Can DDT exposure increase the risk of dementia? JAMA Neurol. Ahead of print.Jan ,2014

29.01.2014

Alzheimer Disease (AD)  is the commonest neuro degenerative disorder, commonly occurring after 60 years of age. Genetic, environmental, and lifestyle factors  are known to influence the risk for AD. Having an apolipoprotein E4 (APOE4) allele is associated with a relative risk between 2 and 3. Environmental factors ( metals, solvents, pesticides) are considered as potential agents that can increase the risk. An association with DDE (a metabolite of DDT) was earlier reported in a small cohort by Richardson et al from Rutgers Robert Wood Johnson Medical School . The team is now reporting a larger study.

Serum samples from 86 AD and 79 controls were collected from two sites in USA (Texas Uni & Emeroy Uni). Normal and AD patents underwent extensive examinations and investigations to confirm their status as ‘AD’ and ‘normal control’.  Serum DDE levels were determined by gas chromatography/ mass spectrometry.

Results

Dichlorodiphenyldichloroethylene (DDE) was detected in 70% of control and 80% of AD cases .The mean levels were  3.8-fold higher in the serum of AD cases .No other organochlorine pesticides were found to be elevated in AD samples compared with control participants.  MMSE scores were significantly lower if the DDE levels were higher.Those with  both APoE allele  and higher DDE were more cognitively impaired.

The odds of AD diagnosis ( adjusted for age, sex,race/ethnicity and location) was 4.18( 2.54-5.82) for those with higher (i.e. in top tertile of the levels) DDE levels.This OR is as high as that for APOE and the recently reported TREM2. 

Authors also report results of a small neuronal culture study that indicated that DDT  increase the APP levels in neurones, suggesting that DDT might be operating by altering sodium channels. There are few human studies that have explored the potential neurotoxicity of DDT/DDE. A recent study from India found that in addition to DDE, dieldrin and β-hexa chlorocyclo hexane were elevated in serum samples from patients with AD ( Singh et al, 2013).

DDT is banned in USA since 1972 though it continued to export it until 1985. UK banned it in 1984.Many countries still use DDT. WHO supported the reintroduction of DDT  for malaria eradication in 2006.India is the biggest manufacturer of DDT.

 Summary of the article:

JAMA Neurol. doi:10.1001/jamaneurol.2013.6030. Jason R. Richardson et al .Elevated Serum Pesticide Levels and Risk for Alzheimer Disease .Published online January 27, 2014.

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