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Here we provide information
on past research projects and results from many of the research projects
in which MATR twins and their family members are participating. Through
their participation in this research, MATR twins are helping provide
information that may contribute to improved health in our communities.
Please note that not all participants in these studies have the disease
or condition being studied. Research requires subjects with and without
the condition under study to enable comparison that will help determine
why some people get a disease or condition and others do not.
Male-Male/Male-Female
Study
Alcohol Studies
Depression Studies
Genes and Bulimia
A New Twin Study
Begins
Mid-Atlantic School-Age
Twin Study (MASATS)
Seizure Study
The Virginia Twin
Study of
Adolescent Behavioral Development (VTSABD)
Update on the Male-Male/Male-Female Study
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In October 1998 we completed our second
round of interviews with twins who are members of male-male (MM) and
male-female (MF) twin pairs born in Virginia between 1940 and 1974.
The goal of this study is to understand the genetic and environmental
factors that may lead to the development of common emotional problems
including depression, anxiety, substance abuse, and eating disorders.
In the first phase of interviews, completed in 1996, we interviewed
more than 6,800 twins, mostly by telephone.
In the recently completed second phase,
more than 5,600 of these twins participated again, this time in a
face-to-face interview that lasted 2-3 hours. We have entered the
data and are now beginning to analyze the data from these interviews.
We will report the results in the future. We believe the findings
from this study will help scientists and health professionals to understand
the causes of these conditions.
Alcohol Studies
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Two research articles on the development
of alcoholism have recently been published. The first of these is
based on information collected from the first phase of the MM/MF study.
This article, which appeared in the January 1999 issue of the American
Journal of Psychiatry, reports that the risk of developing alcoholism
for men, is about half due to genetic factors and about half due to
experiences which are unique to individuals. We found that environmental
factors shared by members of a twin pair, such as parents' use of
alcohol and religious upbringing, were an important influence on whether
men drank alcohol or not. However, we found little evidence that family
environment influenced risk for alcoholism among people who drink.
The second article results are a combination
of data from the first phase of the MM/MF Stress and Coping Twin Study
and data from our fourth interview with female-female twin pairs.
This article, published in the December 1998 issue of Alcoholism:
Clinical and Experimental Research, focused on why individuals
who have their first drink of alcohol in early adolescence are more
likely to develop alcoholism when they are adults. Our results suggest
that, although the age at which a person first uses alcohol is related
to later alcoholism, it does not seem to be a direct cause of alcoholism.
We found that a twin's chances of developing alcoholism are almost
as well predicted by his/her co-twin's age at first drinking alcohol
as by his/her own age at first alcohol use. If drinking age were a
direct cause of alcoholism, we would expect a twin's alcoholism to
be more closely related to his/her OWN age when first using alcohol.
Clearly there are other disadvantages of alcohol use by teenagers,
but it seems that factors other than age at first drink may be more
useful predictors of who is at risk for developing alcoholism.
Depression
Studies
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Understanding differences between people
in their risk for experiencing depression has remained a major focus
of the Stress and Coping Project. Depression can affect people in
many different ways. Some people have episodes that are relatively
mild and still allow them to work, socialize, and do their chores
around the house. For others, however, the depression is much more
disabling, preventing them from completing normal daily activities.
Some people have short episodes of depression lasting a few weeks
from which they quickly recover. For others the episodes last much
longer. Some individuals will have only one episode of depression
in their life while others will have many. In our entire Stress and
Coping twin sample (including female-female, male-male and male- female
twin pairs), we have tried to answer the question, "What features
of depression indicate that a person is at high genetic risk for this
disorder?" We addressed this question by studying twins who had a
history of depression any time in their life, and looking at what
features of their depression predicted the risk of depression in their
co-twins. The answers were fairly clear and consistent with what doctors
tend to find when treating their patients. The co-twins of individuals
who had had only a single episode of depression that lasted only a
brief time and was not very disabling had a relatively low risk for
depression. By contrast, the risk for depression was much higher in
the co-twins if their twins had had many episodes of depression in
their life, if these episodes lasted a long time, and if they were
so severe that they greatly affected normal daily activities.
We know that episodes of depression
are often set off by stressful life events. However, some researchers
have claimed that the role of stress in depression declines over time.
That is, for people who have had multiple episodes of depression,
it takes less and less stress to cause them to go into another depression.
It is as if they (or their brains) were "learning" to be depressed.
Our results clearly confirm that the level of stress needed to cause
depression is lower in people who have had many prior episodes of
depression than in those who have never been depressed before.
Genes
and Bulimia
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Data from female twins
who participated in the Stress and Coping Twin Project are playing
an important role in changing our understanding of what causes bulimia
nervosa, an eating disorder that affects mostly women. People who
suffer from bulimia binge on food and then take steps to get rid of
the food they have eaten; for example, they may exercise excessively
or make themselves vomit.
When the twin data were
analyzed, we found that genes play a major role in the cause of bulimia
(between 68-97%). This was surprising, as bulimia is widely believed
to be primarily due to environmental effects. However, our study's
findings fit in well with data from other studies around the world.
These findings do not take the environment "off the hook" however,
because environmental factors, such as social pressures to be thin,
also contribute to the development of bulimia. These important results
from the Stress and Coping Twin Study were featured on the front page
of the Richmond Times-Dispatch and in many other newspapers
in the US and abroad, as well as on local and national television.
A
New Study Begins
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Dr. Kenneth Kendler (director of the
Stress and Coping Twin Study) recently received a grant from the National
Institute on Drug Abuse to conduct a large twin study about the use
and abuse of a number of legal and illegal drugs. Over the course
of this three-year study, approximately 1,200 male twin pairs will
be asked about their drug use. The drugs covered include legal drugs
(alcohol, nicotine, and caffeine) and illegal drugs (such as, marijuana
and cocaine).
The study has three main purposes. First,
we want to learn about the causes of drug use. Is drug use mainly
due to genetic or environmental influences? Second, we seek to better
understand the roles of environmental factors like the availability
of drugs and peer drug use. Third, we want to determine if the mix
of genetic and environmental causes of drug use is the same or different
from one drug to another. Do genes influence the use of some drugs
more than others? The researchers hope this study will shed new light
on this widespread problem which affects many individuals and their
families in the United States.
The
Mid-Atlantic School Age Twin Study
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For this study, twins between
the ages of 11 and 18 and the mothers of school-age twins were mailed
a questionnaire. This long-term study focuses on genetic and environmental
influences on adolescent adjustment and behavior, including family
relationships, peer interactions, and community characteristics (such
as the availability of drugs).
Although we are still in
the data collection phase of this study, we have completed some preliminary
analyses. So far, we have found that adolescents' religious beliefs
are primarily influenced by their environment and protect them against
drug and alcohol use during this developmental period. Further, good
parent-child communication is a protective factor against drug use,
depression, conduct problems, and oppositional behavior. Among young
twins, the factor most strongly associated with their own drug and
alcohol use is whether their friends use drugs or alcohol. Future
analyses on the complete data will enable us to better understand
how genetic factors, family interactions, and the community environment
influence the healthy development of children and teenagers.
Seizure
Study
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We are continuing our study to find out if inherited
factors are important in determining risk for the occurrence of epileptic
seizures. The information provided by the 640 twins and more than
2,000 family members who have taken part in the study so far have
allowed us to conduct some initial analyses. The results indicate
that hereditary factors are indeed important in determining whether
or not an individual is at risk for having epilepsy, as well as for
determining whether or not a seizure, when one occurs, goes on for
more than just a minute or two. These findings are encouraging and
lead us to believe that it will someday be possible to identify specific
genes that make people susceptible to seizures. In order to do so
we depend on the participation of as many of you as possible. This
is because epilepsy and seizures are very complex and rare disorders,
and it is likely that there is more than one epilepsy or seizure susceptibility
gene. Thus, we need to study an extremely large number of individuals
in order to sort out exactly what is involved in determining risk
for seizures.
If you would like more
information on this research study or want to report that you have
experienced seizures that you have not already told us about, please
contact Daphnee Massante, (804) 828-8112, or Kristin Baldwin. (804)
827-0503, or call 1-800-URA-TWIN and leave a message. We would like
to restate that any information you provide is used only for research
purposes. It is also kept strictly confidential. In order to safeguard
this confidentiality, we have a Certificate of Confidentiality
from the National Institutes of Health. This certificate protects
any information obtained as part of our studies.
The
Virginia Twin Study of Adolescent
Behavioral Development (VTSABD)
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The Virginia Twin Study of Adolescent Behavioral
Development (VTSABD) has completed four phases of data collection
involving more than 1,400 twin families from Virginia. Since the oldest
twins who participated in this study are now young adults, we have
recently started the Young Adult Follow-Up Study (YAFU), directed
by Dr. Judy Silberg. Instead of a home visit, the twins are being
contacted by telephone and asked about their behavior, lifestyle and
background using a computerized interview.
Data from the first three phases of the VTSABD
have been analyzed and published in major scientific journals. Dr.
Lindon Eaves reported in the Journal of Child and Adolescent Psychology
and Psychiatry that both genetic and environmental factors contribute
to most aspects of adolescent behavior, including anxiety and depression,
conduct problems, hyperactivity, and substance use. In a paper published
in the Archives of General Psychiatry, Dr. Judy Silberg and
her colleagues found that the increase in depression among adolescent
girls may be due to the "switching on" of genes at puberty. This study
also showed that the genes for depression influenced the occurrence
of certain stressful life events, demonstrating a possible way depression
can continue from adolescence into adulthood in women.
We still have volumes of data that we are analyzing.
We will report on findings from these analyses and resulting publications
as they occur.
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