“Gender differences are known to play a large role in different medical conditions. For example, it is generally agreed that men have a higher risk of developing Parkinson’s and they are usually diagnosed at a slightly earlier age than females. Underlying these differences may be differences in biology that could impact on whether particular treatments work for one gender and not the other. By underrepresenting one sex in clinical research we may be missing out on critical information. And this equally applies to other characteristics beyond gender (such as ethnicity). The more we know about Parkinson’s – across the different sexes and backgrounds – the more accurately we will be able to target future therapies.”

It is increasingly recognized that women have been and are underrepresented in clinical trials, cardiology trials being a prime example. Given that gender can lead to important differences in how disease occurs and hence can determine different diagnostic and/or therapeutic strategies, gender gaps in clinical research are problematic more generally. How does Parkinson’s research fare in this respect? What are the proportions of men and women with Parkinson’s who participate in clinical trials?

The researchers drew data from trials conducted over a period of 6 years beginning in 2010. Only large studies, recruiting at least 50 male and female participants were considered, while trials investigating secondary or drug induced parkinsonism were excluded. In the resulting 122 trials, which in total recruited some 32,607 people with Parkinson’s, men were consistently overrepresented: 56% of all major trials recruited more than 59% men. The gender gap tended to be more pronounced in North American compared with European trials, while the largest gender gap emerged in neurosurgical trials. The prevalence estimates of men with Parkinson’s has been estimated at 53%, although prevalence itself underestimates true lifetime risk – given that women tend to live longer, they have a longer lifecourse over which Parkinson’s could develop. There is also some indication that fewer women present to specialized clinics where trial participants are usually recruited, and in the authors’ center, male patients make up 70% of referrals. However, the reasons for this are unclear.

Future clinical studies must make efforts to include more women, and trial data to date may have to be interpreted with some caution when extrapolating to women.

Haaxma, C. A., Bloem, B. R., Borm, G. F., Oyen, W. J., Leenders, K. L., Eshuis, S., . . . Horstink, M. W. (2007). Gender differences in Parkinson’s disease. J Neurol Neurosurg Psychiatry, 78(8), 819-824: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2117736/