Is exposure to cyanobacteria an environmental risk factor for amyotrophic lateral sclerosis and other neurodegenerative diseases?

Abstract

There is a broad scientific consensus that amyotrophic lateral sclerosis (ALS) is caused by gene-environment interactions. Mutations in genes underlying familial ALS (fALS) have been discovered in only 5–10% of the total population of ALS patients. Relatively little attention has been paid to environmental and lifestyle factors that may trigger the cascade of motor neuron death leading to the syndrome of ALS, although exposure to chemicals including lead and pesticides, and to agricultural environments, smoking, certain sports, and trauma have all been identified with an increased risk of ALS. There is a need for research to quantify the relative roles of each of the identified risk factors for ALS.

Recent evidence has strengthened the theory that chronic environmental exposure to the neurotoxic amino acid β-N-methylamino-L-alanine (BMAA) produced by cyanobacteria may be an environmental risk factor for ALS. Here we describe methods that may be used to assess exposure to cyanobacteria, and hence potentially to BMAA, namely an epidemiologic questionnaire and direct and indirect methods for estimating the cyanobacterial load in ecosystems. Rigorous epidemiologic studies could determine the risks associated with exposure to cyanobacteria, and if combined with genetic analysis of ALS cases and controls could reveal etiologically important gene-environment interactions in genetically vulnerable individuals.

Key words::

• Amyotrophic lateral sclerosis
• BMAA
• cyanobacteria
• epidemiology
• environmental toxicants

Acknowledgements

We thank all the members of the CAUSE-ALS consortium for their contributions to the background work in this review. The members (listed alphabetically) are: Lorraine Backer, Michael Benatar, Amy Borenstein, Kevin Boylan, Walter Bradley, Larry Brand, Jonathan Chipman, Geoffrey Codd, Paul Cox, Andy Dent, Lora Fleming, Stephanie Foster, Jeffrey Henry, Edward Kasarskis, Deborah Mash, Lorene Nelson, Evadnie Rampersaud , Barry Rosen, Clive Sabel, Bill Scott, Christopher Smith, Elijah Stommel, Tuan Vu, Ashok Verma. This work was supported by a grant from the ALS Recovery Fund.

Disclosure of interests: The authors report no conflict of interest. The authors alone are responsible for the content and writing of this paper. The findings and conclusions in this article are those of the authors and do not necessarily represent the views of the U.S. Geological Survey.