Protection of Genetic Information in Human Egg Cells Across Female Aging
A research paper published in August 2025 in the journal Science Advances by European researchers presented remarkable evidence of the preservation of mitochondrial DNA integrity and a corresponding reduction in the risk of women transmitting genetic diseases to their children, even at later reproductive ages.
The study analyzed mitochondria present in the blood, saliva, and egg cells of 22 European women aged 20 to 42 undergoing IVF, and compared their mutation frequency and patterns to draw conclusions about the effect of aging on mutations in the mtDNA of egg cells.
These were the main findings:
In conclusion, this research shows that:
Mitochondrial mutations do not increase significantly with age, egg cells maintain stable mitochondrial DNA throughout a woman’s life.
Most mitochondrial mutations occur in non-coding regions, meaning they are unlikely to affect essential genes or cause harmful effects.
Very few mutations in egg cells are disease-related, showing strong protection against harmful genetic changes.
Inherited mitochondrial mutations appear at similar levels across all ages and are mainly found in regulatory regions of the genome.
Egg cells selectively remove or prevent harmful mutations, ensuring that the mitochondrial DNA passed to the next generation remains healthy and intact.
Some context on what mtDNA is and how its mutations cause genetic diseases
A common concern that many people experience when expecting a baby is the possibility of their child to inherit a genetic disease. Some of the best-known examples include Cystic Fibrosis, which affects the lungs and digestive system due to thick mucus buildup; Sickle Cell Disease, which causes pain and organ damage as red blood cells are misshaped, and not flexible causing them to block blood flow to the rest of the body; and Huntington’s Disease, a progressive brain disorder that leads to uncontrolled movements and cognitive decline.
Mitochondrial disorders, however, are among the most common heritable diseases. These disorders arise from malfunctions in the mitochondria, a component (organelle) of the cell responsible for generating energy by converting nutrients into the famous molecule adenosine triphosphate, ATP, that then other systems and organs use to function.
The brain relies heavily on ATP to transmit electrical signals between neurons. These cells use ATP-driven pumps to move ions such as sodium, potassium, and calcium in and out of the cell, which maintains the electrical charge needed for communication. In a similar nature, retina in the eye, inner ear hair cells and olfactory tissue convert physical stimuli like light, sound and smell into electrical signals that the brain can interpret. In addition, extraocular, cardiac (heart) and skeletal muscles use ATP to move the machinery that contract and relaxes the muscles. These organs that heavily rely on the energy metabolism are the most affected when the mitochondria malfunctions.
Mutations that affect the energy metabolism (mitochondria) and that can cause epileptic seizures, stroke-like episodes, hearing loss, retinopathy, external ophthalmoparesis, exercise intolerance, and diabetes mellitus, can be found either in the nuclear genome or genomic DNA, which have the instructions to build a human with their particular traits inherited from the mother and the father, or in the mitochondrial genome, which is the only other DNA present in the human body, exclusively inside the mitochondria and encodes some components of the energy metabolism system which is the oxidative phosphorylation system.
Since the mitochondrial DNA, mtDNA, is only inherited from the mother, as the paternal mitochondria are exclusively present in the tale of sperm cells and do not enter the egg during fertilization, there is a great pressure on the maintenance of a low mutation rate on the mtDNA in egg cells. Mutation rates generally increase with age in most tissues and that of mtDNA is significantly higher than the mutation rate observed for nuclear DNA. For these reasons, it was thought that women had a biological clock and that with aging the possibility of transmitting the child mutations was much higher.