Some people view mitochondrial replacement therapy as akin to in vitro fertilization, while others see it as more similar to genome editing, Vox writes.
"Turns out this difference in definition is the key to whether it's accepted," it adds.
In mitochondrial replacement therapy, the nucleus from the mother's egg is removed and inserted into a nucleus-less, but mitochondria-containing donor egg. Fertilization can then occur either before or after the transfer.
As Vox notes, the procedure is allowed, though highly regulated, in the UK. There, patients seeking the procedure must receive a license and must meet certain criteria. Two women are thought to have been treated in this way, Vox says, adding that Australia and Singapore are currently weighing whether to allow mitochondrial replacement therapy.
Meanwhile, the US outlawed human germline modifications, which has been interpreted to include mitochondrial replacement therapy. The ban, Vox notes, appeared to have been more in response to concerns about CRISPR-based gene editing than mitochondrial replacement therapy.