Heteroplasmy

Heteroplasmy is the presence of more than one mitochondrial DNA sequence variant within a cell or individual. The proportions of these variants can differ among cells and change over time.

Mitochondrial DNA: DNA in mitochondria that encodes a small set of proteins, transfer RNAs, and ribosomal RNAs. Heteroplasmy describes variation among copies of this genome.
Mitochondrial disease: A disorder caused by impaired mitochondrial function, often affecting tissues with high energy demands. A pathogenic mitochondrial variant can cause disease when its proportion is sufficiently high.
Mitochondrion: A cell organelle that produces much of the cell's ATP through oxidative phosphorylation. Mitochondria contain the genomes whose sequence mixtures define heteroplasmy.
Mitochondrial replacement controversy: Ethical and regulatory debate over reproductive techniques that alter mitochondrial inheritance. Residual heteroplasmy raises questions about long-term outcomes and acceptable risk.
Mitochondrial bottleneck: A sharp reduction in the number of mitochondrial genomes transmitted during formation of an egg cell. The bottleneck can make variant proportions differ greatly between a mother and her offspring.
Leber hereditary optic neuropathy: An inherited mitochondrial disorder that causes loss of central vision, usually in young adults. Heteroplasmy can influence whether some mitochondrial mutations produce this optic nerve disorder.
Homoplasmy: The state in which mitochondrial DNA copies in a cell or individual carry the same sequence variant. It is the counterpart to a mixture of mitochondrial sequence variants.
Single-cell sequencing: Methods that determine genetic information from individual cells rather than pooled samples. Single-cell measurements can reveal heteroplasmy variation hidden by tissue averages.
Replicative segregation: The random partitioning of genetically distinct organelles or genomes as cells divide. It can produce daughter cells with different mitochondrial variant proportions.
Mitochondrial replacement therapy: Assisted reproductive techniques that place parents' nuclear DNA in an egg or embryo with donor mitochondria. The procedure aims to reduce transmission of disease-causing mitochondrial DNA variants.

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