A new study at Örebro University in Sweden shows that children with ADHD have nearly 50 percent less of a protein that is important for attention and learning. The finding may mean that there are other biochemical disturbances in the brains of individuals with ADHD than was previously believed.
"This indicates that several signal substances are implicated in ADHD and that in the future this could pave the way for other drugs than those in use today," says Jessica Johansson, who is presenting her research findings in a dissertation in medicine at Örebro University.
Jessica Johansson belongs to the Experimental Neuropsychiatric research group that has mapped part of the biochemical changes in cells that underlie ADHD and other neuropsychiatric functional impairments and disorders. Head of the group is Nikolaos Venizelos.
"I usually say that I'm doing research on mental diseases and functional impairments at the cellular level. Many of these are assumed to be the consequence of excessively low levels of important signal substances in the brain, so cell biochemical analyses help us understand the processes that cause the changes."
For the brain to be able to produce the substances required to send signals, it is dependent on various amino acids being transported to the brain. When it comes to ADHD, Jessica Johansson has studied the transport of amino acids tyrosine and tryptophan, which the brain uses in producing the signal substances dopamine, noradrenaline, and serotonin.
By analyzing a certain type of connective tissue cells' (so-called fibroblasts') capacity to transport these substances, the researchers can also reach conclusions about how well the transport into the brain is working. The findings from these studies show that the transport of tryptophan is lower in children with ADHD, compared with children without that diagnosis.
"This probably means that the brain produces less serotonin. Thus far the focus has mainly been on the signal substances dopamine and noradrenaline in the medical treatment of ADHD. But if low levels of serotonin are also a contributing factor, other drugs may be necessary for successful treatment."
The head of the research group Nikolaos Venizelos says that the most unexpected discovery in the study, however, was the dramatically reduced amount of the so-called acetylcholine receptor in children with ADHD says. It functions as a receptor protein for the signal substance acetylcholine and is therefore necessary for key signals involving concentration and learning functions, for example. Drugs that reinforce the acetylcholine effect are used in treating Alzheimer's patients, for instance.
Jessica Johansson has also studied biochemical changes in bipolar disorder (previously called manic-depressive disorder), as there are parallels between ADHD and bipolar disorder. Here it was instead the transport of the amino acid tyrosine that was disturbed, which indicates a reduced production of the signal substances dopamine and noradrenaline.
"Since we have previously seen the same thing in patients with schizophrenia, it's an indication that both disorders have the same deviant amino acid transport, which might be caused by a shared genetic variant."
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