Human eggs accumulate fewer mutations than previously believed.

Research indicates that human eggs may be shielded from certain types of mutations associated with aging. In a recent study, scientists discovered that as women age, there are no signs of accumulating mutations in the mitochondrial DNA of their egg cells.

“When we consider age-related mutations, we typically think about older individuals having more mutations compared to younger ones,” notes Kateryna Makova from Pennsylvania State University. “However, this assumption doesn’t always hold true.”

Mitochondria, which provide the primary energy source for the body’s cells, are inherited solely from the mother. While mitochondrial DNA mutations are generally benign, they can sometimes result in complications that impact muscles and neurons, particularly due to their high energy demands. “Oocytes” [egg cells] serve as this biological reservoir,” explains Ruth Lehmann from Massachusetts Institute of Technology, who was not part of this study.

Prior research has shown that older mothers tend to pass down more chromosomal mutations, leading to the general assumption that a similar pattern exists with mitochondrial DNA mutations. To investigate this, Makova and her team utilized DNA sequencing to identify new mutations across 80 eggs sourced from 22 women aged 20 to 42 years.

The findings revealed that mitochondrial mutations in female eggs do not actually escalate with advancing age, unlike those found in salivary and blood cells. “It seems we have evolved a mechanism that mitigates the accumulation of mutations, allowing for their replication later in life,” remarks Makova.

Previous research has indicated that mitochondrial DNA mutations in macaque eggs showed an increase while their reproductive capacity remained stable until the animal reached about nine years of age. “It would be worthwhile to also study younger women. This could apply to humans as well,” comments team member Barbara Arbetuber from Penn State University.