Variant: m.9997T>C

CA254843

9611 (ClinVar)

Gene: N/A

Condition: mitochondrial disease

Inheritance Mode: Mitochondrial inheritance

UUID: d3351f7b-2393-468d-b00d-ec60dcd29709

Approved on: 2024-07-22

Published on: 2024-08-08

HGVS expressions

NC_012920.1:m.9997T>C
J01415.2:m.9997T>C

Uncertain Significance

• Met criteria codes: PM2_Supporting PP3

• Not Met criteria codes: PS4

Expert Panel

Mitochondrial Diseases VCEP

Criteria Specification Information

Criteria Specification: ClinGen Mitochondrial Disease Nuclear and Mitochondrial Expert Panel Specifications to the ACMG/AMP Variant Interpretation Guidelines Version 1_mtDNA

Evidence submitted by expert panel

Mitochondrial Diseases VCEP

The m.9997T>C variant in MT-TG has been reported in one large family to date (PMID: 8079988). The most common clinical feature in affected family members was cardiomyopathy, however additional clinical features seen include renal failure, muscle cramps, muscle weakness, exercise intolerance, and gastrointestinal dysmotility. Heteroplasmy levels were variable in affected family members and appeared to segregate with cardiomyopathy but not the other clinical features (PMID: 8079988). This variant is present in population databases (absent in gnomAD v3.1.2; one heteroplasmic in the Helix dataset; one homoplasmic occurrence in the Mitomap GenBank sequences; PM2_supporting). Cybrid studies support the deleterious effect of this variant (PMID: 10090480; PS3_supporting). The computational predictor MitoTIP suggests this variant is deleterious (80.3 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, PS3_supporting, PP3.

Met criteria codes

• PM2_Supporting: This variant is present in population databases (absent in gnomAD v3.1.2; one heteroplasmic in the Helix dataset; one homoplasmic occurrence in the Mitomap GenBank sequences; PM2_supporting).
• PP3: The computational predictor MitoTIP suggests this variant is deleterious (80.3 percentile) and HmtVAR predicts it to be deleterious with a score of 0.35 (PP3).

Not Met criteria codes

• PS4: The m.9997T>C variant in MT-TG has been reported in one large family to date (PMID: 8079988). The most common clinical feature in affected family members was cardiomyopathy, however additional clinical features seen include renal failure, muscle cramps, muscle weakness, exercise intolerance, and gastrointestinal dysmotility.