title: Traumatic brain injury, paraquat exposure, and their relationship to Parkinson disease.
abstract: OBJECTIVE
  Traumatic brain injury (TBI) increased risk of Parkinson disease (PD) in many but not all epidemiologic studies, giving rise to speculations about modifying factors. A recent animal study suggested that the combination of TBI with subthreshold paraquat exposure increases dopaminergic neurodegeneration. The objective of our study was to investigate PD risk due to both TBI and paraquat exposure in humans.
  
  
  METHODS
  From 2001 to 2011, we enrolled 357 incident idiopathic PD cases and 754 population controls in central California. Study participants were asked to report all head injuries with loss of consciousness for >5 minutes. Paraquat exposure was assessed via a validated geographic information system (GIS) based on records of pesticide applications to agricultural crops in California since 1974. This GIS tool assesses ambient pesticide exposure within 500 m of residences and workplaces.
  
  
  RESULTS
  In logistic regression analyses, we observed a 2-fold increase in risk of PD for subjects who reported a TBI (adjusted odds ratio [AOR] 2.00, 95% confidence interval [CI] 1.28-3.14) and a weaker association for paraquat exposures (AOR 1.36, 95% CI 1.02-1.81). However, the risk of developing PD was 3-fold higher (AOR 3.01, 95% CI 1.51-6.01) in study participants with a TBI and exposure to paraquat than those exposed to neither risk factor.
  
  
  CONCLUSIONS
  While TBI and paraquat exposure each increase the risk of PD moderately, exposure to both factors almost tripled PD risk. These environmental factors seem to act together to increase PD risk in a more than additive manner.
authors.affiliation: Department of Epidemiology, Fielding School of Public Health, University of California at Los Angeles, Los Angeles, CA, USA. pel27@ucla.edu
authors.forename: Pei-Chen
authors.initials: PC
authors.lastname: Lee
authors.forename: Yvette
authors.initials: Y
authors.lastname: Bordelon
authors.forename: Jeff
authors.initials: J
authors.lastname: Bronstein
authors.forename: Beate
authors.initials: B
authors.lastname: Ritz
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001930:Brain Injuries / Q000453:epidemiology*; D016022:Case-Control Studies; D016009:Chi-Square Distribution; D004781:Environmental Exposure / Q000009:adverse effects*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010269:Paraquat / Q000009:adverse effects*; D010300:Parkinson Disease / Q000453:epidemiology* / Q000209:etiology*; D010575:Pesticides / Q000009:adverse effects*; D012307:Risk Factors
chemical_list: D010575:Pesticides; D010269:Paraquat