Autism is a developmental disorder affecting over 3.5 million Americans. While there is no known cure for it, there are options for treating some of its associated symptoms. A new study by a team of researchers at Cornell University has found a connection between autism and mutations in mitochondrial DNA. This could eventually lead to developing new and more effective types of treatment.
The Centers for Disease Control and Prevention (CDC) point out that autism spectrum disorder (ASD) is very wide. Learning and problem-solving abilities in children with ASD range anywhere from gifted to seriously challenged.
According to the latest statistics provided by the CDC, approximatively 1 in 68 children have been identified with ASD between 2000 and 2012.
The incidence of ASD is the same across all racial, ethnic, and socio-economic backgrounds.
Regarding gender however, boys have a much higher rate of ASD incidence than girls. A boy is 4.5 times likelier to be diagnosed with ASD.
It is not entirely known what causes ASD, but previous research has pointed to a variety of environmental, biological, and genetic factors.
ASD has been found to occur at a higher rate among patients with specific genetic disorders, such as fragile X syndrome, tuberous sclerosis, or Down syndrome.
What are mitochondria?
Previous research has also linked ASD to dysfunctions in the mitochondria.
Mitochondria are bean-shaped tiny parts of the cell responsible for producing energy. This earned them the nickname of "powerhouses of the cell."
In this interactive video from the Wellcome Trust Center for Mitochondrial Research, experts explain the function of mitochondria simply:
While DNA is found in the nucleus of the cell, mitochondria also contain DNA, although this DNA is much smaller than the one found in the nucleus of our cells.
This mitochondrial DNA contains information that helps the mitochondria turn fat, sugar, and protein into energy.
The connection between mitochondrial mutations and ASD
A team of researchers led by Zhenglong Gu, from Cornell University in Ithaca, NY, has investigated 903 children diagnosed with ASD. The researchers found a larger number of harmful mutations in the mitochondrial DNA of children with ASD compared with that of their family members, who do not have the disorder.
The results of the study have recently been published in the journal PLOS Genetics.
"The result of our study synergizes with recent work on ASD, calling attention to children diagnosed with ASD who have one or more developmental abnormalities or related co-morbid clinical conditions for further testing on mitochondrial DNA and mitochondrial function.
Since many neurodevelopmental disorders and related childhood disorders show abnormalities that converge upon mitochondrial dysfunction, and may have mtDNA defects as a common harbinger, future research is needed to elucidate the mitochondrial mechanisms underpinning to these diseases."
Zhenglong Gu, Lead researcher
The findings confirm the conclusions of recent research. A few recent studies have been pointing to the connection between malfunctions in mitochondria and ASD, with mounting evidence that mitochondrial dysfunction is a biological subtype of ASD.
One such study pointed out a 5% prevalence of mitochondrial disease among those affected by ASD. Neuroimaging, in vitro, post-mortem, and in vivo brain studies all confirmed a high prevalence of mitochondrial dysfunction in ASD patients. Further symptoms such as developmental regression, seizures, motor delay, or gastrointestinal abnormalities were much more present among those with both mitochondrial disease and ASD.
Zhenglong Gu and team discovered a unique pattern of heteroplasmic mutations, where both mutant and normal mitochondrial DNA sequences exist in a single cell.
Children with ASD had more than twice as many harmful mutations compared with their siblings who were not affected by ASD.
As mitochondrial DNA is inherited exclusively from the mother, researchers also note that these mutations can be inherited from the mother. They could also form spontaneously during development.
The scientists noted that the risk associated with these mutations is most pronounced in children with lower IQ and poor social behavior compared with their unaffected siblings.
Apart from developmental disorders, metabolic diseases are also associated with mitochondrial dysfunction in people with ASD. The recent findings from Cornell University might help explain such metabolic disorders.
Implications for treatment
While there is no cure for ASD or treatment for its core symptoms, there are a variety of strategies that can help individuals with ASD function better. These include behavioural therapy and dietary approaches.
There is also medication available to help manage energy levels, the ability to focus, depression, or seizures in patients with ASD.
According to the CDC, most scientists agree that genes are a risk factor in the development of ASD. So evaluating mutations in the mitochondrial DNA of high-risk families, as the Zhenglong Gu study did, may improve the diagnosis and treatment of ASD.
"Ultimately, understanding the energetic aspects of neurodevelopmental disorders may lead to entirely new kinds of treatments, and preventative strategies that would target mitochondria."
Zhenglong Gu, Lead researcher