Ethnicity and Parkinson’s: what we know so far

Written by Annie Amjad and Gillian Granville with input from the Parkinson’s UK Involvement Steering Group.

Much of our understanding of Parkinson’s has come from studies carried out in Europe and the United States. These studies either have mostly white participants or do not differentiate between ethnic groups. This isn’t a problem unique to Parkinson’s. Many studies struggle to recruit representative participants. For example, 112,104 volunteers signed up for COVID-19 vaccine trials in a month. 94% were white.

Even from these studies of Parkinson’s, which do not look at ethnicity, we see huge amounts of variation in people with the condition. Age of onset, symptoms and progression are unique to every person. And it’s likely that our current understanding of Parkinson’s is not the full picture. Could people of different ethnicities have different experiences of the condition? We haven’t studied a broad enough population of people with Parkinson’s to know. The research community has a lot of work to do to make studies more appealing and accessible to those from non-White backgrounds.

You can read about some of the initiatives that researchers are making to improve the diversity of research in a previous blog.

2 recent scientific papers review what we currently know about how ethnicity affects Parkinson’s and what differences have been observed. It is clear that the research in this area is limited and more evidence is needed.

Prevalence

Prevalence refers to the total number of people with a condition at a point in time. Our latest estimate is that there are around 145,000 people with Parkinson’s in the UK. We know that the number of people living with Parkinson’s across the world is rising, in part because people are living longer, but we don’t know how many people in the world have the condition.

It’s not currently clear whether ethnicity plays a role in the prevalence of Parkinson’s. Some studies suggest that Parkinson’s is more prevalent in White populations. Whilst it’s possible that environmental factors (such as diet) or genetic factors are partly responsible for this, it can be hard to compare data from different countries because the studies are often carried out in very different ways.

Another important consideration is links with other conditions. For example, a number of studies have shown that people with Type 2 diabetes have an increased risk of developing Parkinson’s. South Asian people are known to be at increased risk of Type 2 diabetes, so this may affect the prevalence of Parkinson’s within this community. Understanding more about the risk factors of Parkinson’s and how ethnicity may be involved is crucial to making sure the correct advice, care and treatment options are available.

Symptoms

Parkinson’s is a complex and varied condition. There are many symptoms and each person may experience them differently. The timing and severity of these symptoms can also vary from person to person. Research suggests that ethnicity may affect which symptoms someone is more likely to experience:

• People from African or Caribbean backgrounds may be more likely to experience slowness of movement (bradykinesia), thinking and memory problems and dementia than other ethnic groups.
• People from Asian backgrounds seem more likely to freeze and experience uncontrolled movements (dyskinesia).

Recognising these differences is important to ensure that people receive a timely diagnosis of Parkinson’s. If certain symptoms are not recognised as being related to Parkinson’s, by people experiencing them and by healthcare professionals, this will lead to a delay in someone’s diagnosis and access to treatment.

Treatment

To get a new drug to market, it has to be safe and effective in clinical trials. However, many clinical trials fail to recruit diverse participants. This means that the results from clinical trials might not apply to everyone.

For example, certain medications may be less effective for people from different ethnicities. It has been reported that levodopa may be less effective for people of African or Caribbean backgrounds, although more evidence is needed to understand why this might be the case. As we move towards personalised treatments, it’s important that we have data to support everyone to access the best medication for them, regardless of their ethnicity. Moving forward, it’s essential that clinical studies are representative of the populations they seek to serve.

Genetic variations

We all share the same basic blueprint for life. All human beings are 99.9% identical in their genetic makeup. But there are subtle variations in our genes that make us individuals. Whilst most of these variations are harmless, sometimes a gene has a difference that means the protein it produces does not work as well as it should. If this protein plays an important role in keeping cells healthy then it may result in someone being at higher risk of developing certain health conditions.

Researchers are still piecing together the genetic and environmental causes of Parkinson’s, but research has already identified small changes in certain genes that may increase someone’s risk of developing Parkinson’s. Although these changes are rare, research is underway to develop treatments that could specifically target the problems associated with these small genetic changes.

Does ethnicity play a role in the likelihood of someone having these specific genetic changes?

More research is needed to properly answer this question, but there have been some large genetic studies that have looked to identify specific genetic variations related to Parkinson’s in people of European and Asian ethnicities. The research highlighted some genetic similarities and differences between these populations. For example, European and Asian populations both had similar variations in the LRRK2 gene. Changes in this gene are the most common genetic cause of Parkinson’s. One observed difference was that Asian populations did not have the variations in the MAPT gene that are seen in European populations. The MAPT gene codes for the production of the tau protein, which has been found in higher levels in people with Parkinson’s and Alzheimer’s.

However, these large genetic studies have not been carried out in populations of people from African, South American, South Asian or Middle Eastern backgrounds. We need to conduct these studies so we can better understand the role of genetic variations in people with Parkinson’s from a range of ethnicities.

Healthcare inequalities

Racial bias is systemic in the UK and our health services are no exception to this. People’s experience of Parkinson’s will be affected by wider inequalities in healthcare.

So far, the only studies comparing healthcare inequalities in Parkinson’s have been conducted in the USA. These studies found that people with Parkinson’s from minority ethnic backgrounds were less likely to receive a timely diagnosis or get specialist care from a neurologist. Several studies have also shown that Black people with Parkinson’s have a higher mortality rate. 

Although the USA may have greater healthcare inequalities than the UK, in part because of a lack of a national health service, we know that health inequalities exist in the UK as well. People from ethnic minority backgrounds are more likely to work in low-paid roles, live in crowded housing and experience poverty in the UK. It’s important to acknowledge the negative impact that poverty has on health outcomes.

Read more about healthcare inequalities on the Charity So White website.

It’s clear that a lot more research is needed to understand the role that ethnicity plays in Parkinson’s. Clinical trials need to be more ethnically diverse, which relies on the research community making studies more accessible to people from different backgrounds. 

In the future, Parkinson’s UK will be asking researchers to report on the characteristics of the participants they recruit to take part in their studies. It is vital that we design research studies that are relevant, interesting and accessible to those currently underrepresented in clinical studies: a crucial part of this is working with people from these backgrounds to design the studies in the first place. We are determined to make research work for everyone affected by Parkinson’s.