Researchers from Cornell University have established the existence of a genetic connection between mitochondrial DNA, or mtDNA, being passed from the mother and a number of forms of autism spectrum disorder observed in the child.
Previous research has also suggested the existence of a connection between mitochondrial functional DNA and developing ASD; however, as the studies underlining this effect were carried out on a small and inconclusive number of subjects, the thesis was never fully confirmed. Because of the scientifically incomplete samples, the mitochondrial dysfunctions and the ASD spectrum could have been attributed to both genetic and environmental causes.
The study was published in the journal PLOS Genetics, and it provided the results of an analysis carried out on 903 families. The scientists compared the mtDNA of children both affected by ASD and their siblings who weren't affected. The mothers were also tested during this process.
The study revealed that in cases of heteroplasmy, or having both mutant and normal mtDNA in a single cell, both affected and unaffected children showed similar numbers of mutant mtDNA. However, the subjects displaying ASD had more than twice the number of harmful mtDNA mutations.
A majority of our cells have two copies of nuclear DNA, one for each parent, as well as hundreds of copies of mtDNA, which can be found in an organelle called mitochondrion. This is where the vast majority of the cell's energy is created. As opposed to nuclear DNA, the mtDNA has been proven to mutate rapidly, which has given the scientists the idea to search for age-related affections that could be linked to these mutations.
According to Zhenglong Gu, associate professor of nutritional sciences and the lead author of the paper, there is a drastic decline in the copies of mtDNA during the period when the egg is produced. This phenomenon is believed to be an evolutionary means to reduce mutations.
However, there still exist some copies of mtDNA that manage to be transmitted to the following generation, which is why the number of pathogenic mtDNA in children could be massively influenced by the mother's environment or physiology.
The discovery could help better diagnosing and treating children who have an ASD caused by a mtDNA mutation. Other childhood disorders could be also influenced by this, and further research could focus on finding links between the mother's age-related affections and the child's different disorders, according to the researchers.
Consequently, further research will be carried out in the search for environment effects, as well as the mother's health during the pregnancy in order to understand the causes for the mtDNA mutations and their presence in children.