What common environmental exposure might be causing the high incidence of ALS in the Northeast?

A potential culprit is the neurotoxin beta-methylamino-L-alanine (BMAA). BMAA is just one of the neurotoxins produced by cyanobacteria. BMAA has been found in the brains of patients who died from ALS and Alzheimer’s Disease.

The 9 patients from the ALS cluster in Enfield, NH lived an average of 0.15 miles from Lake Mascoma, a lake known to have cyanobacterial blooms. Researchers determined that living less than 5 miles from Lake Mascoma made it 2.3 times more likely that an individual would develop ALS, compared to an individual outside of this 5 mile radius. Residents living on Lake Mascoma revealed that they consume fish and shellfish from the lake, wash dishes and shower with lake water, and, in once case, drink boiled lake water. Thus, potential exposure pathways include the direct drinking of lake water, absorption through the skin, or amplification of BMAA through the aquatic food chain. Caller et al. (2009) found cyanobacteria in samples of Lake Mascoma water; however, the authors failed to detect BMAA. Measurement of cyanobacteria density via phycocyanin detection revealed that cyanobacteria levels were as high as 270,000 cells/ml.

Image from Caller et al. (2009)

The mapping of water quality indicators via satellite remote sensing, as shown below, reveals geographic variation in water quality across the Northeast. Differing levels of total nitrogen, a source for algal growth, and chlorophyll-a, an indicator of cyanobacteria presence, demarcate areas in which the potential for cyanobacterial or algal blooms is high.

Image from Torbick et al. (2015)

In a recent study by Torbick et al. (2015), measures of water quality such as chlorophyll-a and total nitrogen were correlated with ALS risk.  Total nitrogen level and Secchi depth, an indicator of water clarity, predicted ALS risk at a 5% significance level. Additionally, chlorophyll-a predicted ALS risk at a 10% significance level. Below is a map of New England that depicts the risk of belonging to an ALS cluster based one’s geographical location, as determined by water quality data. This is one of the first studies to tie location of residence and water quality to risk of sporadic ALS. Such findings support the hypothesis that ALS is triggered by exposure to cyanobacteria neurotoxins. However, given the novelty of studies relating the geographical distribution of ALS cases to water quality, such findings must be replicated. If future studies further support the cyanobacteria hypothesis, the satellite remote sensing techniques used in this study could be employed for the purpose of producing essential public health information about ALS risk.

Image from Torbick et al. (2015)

References:

1. Caller, T.A., Doolin, J.W., Haney, J.F., Murby, A.J., West, K.G., Farrar, H.E., Ball, A., Harris, B.T., Stommel, E.W. (2009). A cluster of amyotrophic lateral sclerosis in New Hampshire: A possible role for toxic cyanobacteria blooms. Amyotrophic Lateral Sclerosis, sup2: 101-108.
2. Torbick, N., Corbiere, M. (2015). A Multiscale Mapping Assessment of Lake Champlain Cyanobacterial Harmful Algal Blooms. Int J Environ Res Public Health, 12: 11560-11578.