Neurodegenerative disorders are highly complex diseases which lead to substantial morbidity and mortality globally. Due to the aging world population, there are approximately 10 million new cases of dementia per year with predictions that approximately 130 million people will be living with the disease by 2050 (13). This results in a large burden within society, both on healthcare and economically. Similar increases in prevalence and burden are seen within Parkinson’s disease (8). The prevalence and risk of neurodegenerative disorders differ globally, and also within groups sharing the same geographical location (13,15). For Alzheimer’s disease and other dementias, the prevalence is suggested to be highest in North America, north Africa and the middle east with lower rates found in sub-Saharan Africa and southern Latin America (7). However, studies within the USA have suggested that minority ethno-racial groups, such as African Americans and Hispanics, may have higher rates of Alzheimer’s disease than whites within their communities (3,22). However, these ethnic groups may have a longer survival time with the disease (16). Additionally, studies have suggested that Parkinson’s disease prevalence is higher for whites in the USA (28). To further understand the disparities in neurodegeneration on a global level, within and between regions and ethnicities, we launched the Uncovering Neurodegenerative Insights Through Ethnic Diversity (UNITED) consortium (1).

Reasons underlying the disparities across regions could be due to multiple reasons relating to genetic and non-genetic factors. Differences in ethnic groups within the same environment lend themselves to possible biological differences such as genetics. For example, carriers of different apolipoprotein E (APOE) allele have been shown to have differential risk profiles for dementia (24). Rates of different APOE variants have also been found to vary across ethnicities, with the suggestion that complex ethnicity-specific haplotypes play a role in Alzheimer disease risk (11,26,10). On the other hand, lifestyle and environmental factors that differ greatly across global regions have been found to impact risk for neurodegenerative disease. This could suggest environmental factors contributing to differential prevalence around the globe. Such modifiable risk factors related to increased dementia risk are education and cardiovascular risk factors. The relationship between education and dementia has also been suggested to vary across ethnicity, however the findings are varied with some studies suggesting that within the USA education is only a risk factors in the white population (6). It is noted that this relationship needs more research globally due to education often representing privilege rather than intelligence (27). Furthermore, cardiovascular risk profiles have been suggested to differ across ethnic groups, and regions world-wide, which could impact dementia risk (2,19,20). This may be one factor contributing to increasing prevalence within developing regions where more westernised lifestyles are being adopted which are often accompanied with more cardiovascular problems. This is supported by rising rates of ailments such as hypertension in developing countries (2,18).

One region where the burden of neurodegenerative diseases is increasing rapidly is within Africa. Currently findings suggest that dementia rates are equal or lower than north American and European populations (21,9,25). However, the results are difficult to interpret due to wide ranges, differing methodologies, lower life expectancy, cultural attitudes and possible underdiagnosis (14,12). With rapid increases in both the number of elderly people in Africa and in the incidence of non-communicable diseases, such as hypertension, dementia rates are also forecasted to increase substantially.

In addition to this, research investigating neurodegenerative diseases in Africa is severely limited. The majority of research published investigating risk factors and pathology are mainly done within Northern America and Europe. Even within these countries research is undertaken in individuals predominantly with a European descent with only 2% of volunteers in Alzheimer’s disease trials being African Americans (5). This is further heightened when looking into neuroimaging research despite neuroimaging biomarkers becoming increasingly important for earlier diagnosis, and disease staging. Similar patterns are also seen within genetics research where a review found that 88% of genome-wide association study participants were of European ancestry, with 72% of discoveries from participants from either the UK, USA or Iceland (23,17). Whilst risk prediction tools developed from this research works fairly well for some diseases in Europeans, unfortunately the same tools do not apply to Africans (4). This is the same regarding neuroimaging research into neurodegeneration where the majority of the knowledge we currently have lacks generalizability.

There is an urgent need to tackle the lack of diversity within neuroimaging of neurodegeneration to produce robust generalizable results. Due to this, the UNITED consortium was set up with the aim of using cutting-edge magnetic resonance imaging (MRI) methods to answer important questions on neurodegenerative diseases (1), such as;

• What does the Alzheimer’s disease brain look like?
• Can you distinguish between different forms of neurodegenerative disorders?
• Does someone’s brain hold information that can predict his or her future risk of disease?

The consortium strives to collaborate with academic and clinical institutions to include individuals all over the world. Through collaboration we aim to undertake more diverse research on neuroimaging in neurodegeneration that will answer these questions and result in more generalizable and applicable knowledge for our diverse global population. UNITED wants to, together with the collaborators, investigate the similarities and differences across- and within- regions, ethnicities and neurodegenerative disorders to gain insights into these diseases. One aim within the consortium is to create publicly available diverse brain maps that will result in a valuable resource for more personalized medicine in clinical environments.

To achieve these aims, collaboration with local researchers and clinicians is key. We welcome groups who have all study designs, including case-control studies, cohort studies and case- or control-only studies. Additionally, the consortium understands the infrastructure, personnel, and time needed to partake in such endeavours and offers support for collaboration where it can be given. Furthermore, the consortium currently also welcomes those without data wishing to contribute through other means such as expertise, a large network to further nurture the UNITED network, to organise events or to work together to set up data acquisition avenues.

Further inclusion of diverse samples within this research field will not only provide more information on neuroimaging profiles of dementia research but also raise awareness of the problem. We hope that a better representation of African researchers and sites will lead to an improved understanding of neurodegenerative diseases in Africa. This knowledge will be essential to tailor diagnosis and clinical care to a patient’s ethnic background. Global information on neurodegenerative diseases combining genetics and environmental differences will be not only beneficial for individuals within Africa but also those who have migrated to other locations across the globe. The UNITED consortium hopes to be a driving force within diverse research into neurodegeneration striving towards a more inclusive future within research and clinical practice.