Mushrooms can really mess with your head.

And not just in a, like, “woah, I can hear colors” way. It turns out, certain mushrooms — and  I am not talking about the magical   kind — can give you something  even gnarlier than a bad trip.

A recent study from the French Alps suggests that   eating the wrong fungi can trigger  the neurodegenerative disease... ALS. Which is scary.

Some people think of ALS as a genetic disease,   so the idea that your lunch could  be involved is unwelcome news. Even scarier? It’s not the only part of the  world where a large group of   ALS patients has emerged due to the local diet.

Fortunately, scientists are on the case. And they’re beginning to understand what foods  are behind these mysterious ALS clusters. [♪ INTRO] The first step in untangling what might cause ALS is understanding what the  disease is in the first place. ALS, or Amyotrophic Lateral Sclerosis,  is a neurological disorder where patients   gradually lose control of their muscles due  to the degeneration of the motor neurons.

As the condition progresses, patients  often struggle to speak, eat, and move. Even if this is all sounding familiar from your  participation in the 2014 Ice Bucket Challenge,   ALS is a complicated disease, and scientists  aren’t totally sure what’s going on with it. There are at least 25 different genetic risk  factors that increase a person’s chance of   developing ALS, including mutations in two genes  that code for proteins found in motor neurons.

But genetics can only explain  about 10% of all ALS cases. Most cases are “sporadic,” which means they appear  without any known family history or genetic cause. So there must be something else going on.

We obviously know that genes aren’t the  only thing that impacts people’s health. Environmental factors play an important role, too. For example, respiratory diseases are more  common in places with lots of air pollution,   and eating 10-day-old potato  salad can make you very sick.

One of the clues that a disease has an  environmental cause is the existence of   a geographic cluster: a specific place  where the disease is much more common. And while ALS is a rare disease overall,  there are places where it is tens,   hundreds, or even a thousand times  more common than it should be. The most famous ALS cluster  occurred in Guam about 70 years ago.

It appeared and disappeared within 3 decades. Now, Guam’s Indigenous Chamoru  people were familiar with ALS,   or at least an ALS-like  disease, for hundreds of years. But the number of cases  skyrocketed after World War II.

In 1954, ALS was an estimated 25 times more  common in Guam than the rest of the world. Globally, there are about 2 new cases of  the disease per 100,000 people per year. Guam had 50 new cases per 100,000 people.

So what changed to cause this cluster? The 1940s, 50s, and 60s were a tough time  for Guam due to the Japanese occupation,   wartime disruption of shipping routes, and  large scale shifts in the island’s economy. The islanders often didn’t have enough to eat,   and many relied more heavily on local  food sources to fill their bellies.

One in particular that became more  popular was a plant called fadang. Fadang is a traditional food  source for the people of Guam,   but consumption skyrocketed during this period. As it turns out, the plant’s seeds,  which can be ground into flour,   contain large amounts of cycasin, a neurotoxin.

Cycasin breaks down into a chemical  called methylazoxymethanol, or MAM. And MAM alone damages DNA and  interferes with the normal cell cycle. To make matters even worse, MAM  breaks down into formaldehyde,   which you may know from jars of creepy  preserved animals in biology class.

Formaldehyde also damages DNA, and  is already directly linked to ALS. So while it’s impossible to say with 100%  certainty, it’s pretty widely accepted that   this increased consumption of fandang  was responsible for Guam’s ALS cluster. The good news is this cluster didn’t last forever.

By the 1980s, the trend started to  reverse as the economic situation   in Guam improved and reliable food imports  allowed islanders to diversify their diet. Today, ALS has all but  disappeared from the territory:   no one born after the 1960s  has developed the disease. And armed with the knowledge of  the link between ALS and fadang,   we can be fairly confident that this particular  cluster has been eliminated once and for all.

But Guam isn’t the only region to  experience increased rates of ALS. A more recent ALS cluster occurred thousands  of miles away and decades later in a small   hamlet called Montchavin,  nestled in the French Alps. In 2009, after diagnosing a third case of  ALS in the small town of only 200 people,   a local doctor called in a team of  researchers to figure out what was going on.

Going door to door, they discovered  that there weren’t just 3 people   with ALS in Montchavin and the surrounding area,   but 14, which is equivalent to an astronomical  incidence of 7,000 cases per 100,000 people. Using a combination of interviews, genetic  tests, and environmental screening,   the team ruled out genetic factors, as  well as obvious contaminants like heavy   metals from the abandoned mines nearby or the  “snow inducer” chemical used by the ski resort. And fadang obviously couldn’t be  the culprit again – the tropical   plant wouldn’t last a minute in the Alps.

But there was a different dietary quirk  that linked all the local ALS patients:   their taste for raw wild mushrooms. Foraging mushrooms can be risky if  you aren’t 100% sure what you’ve got. One species to watch for in the  French Alps is the toxic False Morel,   which is easily mistaken for the tasty true morel.

Among other things, false morels that  haven’t been cooked contain hydrazones,   which break down into DNA-damaging  compounds like MMH and MFH. And guess what MMH and MFH break down into? Formaldehyde.

So based on this French study,  false morels and fadang seem to   have very similar long term health  effects – including triggering ALS. Different dish, same devastating  impact on your nervous system. These stories emphasize how much more  there is to ALS besides genetics.

To understand it, we have to look  beyond the obvious to observe   cultural and environmental patterns  that can explain what DNA can’t. And while you don’t have to worry  about those mushrooms on your pizza,   you probably should think twice about heading  out to the Alps on that foraging mission. And at the very least, make sure  to cook them all the way through. [♪ OUTRO]