, neuropathy, dilated cardiomyopathy, and renal disease. Respiratory chain enzyme testing on muscle showed low cytochrome c oxidase activity but exact values were not provided. The variant was reported to be present at homoplasmy in the proband and was also reported in other maternal family members with varying clinical features, however details were not provided. This variant is absent in the GenBank dataset, Helix dataset, and gnomAD v3.1.2 (PM2_supporting). There are no cybrids, single fiber studies, or other functional assays reported on this variant. The computational predictor MitoTIP suggests this variant is deleterious (95.2 percentile) and HmtVAR predicts it to be deleterious with a score of 0.35 (PP3). In summary, this variant meets criteria to be classified as uncertain significance for primary mitochondrial disease inherited in a mitochondrial manner. This classification was approved by the NICHD/NINDS U24 ClinGen Mitochondrial Disease Variant Curation Expert Panel on July 22, 2024. Mitochondrial DNA-specific ACMG/AMP criteria applied (PMID: 32906214): PM2_supporting, PP3. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
Mitotip	Pathogenic	20
Hmtvar	Benign	0.050

Splicing

Find out detailed SpliceAI scores and Pangolin per-transcript scores at spliceailookup.broadinstitute.org

Publications

LitVar

Other links and lift over

dbSNP: rs121434475; hg19: chrM-9998;