Not only are women far more likely to suffer from ME, but they're also more likely to have more symptoms, and co-occurring conditions that are more severe, according to early results of the largest-ever study into the disease.
The DecodeME study has so far recruited more than 17,000 people in the UK with a diagnosis of ME or myalgic encephalomyelitis - sometimes called chronic fatigue syndrome.
The researchers aim to study 20,000 DNA samples from this growing group to learn whether ME is partly genetic. Not only could it point to treatments but may also help de-mystify a neglected, and often maligned disease.
"For a long time, people didn't even truly believe that this illness existed," says study lead Professor Chris Ponting, from the University of Edinburgh.
"The fact this study is looking into the biological causes of ME… I think it will go a long way not just to help people find treatment eventually, but also debunk some of the really harmful stigma as well."
It is estimated more than 250,000 people in the UK have ME.
It leaves patients with debilitating and persistent exhaustion that's made worse following normal levels of exertion.
But it also causes a wide range of other symptoms, conditions like brain fog, muscle pain even slurred speech. Many people are left house or bed bound by their illness.
Of the participants involved so far, more than 83% are women.
Women in the study were also significantly more likely to have one or more conditions associated with their ME - such as irritable bowel syndrome, fibromyalgia or anaemia - than men.
Combining these findings with the genetic data they are collecting, the researchers hope to gain insights into why different groups of people are affected by ME, in what ways, and what its potential triggers could be.
Many cases of ME, for example, are preceded by an infection of some kind, a similar phenomenon as seen in people with long COVID.
'A real stigma and mistreatment'
The initial findings, says Prof Ponting, suggest their genetic analysis will have to treat men and women differently.
The gender bias may also point to why ME has been neglected for so long, despite affecting huge numbers of people.
There is good evidence from other diseases that less research and fewer drugs are devoted to those affecting women.
"At the real heart of this is [that there] has been a real stigma and mistreatment of people with ME for years," says Sonya Chowdhury, chief executive of Action for ME.
The charity has coordinated recruitment for the study and hopes that this first large-scale investigation will change thinking about ME.
"Having the basic data and the basic science there means that researchers are more likely to take the illness seriously," says Ms Chowdhury. "We should be shocked there hasn't been investment in research for decades."
Pippa Stacey was first diagnosed with ME at the age of 19 and now writes, blogs and campaigns about her illness.
She filmed herself giving her DNA sample for the DecodeME study and shared it with her 14,500 Instagram followers to encourage others to do the same.
"Knowing work of this magnitude is taking place - that in itself is a huge thing," she says. "I feel a level of hope that there's something to reach for."