chrM-1606-G-A

Variant names:

• chrM-1606-G-A
• rs199476143
• unassigned_transcript_4786:c.5G>A

Variant summary

Our verdict is Uncertain significance. The variant received 4 ACMG points: 4P and 0B. PM6_Supporting PS3_Supporting PP3 PM2_Supporting

This summary comes from the ClinGen Evidence Repository: The m.1606G>A variant in MT-TV has been reported in two affected individuals in two families (PMIDs: 9450773, 2056939), however haplogroups were not provided as necessary to apply PS4_supporting. These two individuals had strikingly similar courses, as both were males who were relatively healthy until their 20s/30s when they developed progressive cognitive impairment. Other features seen in both men include bilateral cataracts, bilateral SNHL, imbalance/ataxia, and basal ganglia classifications, with both men harboring the variant at 67-70% heteroplasmy. This variant occurred de novo in one individual (absent in blood and urine from mother and brother; PM6_supporting, PMID:12056939). There is one report of this variant segregating with disease features as a healthy mother of a proband had the variant present at <10% in muscle, however this does not meet criteria to apply PP1_supporting (at least two segregations). This variant is absent in the GenBank dataset, Helix dataset, and gnomAD v3.1.2 (PM2_supporting). Single fiber testing showed higher levels of the variant in COX negative fibers (85%) than in COX positive fibers (57%), p<0.0001 (PS3_supporting, PMID:9450773). The computational predictor MitoTIP suggests this variant impacts the function of this tRNA with a score of 73.6%, as does HmtVar with a score of 0.9 (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 Mitochondrial Disease Variant Curation Expert Panel on June 27, 2022. Mitochondrial DNA-specific ACMG/AMP criteria applied (PMID:32906214): PM6_supporting, PS3_supporting, PM2_supporting, PP3. LINK:https://erepo.genome.network/evrepo/ui/classification/CA120536/MONDO:0044970/014

• Frequency: Mitomap GenBank: Absent
• Consequence: TRNV unassigned_transcript_4786 missense
• Scores: Mitotip Uncertain 16
• Clinical Significance: Uncertain significance reviewed by expert panel P:2 U:1 AMDF
• Conservation: PhyloP100: -0.0990
• Publications: 4 publications found

Genes affected

TRNV (HGNC:7500): (mitochondrially encoded tRNA valine)

MT-RNR2 (HGNC:7471): (mitochondrially encoded 16S RNA) Enables G protein-coupled receptor binding activity; protein self-association; and receptor antagonist activity. Involved in several processes, including leukocyte chemotaxis; negative regulation of cell death; and negative regulation of neuroinflammatory response. Located in several cellular components, including mitochondrion; perinuclear region of cytoplasm; and sperm midpiece. [provided by Alliance of Genome Resources, Apr 2022]

MT-RNR1 (HGNC:7470): (mitochondrially encoded 12S RNA) Enables DNA binding activity and DNA-binding transcription factor binding activity. Involved in several processes, including osteoblast proliferation; regulation of carbohydrate utilization; and regulation of phosphate metabolic process. Located in extracellular space; mitochondrion; and nucleus. [provided by Alliance of Genome Resources, Apr 2022]

MT-RNR1 Gene-Disease associations (from GenCC):

• mitochondrial disease

  Inheritance: Mitochondrial Classification: DEFINITIVE Submitted by: ClinGen

ACMG classification

Our verdict: Uncertain_significance. The variant received 4 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.
• PM6: 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 rank	MANE	Protein	UniProt
TRNV	unassigned_transcript_4786	c.5G>A	p.Ser2Asn	missense_variant	Exon 1 of 1
RNR2	unassigned_transcript_4787	n.-65G>A		upstream_gene_variant
RNR1	unassigned_transcript_4785	n.*5G>A		downstream_gene_variant

Ensembl

Gene	Transcript	HGVSc	HGVSp	Effect	Exon rank	TSL	MANE	Protein	Appris	UniProt
MT-TV	ENST00000387342.1	n.5G>A		non_coding_transcript_exon_variant	Exon 1 of 1	6
MT-RNR2	ENST00000387347.2	n.-65G>A		upstream_gene_variant		6
MT-RNR1	ENST00000389680.2	n.*5G>A		downstream_gene_variant		6

Frequencies

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

Alfa AF: 0.00 Hom.: 0

Mitomap

Disease(s): AMDF

Status: Cfrm-[VUS*]

ClinVar

Significance: Uncertain significance

Submissions summary: Pathogenic:2 Uncertain:1

Revision: reviewed by expert panel

Submissions by phenotype

Ataxia, progressive seizures, mental deterioration, and hearing loss Pathogenic:1

Jun 01, 2002

OMIM

Significance: Pathogenic

Review Status: no assertion criteria provided

Collection Method: literature only

MELAS syndrome Pathogenic:1

Jul 12, 2019

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

Significance: Pathogenic

Review Status: criteria provided, single submitter

Collection Method: clinical testing

The NC_012920.1:m.1606G>A variant in MT-TV gene is interpreted to be a Pathogenic variant based on the modified ACMG guidelines (unpublished). This variant meets the following evidence codes reported in the guidelines: PS3, PS5, PM7

Mitochondrial disease Uncertain:1

Jun 30, 2022

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

Significance: Uncertain significance

Review Status: reviewed by expert panel

Collection Method: curation

The m.1606G>A variant in MT-TV has been reported in two affected individuals in two families (PMIDs: 9450773, 2056939), however haplogroups were not provided as necessary to apply PS4_supporting. These two individuals had strikingly similar courses, as both were males who were relatively healthy until their 20s/30s when they developed progressive cognitive impairment. Other features seen in both men include bilateral cataracts, bilateral SNHL, imbalance/ataxia, and basal ganglia classifications, with both men harboring the variant at 67-70% heteroplasmy. This variant occurred de novo in one individual (absent in blood and urine from mother and brother; PM6_supporting, PMID: 12056939). There is one report of this variant segregating with disease features as a healthy mother of a proband had the variant present at <10% in muscle, however this does not meet criteria to apply PP1_supporting (at least two segregations). This variant is absent in the GenBank dataset, Helix dataset, and gnomAD v3.1.2 (PM2_supporting). Single fiber testing showed higher levels of the variant in COX negative fibers (85%) than in COX positive fibers (57%), p<0.0001 (PS3_supporting, PMID: 9450773). The computational predictor MitoTIP suggests this variant impacts the function of this tRNA with a score of 73.6%, as does HmtVar with a score of 0.9 (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 Mitochondrial Disease Variant Curation Expert Panel on June 27, 2022. Mitochondrial DNA-specific ACMG/AMP criteria applied (PMID: 32906214): PM6_supporting, PS3_supporting, PM2_supporting, PP3.

Computational scores

Source: dbNSFP v4.3

Name	Calibrated prediction	Score	Prediction
Mitotip	Uncertain	16
Hmtvar	Pathogenic	0.90
PhyloP100		-0.099

Other links and lift over

dbSNP: rs199476143; hg19: chrM-1608; COSMIC: COSV63763043;