ORIGINAL RESEARCH ARTICLE
Haplotypic association spanning the 22q11.21 genes
COMT and ARVCF with schizophrenia
AR Sanders1, I Rusu1, J Duan1, JE Vander Molen2, C Hou1, SG Schwab3,4,5, DB Wildenauer3,6,
M Martinez7and PV Gejman1
1Department of Psychiatry and Behavioral Sciences, Evanston Northwestern Healthcare Research Institute, Center for
Psychiatric Genetics, Northwestern University, Evanston, IL, USA;2Department of Human Genetics, University of Chicago,
Chicago, IL, USA;3School of Psychiatry and Clinical Neurosciences, University of Western Australia (UWA), Perth, Australia;
4Centre for Medical Research, UWA, Perth, Australia;5Department of Psychiatry, University of Bonn, Bonn, Germany;6Centre
for Clinical Research in Neurosciences, UWA, Perth, Australia;7Me ´thodologie Statistique et Epide ´miologie Ge ´ne ´tique des
Maladies Multifactorielles, Institut National de la Recherche et de la Sante ´ Me ´dicale, Evry, France
Catechol-O-methyltransferase (COMT) has been implicated in schizophrenia by its function
through its roles in monoamine neurotransmitter metabolism and its impact on prefrontal
cognition, and also by its position through linkage scans and a strong cytogenetic
association. Further support comes from association studies, especially family-based ones
examining the COMT variant, Val108/158Met. We have studied eight markers spanning COMT and
including portions of the two immediately adjacent genes, thioredoxin reductase 2 and
armadillo repeat deleted in velocardiofacial syndrome (ARVCF), using association testing in
136 schizophrenia families. We found nominal evidence for association of illness to rs165849
(P¼0.051) in ARVCF, and a stronger signal (global P¼0.0019–0.0036) from three-marker
haplotypes spanning the 30portions of COMT and ARVCF, including Val108/158Met with Val108/158
being the overtransmitted allele, consistent with previous studies. We also find Val108/158Met to
be in linkage disequilibrium with the markers in ARVCF. These findings support previous
association signals of schizophrenia to COMT markers, and suggest that ARVCF might
contribute to this signal. ARVCF, a member of the catenin family, besides being a positional
candidate, is also one due to its function, that is, its potential role in neurodevelopment, which
is implicated in schizophrenia pathogenesis by several lines of evidence.
Molecular Psychiatry (2005) 10, 353–365. doi:10.1038/sj.mp.4001586
Published online 31 August 2004
Keywords: psychosis; genetics; chromosomes; human; pair 22; allelic association; haplotypes;
Schizophrenia, a chronic, debilitating mental illness
affects approximately 1% of the world population
with symptoms such as delusions, hallucinations, and
disorganized thinking. Evidence from family, twin
and adoption studies indicates that schizophrenia has
a strong genetic contribution but, like other psychia-
tric disorders, cannot be explained by a single gene
defect or environmental factor.1Instead, it is believed
that schizophrenia results from multiple genes, likely
with small effects acting in combination perhaps in
conjunction with environmental factors. As described
below, interest in the catechol-O-methyltransferase
(COMT) gene as a candidate gene for schizophrenia
initially and most prominently has arisen via the
pathophysiological implications of its function, later
complemented by positional evidence, both through
linkage scans and cytogenetic associations.
COMT catalyzes the transfer of methyl groups to
catecholamines, including dopamine, as part of their
degradation.2A COMT knockout mouse demon-
strated a two- to three-fold increased amount of
dopamine in the frontal cortex of male mice, but not
in females, or in the striatum or hypothalamus;3
however, this was not seen in another study.4The
role of COMT may be relatively more important in the
prefrontal cortex since the more effective solute
carrier family 6 (neurotransmitter transporter, dopa-
mine), member 3 (SLC6A3) is scarce there.5COMT
resides within both neurons and glial cells in the
brain,6,7but in the prefrontal cortex and striatum most
COMT mRNAs are found in neurons in humans and
mice.7,8There are two major forms of COMT, a soluble
shorter form (S-COMT) found in the cytoplasm and a
longer membrane-bound form (MB-COMT) found on
the cytoplasmic side of the rough endoplasmic
reticulum,9–12with the latter being the predominant
form, B70% of total COMT protein, expressed in the
Received 30 July 2004; revised 30 July 2004; accepted 02 August
Correspondence: AR Sanders, Department of Psychiatry and
Behavioral Sciences, Evanston Northwestern Healthcare Research
Institute, Center for Psychiatric Genetics, Northwestern Univer-
sity, Evanston, IL 60201, USA.
Molecular Psychiatry (2005) 10, 353–365
& 2005 Nature Publishing Group All rights reserved 1359-4184/05 $30.00
brain.13In addition, catecholamines have a higher
affinity, but a lower reaction velocity, with MB-COMT
than with S-COMT,14making MB-COMT more effec-
tive at the lower physiological dopamine concentra-
tions found in the brain, especially in the prefrontal
cortex,14,15all of which points the greater importance
of MB-COMT in the brain.16COMT, whether MB-
COMT or S-COMT, is an intracellular enzyme;15no
MB-COMT has been found in the cell membrane.12
So, at least in the prefrontal cortex where SLC6A3 is
scarce, another method of getting dopamine into the
cell is necessary to invoke,7perhaps the organic
cation transporters, solute carrier family 22 (organic
cation transporter), member 2 (SLC22A2, also known
as OCT2) or solute carrier family 22 (extraneuronal
monoamine transporter), member 3 (SLC22A3, also
known as OCT3), which are expressed in cortical
neurons and might represent background transporters
for monoamine neurotransmitters.17–19
COMT has six exons, the first two of which are
noncoding; exon 3 begins with the start codon for the
1.5kb (kilobase) MB-COMT mRNA and 150bp later in
exon 3 is the start codon for the 1.3kb S-COMT
mRNA (see review Lundstrom et al20). The proximal
promoter (P1) is located in much of intron 2 upstream
of the start codon for MB-COMT to part-way between
the start codons for the two COMTisoforms in exon 3;
S-COMT mRNA can only be translated into S-COMT
protein since it lacks the start codon for MB-
COMT.13,21The distal promoter (P2) is located in
much of the 50UTR of exon 1, spanning upstream into
the 50-flanking sequence; MB-COMT mRNA can be
translated into MB-COMT protein, and also into S-
COMT protein by using the leaky scanning mechan-
ism of translation initiation.13,21
potential function is presently unknown, two of the
single-nucleotide polymorphisms (SNPs) we have
assayed (rs2097603 and rs2020917) are in this distal
promoter, within several bp from putative regulator
elements, a cCAAT/enhancer-binding protein (CEBP)
site and an estrogen response element (ERE), respec-
tively.21Extension of previously determined13COMT
promoter sequence, coupled with functional deletion
analyses of these promoter regions, showed that
estrogen can specifically downregulate human COMT
gene transcription in a time- and dose-dependent
manner in the presence of estrogen receptors in an
amount comparable to the gender difference in COMT
activity in humans.21For the COMT distal promoter,
the323bp region containing
?287A/G by some authors22–24and ?1217A/G by
others25,26) mediated this effect.21If higher COMT
activity was a risk factor for schizophrenia (see
Discussionbelow), or conversely, lower COMT
activity was somewhat protective against schizophre-
nia, the 20–30% lower COMT activity in women27–29
would be consistent with several observations with
regard to gender differences in schizophrenia as
Interest in the proximal region of chromosome 22q
as harboring a susceptibility gene for schizophrenia
has in part resulted from whole genome linkage scans.
Although linkage has not been found in most such
scans, proximal chromosome 22q has shown one of
the stronger linkages to schizophrenia,31–37especially
when considered in recent meta-analyses of schizo-
phrenia genome scans using different methods.38,39
There are also some linkages here in bipolar disorder
studies40–43and meta-analytically.38Further interest in
the role of COMT, along with its two immediately
adjacent genes, proximally thioredoxin reductase 2
(TXNRD2)44,45and distally armadillo repeat deleted in
velocardiofacial syndrome (ARVCF)46in schizophre-
nia arises from their chromosomal location in the
deleted region of chromosome 22q11.2 associated with
velocardiofacial syndrome (VCFS), the most common
human contiguous gene disorder. Many anomalies
have been reported in VCFS, with behavioral mani-
festations being the most common.47Approximately
30% of VCFS patients develop psychosis, largely
schizophrenia,48–50and schizotypy scores are higher
in nonpsychotic VCFS subjects than controls.50The
region containing TXNRD2, COMT, and ARVCF is
deleted in over 99% of VCFS cases.47,51,52These
deletions would lead to a hemizygous state over the
deleted region, and likely haploinsufficiency for some
of the gene products, which might predispose to
psychosis. In any case, with the exceptions of being
the monozygotic twin of a schizophrenic or being the
offspring of two parents each having schizophrenia,53
VCFS represents the highest known risk factor for
A common COMT coding missense SNP (Val108Met
when numbered according to the S-COMT, Val158Met
in MB-COMT) has been noted,56for which the Val108
allele has three- to four-fold higher enzyme activity
and thermostability (even at 371C) than the
allele (when each is homozygous),56,57with hetero-
zygotes being intermediate.57,58It is thought that
the Val108Met difference in thermal stability is
the source of the difference in enzyme activity56,59
and it is further noted that the variant is located
on the opposite side of the enzyme from the
active site.56,60These findings of increased enzyme
activity and thermostability of Val108were recently
confirmed and further extended in experiments
in human liver tissue and also cultured mammalian
cells, where the increased activity of Val108resulted
immunoreactive protein.61In most tissues (except
the brain), S-COMT predominates, accounting for
about 95% of the total COMT activity.62,63As pointed
out in a recent review,64while the Val108version of
S-COMT has been shown to be three to four times as
active and more thermostable than the108Met version
of S-COMT,56,57the effect of Val158Met on MB-COMT
is unknown. Hence, it is not certain that the
predominant brain form of MB-COMT with its Val158
allele has such an increased activity (compared to
its158Met counterpart), as is the case for Val108in the
S-COMT chiefly assayed
Although it was predicted that VCFS individuals
for inthe periphery.
COMT and ARVCF association with schizophrenia
AR Sanders et al
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Supplementary information accompanies the paper on Molecular Psychiatry website (http://www.nature.com/mp)
COMT and ARVCF association with schizophrenia
AR Sanders et al