CFS/ME can be hard to diagnose
Geneticists have identified a biological basis for seven different subtypes of chronic fatigue syndrome.
The researchers from St George's Hospital, University of London, hope the work could lead to a blood test to distinguish between the forms.
Campaigners hope it will help counter the opinion, which remains in some quarters of the medical profession, that it is a psychological condition.
The research findings are to be presented to a conference in Cambridge.
Chronic fatigue syndrome (CFS), also known as ME, is a condition with a diverse range of symptoms but particularly characterised by profound muscle fatigue after physical exertion.
In its most extreme form, CFS/ME leaves sufferers bed-ridden. There is currently no diagnostic test or cure.
It affects around one in 200 people.
The St George's study looked at 55 patients from the US and UK with the condition, and carried out a genetic analysis of them and 75 healthy blood donors.
It identified the seven distinct subtypes of CFS/ME identified by a specific genetic pattern.
These were linked to specific symptoms.
Type one had the worst anxiety and depression levels, along with poor sleep and high pain levels.
Type two was characterised by significant post-exercise fatigue and joint and muscle pains, while type three was the mildest form of the disease.
The research identified type four as linked to moderate levels of body pain and sleep problems, with type five having stomach complaints and the most marked muscle weakness.
Type six was specifically connected to fatigue, and type seven had the most severe symptoms including pain, swollen glands and headaches.
Type four and type six were the most common forms of the condition.
Dr Jonathan Kerr, who led the St George's research, said: "We must now determine what these sub-types represent, as they appear to be biologically meaningful, and discover their natural history and possibilities for treatment."
Neil Abbot, of ME Research UK, which is organising the conference along with the Irish ME Trust, said: "The discovery of a 'thumb-print' for the illness would be the single greatest advance that could be made because, at the moment, diagnosis is on the basis of a set of vague symptoms association with other illnesses.
"It's a hard illness to get a handle on, so a clinical test would be the single best way forward for everyone."