Being diagnosed with amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig’s disease, can be devastating.

ALS is the most common form of motor neurone disease, a neurodegenerative condition that affects people’s ability to speak, eat, breathe and swallow. It is debilitating and progresses rapidly: on average, people survive just 2–3 years after a diagnosis. Most people are diagnosed between the ages of 40 and 70.

A new study, published today, has found that being exposed to pesticide at work can increase the risk of developing ALS by 61–71%. The study brings together the findings of eight other studies – but not all of them assess risk in the same way. Here’s why we need to interpret the findings with caution.

What we know about ALS causes

Men are around 20% more likely to develop ALS than women.

The disease occurs sporadically in over 90% of patients, meaning the large majority have no known family history or identified genetic cause. The remaining 10% of cases are familial, meaning the person has a known genetic variant or family history of ALS.

However, it’s not well understood exactly what triggers both the sporadic and familial forms of the disease, although an interaction between genes and environment is likely.

Over the last few decades, researchers have been investigating exposure to pesticides as a possible trigger.

Several studies have found associations between........

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