Parkinson’s disease (PD) is a neurodegenerative disease that currently affects approximately 1 million Americans across ages, sexes, and ethnic backgrounds. Risk factors for PD include environmental factors and hereditary or genetic factors, such as ethnicity. Ethnic background influences a person’s risk of developing Parkinson’s, and it may also play a role in determining which PD symptoms a person develops.
In the United States, studies have found that the frequency of PD varies by ethnic background. Multiple studies have looked at data collected over the past three decades and identified hereditary risk factors for PD, including race or ethnicity.
When discussing how much of the population is affected by a disease, the terms “prevalence” and “incidence” are used. The two terms are easy to confuse, but the important thing to understand about them is that they both describe how common a disease is.
Prevalence describes how many people have a disease, while incidence describes how many new cases of a disease are diagnosed. Both terms are used to describe the frequency of a disease in a certain population in a particular time frame. For PD, incidence is used to better understand how factors such as race influence the development of PD.
A 2003 study in northern California found that Hispanic people had the highest incidence of Parkinson’s, followed by non-Hispanic white, Asian, and Black populations. A 2009 study in Pennsylvania found statistically significant differences between Parkinson’s incidence in different ethnic groups. In this study, white and Latino populations had about twice as many new cases of Parkinson’s compared to the African American population.
Both of these studies have significant limitations. Each was limited to small populations in specific geographic areas, making it difficult to generalize their findings to the U.S. population as a whole.
However, in 2010, a nationwide study in the United States found similar evidence showing that both the incidence and prevalence of Parkinson’s was significantly higher in white and Hispanic populations compared to the Black population. This study included more than 450,000 people with Parkinson’s per year over seven years. Although this study looked at a large number of Parkinson’s cases, participants were limited to Medicare beneficiaries aged 65 and older. The study did not provide data on how ethnicity affects the risk of developing PD in people younger than 65.
Ethnicity may also affect the likelihood of developing specific symptoms of Parkinson’s. An analysis of data from multiple studies has found that some symptoms of PD are more common in certain countries and ethnic groups. Symptoms of PD varied in research from different countries as well.
For instance, people with PD in East Asia tended to be more likely to have nausea, vomiting, constipation, and difficulty swallowing. Excessive daytime sleepiness has been reported much more frequently in studies from North America and Europe compared to studies in Asia.
In another study, people of Afro-Caribbean and Indian backgrounds living in the United Kingdom were found to have an increased risk of atypical Parkinson’s marked by bradykinesia (slow movement) and early dementia. This same population did not respond as well as other groups to medications such as levodopa.
In the United States, research has found higher rates of Parkinson’s dementia in African American and Hispanic populations.
Comorbidities of Parkinson’s (conditions that occur along with PD) can also have ethnic variation. In studies from Peru, Mexico, China, and Korea, most people with PD (more than 60 percent) also had depression, while studies in the UK and the United States showed lower rates of depression.
One way to explain the differences seen in PD symptoms between ethnicities is by genetic differences among these groups. Certain genes have been identified that are linked to PD. Several specific mutations (variations in DNA) in these genes tend to be more common in certain ethnic and geographic groups.
For instance, certain mutations of the LRRK2 gene (a PD-related gene) are more common in Asian populations, while other mutations of the same gene are seen more commonly in North African Arab and Ashkenazi Jewish populations. Some of these mutations are also linked to increased occurrence of specific symptoms.
Age, sex, and ethnicity can all influence the risk of developing PD, but how is this information useful? Growing older and being white, Hispanic, or male are all associated with increased risk of Parkinson’s, but these factors are not ones that you have any control over.
However, research on racial and ethnic differences in PD is helping to shed light on ways to treat PD better in specific populations. Research is also being used to look for inequities in how Parkinson’s is diagnosed and treated in people of different ethnicities and in different parts of the country.
Ultimately, these findings may lead to better care for people with a diagnosis of Parkinson’s. Knowledge can lead to hope. The more we know about a disease, the better we can treat it.
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