Episode 124: Characteristics of Young-Onset Parkinson’s Disease

Dan Keller 0:02 Welcome to this episode of Substantial Matters: Life and Science of Parkinson's. I'm your host, Dan Keller, at the Parkinson's Foundation. We want all people with Parkinson's and their families to get the care and support they need. Better care starts with better research and leads to better lives. In this podcast series, we highlight the fruits of that research—the treatments and techniques that can help you live a better life now, as well as research that can bring a better tomorrow.

When people think of Parkinson's disease, they often envision an elderly person with slowness of movement, short shuffling steps, or a prominent resting tremor. However, the disease can and does occur much earlier in life, and this is clinically defined as young onset Parkinson's disease, or YOPD for short. Approximately 4% of all diagnosed cases in the United States fall into the young onset category. Younger individuals will naturally navigate their Parkinson's symptoms differently due to their unique, active life circumstances.

In this first of two interconnected episodes focusing on young onset Parkinson's disease, Dr. Bart Post of Radboud University in the Netherlands explains how young onset Parkinson's differs from later onset disease in terms of genetics, disease progression, therapeutic clinical management, and medication-induced side effects. I first asked him to clarify the age parameters at which the disease is formally considered young onset PD.

Dr. Bart Post 1:46 There is currently a great deal of discussion and debate surrounding this topic within the medical literature. Generally, the scientific consensus states that the age at onset of the disease must be under 40 or 50 years old. Within the literature, there is a clear clinical separation between juvenile parkinsonism—where the age at onset manifests below 21 years old—and young onset Parkinson's disease, which encompasses individuals diagnosed between the ages of 21 and 40, or 21 and 50. Therefore, a single, universally rigid age cutoff does not exist in the papers. In the Netherlands, we clinically establish the cutoff at age 50, though selecting that exact age parameter remains somewhat arbitrary.

Dan Keller 2:25 What does the epidemiological literature indicate regarding a genetic component for young onset Parkinson's disease compared to standard, later onset disease? And how does that genetic profile impact looking backward at family history, or looking forward when planning to have a family?

Dr. Bart Post 2:40 Investigating genetics is extraordinarily compelling, particularly within the young onset population. As a rule, the younger the age of onset, the higher the mathematical probability that the disease stems from an underlying genetic cause. In juvenile parkinsonism, for instance, we see an overwhelmingly high concentration of direct genetic causes.

However, looking specifically at the young onset cohort—patients presenting in their 20s, 30s, and 40s—recent clinical literature demonstrates that approximately 15% to 20% of this population carries an identifiable genetic mutation. Naturally, if a patient presents in their early 20s, that probability peaks. Within this group, a significant portion carries GBA mutations, which serve as prominent genetic risk factors, or LRRK2 mutations, alongside a substantial number of PRKN (parkin) mutations. So, it is a remarkably diverse group with a robust genetic architecture.

The next step—navigating genetic counseling when looking forward to having children—is clinically complex. We conduct extensive genetic counseling for our young onset patients, but these conversations are challenging. For example, if a patient carries an autosomal dominant GBA mutation, there is a direct 50% biological risk of passing that gene variant down to their children. However, even if a child inherits the mutation, there is only about a 30% lifetime probability that they will actually develop clinical Parkinson's disease. Because of these complex probabilities, we dedicate a tremendous amount of clinical time to educating patients before they ever take a genetic test.

Dan Keller 4:17 So, it sounds like some of these variants behave like a dominant gene but present with imperfect or reduced penetrance.

Dr. Bart Post 4:23 Yes, exactly. They function as risk genes. We see the same phenomenon with LRRK2 mutations, which carry roughly a 40% to 50% lifetime penetrance of developing the disease. That is the case for those specific dominant genes. There are other dominant mutations, such as those occurring in the alpha-synuclein (SNCA) gene or the VPS35 gene, which are significantly rarer but exhibit much higher penetrance rates.

Conversely, we also manage autosomal recessive forms of the disease, which include mutations in the PRKN (parkin), PINK1, and DJ-1 genes. Among these, PINK1 and DJ-1 are exceptionally rare. Parkin mutations are more frequent. In a recessive inheritance pattern, an individual must inherit a mutated copy of the gene from both their father and their mother to manifest the disease. If a patient is clinically living with YOPD due to homozygous parkin mutations, they will only pass one copy of that mutated gene to their children. Consequently, their children will be unaffected carriers and will not develop the disease. This is why managing and counseling dominant genes remains uniquely difficult.

Dan Keller 5:20 When someone does develop young onset Parkinson's disease, how does it initially manifest clinically? Is the presentation noticeably different from what you would typically observe in a later onset patient?

Dr. Bart Post 5:30 We have analyzed this deeply, and our findings are strongly corroborated by several multi-center studies across Europe and the United States. What we observe is that young onset patients present with a much higher prevalence of early dystonia at disease onset. Approximately 10% to 20% of young onset patients experience focal dystonia early on—frequently manifesting in the foot—and some individuals will experience this painful muscle cramping long before they ever develop classic bradykinesia or rigidity.

A highly typical presentation we see in this specific patient cohort is exercise-induced dystonia of the foot. For example, a young patient might go out for a run, and after running 5 or 10 kilometers, they suddenly experience an involuntary, painful inversion of the foot. That specific cramping can serve as the very first clinical sign of young onset Parkinson's disease. You almost never observe that specific presentation in a later onset population.

The other major clinical distinction is that we observe significantly less resting tremor at onset in young onset PD; tremor is a feature that is much more prevalent in the older onset age group. Because of these unique presentations, young onset patients experience a far greater delay in receiving an accurate diagnosis compared to older adults. This delay happens because atypical features like exercise-induced dystonia are frequently misdiagnosed as orthopedic or athletic injuries, and honestly, a general practitioner simply does not expect to see Parkinson's disease in a patient who is 32 or 34 years old. If a patient is 65, that fits the classic demographic profile, which immediately triggers the clinician to consider PD. Those represent the biggest differences in clinical presentation and diagnostic timelines.

Dan Keller 7:11 Are there major implications for daily clinical practice based on these differences? For instance, do younger individuals respond differently to dopaminergic medications, or are there separate pharmacological factors you must carefully balance during office visits?

Dr. Bart Post 7:22 Yes, absolutely. Once an accurate diagnosis of young onset Parkinson's disease is established, it triggers a highly nuanced discussion regarding long-term therapeutic management. As we know, levodopa and dopamine agonists represent the foundational mainstays of Parkinson's therapy.

Crucially, the clinical data demonstrates that levodopa-induced dyskinesias are substantially more prevalent and emerge much faster in the young onset population. If a patient is under the age of 40 at onset, after approximately five years of living with the disease and taking levodopa, almost 100% of them will develop motor dyskinesias. In sharp contrast, if a patient experiences disease onset above the age of 70, only about 30% will develop these involuntary movements after five years of levodopa therapy.

Because younger individuals face this heightened susceptibility to dyskinesias, there is a massive, ongoing debate globally regarding prescribing philosophies: should we initiate treatment immediately with levodopa in young onset patients, or should we preferentially start with a dopamine agonist to delay dyskinesia onset? Currently in the Netherlands, and across many international centers, our standard protocol is to start with levodopa, but we maintain a strict low-dose framework, titrating the medication very slowly. Then, after a few years of controlled management, we will strategically combine it with a dopamine agonist. Managing this therapeutic window carefully is the primary focus of treating young onset PD in its early stages.

Dan Keller 8:48 What does the clinical literature indicate in terms of the rate of progression? Is the speed of disease progression faster or slower for younger patients?

Dr. Bart Post 8:55 When I counsel young onset individuals in my clinic—which I do every single day—I often discuss what I call the "paradox of young onset Parkinson's disease." When you are diagnosed at a young age, your biological rate of disease progression is significantly slower than when the disease is acquired at an older age.

For instance, if you are diagnosed at age 35, there is a considerable, highly realistic probability that you will live an active life with the disease for 20, 30, or even more years. If an individual is diagnosed at age 60 or 65, the timeline before encountering advanced complications is compressed. In older onset populations, the average progression timeline toward severe challenges—such as cognitive decline, dementia, or frequent falls—is around 15 years, with the individual eventually succumbing to a secondary complication.

Therefore, the paradox of young onset PD means that while your rate of neurological progression is much slower and your cognitive architecture remains preserved far longer, you ultimately have to live with the physical realities and impairments of the disease for a much longer span of your total life. That is what the long-term data clearly shows.

Dan Keller 9:45 How do younger onset individuals respond to regular physical exercise? Is it as heavily emphasized and recommended for them as it is for the later onset population?

Dr. Bart Post 9:57 Yes, we advocate for and recommend exercise aggressively to all of our patients. We recently conducted a rigorous, large-scale clinical trial in the Netherlands evaluating the therapeutic effects of aerobic exercise compared directly against a control group performing stretching exercises. When analyzing the data cohort, we did not observe any statistically significant differences in the positive outcomes between younger and older individuals. The neuroprotective and symptomatic benefits of exercise were universal. Therefore, when I counsel patients, my guidance is identical: structured, vigorous exercise is mandatory for everyone. There is absolutely no divergence between young onset and late onset populations regarding the power of physical activity.

Dan Keller 10:26 Tremendous insights, Bart. I highly appreciate your perspective. In our next episode, we will pick up this conversation to discuss some of the unique emotional challenges, career impacts, and specialized counseling needs facing the YOPD community. Thank you for being with us today.

The Parkinson's Foundation website features a wide array of evidence-based articles, toolkits, and specialized resources tailored directly for the young onset PD community. A fantastic foundational starting point is our dedicated resource hub, which you can access directly by visiting parkinson.org/yopd. If you utilize our search tool, you will also find a comprehensive guide titled Navigating the Challenges of Young Onset Parkinson's. Among other critical factors, this guide highlights the vital importance of building an expert, interdisciplinary healthcare team early on to pull in specialized practitioners who can actively work to slow clinical progression and mitigate motor symptoms. While a team-based approach is important for all individuals living with PD, it is uniquely vital for those with young onset disease.

Younger brains naturally possess a greater degree of neuroplasticity—the structural ability of the nervous system to grow, adapt, and rewrite neural patterns in direct response to targeted therapies and exercise. Because individuals diagnosed with YOPD have many decades of life ahead of them, establishing an optimized, expert care plan early in the disease course can yield profound cumulative benefits across their entire lifespan.

Additionally, our online portal features direct links to detailed clinical breakdowns regarding the management of levodopa-induced dyskinesias and focal dystonia. You can also explore our widely read publication, 10 Helpful Young Onset Parkinson's Resources, which features links to targeted vocational, financial, and family-planning toolkits. For an even broader selection of educational materials, you can browse our digital library at parkinson.org/library, which features a convenient drop-down topic menu that includes a dedicated section for YOPD publications.

As always, if you need immediate, personalized guidance, our toll-free Parkinson's Foundation Helpline is available to assist you. Our bilingual information specialists are fully equipped to answer your questions in either English or Spanish regarding genetic testing, clinical trials, symptom management, or any other facet of Parkinson's care. You can reach them directly at 1-800-4PD-INFO. To ensure you never miss upcoming educational webinars, research updates, or community events, please take a moment to subscribe to our email registry located at the bottom of our homepage.

If you would like to submit feedback regarding this episode or suggest specific topics for future podcasts, please visit parkinson.org/feedback. If you find our podcast series valuable, please take a moment to subscribe, rate, and review Substantial Matters on Apple Podcasts or your preferred streaming platform.

At the Parkinson's Foundation, our core mission is to ensure that every individual diagnosed with Parkinson's has the clinical backing, community, and resources necessary to live their best possible life today. To fulfill that promise, we will return with a brand-new episode in this podcast series every two weeks. Until next time, for comprehensive information and expert-vetted resources, please visit parkinson.org or call our helpline at 1-800-4PD-INFO, which is 1-800-473-4636. Thank you for listening.

Bart Post, MD was born on March 30, 1972 in Grootebroek, the Netherlands. He obtained his medical degree in 1999 at the University of Maastricht (with honors). In 2000, he started his training as a resident in Neurology at the Academic Medical Centre in Amsterdam, which he completed in December 2008. In 2002, he started a research project on ‘Prognosis in Parkinson’s disease’ that resulted in a PhD thesis in 2009. In 2006, he started a master of Sciences (MSc) education in clinical epidemiology at the EMGO institute in Amsterdam.

In 2009, Dr. Post was certified as a clinical epidemiologist. Since 2010, he has been working as a movement disorder neurologist in the Parkinson Centre in the Radboudumc in Nijmegen (head: prof. dr. B. Bloem). He is part of the steering committee of several large Parkinson trials: the LEAP-trial (Early administration of levodopa in de novo PD); and the CHEVAL-trial (administration of acetylcholine inhibitors in PD patients with hallucinations) and the Fair-Park trial (Iron chelation in early Parkinson’s Disease).

Within the Movement Disorders he is a member of the Multiple System Atrophy (MSA) Study Group. Dr. Post has organized several masterclasses on parkinsonism and movement disorders in the Netherlands. He is a member of the examinations committee of the Dutch neurology Society. He is also a member of two Dutch guideline committees: 1. guideline diagnosis and management of Parkinson’s disease 2. guideline diagnosis and management atypical parkinsonism. In 2018 he was a visiting member of the movement disorders group of Victor Fung in Sydney, Australia.

At the department of neurology of the Radboudumc, he is chair of the residency program for neurologists and, in the Radboudumc, he is co-chair of the central committee for residency programs. Dr. Post is co-director of the Parkinson Foundation Center of Excellence Radboudumc, Nijmegen, the Netherlands. He has a special interest in patients living with Parkinson’s disease at a young age and is heading a program of co-creating care for this patient group.