According to the recent researches of American scientists, which were financed by the largest organisation in the field of autism Autism Speaks, there is a link between autism and mitochondrial dysfunction. This correlation has been known in the past in Parkinson’s and Alzheimer’s disease. The latest studies have yielded new insights in the field of autism.
Mitochondria, as one of the basic unit of cell, have a function of supplying cells with energy. There are several ways of producing energy. One of the methods is a metabolic process called aerobic respiration, where mitochondria use oxygen for energy generation. Free radicals come as a byproduct of this process (e.g. hydrogen peroxide), which have a detrimental effect on the cell and the whole organism. For their destruction cells produce antioxidant enzymes. If, for some reason, there is a disturbance of balance, and antioxidants in the body are less to be found than the free radicals, this leads to oxidative stress.
Scientists at Davis (University of California) in these studies, which were published in the Journal of the American Medical Association (JAMA), found out that cumulative damage and oxidative stress in mitochondria may have an impact on the occurrence of autism. The inability of mitochondria to provide energy to nerve cells, severely affects the function of the cell, and therefore the cognitive function in autism.
10 children with autism from 2 to 5 years of age participated in this experiment and 10 children without any disorder. Despite the small number of children, the scientists consider these results significant, because the children were randomly selected of 1.600 children examined within the previous studies “Childhood Autism Risk from Genetic and the Environment – CHARGE”.
Metabolic processes in the mitochondria of lymphocytes (white blood cells) were analyzed in a blood sample. The significance of this analysis was to focus on cells that receive energy primarily through aerobic respiration, to which mitochondria directly affect. On the contrary, prior studies were used to explore mitochondria of the muscle cell. However, they were able to receive energy also without the use of mitochondria, which means that the final value of these studies may be incomplete, since the mitochondrial dysfunction may remain unnoticed.
The research results show that mitochondria in lymphocytes of children with autism, compared to the control group, have used much less oxygen. In some mitochondrial enzymes oxygen consumption has been one-third of normal values.
Insufficient activity is indicated in other obtained results: increased level of pyruvate (“raw materials” used by the mitochondria for energy production) in blood plasma indicates that mitochondria do not produce enough of this substance and therefore cannot meet the energy needs of the cell. The increased level of free radicals is also recognised (e.g. twice the amount of hydrogen peroxide), which causes detrimental oxidative stress. Among other things, mitochondria use this oxidative stress to create a DNA copy of its own, and in children with autism significantly higher levels of mitochondrial DNA copy are measured.
According to the authors of the study, increasing shortage is possible in the nerve cells rather than in lymphocytes, since the nerve cells take the energy exclusively from mitochondria.
In their future work, scientists will be based on a deeper study of detected differences. The challenge is to understand the exact role of mitochondrial dysfunction in autism. Triggers of dysfunction are varied environmental influences and, depending on their severity or period when the child was exposed to them, some symptoms of autism can be explained.
Scientists also believe that the precise “mapping” of chemical processes in mitochondria contribute to the diagnosis of autism. So far, the method of muscle biopsies has been used for the study of mitochondria. If scientists succeed to make up a test in the form of blood tests and determine indicators specific to autism, it would represent a major contribution to the diagnosis of this disease.
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