The number of new cases of Parkinson’s disease, including early-onset disease, is increasing in the US. The cause of this increase is multifactorial and, together with the symptoms, may differ depending on the age of onset.

Traditionally, Parkinson's disease occurred in people older than 60 but that is no longer the case, Anh-Thu Ngo Vu, MD, a neurologist at Jefferson Health in Philadelphia, has said. "Is it something in the environment, is it our better awareness of Parkinson's disease? It's not likely to be one thing."

Stahl S, Kuhn C. Doctors stumped on why there's a trend of younger people diagnosed with Parkinson's disease CBS News. October 4, 2023.

 

 

Incidence, prevalence up

 

Around 90,000 new cases of Parkinson’s disease are diagnosed in the US each year, up from a previous incidence estimate of 60,000 new cases per year, according to a 2022 study.

New study indicates that new cases of Parkinson’s disease are 50% higher than past estimates [press release]. American Parkinson Disease Association. January 3, 2023.

An earlier study determined that around 1 million people in the US have Parkinson’s disease, and estimated that this prevalence would increase to 1.3 million by 2030.

 

Of the 1 million individuals with Parkinson’s disease, 4% are diagnosed with young-onset disease, which occurs in people younger than 50, according to the Parkinson’s Foundation.

Parkinson’s Foundation. Young-Onset Parkinson's [website]. Accessed October 15, 2024.

 

 

There is also an increased engagement with the medical community, which the APDA says can increase diagnoses as well. Nowadays, people are more likely to go to a doctor for a symptom that, in the past, may have been dismissed as normal aging. 

 

Causal factors

 

Genetics and environmental factors remain linked to Parkinson’s disease, but the specific cause often remains unclear. “It comes down to the patient's story and physical examination," Dr. Vu has said. For instance, Parkinson's disease more likely develops following concussions or exposure to pesticides.

Stahl S, Kuhn C. Doctors stumped on why there's a trend of younger people diagnosed with Parkinson's disease CBS News. October 4, 2023.

 

Researchers have investigated factors that increase the risk of Parkinson’s disease. A 2024 case-control study, published in JAMA Network Open, looked at air pollution and the risk of Parkinson’s disease.

Krzyzanowski B, Mullan AF, Turcano P, et al. Air pollution and Parkinson disease in a population-based study. JAMA Netw Open. 2024;7(9):e2433602.

It included 346 patients (median age 72, males 62.4%) with Parkinson’s disease and 4813 controls (median age 72, males 61.2%). Exposure to air pollution in the form of particulate matter with a diameter of 2.5 µm or less, and exposure to nitrogen dioxide, increased the risk of both Parkinson’s disease and developing dyskinesia.

 

The JAMA authors concluded that “reducing air pollution may reduce risk of Parkinson’s disease, modify the [Parkinson’s disease] phenotype, and reduce risk of dyskinesia.”

Another 2024 study, published in npj Parkinson’s Disease , looked at the different risks of early-onset and late-onset Parkinson’s disease in individuals with mental illness.[5] This nationwide study in Korea involved large numbers of patients in the two groups: early-onset (n=5,707,919, mean age 37.25 years, 59.21% male) and late-onset (n= 4,212,603, mean age 60.67 years, 48.36% male).

Depression, bipolar disorder, schizophrenia, insomnia, and anxiety were all associated with increased risks of early-onset and late-onset Parkinson’s disease, although the risk was greater for early-onset disease. Schizophrenia raised the risk of early-onset disease by four times over that of late-onset disease, and bipolar illness raised the risk by three times.

“Our results suggest that people with mental illnesses aged < 50 years are at a higher risk of [Parkinson’s disease] than those aged ≥50 years,” the authors concluded.

 

Youth-onset Parkinson’s disease

 

The Parkinson’s Foundation states that for most people with Parkinson’s disease, “the disease is caused by a combination of genetics and environmental exposures,” but “genetics plays a larger role” in youth-onset Parkinson’s disease.

Parkinson’s Foundation. Young-Onset Parkinson's [website]. Accessed October 15, 2024.

 

Individuals with early-onset Parkinson’s disease and a strong family history of Parkinson’s disease are more likely to carry genes linked to the disease, such as SNCA, PARK2, PINK1, and LRRK2. Research has suggested that 65% of people with Parkinson’s disease onset under age 20, and 32% of those with onset between age 20 and 30, have a genetic mutation linked to an increased risk of Parkinson’s disease. Still, some people with these genes may not develop Parkinson’s disease.

The Foundation’s PD GENEration study offers free genetic testing for Parkinson's disease-related genes and counseling through medical professionals.

Compared with typical Parkinson’s disease, individuals with youth-onset disease have a greater risk of developing dyskinesias and side effects from dopaminergic medications, including dystonias and motor fluctuations. However, they may have a longer survival, with slower symptom progression and less frequent cognitive problems such as dementia.

“Doctors tailor treatment when it is a younger person with Parkinson's disease,” the Foundation says. Physicians may offer genetic testing or counseling. The fact that younger brains have a higher potential for neuroplasticity means that the brain may handle and respond to the disease and therapy differently than in older patients.

“Each person’s treatment is unique and can require fine adjustments of multiple medications.” The Foundation notes that deep brain stimulation remains a surgical option for people with young-onset Parkinson’s disease.