ing). In addition, the project also addresses the ethi-
cal, legal,and social implications of human genetics
research. This program (known as ELSI) focuses on
privacy and fairness in the use and interpretation of
genetic information, clinical integration of new genetic
technologies, issues surrounding genetics research,
and professional and public education (National Insti-
tute of Health [NIH], 2000). The researchers publish
their results in the journal Science;further informa-
tion can be obtained at http://www.genome.gov.
Three types of studies are commonly conducted
to investigate the genetic basis of mental illness:
1.Twin studiesare used to compare the rates
of certain mental illnesses or traits in
monozygotic (identical) twins, who have an
identical genetic makeup, and dizygotic
(fraternal) twins, who have a different
genetic makeup. Fraternal twins have the
same genetic similarities and differences as
nontwin siblings.
2.Adoption studiesare used to determine a
trait among biologic versus adoptive family
members.
3.Family studiesare used to compare whether
a trait is more common among first-degree
relatives (parents, siblings, children) than
among more distant relatives or the general
population.
Although some genetic links have been found in
certain mental disorders, studies have not shown that
these illnesses are solely genetically linked. Investi-
gation continues about the influence of inherited traits
versus the influence of the environment—the “nature
versus nurture” debate. The influence of environmen-
tal or psychosocial factors is discussed in Chapter 3.Stress and the Immune System
(Psychoimmunology)
Researchers are following many avenues to discover
possible causes of mental illness. Psychoimmunol-
ogy,a relatively new field of study, examines the ef-
fect of psychosocial stressors on the body’s immune
system. A compromised immune system could con-
tribute to the development of a variety of illnesses par-
ticularly in populations already genetically at risk.
So far, efforts to link a specific stressor with a specific
disease have been unsuccessful.Infection as a Possible Cause
Some researchers are focusing on infection as a cause
of mental illness. Most studies involving viral theo-
ries have focused on schizophrenia, but so far none
has provided specific or conclusive evidence. Theories
that are being developed and tested include the exis-
tence of a virus that has an affinity for tissues of the
CNS, the possibility that a virus may actually alter
human genes, and maternal exposure to a virus dur-
ing critical fetal development of the nervous system.2 NEUROBIOLOGICTHEORIES ANDPSYCHOPHARMACOLOGY 27
Figure 2-7.Comparison of computed tomography scan (left), magnetic resonance
imaging scan (center), and positron emission tomography scan (right). (Courtesy of
Monte S. Buchsbaum, MD, The Mount Sinai Medical Center and School of Medicine,
New York, New York.)