People diagnosed with attention deficit/hyperactivity disorder (ADHD), usually detected at an early age in hyperactive children, may have an increased risk of developing Parkinson’s and Parkinson’s-like diseases, a new study suggests.

“Parkinson’s disease is commonly thought of as a neurodegenerative disease associated with aging,” Glen Hanson, PhD, professor at the University of Utah Health and the study’s lead author, said in a press release. “This may be the first time where a childhood disease and its treatment may be linked to a geriatric expression of neurodegenerative disorder.”

The study, “ Increased Risk of Diseases of the Basal Ganglia and Cerebellum in Patients with a History of Attention-Deficit/Hyperactivity Disorder, ” was published in the journal Neuropsychopharmacology.

ADHD is estimated to affect approximately 11% of children ages 4-7 in the United States, according to data from the Centers for Disease Control and Prevention (CDC).

ADHD, characterized by hyperactivity and attention impairments that may interfere with the child’s development, is linked with a deregulated release of the neurotransmitter dopamine, a key signaling molecule that regulates brain cell activity and function.

Parkinson’s disease is also characterized by a lack of dopamine, a consequence of the progressive degeneration and death of nerve cells that produce this neurotransmitter — the so-called dopaminergic neurons.

Treatment for ADHD includes the use of therapeutic stimulants that increase the amount of dopamine in the brain, such as amphetamine, methylphenidate and dexmethylphenidate.

The long-term impact of ADHD, its treatment and the risk of developing brain diseases such as Parkinson’s is largely unknown.

Researchers at the University of Utah performed a retrospective analysis of the Utah Population Database (UPDB), which contains the medical records of more than 11 million people who have lived in the state.

They analyzed data from people born between 1950 and 1992, who were at least 20 years old by the end of 2011 and had no prior diagnosis of Parkinson’s or Parkinson’s-like diseases.

In total, their analysis included 31,769 patients who were diagnosed with ADHD, 4,960 of whom were prescribed stimulant medications — 2,716 received amphetamine salts (sold as Adderall), 1,941 were treated with methylphenidate (sold under the brand names Ritalin, Concerta, Daytrana, Metadate and Methylin) and 303 receiving both therapies.

As controls, they included 158,790 non-ADHD individuals, matched for gender and age with the ADHD group.

Participants with a history of drug or alcohol abuse were excluded from the study to minimize the risk for factors other than ADHD that might influence the risk for later onset of Parkinson’s. However, the team was unable to control other potential sources of interference, including head trauma, brain injuries and environmental toxins.

Researchers found that ADHD patients had more than twice the risk of developing Parkinson’s and Parkinson’s-like diseases.

The risk for early onset — ages 21 to 66 — was 8.6 times higher in ADHD patients prescribed stimulant medications, including methylphenidate, mixed amphetamine salts and dexmethylphenidate (sold as Focalin).

“If we were to follow 100,000 adults over time, in one year we would expect one to two people will develop Parkinson’s disease before age 50,” said Karen Curtin, PhD, associate professor at University of Utah Health. “If we were to follow 100,000 adults prescribed treatment for ADHD over time, we estimate that over a year, eight to nine patients will develop Parkinson’s disease before age 50.”

Addressing the risk for Parkinson’s disease specifically, researchers detected 2.6 times the risk in ADHD patients compared to non-ADHD individuals. In ADHD patients who had been treated, the risk was almost four times higher than that of non-ADHD subjects.

Patients with a more severe type of ADHD may have an intrinsic higher risk, which may or may not be directly attributed to stimulant medication.

“The jury is still out,” Curtin said. “The increased risk we observed in people could be linked to having ADHD itself or perhaps a more severe form of ADHD, which may be more likely to be treated with medications.”

These findings should be considered preliminary, the authors noted, as their analysis may be limited by several factors — a potential misclassification of non-ADHD subjects, an incorrect diagnosis of Parkinson’s-like disease symptoms and a lack of information on dosage and duration of ADHD medication.

“I believe the treatment is still a benefit, especially for children who cannot control their ADHD symptoms,” Hanson said. “Medication really should be considered on a case-by-case basis.”