This team from the University of Utah suggests attention deficit hyperactivity disorder (ADHD) as a key to identifying future risk for Parkinson's disease. While 10-11% of children are diagnosed with ADHD, the very long-term effects of the disorder, and its drug treatment, remain understudied. This team confirms that people with ADHD in childhood have an increased risk of developing Parkinson's disease, much later in life. Preliminary results presented in the journal Neuropsychopharmacology, which at this stage do not call into question the treatment "especially for children who cannot control their symptoms".
Parkinson's disease is generally considered a neurodegenerative disease associated with aging, notes Dr. Glen Hanson, professor of pharmacology and toxicology at the University: "This may be the first time that a childhood disease and its treatment may be linked to a geriatric expression of a neurodegenerative disease”.
This retrospective, population-based study of 31,769 ADHD patients, of whom 4,960 received stimulants and 158,790 ADHD-free control participants matched to the ADHD group on sex and age, finds that:
- patients with ADHD are more than twice as likely to develop Parkinson's disease vs people without ADHD during their childhood or adolescence;
- the estimated risk is 6 to 8 times higher in ADHD patients who received stimulant treatments, including methylphenidate (Ritalin), amphetamine salts (Adderall), and dexmethylphenidate (Focaline).
- The estimate would be that out of 100,000 young people with ADHD followed throughout life, 1 to 2 will develop Parkinson's disease before the age of 50;
- out of 100,000 young people treated for ADHD and followed throughout life, 8 to 9 will develop Parkinson's disease before the age of 50;
- patients with a more severe type of ADHD may have an increased risk of motor neuron disease.
One possible explanation: ADHD is a brain disorder associated with changes in dopamine release, which regulates emotional response. Parkinson's disease is a progressive disorder of the nervous system associated with tremors, stiffness and slowed movements, itself associated with a deficiency of dopamine.
Results still considered preliminary but which confirm those of previous studies which already suggested a link between the abuse of amphetamine and the onset of Parkinson's disease. And as for the treatment of ADHD, whose effects on the risk of Parkinson's remain to be dissociated, " there always remains an advantage, in particular for children who cannot control their ADHD symptoms ", conclude the researchers, pending additional research.