Post: interesting article - ADHD linked to advantageous gene
Posted by Dad on 1/15/02
sciencedaily.com
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Attention-Deficit Hyperactivity Disorder Related To
Advantageous Gene
Irvine, Calif., Jan. 8, 2002 -- A variant form of a gene
associated with attention-deficit hyperactivity disorder
(ADHD) indicates that the disorder is a recent affliction
and may once have helped humans thrive and survive,
according to a UCI College of Medicine study.
The human gene study, which appears in the Jan. 8 issue of
Proceedings of the National Academy of Science, suggests
that behavior now considered inappropriate in a classroom
may be related to behavior that once helped humans overcome
their environment.
Robert Moyzis, professor of biological chemistry, and his
colleagues studied genes from 600 individuals worldwide.
Among numerous new genetic variations of the receptor for
the dopamine neurotransmitter, they found one linked
strongly to both ADHD and a behavior trait called "novelty
seeking," a condition often underlying addiction. Their
analysis of the genetic variations also suggests that this
variation occurred recently in human evolution between
10,000 and 40,000 years ago.
"We found a significant positive selection for the genetic
variation associated with ADHD and novelty-seeking behavior
in the human genome," Moyzis said. "This study strengthens
significantly the connection between genetic variations and
ADHD. It also provides a clue as to why ADHD is so
pervasive and may show us a way to provide more effective
treatments."
The researchers found 56 variations, or alleles (al-LEELEs)
of a gene called DRD4, which produces the receptor for
dopamine, a neurotransmitter. One allele, known as 7R, was
strongly associated with ADHD. By analyzing the variations
in DRD4, they also found that the 7R allele was created
recently and may have provided an evolutionary advantage at
some time in human history. The study could not determine,
however, if that evolutionary selection is still occurring.
Brain cells signal each other with a number of
neurotransmitters, including dopamine. The dopamine system,
among other things, controls movement behavior and may be
involved in learning and responding to psychological
rewards. It also has been implicated in addictive behavior.
ADHD is the most common disorder in early childhood,
affecting about 3 percent of all elementary school children
in the United States. The disorder is marked by
developmentally inappropriate conduct, lack of attention,
impulsive and hyperactive behavior, all occurring before a
child becomes 7 years old. Approximately half of children
with ADHD have the 7R allele.
Between 10,000 and 40,000 years ago, anthropologists concur
that humans were developing the first signs of complex
societies, replete with agriculture, rudimentary
governments and the creation of cities for the first time.
Humans also were rapidly expanding and exploring the
planet. These revolutionary changes in human societies may
have changed the forces that selected for certain genetic
traits.
"Our data show that the creation of the 7R allele was an
unusual, spontaneous mutation, which became an advantage
for humans," Moyzis said. "Because it was an advantage, the
gene became increasingly prevalent. This is very different
from other genes that predispose to genetic disorders,
where the mutations are detrimental. We believe this helps
explain why a disorder with such a strong genetic
association is so common today."
The researchers are now working on determining how the
genetic variations in DRD4 may actually predispose
individuals to ADHD and other behaviors, and on examining
the relationship between other complex genetic variations
and ADHD.
Moyzis's colleagues include Yuan-Chun Ding, Han-Chang Chi,
Deborah Grady, Pam Flodman, M. Anne Spence, Sabrina Schuck
and James Swanson of UCI; Ya-Ping Zhang of the Chinese
Academy of Sciences, Kunming, China; and Atsuyuki
Morishima, Judith Kidd and Kenneth Kidd of Yale University.
The study was supported by grants from the U.S. Department
of Energy and the National Institute of Mental Health.
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