Researchers Discover Link Between Parkinson's and Narcolepsy

Researchers Discover Link Between Parkinson's and Narcolepsy

LOS ANGELES, CA -- May 11, 2007 -- Parkinson's disease is well-known
for its progression of motor disorders. Less well known is that
Parkinson's shares other symptoms with narcolepsy, a sleep disorder
characterized by sudden and uncontrollable episodes of deep sleep,
severe fatigue and general sleep disorder.



Now a team of UCLA and Veterans Affairs researchers think they know why
-- the two disorders share something in common: Parkinson's disease
patients have severe damage to the same small group of neurons whose
loss causes narcolepsy. The findings suggest a different clinical
course of treatment for people suffering with Parkinson's that may
ameliorate their sleep symptoms.



In their report (currently online) in the June issue of the journal
Brain, Jerry Siegel, PhD, professor of psychiatry and biobehavioral
sciences at the Semel Institute for Neuroscience and Human Behavior at
UCLA, assistant resident neurobiologist Thomas C. Thannickal and
associate research physiologist Yuan-Yang Lai have determined that
Parkinson's disease patients have a loss of up to 60% of brain cells
containing the peptide hypocretin.



In 2000, this same group of UCLA researchers first identified the cause
of narcolepsy as a loss of hypocretin, thought to be important in
regulating the sleep cycle. This latest research points to a common
cause for the sleep disorders associated with these two diseases and
suggests that treatment of Parkinson's disease patients with hypocretin
or hypocretin analogs may reverse these symptoms.



More than 1 million people in the U.S. have been diagnosed with
Parkinson's disease, and approximately 20 million worldwide. The
percentage of those afflicted increases with age. Narcolepsy affects
approximately one in 2,000 individuals -- about 150,000 in the United
States and 3 million worldwide. Its main symptoms are sleep attacks,
nighttime sleeplessness and cataplexy, the sudden loss of skeletal
muscle tone without loss of consciousness; that is, although the person
cannot talk or move, they are otherwise in a state of high alertness,
feeling, hearing and remembering everything that is going on around
them.



"When we think of Parkinson's, the first thing that comes to mind are
the motor disorders associated with it," said Siegel, who is also chief
of neurobiology research at the Sepulveda Veterans Affairs Medical
Center in Mission Hills, California. "But sleep disruption is a major
problem in Parkinson's, often more disturbing than its motor symptoms.
And most Parkinson's patients have daytime sleep attacks that resemble
narcoleptic sleep attacks."



In fact, said Siegel, Parkinson's disease is often preceded and
accompanied by daytime sleep attacks, nocturnal insomnia, REM sleep
disorder, hallucinations and depression. All of these symptoms are also
present in narcolepsy.



In the study, the researchers examined 16 human brains from cadavers --
five from normal adults and 11 in various stages of Parkinson's -- and
found an increasing loss of hypocretin cells (Hcrt) with disease
progression. In fact, said Siegel, the later stages of Parkinson's were
"characterized by a massive loss of the Hcrt neurons. That leads us to
believe the loss of Hcrt cells may be a cause of the narcolepsy-like
symptoms of [Parkinson's] and may be ameliorated by treatments aimed at
reversing the Hcrt deficit."



Funding for the study was provided by the National Institutes of Health
and the Medical Research Service of the U.S. Department of Veterans
Affairs.