Am J Psychiatry 161:9, September 2004http://ajp.psychiatryonline.org
Linkage Disequilibrium of the Brain-Derived Neurotrophic Factor
Val66Met Polymorphism in Children With a Prepubertal
and Early Adolescent Bipolar Disorder Phenotype
Barbara Geller, M.D.
Judith A. Badner, M.D., Ph.D.
Rebecca Tillman, M.S.
Susan L. Christian, Ph.D.
Kristine Bolhofner, B.S.
Edwin H. Cook, Jr., M.D.
Objective: Transmission of the brain-derived neurotrophic fac-
tor (BDNF) Val66 allele in children with a prepubertal and early
adolescent bipolar disorder phenotype was examined.
Method: The prepubertal and early adolescent bipolar disor-
der phenotype was defined as current DSM-IV bipolar I disorder
(manic or mixed phase) with at least one cardinal mania crite-
rion (i.e., euphoria and/or grandiosity) to ensure differentiation
from attention deficit hyperactivity disorder. Probands (mean
age=10.7 years, SD=2.7) were obtained by consecutive new
case ascertainment from designated pediatric and psychiatric
venues. Parents and probands were interviewed separately by
research nurses who were blind to the probands’ diagnoses.
Genotyping was done with TaqMan Assay-on-Demand. Analysis
was done with the Family Based Association Test program.
Results: There were 53 complete, independent trios. The
BDNF Val66 allele was preferentially transmitted (Family Based
Association Test: χ2=6.0, df=1, p=0.014).
Conclusions: This finding in child bipolar disorder is consistent
with data for adults with bipolar disorder that show preferential
transmission of the Val66 allele.
(Am J Psychiatry 2004; 161:1698–1700)
Brain-derived neurotrophic factor (BDNF) is heavily
expressed in human brain and has increased expression
beginning in young adulthood (1). Relevance to child psy-
chiatry of differential BDNF expression by age is not yet
known. Preclinically, BDNF has been implicated in nu-
merous mood-relevant neurobiological actions (e.g., anti-
depressant drug response  and the neuroprotective ac-
tion of lithium ), and thus it was hypothesized to be a
good candidate for investigation in bipolar disorders.
Moreover, the Val66 allele is a functional variant in both
human and preclinical studies (4).
Recently, two independent research groups, using
family-based methods, reported that the Val66 allele (at
amino acid position 66 in exon 1 of the BDNF gene on
chromosome 11p13) was preferentially transmitted to
predominantly Caucasian adult probands with bipolar
disorder (5, 6). One Japanese case-control study had nega-
tive findings (7).
Based on functionality of the Val66Met single nucleotide
polymorphism (SNP) (4) and on family-based findings in
adult bipolar disorder (5, 6), preferential transmission of
the Val66 allele in children with a prepubertal and early
adolescent bipolar disorder phenotype was hypothesized.
Probands were a subset of subjects in the NIMH-funded Phe-
nomenology and Longitudinal Course of Pediatric Bipolar Dis-
orders study (8, 9) and were obtained by consecutive new case
ascertainment from designated pediatric and child psychiatry
venues, using methods described in detail elsewhere (9). In brief,
research nurses screened every new child at multiple pediatric
and child psychiatric sites. All children who were not excluded be-
cause of a priori exclusion criteria (e.g., major medical illness)
were interviewed by phone, and, if they still were not excluded,
they were given the complete research assessments.
Comprehensive assessment by research nurses who were blind
to the probands’ diagnoses included the Washington University
in St. Louis Kiddie Schedule for Affective Disorders and Schizo-
phrenia (10) given separately to the probands’ parents about their
children and to the children about themselves (11). The pre-
pubertal and early adolescent bipolar disorder phenotype was
defined as current DSM-IV bipolar I disorder (manic or mixed
phase) with at least one of the two cardinal criteria of mania (i.e.,
euphoria and/or grandiosity). Use of this cardinal symptom ap-
proach was analogous to the DSM-IV requirement of sad mood or
anhedonia for a diagnosis of major depressive disorder. This defi-
nition of a prepubertal and early adolescent bipolar disorder phe-
notype ensured differentiation from attention deficit hyperactiv-
ity disorder. This differentiation was a major contentious issue in
the field of child bipolar disorder, because of overlapping symp-
toms (e.g., hyperactivity, distractibility) between the two disor-
ders (8, 9). Moreover, the cardinal symptom approach also facili-
tated differentiation of a prepubertal and early adolescent bipolar
disorder phenotype from other child psychiatry disorders that
have aggression/irritability as a symptom (e.g., references 12, 13).
The Children’s Global Assessment Scale (14) score needed to be
≤60, which corresponds to definite clinical impairment (15). The
prepubertal and early adolescent bipolar disorder phenotype has
4-year longitudinal validation (8).
After complete description of the study was provided to par-
ents and children, written informed consent was obtained from
parents and written assent from children.
DNA extraction was performed by using a PureGene DNA ex-
traction kit by Gentra Systems Inc. (Minneapolis), and DNA quan-
titation was conducted with the PicoGreen dsDNA kit by Molecu-
lar Probes, Inc. (Eugene, Ore.). SNP genotyping was performed by
using TaqMan Assay-on-Demand (Applied Biosystems, Foster
City, Calif.). Data acquisition was performed on the Analyst AD
Am J Psychiatry 161:9, September 2004
(Molecular Devices, Sunnyvale, Calif.) by using the fluorescence
Genotype data were analyzed with the Family Based Associa-
tion Test program (http://www.biostat.harvard.edu/~fbat/fbat.
htm) and with the ASPEX/sib_tdt program (16). A one-tailed test
was used for analysis because only preferential transmission of
the Val66 allele would be considered significant, based on adult
bipolar disorder studies (5, 6).
The probands’ mean age was 10.7 years (SD=2.7), the
mean age at onset of baseline mania episodes was 7.6
years (SD=3.6), and the mean duration of baseline mania
episodes was 3.2 years (SD=2.5). The mean Children’s Glo-
bal Assessment Scale score was 44.3 (SD=8.5). The pro-
portion of female subjects was 35.8%, of Caucasians was
88.7%, and of prepubertal subjects was 60.4%.
There were 53 complete, independent biological trios
(probands and both biological parents), among which
there were 27 informative trios. The frequency of parental
Val66 alleles was 79.2%. Proband alleles were in Hardy-
Weinberg equilibrium (χ2=0.05, df=2, p=0.98). Analyses
showed preferential transmission of the BDNF Val66 allele
(Family Based Association Test: χ2=6.0, df=1, p=0.014;
sib_tdt: p=0.014). The Val66 allele was transmitted 21
times and not transmitted nine times (both parents in a
trio may transmit the allele). Exploratory analyses by pre-
pubertal status (16 informative trios) were significant
(Family Based Association Test: χ2=6.8, df=1, p=0.009;
sib_tdt: p=0.011). Analyses by gender and by postpubertal
status were not significant, but the number of informative
trios for postpubertal status was small (N=11).
These data suggest that the BDNF Val66 allele confers
susceptibility to a prepubertal and early adolescent bipo-
lar disorder phenotype. To our knowledge, this is the first
significant molecular genetic finding in child bipolar dis-
order. Whether this finding has implications for continu-
ities between child and adult bipolar disorder will be an
important question for future research.
Specificity of preferential Val66 allele transmission for
bipolar disorder is unclear, as this finding has also been re-
ported in one family-based study of probands with child-
hood-onset obsessive-compulsive disorder (17).
Received Aug. 14, 2003; revision received Dec. 16, 2003; accepted
March 9, 2004. From the Department of Psychiatry, Washington
University School of Medicine; and the Department of Psychiatry,
University of Chicago, Chicago. Address reprint requests to Dr. Geller,
Department of Psychiatry, Washington University School of Medicine,
660 S. Euclid Ave., St. Louis, MO 63110; email@example.com
Supported by NIMH grants MH-53063 and MH-57451 to Dr. Geller
and MH-01389 to Dr. Cook; the Theodore and Vada Stanley Founda-
tion (Dr. Geller and Dr. Cook); and the Nathan Cummings Foundation
(Dr. Geller). The authors thank Betsy Zimerman, B.S.N., M.A., and
Marlene Williams, R.N., for help with administration and data collec-
tion; Jeanne Frazier, B.S.N., and Linda Beringer, R.N., for help with
data collection; and Diane Dickel, Heather L. Fritz, and Zhi-Ying Yang
for help with genotyping.
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