Latest
Mind and Matter column from the Wall Street Journal:
Being maltreated as a child can perhaps affect you for life. It
now seems the harm might reach into your very DNA. Two recently
published studies found evidence of changes to the genetic material
in people with experience of maltreatment. These are the tip of an
iceberg of discoveries in the still largely mysterious field of
“epigenetic” epidemiology-the alteration of gene expression in ways
that affect later health.
According to standard theory, genes aren’t supposed to change,
so you can pass them on to generations untainted by your own
mistakes. It now seems they can at least acquire marks of
experience during life, affecting how much they are
“expressed.”
In one study, Avshalom Caspi, Terrie Moffitt and colleagues at
Duke University and King’s College London looked at sequences at
the tips of chromosomes, known as telomeres, in 2,200 Britons born
in 1994-95 and followed since birth. These telomeres contain
repetitive sequences of DNA code “letters.” The number of repeats
shrinks during life in everybody, as a sort of clock for biological
aging.
Studies had begun to
suggest that psychosocial stress can speed up that clock by
eroding telomeres more rapidly, though this research mostly relied
on people’s recall of maltreatment. Then Stacy Drury and colleagues
at Tulane University found shorter telomeres in children who stayed
in Bucharest orphanages, compared with those in foster
families.
The Duke scientists have
measured the effect of exposure to bullying, beating or
domestic violence between the mother and her partner on telomere
length between the ages of 5 and 10. Because blood samples had been
taken from the Britons throughout life, it was possible to compare
telomere length before and after the violence was experienced. On
average, the telomeres did shrink faster in those that experienced
violence than in other children.
But in some individuals they actually grew longer, so the
mystery of telomeres only deepens. The next step, Dr. Moffitt told
me, is to assess subjects’ later health by measuring such things as
memory changes, inflammation, immune function, even tooth decay.
She adds: “So wish us luck!”
Another study,
published earlier this year by Audrey Tyrka of Butler Hospital,
Providence, R.I., and others found that the loss of a parent or
maltreatment as a child resulted in greater “methylation” of some
spots near a gene tied to stress response in adulthood.
Methylation, the addition of a methyl group of atoms to one DNA
“letter,” tends to reduce the activity of nearby genes. The
implication of the Butler study is that adults who recall
maltreatment as children may have reduced activity of a key gene in
the system that responds to the stress hormone cortisol. This may
be linked to increased anxiety or depression.
These are early days in the study of epigenetics. Scientists are
like people finding coins under lampposts but not knowing how many
coins remain in the dark. Although the “methylome”-a complete map
of where methylation happens in the genome-is being talked of,
others caution that we still have almost no idea of both the
causes and effects of most such changes, let alone other epigenetic
effects like histone modification.
But supposing it does become possible to link bad early
experience with bad later health, what then? Epigenetics demolishes
the old-and always misleading-distinction between deterministic
genes and a manipulable environment. To have your fate determined
by your early experiences is not much different from having it
determined by your genes, and when experience acts by changing
genes, the distinction vanishes.
Yet fortunately, given medical advances, genetic determinism is
not necessarily a life sentence, as those who wear glasses for
shortsightedness or take growth hormone for growth problems can
attest. The same will almost certainly be true for epigenetic
determinism: Understanding the mechanism should bring forward
possible cures.