Mitochondrial Disease More Present In Older Moms; Could Improve Genetic Counseling

mitochondria
Scientists believe mitochondria play a role in several conditions, including Alzheimer's disease, autism, cancer, cardiovascular disease, Parkinson's disease, and type 2 diabetes. Photo courtesy of Gary Carlson

It’s a widely known truth that older mothers have increased chances of giving birth to children with a wide variety of illnesses, but the reason for this has been quite unclear. Recently a study revealed that increased maternal age was associated with higher rates of mitochondrial mutations, a finding which may explain the higher rates of mitochondrial diseases associated with children of older mothers.

Researchers from Pennsylvania State University have discovered what they describe as the “maternal age effect.” According to a press release, this “maternal age effect” could be used to predict the accumulation of a certain type of mutation, called mitochondrial DNA mutation, in the maternal eggs. The finding could help improve the accuracy of genetic counseling, which means that prospective parents will have a better idea of their offsprings' chances of being affected by certain types of genetic conditions.  

Mitochondria are structures within cells which produce energy, but they also happen to contain their own sets of DNA. Mutations in mitochondrial DNA are known to cause a number of serious and often life-threatening conditions, which have been appropriately named mitochondrial disease. “Many mitochondrial diseases affect more than one system in the human body," said Kateryna Makova, professor of biology and one of the study's primary investigators in the press release. "They affect organs that require a lot of energy, including the heart, skeletal muscle, and brain. They are devastating diseases and there is no cure, so our findings about their transmission are very important." Mitochondrial DNA mutations account for more than 200 diseases and can contribute to other conditions, such as diabetes, cancer, and Parkinson’s disease.

To test their theory of mitochondrial DNA health being connected with a mother’s age, the researchers enlisted the help of 39 healthy mother-child pairs, who had maternal ages ranging from 25 to 59. The scientists took DNA from the volunteers' blood and cheeks.

Greater rates of mitochondrial DNA variants were discovered in older mothers as well as their children. While Makova and her team expected to find mutated genes in older mothers, the fact that these mothers passed on these genes to their children did surprise the team. As we age, our DNA continues to divide, and increased division means increased chances of creating mutations. Understanding that these mutations are able to be passed on from mother to child via the mitochondrial DNA is a huge breakthrough.

For those contemplating becoming “older mothers” — a woman who gives birth past the age of 35 — there is good news. The researchers also found that while these women can pass on their older, more mutated DNA, the chances of this are not as big as you may believe. A developing egg goes through a “bottleneck” period where the number of mitochondrial DNA it receives begins to decrease. The results from this study have reassured researchers that this “bottleneck” is quite small, meaning knowing the size of the bottleneck will allow genetic counselors to make more accurate predictions on the rate of disease transmission, and the fact that this bottleneck is so small means that the percentages or passing on unfavorable traits are dramatically lowered than previously believed.  

Source: Makova K, Rebolledo-Jaramillo B, Su MSW, et al. Maternal age effect and severe germ-line bottleneck in the inheritance of human mitochondrial DNA. PNAS. 2014.

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