The mitochondrial genome has two distinct versions in the human reference genomes we support:
NC_001807.4 (on hg19)
NC_012920.1 (on GRCh37, hg38 and GRCh38)
On VarSome, we use the following conventions:
On hg19: "chrM" = NC_001807.4, "MT" = NC_120920.1
On hg38: "chrM" = "MT" = NC_120920.1
We have lifted over variants from source databases to cover both versions of the mitochondrial genome on hg19/GRCh37. Please note, however, that as for any lift-over on variants, the results may be inaccurate or missing from the target genome.