Mar 25, 2021 - Inside 23andMe

Scientists uncover new information about how hard-to-treat genetic diseases are inherited

Screenshot 2022-10-11 at 11-02-16 23andMe Rare Disease Research Study

A new study by scientists at 23andMe, the Hospital for Sick Children (SickKids), and the University of Toronto offers insight into how the nuclear genome controls the emergence of mutations in mitochondrial DNA.

Published in Scientific Advances, the new findings will help researchers studying serious mitochondrial diseases.

“Mitochondrial diseases represent a very large spectrum, and many are fatal,” said Neal Sondheimer, M.D., Ph.D., principal investigator of the study and Staff Physician in Clinical and Metabolic Genetics at SickKids. “With a better understanding of how mitochondrial variants emerge, we can explore new possibilities for the prevention or possibly the treatment of disease.”


We often refer to genetics as if each person has one genome, but we all actually have two genomes – the nuclear genome and mitochondrial genome.

The mitochondrial genome (known as mtDNA) is uniquely inherited only from our mother. It operates under separate rules for inheritance and repairs to its structure. Mitochondria act like tiny cellular power plants in our bodies. Even though mtDNA represents just a small fraction of our DNA, they have outsized importance. Even small differences in mtDNA can cause serious mitochondrial diseases. Those differences may have a significant impact on such things as Alzheimer’s disease, aging, autism, preterm birth, and more.


Mitochondrial function and DNA maintenance rely on nuclear genome-encoded components. The presence of mtDNA mutation leads to a phenomenon called heteroplasmy – an area of focus for this study.

Heteroplasmy occurs when two or more variants of mtDNA exist in the same cell. The study used data from almost one million 23andMe customers, who consented to participate in research, to calculate heteroplasmy and then identify regions of the nuclear genome that were associated with heteroplasmy. Two candidate areas in the nuclear genome associated with heteroplasmy are known to be involved in the replication of mtDNA.

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