CFS is a complex and debilitating disorder and is often so hard to diagnose that some experts have questioned if it is in fact a real illness.

The researchers identified certain common genetic traits or gene profiles in people suffering from chronic fatigue syndrome (CFS) and their findings suggest that there is a genetic basis for the disorder.

People with the condition experience profound fatigue and no amount of sleep, bed rest or relaxation appears to help but physical or mental activity often make the patient feel worse.

CFS is also known as ME (myalgic encephalomyelitis) and becomes apparent when a significant loss of the ability to function as normal is noticed.

CFS patients commonly suffer from the condition for years.

According to senior researcher, Dr. William Reeves, they have discovered the first credible evidence of a biological basis for CFS.

Dr. Reeves says the genetic make-up of the body is related to the ability to adapt to the challenges and stresses that happen in life such as infections, trauma and adverse events.

In the study, the CFS Computational Challenge, or C3, 227 patients, all with CFS, were evaluated over a two day period, their blood and urine samples were tested and in total 20,000 genes were examined.

The CDC says in order that the correct diagnosis is made it is important that doctors eliminate any other known illness many which are often treatable, can make a patient feel chronic fatigue, such as alcohol or substance abuse, autoimmune disease, bipolar affective disorders, cancer, chronic mononucleosis, eating disorders, hormonal disorders, hypothyroidism, major depressive disorders, multiple chemical sensitivities, myalgic encephalomyelitis, neurasthenia, obesity, reactions to prescription drugs, schizophrenia, sleep apnea and narcolepsy, subacute infections and fibromyalgia syndrome.

The CDC advises that a patient must satisfy two of the criteria to receive a diagnosis of CFS:

Six months or more of chronic fatigue, which is not connected to any other known medical condition. Have four or more of the following symptoms at the same time: substantial impairment in short-term memory or concentration, sore throat, tender lymph nodes, muscle pain, multi-joint pain without swelling or redness, headaches of a new type, pattern or severity, unrefreshing sleep or post-exertional malaise which lasts over 24 hours when a person feels unwell for longer than 24 hours after exertion

The patient must have had these symptoms (four of them at the same time) for six consecutive months (or recurring very often).

The researchers believe the development may lead to improved diagnosis and treatment of CFS.

The study is published as a series of 14 articles in the April issue of Pharmacogenomics.