Blue-green algal blooms in rivers and lakes release multiple toxins. For decades exposure to one of these toxins has been linked to Amyotrophic lateral sclerosis (ALS), often known as motor neuron disease (MND). A direct causal relation remains under debate. Instead, it is probably just one of many factors that increase risk for the disease. This consensus is based on 9 experts answers from this question: Does blue-green algae cause Motor Neuron Disease?
Algal outbreaks are on the rise, likely due to climate change and contamination of water bodies. From Australia to Spain, explosive growth of blue-green algae in rivers, lakes or shallow seas turns water green and consumes its oxygen, leading to mass death of fish and other animals. These events can be devastating not only for wildlife but also for the wider ecosystem and people, as they render water toxic.
Blue-green algae or cyanobacteria can release a plethora of substances, many of which are toxic to humans writes microbiology expert Dr James Metcalf. Some of these irritate skin and eyes and lead to liver and gastrointestinal damage, notes Dr Walter Bradley, from the University of Miami. And there is one, known as BMAA, that has been linked to Amyotrophic lateral sclerosis (ALS), sometimes known as Motor neuron disease (MND). While there is still much debate on such link, our experts suggest that BMAA may not normally cause ALS on its own in humans, but it is a risk factor and merits further research.
Seeds, bats and indigenous communities
MND is characterised by the degeneration and death of motor neurons, which impairs muscle movements and normally results in muscle weakness, cramps and spasms. It is a rare disease, with less than a 1 in 300 risk to develop it during one’s lifetime. In small indigenous communities in the Pacific, however, it turned out to be far more common.
Amongst the indigenous people of Guam and other Mariana islands, incidence of MND was found to be up to 50 times higher. No genetic factor was found to explain such a striking phenomenon, and so the search turned to environmental factors. Seeds from cycad trees were found to be one of their staple foods, writes Neurotoxicity expert Dr Rachael Dunlop from Macquarie University. Fruit bats also fed on these seeds. The key puzzle piece missing was found below ground. There, blue-green algae were growing among the roots of cycad trees, Dunlop explains. BMAA from algae was being passed on to the plant and its seeds, it turned out, and getting to the people directly through the seeds or indirectly via the bats. Indeed, she says, the toxin was detected in both seeds and bats.
Interestingly, the toxin becomes more concentrated higher up in the food chain, as seeds are eaten by bats and bats are consumed by humans. This process is known as biomagnification and also explains why BMAA has been detected in top predators such as dolphins.
You would think that the risk would disappear by just avoiding eating the toxin. However, Bradley explains that algal toxins can form aerosols and thus get into the lungs. In fact, Dunlop says, epidemiological studies show that people living besides contaminated lakes are as much as 25 times more likely to get MND.
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🦠What are blue-green algae and what toxins do they release? ⚛Can BMAA from blue-green algae be found in seeds of cycad trees ☠Have studies conclusively proven that BMAA alone causes ALS in humans? 🐟What is biomagnification and how does it relate to BMAA in the food chain?Does BMAA really cause disease?
Correlation doesn’t imply causation, and the link between BMAA and MND doesn’t necessarily mean that one causes the other. In the 80s, however, a report showed that feeding monkeys with BMAA led to parkinsonian features. More recently, Dunlop explains, another study found that it led to tangles building up in their brains, similarly to what happens in human patients. However, more recent rodent studies trying to see whether injection of BMAA leads to MND-like symptoms have been inconclusive, with some describing neurological damage and others reporting lack of adverse effects. Whether or not a small dose of BMAA can cause neurodegeneration in the long run may depend on when exposure happens, argues Tim Downing, a toxicology expert from Mandela University.
MND is a syndrome where different forms of the disease exist, and so do different genetic and environmental causes writes Dr Paul Cox, neuroscience expert from Brain Chemistry Labs. While a number of gene mutations have been linked to MND, in over 9 in 10 patients the cause of the disease is unknown. There is evidence to suggest that BMAA can be an environmental risk factor for MND, but several of these are typically required to coincide before the disease develops, Cox says.
Experts also point out that, on its own, exposure to cyanobacteria won’t cause MND. ‘Otherwise we’d all have MND since blooms are so common’, says Dunlop.
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🧪How is BMAA linked to Amyotrophic Lateral Sclerosis (ALS)? 🤔Is there conclusive evidence that BMAA alone causes ALS in humans? 🚨Are people living near contaminated lakes at a higher risk of developing ALS?A wolf in sheep’s clothing
At least two different mechanisms have been described to explain why BMAA is toxic to neurons, according to Bradley. Both rely on it mimicking the appearance of key brain chemicals. First, BMAA by-products are structurally similar to the neurotransmitter glutamate. Thus, if enough is absorbed by the body, it may over-stimulate neurotransmitter receptors and lead to neuronal death. On the other hand, BMAA also looks similar to the protein-making amino acid serine, so once absorbed it may be mistakenly incorporated into neuronal proteins. As shown by a study led by Dunlop, this renders them aberrant and could kill the neurons. Recent research by Elisabeth Proctor and colleagues has found that replacing serines by BMAA indeed destabilised a MND-linked protein, and suggests that levels of BMAA may be used as a marker to diagnose MND.
In any case, the jury is still out and several of our experts stress that further research is needed before we can say whether algal toxins really cause MND or not. A definitive answer would require knowing more about just how BMAA damages motor neurons – but also working out the dose, exposure period and route required to make it toxic to neurons at all.
Takeaway
Some algal toxins are neurotoxic, but short term exposure is unlikely to lead to neurodegeneration. Still, stay away from contaminated waters and avoid eating local produce which may have absorbed toxins.
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⚙️Why is further research needed to confirm the link between BMAA and ALS? ☣️Is short-term exposure to algal toxins likely to cause neurodegeneration?