M-4332-G-A

Position:

• chrM-4332-G-A

Variant summary

Our verdict is Uncertain significance. Variant got 3 ACMG points: 3P and 0B. PM2_Supporting PS3_Supporting PP3

This summary comes from the ClinGen Evidence Repository: The m.4332G>A variant in MT-TQ has been reported in one individual from one family to date (PMID:11171912), in a man with an atypical presentation of mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS). This individual had hearing loss beginning in his 20s and a stroke-like episode in his 40s. Muscle biopsy showed ragged red fibers and COX-deficient fibers, along with decreased activity of respiratory chain complex IV. The variant was present at 81% in muscle and undetectable in fibroblasts and skin. While the variant was absent in blood from his mother and brother, it was also undetectable in the proband’s blood, therefore it is unclear if this was a de novo variant. There are no large families reported in the medical literature to consider for evidence of segregation. Of note, there is another individual reported with MELAS and this variant, however insufficient clinical details were provided to include this case for consideration for this variant curation (PMID:20064630). The computational predictor MitoTIP suggests this variant impacts the function of this tRNA (81st percentile) as does HmtVar with a score of 0.7 (PP3). This variant is absent in the GenBank dataset, Helix dataset, and gnomAD v3.1.2 (PM2_supporting). Single fiber testing showed higher levels of heteroplasmy in COX-negative fibers (mean 99.3% and ranging from 98.8-99.7%, n=13) than in COX-positive fibers (mean 70.5% and ranging from 46.5-94.5%, n=11; p=0.002; PMID:11335700; PS3_supporting). 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 January 23, 2023. Mitochondrial DNA-specific ACMG/AMP criteria applied (PMID:32906214): PM2_supporting, PP3, PS3_supporting. LINK:https://erepo.genome.network/evrepo/ui/classification/CA254844/MONDO:0044970/014

• Frequency: Mitomap GenBank: Absent
• Consequence: MT-TQ ENST00000387372.1 non_coding_transcript_exon
• Scores: Mitotip Pathogenic 17
• Clinical Significance: Uncertain significance reviewed by expert panel P:1 U:1 O:1 Encephalopathy-/-MELAS
• Conservation: PhyloP100: 3.85

Genes affected

MT-TQ (HGNC:7495): (mitochondrially encoded tRNA glutamine)

TRNQ (HGNC:):

MT-TI (HGNC:7488): (mitochondrially encoded tRNA isoleucine)

ACMG classification

Verdict is Uncertain_significance. Variant got 3 ACMG points.

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

Transcripts

RefSeq

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	MANE	Protein	UniProt
TRNQ	TRNQ.1	n.69C>T		non_coding_transcript_exon_variant	1/1
TRNI	TRNI.1			downstream_gene_variant

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	#exon/exons	TSL	MANE	Protein	Appris	UniProt
MT-TQ	ENST00000387372.1	n.69C>T		non_coding_transcript_exon_variant	1/1
MT-TI	ENST00000387365.1			downstream_gene_variant

Frequencies

GnomAD4 exome Cov.: 0

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

Gnomad homoplasmic AF: 0.0 AC: 0 AN: 56431

Gnomad heteroplasmic AF: 0.000018 AC: 1 AN: 56431

Mitomap

Encephalopathy-/-MELAS

ClinVar

Significance: Uncertain significance

Submissions summary: Pathogenic:1 Uncertain:1 Other:1

Revision: reviewed by expert panel

Submissions by phenotype

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

Pathogenic, no assertion criteria provided	literature only	OMIM	Feb 13, 2001	- -
not provided, no classification provided	literature only	GeneReviews	-	- -

Mitochondrial disease Uncertain:1

Uncertain significance, reviewed by expert panel

curation

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

Jan 23, 2023

The m.4332G>A variant in MT-TQ has been reported in one individual from one family to date (PMID: 11171912), in a man with an atypical presentation of mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS). This individual had hearing loss beginning in his 20s and a stroke-like episode in his 40s. Muscle biopsy showed ragged red fibers and COX-deficient fibers, along with decreased activity of respiratory chain complex IV. The variant was present at 81% in muscle and undetectable in fibroblasts and skin. While the variant was absent in blood from his mother and brother, it was also undetectable in the proband’s blood, therefore it is unclear if this was a de novo variant. There are no large families reported in the medical literature to consider for evidence of segregation. Of note, there is another individual reported with MELAS and this variant, however insufficient clinical details were provided to include this case for consideration for this variant curation (PMID: 20064630). The computational predictor MitoTIP suggests this variant impacts the function of this tRNA (81st percentile) as does HmtVar with a score of 0.7 (PP3). This variant is absent in the GenBank dataset, Helix dataset, and gnomAD v3.1.2 (PM2_supporting). Single fiber testing showed higher levels of heteroplasmy in COX-negative fibers (mean 99.3% and ranging from 98.8-99.7%, n=13) than in COX-positive fibers (mean 70.5% and ranging from 46.5-94.5%, n=11; p=0.002; PMID: 11335700; PS3_supporting). 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 January 23, 2023. Mitochondrial DNA-specific ACMG/AMP criteria applied (PMID: 32906214): PM2_supporting, PP3, PS3_supporting. -

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
Mitotip	Pathogenic	17
Hmtvar	Pathogenic	0.70

Splicing

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

Publications

LitVar

Other links and lift over

dbSNP: rs199476141; hg19: chrM-4333;