Sex differences in risk

The research record

This is the project's file for this landmark, as written and checked. Sources are listed at the end; anything not yet confirmed is marked "Not yet verified".

Who

G. F. Wooten, L. J. Currie, V. E. Bovbjerg, J. K. Lee and J. Patrie, Department of Neurology, University of Virginia.

What happened

Wooten et al. (J Neurol Neurosurg Psychiatry, April 2004) pooled seven population-based incidence studies. Men had a relative risk of about 1.5 compared with women. The authors listed possible reasons: toxicant exposure, head injury, oestrogen's possible protection of neurons, mitochondrial differences and X-linked genes. A 2007 letter by K. S. M. Taylor, J. A. Cook and Carl Counsell (University of Aberdeen) said the analysis left out informative studies, did not test for differences between studies, and quoted some crude rates as age-adjusted. Their own pooling of 17 studies (over 2,500 people with Parkinson's) gave a male-to-female ratio of 1.46 (95% CI 1.24 to 1.72), close to Wooten's 1.49, but with high heterogeneity (I² 85%). Ratios were higher in Western than in Asian studies and in studies with a mean onset age of 70 or older, and heterogeneity stayed high within those groups.

Why it moved us toward a cure

It is a clue about what drives the disease. If oestrogen or an X-linked gene protects women, that is a lead for a protective therapy; if men simply meet more toxins, it points to environmental causes. No hormone or sex-based treatment has been shown to slow Parkinson's, and this file has no parent landmark because it is an origin observation.

Outcome

Open. Two meta-analyses agree on a ratio of about 1.5, but it varies widely between studies. The cause is not known.

Sources

• Wooten et al., JNNP 2004;75(4):637–639, DOI 10.1136/jnnp.2003.020982, PMID 15026515
• Taylor, Cook & Counsell, JNNP 2007;78(8):905–906, DOI 10.1136/jnnp.2006.104695, PMID 17635983
• Not yet verified: the pooling method in Wooten's own paper (beyond the abstract); the 1.49 figure is as quoted by Taylor et al.; any sex differences in progression; oestrogen trials.