A rigorous study in Italy has confirmed claims that professional soccer players have a higher than normal risk of developing a type of motor neuron disease, also known as amyotrophic lateral sclerosis. The reason remains a mystery. ALS involves the death of motor neurons, the nerve cells responsible for voluntary movement, and eventually leads to paralysis and death. Adriano Chiò’s team at the University of Turin surveyed the medical records of 7000 professional footballers who played in Italy’s first or second division between 1970 and 2001.
Based on the normal incidence of the disease and the players’ ages, the researchers calculated that there should have been 0.8 cases of ALS in this group. Instead, there were five. The study was prompted by what the Italian press dubbed “the motor neuron mystery” – the discovery a few years ago of 33 cases of ALS during an investigation of illicit drug use among 24,000 pro and semi-pro players in Italy. Dubious about the methodology of that initial investigation, Chiò’s group applied stricter diagnostic criteria to their data, such as only including players born in Italy. “I think the researchers have been conservative,” says Ammar Al-Chalabi of the Institute of Psychiatry in London, who has written a commentary on the study in Brain.
The researchers found that the mean age of onset was just 41. “They develop it about 20 years earlier than usual,” says Chiò. He also found that the longer people play football the greater the risk. In the US, ALS is known as Lou Gehrig’s disease after the baseball legend diagnosed with it in 1939. Clusters of cases have been reported in American football, but until now no large-scale studies have found any clear link between sport and ALS. The cause of ALS remains unknown, as does the reason for the higher rate among footballers. Genes undoubtedly contribute, but the disease could be triggered by head trauma, performance-enhancing drugs or some other toxin to which footballers are exposed. Certain viruses are also being investigated as potential causes.
Although the disease is certainly not limited to sportspeople, Al-Chalabi says it could also be that people prone to ALS are drawn to sport. “There could be some quality in their neuromuscular make-up that not only makes them good at sport, football particularly, but also makes them susceptible to ALS.”
Journal reference: Brain (vol 128, p 472)
March 15, 2005
Original web page at New Scientist