What does ethnicity have to do with Parkinson's disease?

I have recently started working at the Preventive Neurology Unit (QMUL) on a new project called the East London Parkinson’s Project. It has been exciting to be starting a new project, especially when the subject is so interesting; the way that ethnicity can affect Parkinson’s disease (PD). This is really important to study because up until now most studies of PD have been based on white participants or a single ethnic group that does not allow us to compare any differences between different ethnicities. Unfortunately due to the lack of research in this area we know very little about even some of the most basic information regarding PD and ethnicity.

For example there is not even a consensus as to whether people from different ethnicities have a different chance of developing PD. This is usually one of the first things that we learn about any condition. Previously PD was thought of as more common in white people and some studies have confirmed this, however other studies have found that people of all ethnicities have similar rates of PD. The results seem to vary depending on the way the study was carried out and there is a distinct lack of large scale multi-centre studies to more accurately answer this question.

If we are still struggling to determine something as simple as the rates of PD in different ethnicities then you can imagine how difficult is to work out more complicated relationships between ethnicity and PD. For example a study in Israel looked at differences in PD between Ashkenazi Jews (a distinct group of Jews who have lived throughout Europe since the 7^th/8^th century) and Yemenite Jews (a group of Jews who evolved completely separately to the rest of the Jewish population after arriving in Yemen around the second century). The study showed that Yemenite Jews with PD had more severe symptoms and the PD progressed faster than in Ashkenazi Jews. This is interesting because all the participants live in Israel now so have a relatively similar environment raising the possibility that the differences observed are genetic. Having said that Yemenite and Ashkenazi Jews have different diets and lifestyles to each other and it is possible that this could be having an effect. This is just one study out of hundreds I could have discussed but I think it demonstrates some of the interesting trends we notice between ethnicity and PD but also some of the complications when trying to analyse these differences.

To make any headway with this difficult issue we need more studies that explore this tangled relationship between PD and ethnicity.

J Neural Transm (Vienna). 2008 Sep;115(9):1279-84. doi: 10.1007/s00702-008-0074-z. Epub 2008 Jul 30.

Clinical characteristics of Parkinson's disease among Jewish Ethnic groups in Israel.

Djaldetti R, Hassin-Baer S, Farrer MJ, Vilariño-Güell C, Ross OA, Kolianov V, Yust-Katz S, Treves TA, Barhum Y, Hulihan M, Melamed E.

Yemenite Jews in Israel are a distinctive ethnic division of the Jewish diaspora. Clinical findings, disease course and genetic tests for the LRRK2 6055G > A (G2019S) mutation were compared between Ashkenazi and Yemenite Israeli patients with Parkinson's disease (PD). Age of onset was significantly younger in the Yemenites (P < 0.001). There were no differences in the distribution of initial symptoms, environmental risk factors or rate of motor/non-motor phenomena. The Yemenite group had a more severe disease (P < 0.001), and a more rapid disease course (P = 0.006). The frequency of Lrrk2 substitution was 12.7% in the Ashkenazi group and was not observed in the Yemenites. These results show that there are differences between Israeli Jewish ethnic groups in the severity and progression of PD, but not in clinical symptoms. The high frequency of Lrrk2 G2019S in the Ashkenazi and its absence in the Yemenite Jews suggests a specific ancestral pattern of inheritance in Ashkenazi Jews.