rs199474658

Variant names:

• chrM-3271-T-C
• rs199474658
• unassigned_transcript_4788:c.42T>C

Variant summary

Our verdict is Pathogenic. The variant received 10 ACMG points: 10P and 0B. PS4 PP1_Moderate PP3 PM2_Supporting PS3_Moderate

This summary comes from the ClinGen Evidence Repository: The m.3271T>C variant in MT-TL1 gene has been reported in more than 40 affected individuals from 20 kindreds (PS4; PMIDs: 1932147, 8482977, 7993661, 8908402, 9766710, 9427220, 11404119, 11828557, 10214753, 12609508, 16006433, 15794182, 16353243, 18206799, 20972245, 25680467, 33951347). The age of onset ranged from early childhood to the late 30s. This variant has been seen in individuals with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS; accounts for approximately 10% of cases of MELAS and is the second most common cause) as well as in one individual with myoclonic epilepsy with ragged red fibers (MERRF). Other features seen in affected individual include muscle weakness, exercise intolerance, fatigue, developmental delay, axonal neuropathy, dementia, migraines, seizures, diabetes, growth hormone deficiency, lipoma, sensorineural hearing loss, hypertrophic cardiomyopathy, Wolff-Parkinson-White arrhythmia, optic atrophy, and short stature. Muscle biopsies showed ragged red fibers, COX-negative fibers, paracrystalline inclusions, hypertrophic/atrophic fibers, enlarged mitochondria, abnormal cristae, increased fat droplets, and variable respiratory chain enzyme activities. Heteroplasmy levels were variable but were highest in muscle and urine, and levels were as high as homoplasmic in muscle. This variant segregated with disease in multiple affected members across several families and several healthy family members had lower levels of the variant (PP1_moderate; PMIDs: 9427220, 16006433, 15794182, 18206799, 25680467). There is one report of a de novo occurrence, however technology at the time could have missed low level variants and the tissue(s) tested was not specified (PMID:11828557). This variant is absent in the GenBank dataset, Helix dataset, and gnomAD v3.1.2 (PM2_supporting). The computational predictor MitoTIP suggests this variant is pathogenic (78.3 percentile) and HmtVAR predicts it to be pathogenic score of 0.85 (PP3). Cybrid studies and other assays supported the functional impact of this variant (PS3_moderate; PMIDs: 12527767, 12729737, 15870203, 16120315, 10660592, 9744809, 7603512, 8280119). In summary, this variant meets criteria to be classified as pathogenic 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 April 25, 2023. Mitochondrial DNA-specific ACMG/AMP criteria applied (PMID:32906214): PS4, PP1_moderate, PM2_supporting, PP3, PS3_moderate. LINK:https://erepo.genome.network/evrepo/ui/classification/CV9590/MONDO:0044970/014

• Frequency: Mitomap GenBank: Absent
• Consequence: TRNL1 unassigned_transcript_4788 synonymous
• Scores: Mitotip Pathogenic 17
• Clinical Significance: Pathogenic reviewed by expert panel P:6 O:1 MELAS-/-DM-/-MERRF-like
• Conservation: PhyloP100: 2.98
• Publications: 7 publications found

Genes affected

TRNL1 (HGNC:7490): (mitochondrially encoded tRNA leucine 1 (UUA/G)) Implicated in cardiomyopathy. [provided by Alliance of Genome Resources, Apr 2022]

MT-ND1 (HGNC:7455): (mitochondrially encoded NADH dehydrogenase 1) Enables NADH dehydrogenase (ubiquinone) activity. Involved in mitochondrial electron transport, NADH to ubiquinone and mitochondrial respiratory chain complex I assembly. Located in mitochondrial membrane. Part of mitochondrial respiratory chain complex I. Implicated in several diseases, including MELAS syndrome; neurodegenerative disease (multiple); optic nerve disease (multiple); toxic shock syndrome; and type 2 diabetes mellitus. Biomarker of Alzheimer's disease; Parkinson's disease; and multiple sclerosis. [provided by Alliance of Genome Resources, Apr 2022]

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-RNR2 Gene-Disease associations (from GenCC):

• mitochondrial disease

  Inheritance: Mitochondrial Classification: LIMITED Submitted by: ClinGen

ACMG classification

Our verdict: Pathogenic. The variant received 10 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.
• PP1: 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: ENST00000386347.1. You can select a different transcript below to see updated ACMG assignments.

RefSeq Transcripts

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

Ensembl Transcripts

Sel.	Gene	Transcript	Tags	HGVSc	HGVSp	Effect	Exon Rank	Protein	UniProt
	MT-TL1	ENST00000386347.1	TSL:6	n.42T>C		non_coding_transcript_exon	Exon 1 of 1
	MT-ND1	ENST00000361390.2	TSL:6	c.-36T>C		upstream_gene	N/A	ENSP00000354687.2
	MT-RNR2	ENST00000387347.2	TSL:6	n.*42T>C		downstream_gene	N/A

Frequencies

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

Alfa AF: 0.00 Hom.: 0

Mitomap

Disease(s): MELAS-/-DM-/-MERRF-like

Status: Cfrm-[P]

ClinVar

ClinVar submissions as Germline

Significance: Pathogenic

Revision: reviewed by expert panel

Pathogenic	VUS	Benign	Condition
3	-	-	MELAS syndrome (4)
1	-	-	MELAS syndrome;C0162672:MERRF syndrome (1)
1	-	-	Mitochondrial disease (1)
1	-	-	not specified (1)

Computational scores

Source: dbNSFP v4.9

Name	Calibrated prediction	Score	Prediction
Mitotip	Pathogenic	17
Hmtvar	Pathogenic	0.85
PhyloP100		3.0

Other links and lift over

dbSNP: rs199474658; hg19: chrM-3272;