A federally funded team of researchers including
several from Johns Hopkins has identified six regions of
the human genome that might play a role in susceptibility
to obsessive compulsive disorder.
"OCD once was thought to be primarily psychological in
origin," said Yin Yao Shugart, statistical geneticist and
associate professor of
epidemiology at the
Johns Hopkins Bloomberg
School of Public Health. "But now there is growing
evidence that there is a genetic basis behind OCD, which
will help us better understand the condition."
OCD is characterized by intrusive and senseless
thoughts and impulses that together are defined as
obsessions, along with repetitive and intentional
behaviors, referred to as compulsions. OCD is estimated to
affect up to 3 percent of the American population.
In what the research team describes as the first
whole-genome scan to look for genetic "markers" or
similarities in the genomes of people with OCD, results
identified six potentially significant regions in the
genome, which lie on five different chromosomes, that
appear "linked" to OCD. It's likely that any genes directly
associated with OCD are to be found in these regions.
"We've long suspected that rather than being caused by
a single gene, OCD has multiple genetic associations," said
Jack Samuels, an epidemiologist and assistant professor of
psychiatry at the Johns Hopkins School of Medicine.
To conduct the study, which was published online June
6 in Molecular Psychiatry, the researchers collected blood
samples from 1,008 individuals from 219 families in which
at least two siblings were clinically diagnosed with
DNA from each sample was analyzed by the
Johns Hopkins Center
for Inherited Disease Research using both molecular
biology and statistical analysis computer programs.
Specific DNA sequences — known as genetic markers
— on chromosomes 1, 7, 6 and 15 and two markers on
chromosome 3 appear more frequently in the patients with
OCD than in those without it. The researchers want to
further analyze the genetic regions they identified in this
report and use more markers to possibly narrow down these
regions to identify OCD risk genes.
The researchers suggest that whatever genes are found
don't directly cause OCD but increase risk for it in
conjunction with other genes or environmental factors.
"OCD is a relative newcomer to these genetic linkage
studies," Shugart said, "so it's extremely important to
follow up these findings by looking at more families and
using more markers to assess the role of gene-environment
interactions in OCD. "We are also very interested in
finding genes underlying the different subtypes of OCD,"
Careful genetic analysis of different clinical
categories of OCD has been limited by currently existing
computer programs used in analyzing this type of data. The
vast amount of data used in whole-genome analysis requires
fine-tuned statistical calculations. The research team is
eager to develop new methods in this area. "We predict that
such findings may have immediate clinical implications for
OCD patients," Shugart said.
The researchers were funded by the National Institute
of Mental Health, the National Institutes of Health and the
Johns Hopkins Bloomberg School of Public Health.
Authors on the paper from Johns Hopkins are Shugart,
Samuels, V.L. Willour, M.A. Grados, Y. Wang, B. Cullen, R.
Hoehn-Saric, D. Valle, K.-Y. Liang, M.A. Riddle and G.