rs118192101

Variant names:

• chrM-8313-G-A
• rs118192101
• unassigned_transcript_4803:c.19G>A

Variant summary

Our verdict is Likely pathogenic. The variant received 5 ACMG points: 5P and 0B. PM6_Supporting PS3_Supporting PP3 PM2_Supporting PS4_Supporting

This summary comes from the ClinGen Evidence Repository: The m.8313G>A variant in MT-TK has been reported in two unrelated probands with primary mitochondrial disease (PS4_supporting). One of these individuals had a severe gastroenteropathy, peripheral neuropathy, seizures, dementia, ataxia, retinitis pigmentosa, deafness, and died by age 15 years (PMID:9380435). The other individual had onset in her 20s of myopathy, nasal speech and swallowing difficulty, peripheral neuropathy, ptosis, and osteoporosis. Her condition was progressive and after several years she was non-ambulatory, had bulbar failure, and required tracheostomy and tube feeding (PMID:19618438). In both individuals, the variant was heteroplasmic, ranging from 54% in fibroblasts to 74-82% in muscle. In one of the reported cases, the variant was reported de novo as it was absent in blood from the proband’s mother, maternal aunt, and two brothers (PMID:9380435), however no additional tissues were tested (including that blood in the proband was not tested) and technology performed at the time of publication would not detect low heteroplasmy levels of the variant. In the other case, multiple tissues from the mother were tested as was muscle from two healthy brothers and the variant was not detectable (PMID:19618438), confirming de novo occurrence (PM6_supporting). Of note, three additional unrelated probands in a large cohort of individuals with autism spectrum disorder were reported to have this variant (PMID:35778412), however additional clinical details were not provided and there was no evidence these individuals had other features of primary mitochondrial disease. There is one occurrence of this variant in population databases (MITOMAP GenBank sequences, 1/59,389 or 0.002%; absent in Helix dataset and gnomAD v3.1.2). Although there is one occurrence, the frequency is still low (PM2_supporting). The computational predictor MitoTIP suggests this variant is pathogenic (73.6 percentile) and HmtVAR predicts it to be pathogenic score of 0.85 (PP3). Several functional studies reported show the deleterious effects of this variant (PS3_supporting). A single fiber study (PMID:19618438) demonstrated higher levels of variant in COX-negative fibers (96.44%; n =10) than in COX-positive fibers (72.11%; n= 10; P<0.001). A cybrid study (PMID:12737626) showed that cybrids with high levels of the variant had severe respiratory chain defects, diminished O2 consumption, and translational defects. Furthermore, a 7000-fold loss of aminoacylation efficiency was reported (PMIDs: 15477393, 15100439). In summary, this variant meets criteria to be classified as uncertain significance however, after extensive discussion, this Expert Panel elected to modify the classification to likely pathogenic given consistent functional evidence of a severe deleterious effect across multiple assays. This classification was approved by the NICHD/NINDS U24 ClinGen Mitochondrial Disease Variant Curation Expert Panel on March 13, 2023. Mitochondrial DNA-specific ACMG/AMP criteria applied (PMID:32906214): PS4_supporting, PM2_supporting, PP3, PM6_supporting, PS3_supporting. LINK:https://erepo.genome.network/evrepo/ui/classification/CA254837/MONDO:0044970/014

• Frequency: Mitomap GenBank: Absent
• Consequence: TRNK unassigned_transcript_4803 missense
• Scores: Mitotip Uncertain 16
• Clinical Significance: Likely pathogenic reviewed by expert panel P:2 MNGIE-like-/-Progressive-mito-cytopathy
• Conservation: PhyloP100: 7.31
• Publications: 1 publications found

Genes affected

TRNK (HGNC:7489): (mitochondrially encoded tRNA lysine)

MT-ATP6 (HGNC:7414): (mitochondrially encoded ATP synthase 6) Contributes to proton-transporting ATP synthase activity, rotational mechanism. Involved in mitochondrial ATP synthesis coupled proton transport. Part of mitochondrial proton-transporting ATP synthase complex. Implicated in Leber hereditary optic neuropathy; NARP syndrome; Parkinson's disease; multiple sclerosis; and systemic lupus erythematosus. [provided by Alliance of Genome Resources, Apr 2022]

MT-ATP8 (HGNC:7415): (mitochondrially encoded ATP synthase 8) Contributes to proton-transporting ATP synthase activity, rotational mechanism. Involved in mitochondrial ATP synthesis coupled proton transport. Part of mitochondrial proton-transporting ATP synthase complex. Implicated in multiple sclerosis and urinary bladder cancer. [provided by Alliance of Genome Resources, Apr 2022]

MT-CO2 (HGNC:7421): (mitochondrially encoded cytochrome c oxidase II) Contributes to cytochrome-c oxidase activity. Predicted to be involved in mitochondrial electron transport, cytochrome c to oxygen and positive regulation of vasoconstriction. Located in mitochondrial inner membrane. Part of respiratory chain complex IV. Biomarker of Huntington's disease and stomach cancer. [provided by Alliance of Genome Resources, Apr 2022]

MT-CO2 Gene-Disease associations (from GenCC):

• mitochondrial disease

  Inheritance: Mitochondrial Classification: DEFINITIVE Submitted by: ClinGen
• cytochrome-c oxidase deficiency disease

  Inheritance: AR Classification: SUPPORTIVE Submitted by: Orphanet
• MELAS syndrome

  Inheritance: Mitochondrial Classification: SUPPORTIVE Submitted by: Orphanet
• Leigh syndrome

  Inheritance: Mitochondrial Classification: LIMITED Submitted by: ClinGen

ACMG classification

Our verdict: Likely_pathogenic. The variant received 5 ACMG points.

• PS3: For more information check the summary or visit ClinGen Evidence Repository.
• PS4: For more information check the summary or visit ClinGen Evidence Repository.
• PM2: For more information check the summary or visit ClinGen Evidence Repository.
• PM6: For more information check the summary or visit ClinGen Evidence Repository.
• PP3: For more information check the summary or visit ClinGen Evidence Repository.

Variant Effect in Transcripts

ACMG analysis was done for transcript: ENST00000387421.1. You can select a different transcript below to see updated ACMG assignments.

RefSeq Transcripts

Selected	Gene	Transcript	Tags	HGVSc	HGVSp	Effect	Exon Rank	Protein	UniProt
There are no transcript annotations for this variant.

Ensembl Transcripts

Selected	Gene	Transcript	Tags	HGVSc	HGVSp	Effect	Exon Rank	Protein	UniProt
	MT-TK	ENST00000387421.1	TSL:6	n.19G>A		non_coding_transcript_exon	Exon 1 of 1
	MT-ATP6	ENST00000361899.2	TSL:6	c.-214G>A		upstream_gene	N/A	ENSP00000354632.2
	MT-ATP8	ENST00000361851.1	TSL:6	c.-53G>A		upstream_gene	N/A	ENSP00000355265.1

Frequencies

Mitomap GenBank The variant is not present, suggesting it is rare .

Mitomap

Disease(s): MNGIE-like-/-Progressive-mito-cytopathy

Status: Cfrm-[LP]

ClinVar

ClinVar submissions as Germline

Significance: Likely pathogenic

Revision: reviewed by expert panel

Pathogenic	VUS	Benign	Condition
1	-	-	Mitochondrial disease (1)
1	-	-	Mitochondrial DNA depletion syndrome 1 (1)

Computational scores

Source: dbNSFP v4.9

Name	Calibrated prediction	Score	Prediction
Mitotip	Uncertain	16
Hmtvar	Pathogenic	0.85
PhyloP100		7.3

Other links and lift over

dbSNP: rs118192101; hg19: chrM-8314;