Image copyright dragana991 Image caption Researchers linked an overactive immune system with ME-like symptoms

An overactive immune system may help explain the cause of chronic fatigue syndrome, scientists from King's College London have suggested.

Many sufferers of CFS, or ME, say their condition began with a challenge to their immune system like an infection.

The scientists studied 55 patients with Hepatitis C who were given a drug that causes a similar response to a virus.

Eighteen of those patients had an overactive immune system and went on to develop CFS-like symptoms.

'It is a light in the fog'

Chronic fatigue syndrome is a long-term illness characterised by extreme tiredness.

Scientists from the Institute of Psychiatry, Psychology and Neuroscience at King's College recruited 55 patients who had hepatitis C. A treatment for hepatitis C is the drug interferon-alpha which challenges the immune system in the same way as a powerful infection.

The team measured fatigue and immune markers before, during and after treatment, tracking which people developed the persistent CFS-like illness.

In the 18 patients who developed CFS-like symptoms the team found a much stronger immune response to the medication. Significantly these patients also had an overactive immune system before the treatment started.

Lead researcher Dr Alice Russell from the Institute of Psychiatry, Psychology & Neuroscience (IoPPN) said:

"For the first time, we have shown that people who are prone to develop a CFS-like illness have an overactive immune system, both before and during a challenge to the immune system.

"Our findings suggest that people who have an exaggerated immune response to a trigger may be more at risk of developing CFS."

Senior researcher, Prof Carmine Pariante, added: "This is a light in the fog, a direction of travel. Although screening is a long way off, our results are the first step in identifying those at risk and catching the illness in its crucial early stages."

What is ME?

Myalgic encephalomyelitis or ME is also known as Chronic Fatigue Syndrome (CFS)

The long-term illness affects about 250,000 people in the UK

As well as fatigue, it can cause sleep problems and muscle and joint pain

Living with CFS/ME can be difficult. Extreme tiredness and other physical symptoms can make it hard to carry out everyday activities

There is currently no cure for ME

Source: NHS Choices

Dr Charles Shepherd, the ME Association's medical adviser, said: "This research adds to the growing weight of scientific evidence which indicates that the body's immune system is playing an important role in the causation of ME/CFS."

The study is one of five research projects funded by the Medical Research Council into the causes of ME.

In June, Scottish National Party MP Carol Monaghan led an emotional Westminster Hall debate into a common treatment, graded exercise therapy (Get), which is available on the NHS. She argued it was often damaging and in need of revision.

Others have defended the treatment.

The health watchdog, NICE, is currently updating its guidelines for treatment of CFS in England, but publication is not due until 2020.