Why delayed onset of mental illness? Genes impact suspect brain areas late

Why delayed onset of mental illness? Genes impact suspect brain areas late


Twins are the best way to address nature/nurture
questions. Identical twins, or monozygotic, share almost one hundred percent of their
DNA. And fraternal twins, or dizygotic, share out about fifty percent. So by seeing how
much more alike the identical twins are than non-identical, we can get a sense for how
much the DNA matters for brain or behavior or all kinds of different variables. Of course,
its not nature versus nurture. Its nature and nurture — and the interaction between
the two that’s really the key. These days that’s usually called G by E interactions
— G for genes and E for environment. But what this paper demonstrates is that we need
to add a third component to the G and the E. And that third component is age. And what
that means is that in order to understand the effect of a particular gene in a particular
environment, we also need to know where that individual is in the course of their development.
So it may not seem that surprising land that age would matter, but
to actually identify the specific facts and figures about how this age by Jean by environment
interaction (works) hasn’t been all that easy, partly because we have to follow people over
time as they go from a child to an adolescent to a young adult. And in and this case, the
people have been identical or non-identical twins, but also their brothers and sisters.
Genetically, they also I’ll share fifty percent their genes. And over the past decade we followed
about eight hundred people, having them come to
the NIH at about two year intervals where we did a scan of their brain. We see how they’re
doing in school, in life, their behavior, their emotions, their cognition. And we see
how these factors change over the course of development. The main thing that we found
was that it’s a moving target. So which parts of the brain are more or less heritable changes
a lot as you go from a baby to it a child to a teenager to an adult. And so what we’ve
been able to do with these movies that you’re seeing is to actually demonstrate the specifics
of these changes. And what we see here are the areas in red other areas in the brain
that are most charitable. And what we see is that it’s not a one-size-fits-all. That
certain parts of the brain become more heritable during adolescence. Other parts are more heritable
in your early childhood, others in in middle ages. And why we think this is important is
that the same brain areas that are changing in heritability during adolescence are also
the parts for the brain that we acquired most recently in our evolutionary history and also
they’re the parts of the brain that are involved in illnesses that happen during adolescence.
This has been one of the big mysteries in psychiatry. Why do things happen when they
do? For a genetic illness like schizophrenia, you’re born with those genes. You’re born
with those risks. So why doesn’t it manifest when it does? Until late adolescence or young
adulthood. This has always been one of the big research questions for us. And now we
think we might have some insight into that. Because one way of looking at this is that
the reason these brain parts get more heritable
during adolescence is because they get expressed then. That if they’re not being expressed
any younger it doesn’t matter if you’re identical or non-identical, because those genes aren’t
doing anything. But whether it’s puberty or other unknown timing factors, when these genes
then become expressed, those parts for the brain become more heritable. But if this process
goes awry, then it also may be why these illnesses are unleashed when they happen. Most
illnesses actually manifest during adolescence — psychosis, bipolar disorder, eating disorders,
substance abuse, anxiety, panic attacks. So literally over fifty percent of mental illnesses
when they happen occur during this adolescent period. And we’re particularly interested
in these parts of the brain that become more red during late adolescence, when many of
the illnesses are emerging. And they’re parts of the brain that we’ve acquired most recently
in our evolutionary history — so the most difference
between us and chimpanzees and bonobos. So its all is converging upon this common story
— the things that take the longest to develop also have genetic factors that impact later
and later in life. So the next step for us now will be to really try to explore this
link between the illnesses that have their onset during this time and the typical brain
changes possibly driven by the same underlying genes. At one age this particular gene might
affect this particular brain in this way, and at a different age no effect — or even
an opposite effect. And so I think the whole field will be affected by these sort of findings,
in terms of really trying to introduce age into the G
by E interaction question.

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