Transcript Epidemiology of Parkinson’s disease

Epidemiology of
Parkinson’s Disease
Kelly Sullivan, MSPH
Associate of Research
Parkinson’s Disease and Movement
Disorders Center
Department of Neurology
University of South Florida
Importance of Epidemiology
Health care and planning
 Tool for investigation of the cause
of PD
 Defining disease
characteristics such as
prevalence, incidence, and
mortality
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Origins of Parkinson’s
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Parkinson's disease was first formally
described in "An Essay on the Shaking
Palsy," published in 1817 by a London
physician named James Parkinson
It has probably existed for many thousands of
years
Symptoms and potential therapies mentioned
in:
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Ayurveda, the system of medicine practiced in
India as early as 5000 BC
First Chinese medical text, Nei Jing, which
appeared 2500 years ago
Prevalence
How many people have PD?
Estimated 1 million patients in US
 Second most common age-related
neurodegenerative disorder
 Second in frequency only to Alzheimer’s disease
 World-wide estimates vary
 15/100,000 in China
 657/100,000 in Argentina
 100 - 250/100,000 in North America and Europe
 Prevalence is predicted to triple over the next 50
years as average age of population increases.
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Incidence
Quantifies the number of individuals who
are newly diagnosed with PD in a given time
period
 Unaffected by factors affecting disease
survival
 Accurate measurements of the incidence of
PD are relatively difficult
 Clinical manifestations of PD may be
preceded by a long latent stage and have a
slow clinical progression
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Incidence
Difficult to know how many people are
diagnosed each year:
 Symptoms may develop and progress
slowly
 Diagnostic criteria may vary
 Patient populations vary with respect
to doctor visits
Incidence
China: 1.5/100,000
 Finland: 14.8/100,000
 US: 20/100,000
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Variations may be due to different
diagnostic criteria and methods of case
ascertainment in studies
 Lifetime risk of PD: 1 in 40
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Age
The incidence of PD increases with age
 Symptoms of Parkinson’s disease may
appear at any age
 The median age of onset for idiopathic PD is
62.4 years
 Onset before age 30 is rare, but up to 10% of
cases of idiopathic PD begin by age 40
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Age
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Prevalence increases with age from
age 50-90
Affects 0.3% of general US population
Affects 3% of those older than 65
Aging alone does not cause PD
May increase susceptibility to other
factors or allow them to be expressed
Gender
Slightly more common in men than in
women
 Estimated 12-15 men for every 10
women
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Ethnicity
Present worldwide, in all populations
 No region found to be free of PD
 More common in white people in Europe and
North America
 (100-350/100,000)
 Lower rates in China, Nigeria and Sardinia
 The disorder occurs in all races but is
somewhat more prevalent among Caucasians
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Ethnicity
Generally less common among AfricanAmericans and Asians
 one-fifth to one-tenth as prevalent as in
whites
 In Africa less common among blacks than
whites
 Door-to-door screening in Mississippi
 PD prevalence was not significantly
different in whites and blacks after
adjusting for age differences (poor
diagnostic criteria)
 Higher prevalence in whites with stronger
diagnostic criteria
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Ethnicity
Two other studies conducted
 PD incidence in African-Americans and in AsianAmericans was similar to rates for EuropeanAmericans
 Door-to-door survey in Taiwan
 Prevalence of PD =119/100,000
 Similar to that of a white population and much
higher than that of previous studies of Asian
populations
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Ethnicity
Differences in findings
 Suggest environmental factors
more important than racial factors
 Further studies needed
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Other factors?
 Differences in access to
healthcare?
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Ethnicity
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The disease was once thought to affect
primarily whites, but recent studies have
demonstrated equal prevalence in African
Americans and whites living in the same
geographic area.
Retrospective epidemiologic studies
performed in various major cities have
yielded contradictory information.
Variations in the prevalence of the disease
in individual racial groups in different
geographic areas have suggested an
increased risk associated with rural living.
Time
Hard to evaluate
 Few studies that track over long period of time
 Studies might use different methods or have
different diagnostic criteria
 Two studies  different conclusions
 Greater awareness - well-known people have
developed PD
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Time
Study in Olmsted County, Minnesota
1935-1988
 Tracked number of people diagnosed with
PD each year
1935-1944: 9.2/100,000 diagnosed
1975-1984: 16.3/100,000 diagnosed
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Time
NIH study of world-wide PD trends
 Statistically controlled for age
differences
 Concluded that the prevalence and
incidence of PD appear to have
remained unchanged over the past 40
years
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Causes
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The cause of Parkinson’s disease is
unknown.
Many researchers believe that several
factors combined are involved: free
radicals, accelerated aging,
environmental toxins, and genetic
predisposition.
What Causes Parkinson's?
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Why an individual develops Parkinson's
disease remains unclear.
The cause is probably a combination of
genetic and environmental factors, and
may vary from person to person.
Although the cause of Parkinson's
remains unknown, scientists have
identified factors that contribute to
Parkinson's in some patients.
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People over age 60 have a two-to-four
percent risk of developing Parkinson's
disease, compared with the one-to-two
percent risk in the general population.
Risk Factors and
Protective Factors
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The single biggest risk factor for PD is advancing
age
Men have a slightly elevated risk compared to
women
Family history is also an important risk factor
 Individuals with an affected first-degree relative
are estimated to have an approximately doubled
risk for developing PD
 This increase cannot be explained by presence of
any of the known genetic causes of PD, which
together account for only a small percentage of
familial cases
Risk Factors and
Protective Factors
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Caffeine consumption is associated with a reduced
incidence of PD
Cigarette smoking has been associated with a
reduced risk of PD
It is not known whether smoking confers a genuine
protective effect, or whether individuals who are
prone to develop PD for other reasons are also
prone to avoid smoking
Nonetheless, the negative impact on general health
from smoking is enormous, far in excess of any
slight reduction in risk for PD
Smoking cannot be recommended as a strategy for
avoiding PD
Risk Factors
Environment
Environmental factors may play a role
in PD
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Several members of some families with
widely different ages developed PD within a
short period of time
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The vast majority of cases of PD are
thought to be due to the potential
interactions of genes and the
environment
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Environmental Factors
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Factors include: physical trauma,
exposure to chemicals and infections,
and nutrition
Rural Living
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A strong and consistent finding is that
the risk of PD is increased by:
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rural living
exposure to well water
agricultural work
Suggests that pesticides and/or
herbicides may cause or contribute to
PD
Environmental Toxins
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These conclusions are strengthened
by several identified toxins that
induce parkinsonism in animal
models, and even in humans
MPTP - originally identified as a
contaminant in a batch of "street
heroin" in Berkeley, California in the
1980s
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Addicts who injected it developed a
clinical syndrome almost identical to PD
Environmental Toxins
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The identification of MPTP led to much
productive work on the cellular
pathogenesis of PD
However, numerous toxicological studies
have demonstrated that MPTP itself is
extremely rare in the environment, and
thus is not a significant contributor to
idiopathic PD
It remains to be seen if any single agent
will eventually be shown to account for
more than a small fraction of PD cases
Genetics and Pathogenesis
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While the known genes for PD are
responsible for only a minority of
cases, they have provided
extraordinary insight into the
molecular pathology of the disease
Genetics
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Roughly one-fifth of Parkinson's disease
patients have at least one relative with
parkinsonian symptoms
 Suggests that a genetic factor may be
involved
Several genes that cause symptoms in
younger patients have been identified
Most researchers believe, however, that
most cases are not caused by genetic
factors alone
Genetics
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Genetic research studies over the past
seven years have uncovered a total of 10
genes associated with PD
For most cases of PD, however, these genes
are not thought to play a role
Small as their role may be, genes provide a
crucial opportunity for us to study how the
brain works
Genetics
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Because most patients do not have a clear
history of either familial or environmental
risk factors, the disorder may be due to a
combination of genetic and environmental
"influences" or "causes"
In a small number of cases worldwide there
is a strong inheritance pattern
A genetic predisposition for Parkinson’s
disease is possible, with the onset of disease
and its gradual development dependant on a
trigger, such as trauma, other illness, or
exposure to an environmental toxin
Genetics
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In large epidemiological studies, researchers have
found that people with an affected first-degree
relative, such as a parent or sibling, have a two-tothree fold increased risk of developing Parkinson's,
as compared to the general population
The vast majority of Parkinson's cases are not
directly inherited, but researchers have discovered
several genes that can cause the disease in a small
number of families
Because genetic forms of a disease can be studied
in great detail in the laboratory, and because
understanding the rare genetic forms of Parkinson's
disease may help to understand more common
forms of the disease, genetic aspects of PD are
currently the subject of intense research
PD and Genetic Testing
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Genetic testing in the general PD population - at
the current stage of scientific knowledge - is not
going to be helpful
Researchers are still trying to determine which
genetic factors contribute to the development of
PD for the average patient
This is a very challenging task because we
suspect that the interaction of genes with each
other and with the environment is probably
unique to each individual
Until we gain this level of knowledge, we are a
long way off from being able to offer the public
PD genetic testing and accurate risk information
for family members
PD Genetics and the Future
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The recent identification of genes that
cause PD in a small group of PD families
is helping us to understand the
processes that lead to the development
of PD
Future research will undoubtedly reveal
additional PD-associated genes and
susceptibility factors, which will help us
to further understand the cause of PD
and lead to better diagnosis and
treatment