Biological Psychiatry

Original Paper

Neuropsychobiology 2004;49:178–181DOI: 10.1159/000077362

Association Study of a Brain-DerivedNeurotrophic Factor (Val66Met) GeneticPolymorphism and Panic Disorder

Pok Lama Chih-Ya Chengb Chen-Jee Hongb,c Shih-Jen Tsaib,c

aDepartment of Psychiatry, Shin-Kong Wu Ho-Su Memorial Hospital, bDepartment of Psychiatry,Taipei Veterans General Hospital, and cDivision of Psychiatry, School of Medicine, National Yang-Ming University,Taipei, Taiwan, ROC

Shih-Jen Tsai, MDPsychiatry Department, Taipei Veterans General HospitalNo. 201 Shih-Pai Road, Sec. 211217, Taipei, Taiwan (ROC)Tel. +886 2 2875 7027, ext. 276, Fax +886 2 2872 5643, E-Mail sjtsai@vghtpe.gov.tw

ABCFax + 41 61 306 12 34E-Mail karger@karger.chwww.karger.com

© 2004 S. Karger AG, Basel0302–282X/04/0494–0178$21.00/0

Accessible online at:www.karger.com/nps

Key WordsAssociation study W Agoraphobia W Polymorphism W

Brain-derived neurotrophic factor W Panic disorder W

Mitral valve prolapse

AbstractBrain-derived neurotrophic factor (BDNF), a member ofthe neurotrophic factor family, plays an important role inthe development, maintenance and function of severalneuronal systems. Recent studies have demonstratedthat antidepressants, commonly used for panic disordertreatment, can increase central BDNF. In addition, ani-mals with BDNF deficits have higher levels of anxietywhen exposed to stressors in comparison to normal con-trols. The present study tested the hypothesis that theBDNF gene Val66Met polymorphism is associated withpanic disorder. In this study, therefore, the incidence ofthis polymorphism was compared in 103 panic disorderpatients and 180 normal controls. The genotype and

allele frequencies for the BDNF gene Val66Met polymor-phism did not differ comparing the two groups. Further-more, no association was demonstrated between thisBDNF polymorphism and either mitral valve prolapse oragoraphobia in panic disorder patients. These findingssuggest that the investigated BDNF polymorphism doesnot play a major role in the pathogenesis of panic disor-der in this Chinese population. Further studies exploringthe relationship between genetic variations of BDNF andthe cerebral atrophy associated with, and antidepressanttreatment response in, panic disorder may be appro-priate.

Copyright © 2004 S. Karger AG, Basel

Introduction

Panic disorder is an anxiety disorder that causes con-siderable short- and long-term morbidity; however, its eti-ology remains unclear. Research over the past two de-cades using challenge studies and a variety of panicogenicagents has suggested a network model involving dysregu-lation of multiple neuronal systems, including mono-amine and neuropeptide [1]. In addition, the results of

The experiments in this study were performed in the MolecularGenetic Laboratory, Department of Psychiatry, Taipei Veterans Gen-eral Hospital, Taipei, Taiwan, ROC.

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Brain-Derived Neurotrophic Factor andPanic Disorder

Neuropsychobiology 2004;49:178–181 179

molecular epidemiological studies indicate the possibleinvolvement of genetic factors in the etiology of panic dis-orders [2].

Brain-derived neurotrophic factor (BDNF), a memberof the neurotrophin family, is important for neuronalgrowth, development, differentiation and survival [3]. Inaddition, BDNF can modulate synaptic plasticity and itsmolecular mediators across multiple neurotransmittersystems, as well as the intracellular signal transductionpathway [3]. Recently, an accumulation of evidence hasindicated that BDNF may be involved in the pathophysi-ology of anxiety disorders. Data derived from an animalstudy have demonstrated that, compared with wild-typemice, BDNF mutants were hyperactive after exposure tostressors and had higher anxiety levels when evaluatedusing the light/dark exploration test [4]. Furthermore, thefact that selective serotonin reuptake inhibitors (SSRIs)and other antidepressants suppress panic attacks and thatchronic administration of these antidepressants increasesBDNF expression in the rat cerebral cortex [5] suggeststhat BDNF may play some role in the pathophysiology ofpanic disorder.

From the above findings, it appears reasonable to sug-gest that BDNF may represent an appropriate candidategene, as genetic variations appear to confer risk for panicdisorder. The human BDNF gene has been mapped tochromosome 11 [6]. Recently, a significant associationhas been reported between a novel polymorphism(G196A) in the coding region of the BDNF gene, whichresults in an amino acid change (Val66Met), and specificcognitive functions [7, 8], personality traits [9], Alzhei-mer’s disease [10], and obsessive-compulsive [11], bipolar[12], and eating disorders [13], although not in all studies[14, 15]. In the current investigation, therefore, the rela-tionship between the BDNF gene Val66Met polymor-phism and panic disorder was examined in a Chinesesample population. Since panic disorder patients oftenare comorbid with mitral valve prolapse or agoraphobia,we also tested if this BDNF polymorphism is associatedwith mitral valve prolapse or agoraphobia in the patientgroup.

Material and Methods

SubjectsThe study group included 103 psychiatric outpatients who met

the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV)criteria for panic disorder. Each patient was assessed by a board-certified psychiatrist blind to genotyping. Thyroid function was eval-uated for each patient to rule out hyperthyroidism. Of the 103

patients, 92 underwent M-mode and two-dimensional echocardio-gram evaluation. The criteria for the diagnosis of mitral valve pro-lapse were: a posterior excursion of 2 mm or more in one or bothleaflets during systole on M-mode examination [16], and/or a back-ward displacement of one or both mitral valve leaflets beyond animaginary line drawn across the atrioventricular ring during systoleon two-dimensional examination [17].

For comparison, 180 normal volunteers were also enrolled to testthe association between the BDNF polymorphism and panic disor-der. The study population consisted entirely of ethnic Chinese whohad given their written, informed consent.

Laboratory MethodsFor BDNF gene Val66Met polymorphism genotyping, genomic

DNA was extracted from EDTA-containing venous blood samples.The DNA fragments of interest were amplified using polymerasechain reaction with the primers 5)-ACTCTGGAGAGCGTGAAT-3)and 5)-ATACTGTCACACACGCTC-3). The Val66Met polymor-phism was differentiated using the NlaIII restriction enzyme. Theproblem of partial digestion was monitored by an internal restrictionsite and a control sample of digestible homozygous Val/Val.

Statistical AnalysisThe categorical data were analyzed using the ¯2 test, or Fisher’s

exact test where necessary. For continuous variables, the differenceswere evaluated using Student’s t test or one-way analysis of variance.Data are presented as mean B SD.

Results

Comparing the panic disorder and control popula-tions, the mean ages (38.5 B 10.3 and 37.4 B7.7 years,respectively) and sex distributions (male/female 45/58and 68/112, respectively) were similar (p = 0.366 and p =0.377, respectively). The genotypes and allele distribu-tions for the BDNF gene Val66Met polymorphism for thetwo groups are presented in table 1. The Val66Met geno-type distributions for these two groups were in the Hardy-Weinberg equilibrium. Neither genotype (p = 0.140) norallele frequencies (p = 0.163) were statistically differentcomparing the two groups. Further, no statistically signifi-cant association was demonstrated comparing genotypedistribution for panic disorder with or without agorapho-bia, and with or without mitral valve prolapse (table 1).

Discussion

This study found no association between panic disor-der and the studied BDNF genetic polymorphism. Ournegative finding suggests that the BDNF gene Val66Metpolymorphism does not play a major role in panic disor-der susceptibility. It is possible that additional variants of

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180 Neuropsychobiology 2004;49:178–181 Lam/Cheng/Hong/Tsai

Table 1. BDNF genotype distributions and allele frequency in panic disorder patients and normal control subjects

Patient group n Genotype

Val/Val Val/Met Met/Met p

Allele frequency

Val Met p

Panic disorders 103 30 (29.1) 53 (51.5) 20 (19.4) 0.140a 113 (54.9) 93 (45.1) 0.163a

With agoraphobia 39 8 (20.5) 23 (59.0) 8 (20.5) 0.312b

Without agoraphobia 64 12 (34.4) 30 (46.9) 12 (18.8)With mitral valve prolapse 33 10 (30.3) 16 (48.5) 7 (21.2) 0.836c

Without mitral valve prolapse 59 17 (28.8) 32 (54.2) 10 (16.9)Controls 180 34 (18.9) 107 (59.4) 39 (21.7) 175 (48.6) 185 (51.4)

Figures in parentheses indicate percentages.a Compared with the control group.b Compared with panic disorder patients without agoraphobia.c Compared with panic disorder patients without mitral valve prolapse.

the gene, not detected by analysis of the Val66Met poly-morphism, may influence the development of panic disor-der. Before definitely excluding a role for the BDNF genein the etiology of panic disorders, further studies areneeded examining other BDNF variants and examininglarger sample populations. An alternative interpretationof our negative results is that while the BDNF geneVal66Met polymorphism may not be involved in the pri-mary etiological mechanism of panic disorder, it mayaffect disease phenotype. To test this hypothesis, we fur-ther analyzed the relationship between the Val66Metpolymorphism and panic disorder patients stratified ac-cording to agoraphobia and mitral valve prolapse status.No statistically significant associations were demon-strated, however. Finally, our control samples were notscreened for panic disorder, which may have decreasedsensitivity substantially. According to Owen et al. [18],however, it is not necessary to screen controls for relative-ly uncommon disorders with a lifetime risk of 1% orbelow, since chance inclusion of a few affected cases willhave little effect on statistical power. Given the relativelylow prevalence of panic disorder (0.4%) in an epidemio-logical study of a community population in Taiwan [19], afalse-negative result due to inclusion of panic disorder inthe control group is less likely.

Recently, an association between the BDNF polymor-phism and brain morphology has been demonstrated inschizophrenic patients using a (GT)n dinucleotide repeatof the BDNF gene (located 1.04 kb upstream from thetranscription site) [20]. Since the sizes of the temporallobe and amygdala were found to be abnormally reducedin panic disorder patients [21–23], and as BDNF also

appears to be related to stress-related brain atrophy [24],BDNF genetic polymorphisms may be candidates forstudy in these patients. Furthermore, it has been demon-strated that SSRIs, a standard treatment for panic disor-der, can elevate central BDNF levels in an animal study[5]. Whether BDNF may underlie the therapeutic mecha-nism in the treatment of panic disorder, and whether spe-cific polymorphisms are associated with the therapeuticeffect of SSRIs may warrant further study.

Acknowledgments

This work was supported by grant NSC 91-2314-B-075-048 fromthe National Science Council, Taiwan, ROC, and grant VGH-90-163from the Taipei Veterans General Hospital.

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References

1 Zacharko RM, Koszycki D, Mendella PD,Bradwejn J: Behavioral, neurochemical, ana-tomical and electrophysiological correlates ofpanic disorder: Multiple transmitter interac-tion and neuropeptide colocalization. ProgNeurobiol 1995;47:371–423.

2 van den Heuvel OA, van de Wetering BJ, Velt-man DJ, Pauls DL: Genetic studies of panicdisorder: A review. J Clin Psychiatry 2000;61:756–766.

3 Hallbook F, Lundin LG, Kullander K: Lampe-tra fluviatilis neurotrophin homolog, descen-dant of a neurotrophin ancestor, discloses theearly molecular evolution of neurotrophins inthe vertebrate subphylum. J Neurosci 1998;18:8700–8711.

4 Rios M, Fan G, Fekete C, Kelly J, Bates B,Kuehn R, Lechan RM, Jaenisch R: Condition-al deletion of brain-derived neurotrophic factorin the postnatal brain leads to obesity andhyperactivity. Mol Endocrinol 2001;15:1748–1757.

5 Nibuya M, Morinobu S, Duman RS: Regula-tion of BDNF and trkB mRNA in rat brain bychronic electroconvulsive seizure and antide-pressant drug treatments. J Neurosci 1995;15:7539–7547.

6 Maisonpierre PC, Le Beau MM, Espinosa R3rd, Ip NY, Belluscio L, de la Monte SM,Squinto S, Furth ME, Yancopoulos GD: Hu-man and rat brain-derived neurotrophic factorand neurotrophin-3: Gene structures, distribu-tions, and chromosomal localizations. Geno-mics 1991;10:558–568.

7 Egan MF, Kojima M, Callicott JH, GoldbergTE, Kolachana BS, Bertolino A, Zaitsev E,Gold B, Goldman D, Dean M, Lu B, Weinber-ger DR: The BDNF val66met polymorphismaffects activity-dependent secretion of BDNFand human memory and hippocampal func-tion. Cell 2003;112:257–269.

8 Tsai SJ, Hong CJ, Yu YWY, Chen TJ: Associa-tion study of a brain-derived neurotrophic fac-tor (BDNF) Val66Met polymorphism and per-sonality trait and intelligence in healthy youngfemales. Neuropsychobiology 2004;49:13–16.

9 Itoh K, Hashimoto K, Kumakiri C, Shimizu E,Iyo M: Association between brain-derived neu-rotrophic factor 196 G/A polymorphism andpersonality traits in healthy subjects. Am JMed Genet 2004;124B:61–63.

10 Ventriglia M, Bocchio Chiavetto L, Benussi L,Binetti G, Zanetti O, Riva MA, Gennarelli M:Association between the BDNF 196 A/G poly-morphism and sporadic Alzheimer’s disease.Mol Psychiatry 2002;7:136–137.

11 Hall D, Dhilla A, Charalambous A, Gogos JA,Karayiorgou M: Sequence variants of thebrain-derived neurotrophic factor (BDNF)gene are strongly associated with obsessive-compulsive disorder. Am J Hum Genet 2003;73:370–376.

12 Sklar P, Gabriel SB, McInnis MG, Bennett P,Lim YM, Tsan G, Schaffner S, Kirov G, JonesI, Owen M, Craddock N, DePaulo JR, LanderES: Family-based association study of 76 can-didate genes in bipolar disorder: BDNF is apotential risk locus. Mol Psychiatry 2002;7:579–593.

13 Koizumi H, Hashimoto K, Itoh K, NakazatoM, Shimizu E, Ohgake S, Koike K, OkamuraN, Matsushita S, Suzuki K, Murayama M, Hi-guchi S, Iyo M: Association between the brain-derived neurotrophic factor 196G/A polymor-phism and eating disorders. Am J Med Genet,in press.

14 Tsai SJ, Hong CJ, Liu HC, Liu TY, Hsu LE,Lin CH: Association analysis of brain-derivedneurotrophic factor Val66Met polymorphismswith Alzheimer’s disease and age of onset. Neu-ropsychobiology 2004;49:10–12.

15 Hong CJ, Hou SJ, Yen FC, Tung CL, Pan GM,Tsai SJ: Association study of a brain-derivedneurotrophic-factor genetic polymorphism andmood disorders, age of onset and suicidal be-havior. Neuropsychobiology 2003;48:186–189.

16 Popp RL, Brown OR, Silverman JF, HarrisonDC: Echocardiographic abnormalities in themitral valve prolapse syndrome. Circulation1974;49:428–433.

17 Morganroth J, Mardelli TJ, Naito M, Chen CC:Apical cross-sectional echocardiography. Stan-dard for the diagnosis of idiopathic mitralvalve prolapse syndrome. Chest 1981;79:23–28.

18 Owen MJ, Holmans P, McGuffin P: Associa-tion studies in psychiatric genetics. Mol Psy-chiatry 1997;2:270–273.

19 Weissman MM, Bland RC, Canino GJ, Fara-velli C, Greenwald S, Hwu HG, Joyce PR,Karam EG, Lee CK, Lellouch J, Lepine JP,Newman SC, Oakley-Browne MA, Rubio-Sti-pec M, Wells JE, Wickramaratne PJ, WittchenHU, Yeh EK: The cross-national epidemiologyof panic disorder. Arch Gen Psychiatry 1997;54:305–309.

20 Wassink TH, Nelson JJ, Crowe RR, AndreasenNC: Heritability of BDNF alleles and theireffect on brain morphology in schizophrenia.Am J Med Genet 1999;88:724–728.

21 Vythilingam M, Anderson ER, Goddard A,Woods SW, Staib LH, Charney DS, BremnerJD: Temporal lobe volume in panic disorder –A quantitative magnetic resonance imagingstudy. Psychiatry Res 2000;99:75–82.

22 Uchida RR, Del-Ben CM, Santos AC, AraujoD, Crippa JA, Guimaraes FS, Graeff FG: De-creased left temporal lobe volume of panicpatients measured by magnetic resonanceimaging. Braz J Med Biol Res 2003;36:925–929.

23 Massana G, Serra-Grabulosa JM, Salgado-Pi-neda P, Gasto C, Junque C, Massana J, Mer-cader JM, Gomez B, Tobena A, Salamero M:Amygdalar atrophy in panic disorder patientsdetected by volumetric magnetic resonanceimaging. Neuroimage 2003;19:80–90.

24 Smith MA, Makino S, Kvetnansky R, PostRM: Stress and glucocorticoids affect the ex-pression of brain-derived neurotrophic factorand neurotrophin-3 mRNAs in the hippocam-pus. J Neurosci 1995;15:1768–1777.

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19

3.14

0.28

.22

- 11

/12/

2014

8:2

9:47

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