Researchers Discover Link Between Parkinson’s and Narcolepsy
 
 Parkinson's disease is well-known for its progression of motor disorders: 
stiffness, slowness, tremors, difficulties walking and talking. 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 May issue of the journal Brain, 
Jerry Siegel, 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 percent 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, Calif. "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." 
 

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