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ADHD linked to
rare gene counts
By Tina Hesman Saey
Rare genetic factors that may lead to
attention-deficit/hyperactivity disorder
appear to be some of the same ones that
are related to autism, schizophrenia and
other brain disorders.
Previous studies have attempted — and
mostly failed — to link common genetic
variants to attention-deficit/hyperactivity disorder, better known as ADHD.
A new study bolsters the idea that many
different rare variants, some found only
in single families or individuals, can be
responsible for the condition. What’s
more, variants of the same genes associated with ADHD have also been linked to
autism spectrum disorders, schizophrenia and bipolar disorder.
“This really gives substance to the
argument that there are shared genetic
links between neuropsychiatric disorders,” says Russell Schachar, a child
psychiatrist at the Hospital for Sick
Children in Toronto, who led the study
with Stephen Scherer, a geneticist at
the hospital.
ADHD affects about 7 percent of
school-age children in the United States.
It persists throughout life. People with
the disorder may have trouble concentrating, act impulsively and be overly
active. Symptoms fall on a continuum of
severity, much like high blood pressure,
says Josephine Elia, medical codirector of
the Center for Management of ADHD at
Children’s Hospital of Philadelphia.
Up to 75 percent of people with autism
spectrum disorders also have symptoms
of ADHD, but researchers did not know
if the genetic causes were the same as
in people who have ADHD alone. Previ-
ous research has shown that people with
autism or schizophrenia tend to have
more missing or duplicated genes than
usual. Healthy people may have extra
copies of several genes or lack some
entirely, but missing or doubling up on
certain genes can lead to disease. These
differences in gene number are known
as copy number variations.
Cells may navigate with trail marks
Secreted molecules could help steer cellular migrations
By Nadia Drake
Cells seeking paths through the body’s
tangle of tissues might adapt the navigational strategy of Hansel and Gretel,
who dropped pebbles and bread crumbs
to help lead them out of a freaky forest.
Instead of using markers telling them
where to go, though, cells might use repellent molecules telling where not to go.
In a new study, scientists suggest these
Simulations show that an amoeba’s
success at moving through a maze can
be aided by chemical repellent markers
dispensed by the cell along its way.
markers help trailblazing cells move away
from areas where they’ve gotten stuck.
Cells moving through complex environments are directed, in part, by spatial
differences in chemical concentrations,
known as gradients. But the gradient
alone isn’t enough to explain successful
cell navigation in complex situations, says
physicist Inbal Hecht of Tel Aviv University in Israel, who coauthored the study
appearing August 4 in PLoS ONE.
Hecht and colleagues used a simulated
gradient and a computerized version of
the amoeba Dictyostelium. The team had
the amoeba find its way from one end of
the gradient to the other, and put mazes
and other obstacles in its way.
On its own, the computerized amoeba
made it through the maze only 30 percent
of the time. When it could secrete repellent markers, the amoeba’s success rate
rose to 99 percent.
“This is really a proof of principle,” says
physicist and coauthor Eshel Ben-Jacob
of Tel Aviv University. Real cells probably
use more complex strategies, he says.
