The Medical Post
VOLUME 37, NO. 07, February 20, 2001
Parsi hold valuable PD clue
By Edward Susman
MUMBAI, INDIA – Researchers believe omewhere in the genetic code of the
Parsi of
India there's a clue to what causes Parkinson's disease. The Parsi have
one of the highest
rates of Parkinson's disease in the world, despite the fact they live in
areas
where the disease incidence is far lower than places such as North
America, said Dr. Uday
Muthane, consultant neuroscientist at the National Institute of Mental
Health and Neurosciences at
Bangalore.
Dr. Muthane said studies of the Parsi offer tantalizing clues because
they are a
lighter-skinned group than others in Asia, and they live in areas where
exposure to
viruses is high. Both skin colour and exposure to viruses such as
encephalitis have been
implicated as triggers of Parkinson's, Dr. Muthane told the 7th National
Movement Disorder and Parkinson's Disease Surgery Workshop here.
"No one knows what causes Parkinson's disease," said Dr. Mohit Bhatt, a
founder of
the Parkinson's Disease Foundation of India and a consultant neurologist
at the Jaslok Hospital
here, near Bombay.
"There has been a lot of speculation as to what causes the disease, but
while skin colour
and viral infections are implicated, a convincing connection is still
lacking."
Dr. Muthane said epidemiological studies indicate darker skin colour
appears to protect
people against Parkinson's. He noted in North America more than 280
people per 100,000 develop
Parkinson's, compared to 243 per 100,000 in Italy, 59 per 100,000 in
Nigeria and 44 per 100,000 in China.
Surprisingly, studies of the mid-brains of people in different areas of
the world found
fewer neurons in the substantia nigra of people with arker skin colour,
Dr. Muthane said. Diminished numbers of neurons also are associated with
Parkinson's; so is exposure to infections such as viral Japanese
encephalitis, endemic in parts of Asia, he added.
Dr. Muthane suggested while Parkinson's disease rates are lower among
dark-skinned
peoples, despite fewer cells in the substantia nigra and exposure to the
virus, the increased
rate among the Indian Parsis might show the impact of the combination of
genetic (skin colour) and environmental (exposure to virus) factors to
development of Parkinson's.
"The question arises as to what predisposes populations with increased
number of
melanin-containing neurons toward increased incidence of Parkinson's
disease around the globe," he said.
Dr. Muthane said other worldwide viral infections such as influenza
epidemics might also
affect the cells in the substantial nigra and might explain why the
rates are high in North America and Europe.
Dr. Bhatt said exposure to chemicals which destroy cells in the
substantia nigra produce
Parkinson's-like disease. "If exposure to chemicals can cause
Parkinson's disease, why could it not
also be caused by viral exposure?"
© Copyright 2001 the Medical Post.
--
Judith Richards, London, Ontario, Canada
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