Transcript genetic epidemiology

Chapter 10
Special Epidemiologic Applications
Learning Objectives
• Distinguish between molecular and genetic
epidemiology
• Define the term environmental epidemiology
• Describe two applications of occupational
epidemiology
• State a role for epidemiology in the primary
prevention of unintentional injuries and
violence
Introduction
• Scientists utilize epidemiologic methods and
concepts with respect to a wide range of
health-related and other phenomena including:
– Genetically associated diseases
– Environmental health
– Unintentional injuries
– Screen-based media use
– Sewage epidemiology
Molecular and Genetic
Epidemiology
• Traditionally, epidemiologic research uncovers
associations between exposures and health
outcomes, often without fully developing an
explanation for the observed associations.
– Molecular and genetic methods have increased the
ability of scientists to expand the knowledge base
of disease causality.
Human Genome Project
(HGP)
• Jointly coordinated by the U.S. Department of
Energy and the National Institutes of Health
– Completed in 2003
– One goal was to identify all of the genes in human
DNA.
– HGP will provide valuable information for
epidemiologic research
• Example: Studying genetic and environmental
interactions
Molecular Epidemiology
• A subfield of epidemiology that uses molecular
markers in addition to genes to establish
exposure-disease relationships
Genetic Marker
• “The term genetic marker is used…in
reference to susceptibility genes.”
• When these genes are present, the person may
have increased susceptibility to specific
exposures.
• An example is the linkage between the gene
CYP2D6 and susceptibility to the effects of
exposure to benzo-a-pyene, a hazardous
chemical.
Genetic Epidemiology
• The field of genetic epidemiology has a
narrower focus than molecular epidemiology.
• It is concerned with “…the identification of
inherited factors that influence disease, and
how variation in the genetic material interacts
with environmental factors to increase (or
decrease) risk of disease.”
Genetic Epidemiology (cont.)
• Examples of conditions that are known or
believed to have a genetic basis are:
– Hemophilia
– Tay-Sachs disease
– Sickle cell disease
– BRCA1 and BRCA2 genes
– Down Syndrome
– Congenital malformations
Sex-Linked Disorder
• Hemophilia (bleeding disorder) is caused by an
abnormal gene on an X chromosome.
– Affected persons are almost always males.
– Males inherit the trait from their mothers who are
carriers.
– Females can be carriers of the abnormal gene,
which can be inherited from their affected fathers.
Autosomal Recessive
• Denotes those diseases for which two copies of
an altered gene are required to increase risk of
the disease
• Examples: Tay-Sachs disease, sickle cell
disease
Autosomal Dominant
• Refers to a situation in which only a single
copy of an altered gene located on a nonsex
chromosome is sufficient to cause an increased
risk of disease.
Chromosomal Abnormalities
• Example: Down syndrome
– Associated with the presence of an extra twentyfirst chromosome
Source: Reprinted from Centers for Disease Control and Prevention. Down syndrome prevalence at birth—United States, 1983-1990.
MMWR. 1994;43:619
Congenital Malformations
• Congenital malformations are defects present
at birth.
• They include structural birth defects (defined
on next slide) and those that are produced by
chromosomal abnormalities.
Major Structural Birth Defects
1) “…result from a malformation,
deformation, or disruption in one or more
parts of the body;
2) are present at birth; and
3) have a serious, adverse effect on health,
development, or functional ability.”
A photograph of a child with cleft
feet, or “lobster claw” feet
Source: Reprinted from Centers for Disease Control and Prevention. Public Health Image Library, ID# 2631. Available at:
http://phil.cdc.gov/phil/details.asp. Accessed July 21, 2008.
Environmental Epidemiology
• Refers to the study of diseases and conditions
(occurring in the population) that are linked to
environmental factors.
Environmental Epidemiology
(cont.)
• Representative topics:
– Air pollution
– Global warming
– Toxic chemicals
– Heavy metals
– Nuclear Facilities
Air Pollution
• Epidemiologic research has examined a
number of adverse health outcomes as possible
consequences of exposure to air pollution:
– Mortality, coronary heart disease, chronic
obstructive pulmonary disease, asthma, and lung
cancer
Extreme Air Pollution Episodes
• Severe, deadly inversion layer in Donora,
Pennsylvania (1948)
• Killer pea-souper fog, London, England (1952)
Global Warming
• Global warming refers to the gradual increase
in the earth’s temperature over time.
• Historical data indicate that the earth’s
temperature has warmed approximately 0.6
degrees Celsius since the end of the nineteenth
century and about 0.4 degrees Celsius within
the past 25 years.
Factors Contributing to
Global Warming
• Use of fossil fuels such as coal and petroleumbased fuels that release greenhouse gases
– Carbon dioxide, methane, chlorofluorocarbons,
and nitrous oxide
• Widespread deforestation in many parts of the
world, particularly the Brazilian Amazon
jungle
Potential Impacts of Global
Warming
• Global warming linked to:
– Northward movement of disease-carrying
arthropods (e.g., mosquitoes)
– Melting glaciers
– Extreme climatic conditions such as heat waves
Toxic Chemicals
• Chemicals and pesticides are used extensively
in industry, at home, and in agriculture.
– DDT
• Use discontinued because of possible adverse animal
and human health effects, e.g., damage to bird species.
– Dioxins
• Possible disrupters of immune, endocrine, reproductive,
and nervous systems
– Polychlorinated biphenyls (PCBs)
• Dioxin-like chemicals designated as probable human
carcinogens
Heavy Metals
• Industrial sites, metal smelters, some mining
operations, and coal-fired power plants can
release heavy metals into the environment.
– Endanger the health of people who live nearby and
employees
– Examples: lead and mercury
Lead
• Lead exposure is associated with serious
central nervous system effects and other
adverse health consequences, even when
ingested at low levels.
– Formerly an additive in paints and motor vehicle
fuels
– Found in automobile batteries and solder used in
electronics
Mercury
• A highly toxic metal that is a particular hazard
to the unborn children of pregnant women
• Released into the environment as a by-product
of industrial processes.
– Certain types of fish are believed to contain
unhealthful mercury levels.
Nuclear Facilities
• Include weapons production plants, test sites,
and nuclear power plants
– Potential sources for exposure of the population to
ionizing radiation
• Example: Accident in Chernobyl, Ukraine (April
26, 1986)
–Nearby population and the residents of many
European countries exposed to radiation
–Caused an increase in thyroid cancer among
persons who were exposed as children
Epidemiology and
Occupational Health
• Occupational epidemiology focuses on adverse
health outcomes associated with the work
environment.
Epidemiology and
Occupational Health (cont.)
• Potential hazards encountered at work include:
– High noise levels
– Fumes and dusts
– Toxic chemicals
– Biohazards
– Stress
• Exposure levels among employees are often
much higher than in the general population.
Unintentional Injuries
• Injury epidemiology studies the distribution
and determinants of injuries (intentional and
unintentional) in the population.
• This term is preferred to “accident,” the use of
which should be avoided.
Unintentional Injuries (cont.)
• Fifth most frequent cause of mortality in the
U.S. (2005)
• Many are highly preventable.
• Leading causes of injury death (Figure 10-7)
are:
– Motor-vehicle traffic deaths
– Firearm deaths
– poisonings
Unintentional Injuries (cont.)
• The highest death rates from injuries among
children and young adults occur during the
first five years of life.
• Sports-related children’s injuries include
traumatic brain injuries.
• Traumatic injuries (e.g., ankle injuries)
sometimes occur during participation in
collegiate sports.
• Falls are the leading cause of fatal and nonfatal
injuries for persons aged 65 years and older.
Other Applications of
Epidemiology
• Sewage Epidemiology
• Descriptive Epidemiology of Screen-Based
Media Use
• Physical Dating Violence
• Forensic Epidemiology
Sewage Epidemiology
• Refers to monitoring levels of excreted drugs
in the sewer system in order to assess the level
of illicit drug use in the community.
– Research conducted in Milan, Italy; Lugano,
Switzerland; and London, England found that
cocaine consumption rose in Milan on weekends
and heroin consumption varied among the three
cities.
Descriptive Epidemiology of
Screen-Based Media Use
• Marshal et al. conducted a systematic review in order
to:
– “…(i) estimate the prevalence and dose of television (TV)
viewing, video game playing and computer use, and
– (ii) assess age-related and (iii) secular trends in TV viewing
among youth (≤ 18 yr).”
• Researchers found that young people watched TV for
an average of 1.8 to 2.8 hours per day. The authors
concluded that media-based inactivity did not
contribute greatly to youth sedentariness.
Physical Dating Violence
• “Dating violence is defined as physical,
sexual, or psychological violence within a
dating relationship.”
• Youth Risk Behavior Surveillance System
– “…measures the prevalence of health risk
behaviors among high school students…”
– The overall prevalence of dating violence was
8.9% and was similar for both males and females.
Forensic Epidemiology
• “The use of epidemiological reasoning,
knowledge, and methods in the investigation
of public health problems that may have been
caused by or associated with intentional and/or
criminal acts.”
• One of the stimuli for the development of this
specialization was the 2001 bioterrorism attack
(distribution of anthrax bacteria through the
postal system) in the U.S.
Conclusion
• Additional uses of epidemiology covered in
this chapter were taken from the fields of:
– Molecular and genetic epidemiology
– Environmental health
– Injury epidemiology
• The number and range of applications of
epidemiology are likely to increase in the
future as are opportunities for research and
employment.