The exact cause has not yet been found, but elite athletes appear disproportionately affected by MND.
Two studies from 2005 and 2009 showed professional footballers have an increased risk of developing MND.
A 2022 study by the University of Glasgow involving 400 former Scotland rugby union players concluded they had an increased risk of developing the condition.
Researchers at Durham University also found rugby players who have suffered multiple concussions have biological differences that may make them more prone to developing MND.
The MND Association acknowledges there is a “correlation” between contact sports and MND. It added that while the athletes studied were more likely to develop MND, it did not show the sports directly caused the condition.
The charity also emphasises that “reported MND cases in these studies is still relatively low, and so concluding there is a definite increased risk could be misinterpreted if this is simply a cluster due to random chance”.
Moody had a distinguished rugby union career – playing an integral role at flanker and coming off the bench to help England win the 2003 World Cup in Australia.
He started for England in the 2007 World Cup final defeat before going on to captain the team at the 2011 tournament.
His diagnosis is the latest in the sport after former Scotland rugby union international Doddie Weir and ex-England rugby league star Rob Burrow.
Moody’s Leicester Tigers team-mate Ed Slater was diagnosed with MND in 2022, aged 33, following six months of testing.
Former Liverpool and Bradford City defender Stephen Darby was also diagnosed with the condition aged just 29.
David ‘Syd’ Lawrence – who was the first British-born black cricketer to represent England – died in 2025 just a year after receiving his diagnosis.
In the United States, baseball player Lou Gehrig died from the condition aged 39.
This article is the latest from BBC Sport’s Ask Me Anything team.
A version of this article was first published by BBC News in June 2024.