Mitochondrial DNA and Autism Link

Definition

Mitochondrial DNA

Mitochondrial DNA (mtDNA or mDNA) is the DNA located in mitochondria, cellular organelles within eukaryotic cells that convert chemical energy from food into a form that cells can use, adenosine triphosphate (ATP). In humans, the 16,569 base pairs of mitochondrial DNA encode only 37 genes. Human mitochondrial DNA was the first significant part of the human genome to be sequenced. Most species, including humans, mtDNA is inherited solely from the mother. Mitochondrial DNA is maternally inherited and enables genealogical researchers to trace maternal lineage far back in time.

Main Digest

Previous research suggested a link between mitochondrial functional defects and ASD, but those studies included small sample sizes and could not verify whether the cause was genetic or environmental.

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The Study

The current study, published Oct. 28 in the journal PLOS Genetics, analyzed mtDNA in 903 families, where the researchers compared the mtDNA of an affected child and an unaffected sibling and their mother. They found that in instances when the children had both mutant and normal mtDNA in a single cell, called heteroplasmy, all the children showed similar numbers of mutant mtDNA. Still, the autistic children had more than twice as many harmful mtDNA mutations as their non-autistic siblings.

"When we compared the inheritance between the mother and the children, we confirmed this particular pattern, which is the child with autism inherited more bad mutations than their siblings during the process of passing mitochondrial DNA from mother to children," said Zhenglong Gu, associate professor of nutritional sciences and the paper's senior author.

"We show not only that mitochondrial DNA heteroplasmy is associated with autism, but also, among autistic kids, these pathogenic mitochondrial DNA mutations are significantly associated with intellectual disability and other neurological and developmental defects," said Yiqin Wang, a graduate student in Gu's lab and the paper's first author.

The current findings may lead to better diagnosis and treatment of children with a sub-type of autism caused by pathogenic mtDNA mutations.

Analyzing mtDNA could help diagnose some forms of autism in the future.

Interventions restoring mitochondrial function might also be useful for treatment, Gu said. These findings also have relevance for other childhood neurodevelopmental disorders, which may be caused by disease-causing mtDNA mutations and is a subject for future work, he said.

Nuclear DNA

Most human cells carry two copies of nuclear DNA, one copy from each parent, and hundreds of copies of mtDNA, which exist in an organelle called the mitochondrion, where most of a cell's energy is created. Aside from the nuclear genome in the cell's nucleus, the mitochondrion is the only organelle that contains DNA. Compared to nuclear DNA, mtDNA is known to mutate rapidly, which has prompted Gu to look for age-related diseases and pediatric diseases linked to these mutations.

During egg production, there is a dramatic reduction in the number of copies of mtDNA to eliminate bad mutations passed from mother to child. But some bad mutations still pass to the next generation, and the number of pathogenic mtDNA in children may be affected by the mother's environment or physiology, Gu said.

"Does the mother have inflammation or diabetes, or is she obese?" Gu said. "These things could make the process of cleaning up mutations less efficient. This could give us some insight into why autism is rising" and will be a subject for future studies, Gu said.

Future work will also include looking into the effects of the environment, diet, and the mother's health on mtDNA in children, Gu said. He said the group is also developing better tools for efficient and cost-effective mtDNA sequencing.

Martin Picard, an assistant professor of behavioral medicine at Columbia University, is a co-author of the paper. The study was funded by Cornell University, the National Science Foundation, the National Institutes of Health, and the ENN Science and Technology Development Company.

Resources That Provide Relevant Information

• DNA that Causes Autism and Schizophrenia
• Link to Autism in Boys Found in Missing DNA
• Intellectual Disability Gene Discovered
• Are Genetics to Blame for Intellectual Disability
• Gene Identified as Cause of Forms of Intellectual Disability
• Nab2/ZC3H14 Protein and Inherited Intellectual Disability

Attribution/Source(s):

This peer reviewed article relating to our Autism Information section was selected for publishing by the editors of Disabled World due to its likely interest to our disability community readers. Though the content may have been edited for style, clarity, or length, the article "Mitochondrial DNA and Autism Link" was originally written by Cornell University, and published by Disabled-World.com on 2016-10-31 (Updated: 2022-08-12). Should you require further information or clarification, Cornell University can be contacted at cornell.edu. Disabled World makes no warranties or representations in connection therewith.

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