Biological markers of narcolepsy

Aug 2 2007

The first report to identify the biological markers of narcolepsy using gene expression in white blood cells finds that the MX2 gene, which is relevant to the immune system, is significantly less expressed in narcoleptics compared with normal subjects.

This underlies the abnormalities in the blood cells of persons suffering from narcolepsy, according to a study published in the August 1st issue of the journal SLEEP.

Susumu Tanaka, PhD, of the Tokyo Institute of Psychiatry in Japan, conducted the study from a pool of total ribonucleic acid (RNA) , a nucleic acid polymer that plays several important roles in the processes that translate genetic information from DNA into protein products , from 12 patients with narcolepsy with cataplexy and from 12 age- and sex-matched healthy controls. The pooled samples were initially screened for candidate genes for narcolepsy by differential display analysis using annealing control primers (ACP).

The second screening of the samples was carried out by semiquantitative polymerase chain reaction (PCR) , a biochemistry and molecular biology technique for isolating and exponentially amplifying a fragment or sequence of interest of DNA, via enzymatic replication, without using a living organism , using gene-specific primers.

Finally, the expression levels of the candidate genes were further confirmed by quantitative real-time PCR using a new set of samples: 20 patients with narcolepsy with cataplexy and 20 healthy controls.

According to the study, the second screening revealed differential expression of four candidate genes, among which MX2 was confirmed as a significantly down-regulated gene in the white blood cells of narcoleptic patients by quantitative real-time PCR.

"In narcolepsy, it has been suggested that specific alterations in the immune system occur, and it's important for pathophysiology of this disorder," said Tanaka. "We thought that we can get these specific alterations by a differential display method using white blood cells. In this study, we applied the new ACP technology to RNA extracted from blood cells and successfully identified the MX2 gene as a dysregulated gene in narcoleptic patients. However, the direct relationship of this gene in narcolepsy has not been elucidated. Further study is needed to explore the functional relationship between the MX2 gene and narcolepsy and characterize the effect of interferons in narcolepsy."

Narcolepsy is a sleep disorder that causes people to fall asleep uncontrollably during the day. It also includes features of dreaming that occur while awake. Other common symptoms include sleep paralysis, hallucinations and cataplexy.

About one out of every 2,000 people is known to have narcolepsy. The chance that you have narcolepsy is higher when a relative also has it. It is very rare for more than two people in the same family to have this sleep disorder. It affects the same number of men and women.

Those who suspect they might be suffering from narcolepsy, or another sleep disorder, are urged to consult with their primary care doctor or a sleep specialist.

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