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Further evidence of MAO-A gene variants associated with bipolar disorder.

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American Journal of Medical Genetics Part B (Neuropsychiatric Genetics) 144B:37 –40 (2007)
Further Evidence of MAO-A Gene
Variants Associated With Bipolar Disorder
Daniel J. Müller,1,3 Alessandro Serretti,2* Tricia Sicard,3 Subi Tharmalingam,3 Nicole King,3
Paola Artioli,4 Laura Mandelli,2 Cristina Lorenzi,4 and James L. Kennedy3**
Department of Psychiatry, Charite´ University Medicine Berlin, PUK der Charite´ im SHK, Charite´ Campus Mitte, Berlin, Germany
Institute of Psychiatry, University of Bologna, Bologna, Italy
Neurogenetics Section, Centre for Addiction and Mental Health, Department of Psychiatry, University of Toronto, Toronto, ON, Canada
Department of Psychiatry, San Raffaele Scientific Institute, Milan, Italy
The aim of this study was to investigate MAOA
gene variants in bipolar disorder by using a
family-based association approach. The first sample included 331 nuclear families from Western
and Central Canada with at least 1 offspring
affected with bipolar disorder comprising a total
of 1,044 individuals. All subjects were genotyped
for MAOA–941T > G and uVNTR gene variants
using PCR techniques. Haplotype TDT was statistically significant (LRS ¼ 12.17; df ¼ 3; P ¼ 0.0068;
permutation global significance ¼ 0.00098), with
the T-4 haplotype significantly associated with
bipolar disorder (OR ¼ 1.63, 95% CI ¼ 1.11–2.37).
Single marker analysis evidenced a borderline
association for MAOA–941T > G (P ¼ 0.04), but not
for the uVNTR. Pooling the Canadian sample with
a second previously reported Italian sample
genotyped for the uVNTR variant, negative
results were obtained as well. No different results
were detected when analyzing female subjects
separately. In conclusion, our family-based association study gives mild but further support of
the involvement of MAOA variants in bipolar
disorder. ß 2006 Wiley-Liss, Inc.
bipolar disorder; affective disorder; MAO-A; genetics
Please cite this article as follows: Müller DJ, Serretti A,
Sicard T, Tharmalingam S, King N, Artioli P, Mandelli L,
Lorenzi C, Kennedy JL. 2007. Further Evidence of MAOA Gene Variants Associated With Bipolar Disorder. Am
J Med Genet Part B 144:37–40.
Grant sponsor: Canadian Institutes of Health Research (CIHR);
Grant sponsor: CIHR postdoctoral fellowship award.
*Correspondence to: Alessandro Serretti, M.D., Institute of
Psychiatry, University of Bologna, Viale Carlo Pepoli 5, 40123
Bologna, Italy. E-mail:
**Correspondence to: James L. Kennedy, M.D., Neurogenetics
Section, Centre for Addiction and Mental Health, Department of
Psychiatry, University of Toronto, 250 College Street R30,
Toronto, ON, M5T 1R8, Canada.
Received 21 March 2006; Accepted 23 May 2006
DOI 10.1002/ajmg.b.30380
ß 2006 Wiley-Liss, Inc.
The gene coding for the monoamine oxidase A, the principal
enzyme for the degradation of biogenic amines, is of particular
interest for mood disorders [Preisig et al., 2005]. Pharmacological and genetic observations suggest that variations in either
the structural or in the regulatory sequences of the MAOA gene
could be associated with behavioral or physiological variability
in humans [Shih et al., 1999; Shih, 2004]. MAOA-deficient mice
have elevated brain levels of serotonin (5-HT), norepinephrine
(NE), and dopamine (DA), which are MAO-preferred substrates, and manifest aggressive behavior [Cases et al., 1995;
Shih and Chen, 1999]. The MAOA gene is located on the short
arm of the X chromosome (Xp11.23) [Sabol et al., 1998] and
several different polymorphisms in the MAOA gene have been
reported. Two of them gained interest for their functional
relevance. First, a G to T substitution at position 941 has been
reported [Hotamisligil and Breakefield, 1991], with the 941 T
allele associated with lower MAOA activity in human male
fibroblast lines. Second, a polymorphism located 1.2 kb
upstream of the MAOA coding sequence that affects the
transcriptional activity of the MAOA gene promoter has been
described [Sabol et al., 1998]. This gene polymorphism consists
of 30 bp repeated sequence present in 3, 3.5, 4, or 5 copies. In
luciferase reporter gene assays, allele copies 3.5 and 4 proved to
be 2–10 times more active than the shorter one (3), while
opposite findings were reported for the rarer allele copy 5
[Sabol et al., 1998; Deckert et al., 1999].
Previous reports of MAOA studies in bipolar disorder were
mixed but with some evidence of association. Despite negative
findings [Sasaki et al., 1998], meta analyses reported mild but
significant associations for the 941 T variant [Rubinsztein
et al., 1996; Furlong et al., 1999] in bipolar disorder. As for the
uVNTR variant, evidence was less unequivocal with negative
findings [Rubinsztein et al., 1996; Furlong et al., 1999; Kirov
et al., 1999; Kunugi et al., 1999; Syagailo et al., 2001; Serretti
et al., 2002], though significant sex-specific effects were
observed [Deckert et al., 1999; Lin et al., 2000; Preisig et al.,
2000; Schulze et al., 2000; Gutierrez et al., 2004]. The aim of
this study was to investigate the possible association of the two
MAOA gene variants with bipolar disorder in a large sample of
nuclear families recruited in the Toronto area and Central
Canada. The Canadian sample has subsequently been pooled
with an Italian sample where results for the VNTR polymorphism were previously reported yielding no significant
results to detect possible false negative findings due to the
sample size [Serretti et al., 2002].
The Canadian sample was composed of 336 patients
(212 females and 124 males), affected with bipolar disorder
Müller et al.
(n ¼ 319) and schizoaffective disorder, bipolar type (n ¼ 17),
from 331 nuclear families recruited in the Toronto area and
Central Canada. Patients mean age was 35.36 10.37 years
with a mean age at the onset of 20.00 7.58 years.
Diagnostic assessment procedures for this sample have been
published in detail elsewhere [Carter et al., 2003]. Briefly, a
semi-structured clinical interview (SCID-I) [First et al., 1995]
was performed to assign best estimate consensus DSM-IV
A second sample was composed by Italian patients,
with probands affected by Bipolar disorder (n ¼ 309), from
99 nuclear families recruited in the area of Milan (Northern
Italy). The sample was composed of 154 females (49.8%) and
155 males (50.2%), a mean age of 31.80 7.70 years and a mean
age at the onset of 23.13 5.41 years. Findings on the uVNTR
polymorphism of this sample were reported in the context of a
previous study [Serretti et al., 2002]. Lifetime diagnoses were
assigned according to DSM-IV criteria on the basis of the
Structured Clinical Interview for DSM-IV, axis I disorders
(SCID-I) and all available sources of information. Informed
consent was obtained from all subjects after the aim of the
study had been fully explained.
Genomic DNA was obtained from peripheral leukocytes,
using high salt extraction methods [Lahiri and Nurnberger,
1991]. Genotypes of the MAOA-VNTR polymorphism was
determined by Polymerase Chain Reaction (PCR). PCR was
performed with primers: 50 -GGACCTGGGCAGTTGTGC-30 ,
and 50 -CCCAGGCTGCTCCAGAAA-30 . Two and a half microliters of 20 ng/ml stock genomic DNA was used in a 20 ml
reaction volume in the Canadian sample while 100 ng DNA
was diluted to 5 ml in the Italian sample. Amplification was
performed with an annealing temperature of 598C (Canadian
sample) and 618C (Italian sample). PCR products were
resolved using 3.0% high resolution plus agarose gel for
2.5 hr at 100 volts [Sabol et al., 1998]. The MAOA941T > G
polymorphism was analyzed by Applied Biosystems (ABI)
Taqman assay only in the Canadian sample [Hotamisligil and
Breakefield, 1991]. An ABI Taqman assay was specially
designed (Assay-by-design) using the following primers; forward ¼ CTTCCAGCAGAGAGAAACCAGTTAA and reverse ¼
GGCCTCCTTGTAATACATCATGCA. The assay was analyzed on the ABI7000 sequence detection instrument (Applied
Biosystems, Inc., Foster City, CA). For each 10 ml reaction, we
used 1 ml of 20 ng/ml DNA, 5.0 ml of Taqman reaction mix, 0.25 ml
of ABI assay, and 3.75 ml of water.
Statistical Analysis
The transmission disequilibrium test (TDT) was applied for
single marker and haplotype family-based association analysis
[Spielman et al., 1993].
ETDT22 (extended TDT analysis) [Sham and Curtis, 1995]
was used for single allele significance in single marker analysis
and applied for X-linked analyses. Haplotype analyses were
performed with the program TDTPHASE 2.403 [Dudbridge,
2003] that also includes an option for X-linked analyses.
Haplotypes-analyses were performed with the COCAPHASE
2.35 program [Dudbridge, 2003]. Using a standard unconditional logistic regression, this program performs likelihood
ratio tests (LRT) under a log-linear model of the probability
that an haplotype belongs to the case rather than the control
group; the expectation–maximization (EM) algorithm is used
to resolve uncertain haplotypes and provides maximumlikelihood estimates of frequencies. Permutation analyses
were used to determine empiric P levels, by using 10,000
TABLE I. Haplotype Frequencies for MAOA 941T > G and
VNTR Polymorphisms, in the 331 Families of Bipolar Patients
(Canadian Sample)
MAOA 941T > G
Haplotype frequency
We calculated the power of our sample (Canadian) to detect
transmission differences for TDT analysis with an alpha level
of 0.05. We had a sufficient power (0.80) to detect a genotypic
relative risk of 1.81 (Aa) and 3.08 (AA) with a minimum
detectable difference of frequency of 0.17 between the two
groups (considering a frequency of the disease allele of 0.4,
a disease prevalence of 0.01, a phenocopy rate of 0.1, a
penetrance of 0.8, a codominant transmission model, and a
strong LD (D-prime ¼ 0.9) between disease and marker)
[Purcell and Sham, 2001; Purcell et al., 2003].
In the Canadian sample, MAOA–941T > G and VNTR
were in strong linkage disequilibrium (Chi-sq ¼ 863.85 df ¼ 4
P ¼ 0.0001; D0 ¼ 0.84), with high frequency rate of the T-4
haplotype in the sample of 331 nuclear families (Table I).
Single marker TDT, performed with ETDT22, showed a
positive, though marginal, association between the T allele
of the 941T > G polymorphism and bipolar disorder (Chisquared for allele-wise TDT ¼ 4.11; df ¼ 1; P ¼ 0.04), while no
association was detected for the VNTR polymorphism (Chisquared for allele-wise TDT ¼ 1.70; df ¼ 2; P ¼ 0.43) (Table II).
Similar results were obtained using COCHAPHASE single
marker analysis (941T > G: LRS ¼ 4.58; df ¼ 1; P ¼ 0.032;
VNTR: LRS ¼ 2.21; df ¼ 3; P ¼ 0.53) (see Table II).
Considering males and females separately, neither the
VNTR nor the 941T > G polymorphism were associated to
bipolar disorder (in males, respectively: P > 0.11, in females,
respectively: P > 0.14), probably because of decrease in sample
By the haplotype TDT analysis, the T-4 haplotype was found
significantly associated with bipolar disorder (LRS ¼ 14.94;
TABLE II. Individual Transmissions for MAOA 941T > G
(P ¼ 0.04) and VNTR Alleles (P ¼ 0.43) in the Canadian Sample
MAOA markers
941T > G
(Chi-sq, P)
(4.11, 0.04)
(1.70, 0.43)
Transmitted allele count.
Untrasmitted allele count.
Bipolar Disorder and MAO-A
TABLE III. Transmissions of the 941T > G and VNTR Haplotype in Bipolar Patients
(P ¼ 0.021) in the Canadian Sample
MAOA markers
941T > G
Transmitted haplotype count.
Untrasmitted haplotype count.
df ¼ 6; P ¼ 0.021; permutation analysis ¼ 0.02) (Table III). We
repeated the calculations dropping rare haplotypes (frequency
<0.01) and the result was even more significant (LRS ¼ 12.17;
df ¼ 3; P ¼ 0.0068; permutation analysis ¼ 0.00098). Carriers
of the T-4 haplotype had a significant risk effect (OR ¼ 1.63;
95%CI ¼ 1.11–2.37). Considering exclusively females did not
change the observed haplotype frequencies.
The Italian sample was only genotyped for the VNTR
polymorphism. According to the data found in the Canadian
sample, single marker TDT did not reveal a significant
association between the VNTR polymorphism and bipolar
disorder (Chi-squared for allele-wise TDT ¼ 1.31 df ¼ 1
P ¼ 0.29; LRS 1.09 df ¼ 1 P ¼ 0.30, permutation analysis ¼ 0.21). Finally, merging the Italian sample with the
Canadian one, no significant TDT was still observed for the
VNTR polymorphism (Chi-squared for allele-wise TDT ¼ 0.43
df ¼ 2 P ¼ 0.80; LRS ¼ 0.82 df ¼ 3 P ¼ 0.84, permutation analysis ¼ 0.85) (data not shown).
In the present sample, we observed a marginal association
between the MAOA gene and bipolar disorder with one single
nucleotide polymorphism (941T > G) and with haplotype
analyses using a family-based association strategy. The use of
those strategies has the purpose of circumvent biases linked to
the traditional case-control association studies, for example
population stratification (or admixture) due to ethnic variation
[Falk and Rubinstein, 1987; Spielman et al., 1993].
Consistent with functional analyses [Hotamisligil and
Breakefield, 1991], our data suggest an association of increased
bipolar affective disorder risk in particular with the MAOA 941
T which would be expected to correlate with relatively low
levels of MAOA activity. This finding is in line and in the same
direction of the one observed in previous reports in Caucasians
[Rubinsztein et al., 1996; Furlong et al., 1999; Preisig et al.,
2000]. Interestingly, the other polymorphism we investigated,
the MAOA VNTR, presented a moderate overtransmission of
the allele 4 which was more present also in panic disorder
subjects [Deckert et al., 1999]. However, a number of negative
articles were also reported, as stated in the introduction
section as well as discrepancies in the risk haplotype. The two
markers used in the present study could be considered quite
informative of the MAOA gene, firstly because it has been
reported that all the 90 kb length of the MAOA gene can be
represented by a single block with strong LD within it [Jansson
et al., 2005], then because the two polymorphism we analyzed
are in strong LD and they located at approximately 70 kb from
each other spanning a large part of the gene (Regarding
haplotype structure, the reader is referred to www.hapmap.
org or¼
4128 in order to retrieve the latest version of haplotype
interpretation of the MAOA gene).
Our sample size allowed us to observe effect sizes in the
medium range and this means that smaller differences were
not observable. In detail, we could reliably observe a difference
of about 0.17 between the two groups; therefore, the observed
value of 0.11 (OR ¼ 1.63) should be considered with caution.
However, single gene variants are not expected to have much
smaller effects than this on complex traits; therefore, the risk of
having an underpowered sample should not be considered high
[Kendler, 2005].
A possible explanation of our borderline findings is that
genetic influence is limited to other features that are
independent from both diagnoses and symptomatology factors
[Kendler, 2005]. This view is recently gaining interest following, as example, some reports of associations with antidepressant response (for a review see Serretti et al., 2005), or with
neuropsychology traits [Egan et al., 2001]. Such strategies try
to circumvent the complexities of psychiatric disturbances
following more linear hypotheses of functional polymorphisms
associated with simple traits. A more comprehensive analysis
of those features should, therefore, complement future studies.
Finally, family-based association studies are not free from
biases. In most instances case-control studies are more powerful compared to them. For instance, if we consider that for a
TDT analysis one needs to recruit not only cases but also both
parents, the samples appear generally undersized. Moreover, a
bias toward a selection of younger probands is implicit in the
method [Khoury and Yang, 1998; Schulze et al., 2001].
In conclusion, our family-based association study gives mild
but further support of the involvement of MAOA variants in
mood disorders.
This work was supported by a Canadian Institutes of Health
Research (CIHR) operating grant to J.L.K. and a CIHR
postdoctoral fellowship award to D.J.M.
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associates, evidence, disorder, variant, genes, mao, bipolar
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