No influence of 5-HTTLPR gene polymorphism on migraine symptomatology, comorbid depression, and chronification.
ABSTRACT The serotonergic system is thought to play an important role for mediating susceptibility to migraine and depression, which is frequently found comorbid in migraine. The functional polymorphism in the serotonin transporter gene linked polymorphic region (5-HTTLPR/SLC6A4) was previously associated with attack frequency and, thus, possibly with chronification.
We hypothesized that patients with the "s" allele have higher attack frequency and, paralleling results in depression research, higher scores of depression.
Genetic analysis of the SLC6A4 44 bp insertion/deletion polymorphism (5-HTTLPR) was performed in 293 patients with migraine with and without aura. Self-rating questionnaires were used for assessment of depression.
Multinomial logistic regression analysis found no evidence for association of the 5-HTTLPR polymorphism with either depression or migraine attack frequency.
We were not able to demonstrate any influence of the serotonin transporter 5-HTTLPR polymorphism on migraine phenomenology (attack frequency or comorbid depression), thereby excluding this variant to be a common genetic denominator for chronic migraine and depression.
- SourceAvailable from: Arjun Muralidharan
Article: Pain, analgesia and genetics.[Show abstract] [Hide abstract]
ABSTRACT: In the clinical setting, there is marked intersubject variability in the intensity of pain reported by patients with apparently similar pain states, as well as widely differing analgesic dosing requirements between individuals to produce satisfactory pain relief with tolerable side-effects. Genetic and environmental factors as well as their interaction are implicated, and these are discussed in this review. Pioneering work undertaken in mice more than a decade ago, showed a strong genetic contribution to levels of nociception/hypersensitivity as well as levels of antinociception produced by commonly available analgesic agents. To date more than 300 candidate 'pain' genes have been identified as potentially contributing to heritable differences in pain sensitivity and analgesic responsiveness in animals and humans, with this information available in a publicly accessible database http://www.jbldesign.com/jmogil/enter.html. Since then, many genetic association studies have been conducted in humans to investigate the possibility that single nucleotide polymorphisms (SNPs) in an individual gene may explain drug inefficacy or excessive toxicity experienced by a small subset of the whole population who have the rare allele for a particular SNP. Despite the fact that SNPs in more than 20 genes that affect pain sensitivity or contribute to interindividual variability in responses to analgesic medications have been identified in the human genome, much of the data is conflicting. Apart from deficiencies in the design and conduct of human genetic association studies, recent research from other fields has implicated epigenetic mechanisms that facilitate dynamic gene-environment communication, as a possible explanation.Journal of Pharmacy and Pharmacology 11/2011; 63(11):1387-400. · 2.03 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: A growing body of literature suggests that comorbid anxiety disorders are more common and more prognostically relevant among migraine sufferers than comorbid depression. Panic disorder (PD) appears to be more strongly associated with migraine than most other anxiety disorders. PD and migraine are both chronic diseases with episodic manifestations, involving significant functional impairment and shared symptoms during attacks, interictal anxiety concerning future attacks, and an absence of identifiable secondary pathology. A meta-analysis of high-quality epidemiologic study data from 1990 to 2012 indicates that the odds of PD are 3.76 times greater among individuals with migraine than those without. This association remains significant even after controlling for demographic variables and comorbid depression. Other less-rigorous community and clinical studies confirm these findings. The highest rates of PD are found among migraine with aura patients and those presenting to specialty clinics. Presence of PD is associated with greater negative impact of migraine, including more frequent attacks, increased disability, and risk for chronification and medication overuse. The mechanisms underlying this common comorbidity are poorly understood, but both pathophysiological (eg, serotonergic dysfunction, hormonal influences, dysregulation of the hypothalamic-pituitary-adrenal axis) and psychological (eg, interoceptive conditioning, fear of pain, anxiety sensitivity, avoidance behavior) factors are implicated. Means of assessing comorbid PD among treatment-seeking migraineurs are reviewed, including verbal screening for core PD symptoms, ruling out medical conditions with panic-like features, and administering validated self-report measures. Finally, evidence-based strategies for both pharmacologic and behavioral management are outlined. The first-line migraine prophylactics are not indicated for PD, and the selective serotonin re-uptake inhibitors used to treat PD are not efficacious for migraine; thus, separate agents are often required to address each condition. Core components of behavioral treatments for PD are reviewed, and their integration into clinical headache practice is discussed.Headache The Journal of Head and Face Pain 12/2012; · 2.94 Impact Factor
Chapter: Pharmacogenetics of Pain12/2013: pages 1-12;
No Influence of 5-HTTLPR Gene Polymorphism on Migraine
Symptomatology, Comorbid Depression, and Chronification
Thomas Wieser, MD; Kathrin Dresler, MD; Stefan Evers, MD, PhD; Charly Gaul, MD; Dorothea König;
Daniela Hölzl; Klaus Berger, MD; Dale Nyholt, PhD; Thomas Deufel, MD
Background.—The serotonergic system is thought to play an important role for mediating susceptibility to migraine and
depression, which is frequently found comorbid in migraine. The functional polymorphism in the serotonin transporter gene
linked polymorphic region (5-HTTLPR/SLC6A4) was previously associated with attack frequency and, thus, possibly with
Objective.—We hypothesized that patients with the “s” allele have higher attack frequency and, paralleling results in
depression research, higher scores of depression.
Methods.—Genetic analysis of the SLC6A4 44 bp insertion/deletion polymorphism (5-HTTLPR) was performed in 293
patients with migraine with and without aura. Self-rating questionnaires were used for assessment of depression.
Results.—Multinomial logistic regression analysis found no evidence for association of the 5-HTTLPR polymorphism with
either depression or migraine attack frequency.
Conclusion.—We were not able to demonstrate any influence of the serotonin transporter 5-HTTLPR polymorphism on
migraine phenomenology (attack frequency or comorbid depression), thereby excluding this variant to be a common genetic
denominator for chronic migraine and depression.
Key words: migraine, serotonin transporter, polymorphism, depression, chronification
Abbreviations: 5-HT serotonin, 5-HTTLPR serotonin transporter linked polymorphic region, ICHD-II International Classi-
fication of Headache Disorders Version II, MA migraine with aura, MO migraine without aura, CM chronic
migraine, TTH tension-type headache, DMKG Deutsche Migräne und Kopfschmerzgesellschaft (German
Headache Society), BDI Beck Depression Inventory, CES-D Center for Epidemiologic Studies Depression
From Neurologie, Krankenhaus Göttlicher Heiland, Vienna, Austria (T. Weiser); Abteilung für Allgemeine Anästhesie und
Schmerztherapie, Medizinische Universität Wien, Vienna, Austria (T. Weiser); Friedrich-Schiller-Universität Jena, Institut für
Klinische Chemie und Laboratoriumsdiagnostik, Universitätsklinikum Jena, Jena, Germany (K. Dresler; T. Deufel); Klinik für
Neurologie, Universitätsklinikum Münster, Münster, Germany (S. Evers); Klinik für Neurologie, Martin-Luther-Universität Halle/
Wittenberg,Halle/S.,Germany (C.Gaul);Genetic Epidemiology Laboratory,Queensland Institute of Medical Research,Brisbane,
Queensland, Australia (D. Nyholt); Institut für Klinische, Biologische und Differentielle Psychologie, Fakultät für Psychologie,
Universität Wien,Vienna,Austria (D. König); Medizinische Statistik und Informatik, Medizinische Universität Wien,Allgemeines
Krankenhaus, Vienna, Austria (D. Hölzl); Institut für Epidemiologie und Sozialmedizin, Universitätsklinikum Münster, Münster,
Germany (K. Berger).
Address all correspondence to T. Wieser, KH Göttlicher Heiland, Dornbacherstr. 20-28, 1170 Vienna, Austria.
Accepted for publication February 4, 2009.
Conflict of Interest: None
Published by Wiley Periodicals, Inc.
© 2009 the Authors
Journal compilation © 2009 American Headache Society
Serotonin (5-hydroxytryptamine, or 5-HT) and
the serotonergic system are believed to play an
important role in the pathophysiology in several neu-
ropsychiatric disorders such as anxiety,1depression,2,3
obsessive-compulsive disorder,4drug addiction,5,6and
also headache.7-9This is based to a great part on the
effect of drugs acting upon this system to modulate
the course of disease (selective serotonin reuptake
inhibitors and tricyclic antidepressants for depression
and 5-HT 1B/1D agonists for migraine) and to a
lesser part to experiments using brain imaging tech-
niques10,11and animal models.12
After release of 5-HT from axonal terminals of
serotonergic neurons, its synaptic effects are termi-
nated by reuptake into the nerve endings.13This
reuptake is mediated by a 5-HT transporter SLC6A4
(also commonly known as SERT, 5HTT, or 5-HTT),
which is mainly expressed in serotonergic neurons in
the raphe nuclei of the pons and upper brainstem,14
structures that have been shown to be important in
migraine pathogenesis.15-17Transcriptional activity
and, in consequence, reuptake capacity are geneti-
cally modified by several positive and negative regu-
latory elements within the SLC6A4 promoter region
and by a 17 bp variable number tandem repeat
element in intron 2.18-21Humans carry a common
44-base pair insertion/deletion polymorphism in the
promoter region of the SLC6A4 gene (serotonin
transporter linked polymorphic region; 5-HTTLPR)
that is found in 2 forms, long (l) and short (s). Indi-
viduals with either 1 or 2 copies of the s-allele (40-
70% of a given population) appear to have fewer
5-HT transporters than individuals with an l/l geno-
type. Furthermore, the l/l genotype is associated with
a 1.4 to 1.7 times increase in mRNA and an about
twofold increase in uptake capacity.22,23
Familial hemiplegic migraine, a rare and severe
subtype of migraine with aura (MA), is transmitted
in an autosomal dominant fashion; however, the
common forms of migraine, comprising migraine
without aura (MO) and migraine with typical aura
(International Classification of Headache Disorders
Version II [ICHD-II] 1.1, 1.2.1-3), follow a complex
pattern of inheritance and are multifactorial in etiol-
ogy. Bearing that in mind, it seemed an interesting
hypothesis that alterations in 5-HT metabolism might
predispose to migraine attacks; studies in migraine
patients, however, gave contrasting results.24-28It was
shown in one study that the s-allele is associated with
higher risk to develop an MA phenotype compared
with controls,29but other studies could not replicate
these results.30,31Interestingly, although, in the latter
study there was significant association with attack
Results are more consistent regarding the role of
this SLC6A4 polymorphism in depression.There was
no association between a certain genotype and
depression per se; yet, individuals with a “risk” geno-
type are clearly more prone to develop depression in
response to stressful life events.23,32-35This suggests
that the presence of additional interacting genetic
and/or environmental factors is a prerequisite for the
5-HTTLPR genotype to be effective in the etiology of
Comorbidity of migraine headache and major
depression has been reported in up to 80% of
patients37-40and it contributes significantly to disabil-
ity for each individual.40Studies have suggested a
shared common risk factor increasing the probability
of acquiring either condition rather than finding
The aim of this study was to investigate whether
5-HTTLPR genotype is a genetic factor relating
migraine and depression. Our first hypothesis is that,
rather than causing migraine itself, the effect of a
5-HTTLPR “risk” genotype would be (1) comorbid-
ity of depression; and (2) higher attack frequency
when migraine is present.
As chronification in headache is in contrast to
other pain syndromes defined by headache frequency,
we then further hypothesize that 5-HTTLPR geno-
type is a genetic risk for frequent headaches and thus
should be associated with headache chronification.
PATIENTS AND METHODS
A first set of patients was recruited from 3
university-based headache clinics (departments of
Neurology of the Universities of Vienna, Münster,
and Halle); a second set was included originating
from a large, cross-sectional, population-based study
conducted by the German Headache Society between
2000 and 2005 to investigate prevalence of headache
in Germany (DMGK). Migraine was diagnosed in all
patients according to the International Headache
Society (IHS) criteria of 2003 (ICHD-II);44only
patients with MA (IHS 1.2.1-3), MO (IHS 1.1), and
chronic migraine (CM, IHS 1.5.1) were included.The
study and the use of patients for the present investi-
gation were evaluated and approved by each local
ethics committee separately; all patients gave their
written informed consent prior to entering the study.
Age- and sex-matched controls were taken from
the headache prevalence study and comprised 2
groups (1) of individuals without any kind of
headache; and (2) patients with tension-type head-
ache (infrequent, frequent, and chronic) (TTH)
In patients, migraine frequency, age at onset,
duration and course of disease, migraine characteris-
tics (attack duration, intensity, accompanying symp-
toms, triggers, type of aura when present), other
headaches, and other diseases (diabetes, thyroid,
cardiac, etc) were carefully recorded. Family history
and medication for headache (type, dosage, prophy-
laxis) as well as for other conditions were also docu-
mented. Patients with concomitant diseases prone to
depression (eg, cancer, chronic low back pain) were
To compare our results with those published by
Kotani et al,31patients were grouped according to
attack frequency with group I having less than
2 attacks per month, group II with between 2 and
3.5 attacks per month, and group III with more than
3.5 attacks per month.
Depression.—To investigate depression, self-rating
questionnaires were used.All patients completed the
“Beck Depression Inventory” (BDI) or the “Allge-
meine Depressions Skala,”the German version of the
Center for Epidemiologic Studies Depression Scale
(CES-D),which are both validated screening tools for
depressive symptoms and consist of items assessing
fatigue, withdrawal, hopelessness, and listlessness
Patients were grouped in 3 groups regarding
depression as set out in the manual for the BDI; this
assignment is validated in numerous studies and has
been proven useful for pain research and has been
adapted for the CES-D. Group I is normal, with no
indication of depression (0-10 points BDI, 0-16 CES-
D), group II includes patients with mild to moderate
depression (11-17 points BDI, 17-23 CES-D), and
group III includes patients with clinical relevant
depression (>17 points BDI, 24-60 CES-D).45
Genetics.—Venous blood samples were taken from
all participants and genomic DNA extracted accord-
ing to standard procedures.49The 5-HTTLPR poly-
morphism is a 44 bp insertion/deletion polymorphism
in the untranslated promotor region of the 5-HT
transporter gene SLC6A4 located about 1 kilobase
upstream; it can be easily detected by PCR amplifi-
cation of the region using flanking primers.Extracted
DNA was amplified according to the protocol pub-
lished by Lesch et al.23Two fragments are generated
according to the presence or absence of the 44 bp
long element containing 16 repeats; they have a
length of 484 and 528 base pairs (short and long
allele), respectively, and were visualized on a 2%
agarose gel after ethidium bromide staining.
Statistical Analysis.—The sample size calculation
was based on the comparison between 2 comple-
mentary genetic groups (either the s/s + s/l vs l/l or
s/s vs s/l + l/l) with regard to the migraine attack fre-
quency per month. Assuming a group difference of
1.5 attacks per month, a standard deviation of 3 for
the monthly migraine attack frequency, and a
minimum sample size fraction of 13% for the
homozygotic groups (either s/s or l/l), the t-test at
level 0.05 would have a power of at least 80% with
a total of 285 patients. The assumption of a
minimum sample fraction of 13% in the homozy-
gotic groups is in accordance with the frequencies
observed in other samples being at least 12.9%.29
Assuming a dropout rate of 5%, the sample size was
fixed at 300 patients.
Using the observed allele frequencies, expected
genotype frequencies according to Hardy–Weinberg
law were calculated and compared with observed
genotype frequencies. Patients from the 3 recruiting
centers and the DMKG study cohort were compared
with respect to the baseline characteristics (age, sex,
migraine attacks per month and depression. Quantita-
tive variables are summarized by means ? standard
The frequency of migraine attacks per month was
analyzed on a logarithmic scale by a 2-way analysis
tive and dominance terms) and the interaction
between the factors. Depression was analyzed by a
proportional odds logistic regression analysis with the
factors genotype and origin, including the interaction
the association of genotype with migraine vs no
migraine,includingTTH and migraine vs no migraine
excluding TTH were analyzed by logistic regression
analyses.The association between genotype and MO
as well as between genotype and MA was analyzed by
similar logistic regression analyses.P values below .05
are considered nominally significant.
Multinomial logistic regression50was used to
study the cross-sectional association of depression
risk and frequency of migraine attacks with the
SLC6A4 44 bp insertion/deletion polymorphism. In
the multinomial logistic regression,the response vari-
able depression risk was coded as 1 (normal), 2 (mild
to moderate depression), and 3 (clinical relevant
depression). The response variable migraine attack
frequency was coded analogous to Kotani et al (2002):
1 = 0 to <2, 2 = 2 to 3.5, and 3 ? 3.5 attacks/month.
The stimulus (ie, explanatory) variable SLC6A4-
polymorphism was coded according to Table 1. In
addition, analogous to Kotani et al,31the mean
migraine attack frequency scores between group S (s/s
genotype) and group L (s/l, l/l genotype) were com-
pared by a t-test. P < .05 was considered nominally
significant. All statistical analyses were performed
using the R statistical package.51
variables by counts and
Out of the original 295 study patients, 293
patients were analyzed; 2 patients had to be omitted
because of incomplete data sets. Patient characteris-
tics are given in Table 2 for the 4 patient cohorts
Clinical Findings:Headache.—In total,253 patients
(86%) were female; 58 had MA (20%) and 235 MO;
the mean age of participants was 43.3 years. Mean
attack frequency per month was 3.7,with 75% having
1 attack per week or less and 17% having between 4
and 10 attacks per month;7 patients (2%) fulfilled the
criteria for CM (more than 15 headache days/month).
When grouped according to the Kotani study (see
above), 95 patients were in group I (16 MA and 79
MO), 93 in group II (22 MA and 71MO), and 105 in
group III (20 MA and 85 MO).Mean attack duration
was 33.5 hours; mean attack intensity was 6.9 on the
11-point visual analog scale. Participants had a mean
of 10 days per month with headache and a mean
disease duration of 25 years. Family history with at
least 1 first or second degree relative also suffering
from migrainous headache was positive in 123
patients (27 MA and 96 MO).
In 83 (28%) patients, other forms of headache
were present in addition to migraine; cervicogenic
headache was diagnosed in 3,cluster headache in one
of the cases,60 patients suffered from a infrequent or
frequent episodic tension-type headache (eTTH)
(IHS 2.1 and 2.2) and 8 from chronic tension-type
headache (cTTH) (IHS 2.3).Eleven patients reported
overuse of acute relief medications (IHS 8.2).
The samples from the different university clinics
did not differ in any of the aspects investigated
(Table 2);patients recruited from the epidemiological
study were markedly less affected compared with
patients recruited in the university outpatient clinics.
Accordingly,the factor“origin”was highly significant
Table 1.—Variable Coding for the 5-HTTLPR Polymorphism
Model s/ss/l l/l
Dominant MOI for allele s
Recessive MOI for allele s
Dominant MOI for allele l
Recessive MOI for allele l
Allelic for allele s
The allelic model is coded as a numeric variable (ie, integer).
All other models are coded as a factor (ie,categorical) variable.
Because the dominant MOI for allele s is equivalent to reces-
sive MOI for allele l, and the dominant MOI for allele l is
equivalent to recessive MOI for allele s, only results for the
dominant and recessive MOI for allele s are reported.
5-HTTLPR = serotonin transporter linked polymorphic re-
gion; MOI = mode of inheritance.
(F = 26.19,d.f.1 = 3,d.f.2 = 280,P < .0001) in the 2-way
ANOVA for the frequency of migraine attacks.
Clinical Findings: Depression.—Depression ac-
cording to the study criteria outlined above was
absent in 185 patients (63%), and mild depression
was found in 60 (20%); 51(17%) patients had clini-
cally relevant depression. There were no significant
differences regarding depression between university-
based outpatient clinics. However, in patients of the
epidemiological study,the status“no depression”was
found more frequently although the difference
between the cohorts is not significant in the propor-
tional odds regression analysis for depression (chi-
square test = 6.43, d.f. = 3, P = .093). In general, grade
of depression increased with attack frequency but not
with duration of disease, but failed to reach signifi-
The status “no depression” and “mild depres-
sion” was equally distributed over migraine groups
with rare attacks (Kotani groups I and II, ie, less than
4 attacks per month); the number of patients with
“clinically relevant depression” increased with attack
frequency (group I n = 10 [10%], group II n = 16
[17%], and group III n = 25 [24%]). Some 50% of
patients with clinically relevant depression were
found in the high attack group (Kotani group III).
However, the difference failed to reach significance
(c2= 8.59, d.f. = 4, P = .073).
Genetic Analysis.—Overall, the 5-HTTLPR poly-
morphism genotypes were distributed according to
Hardy-Weinberg Law (c2= 0.0029, d.f. = 1, P = 1) in
controls and patients.
No Association of 5-HTTLPR Genotype With
Migraine Status.—Within the cohort from the epide-
miological study, no statistically significant associa-
tion was found between genotype and migraine
(c2= 1.27, d.f. = 2, P = .53); this was true also when
controls with TTH were excluded (controls without
TTH: c2= 1.34, d.f. = 2, P = .51, data not shown).
Further, no association of genotype was found with
migraine subtypes MA (c2= 2.28, d.f. = 2, P = .32) or
MO (c2= 1.24, d.f. = 2, P = .54) (data not shown). To
investigate the influence of possible bias introduced
by our use of clinic-based controls, only the subset of
patients recruited for the epidemiological study
(n = 93) were analyzed. This provided a representa-
Table 2.—Characterization of the Headache Cohort
OriginDMKG (n = 94)Halle (n = 53)Münster (n = 99)Vienna (n = 47)All (n = 293)
Sex, n (%)
Attacks per month
44.78 ? 10.4947.40 ? 11.1340.62 ? 12.3041.85 ? 14.14 43.31 ? 12.10
2.28 ? 3 .56
27.02 ? 11.94
5.63 ? 4.52
20.17 ? 8.31
3.53 ? 2.60
23.60 ? 11.05
4.87 ? 3.67
21.47 ? 16.03
3.71 ? 3.68
25.00 ? 12.98
Summary of quantitative characteristics (mean ? standard deviation, percents, and counts in each cohort). Age and disease
duration in years.Patients from the different sites did not differ significantly in all aspects relevant for the study except that patients
from the epidemiological study had markedly less attacks per month.
Figure.—As could be shown in several studies before, depres-
sion increases with headache severity.
tive control group not only matched to ethnicity, age,
and sex but also recruited in the identical way (con-
trols n = 244, with n = 118 “no headache” and n = 126
“infrequent or frequent tension-type headache”).
No Association of 5-HTTLPR Genotype With
Migraine Attack Frequency or Depression.—As
shown in Table 3,no positive association between any
genotype and the frequency of migraine attacks was
found; results even indicate a negative association,
although this result does surpass our nominal signifi-
cance threshold in the 2-way ANOVA (F = 2.65,
d.f.1 = 1, d.f.2 = 280, P value = .07; no statistically sig-
nificant interaction term). The trend toward a nega-
tive association was most pronounced in the data of
the epidemiological study and stronger in the data
from the Viennese outpatient clinic, but was not well
or not at all detected in the other 2 university centers
(data not shown). There was also no association of
any genotype with depression.
Genotype With Depression Risk and Migraine
Phenotype.—Multinomial logistic regression analysis
found no evidence for association of the 5-HTTLPR
polymorphism with either depression risk or migraine
attack frequency (Kotani groups), with all tests pro-
ducing P values > .05.There was no significant differ-
ence in migraine attack frequency score between
group L (2.05 ? 0.05) and group S (1.94 ? 0.12).The
mean score for l/l individuals (2.12 ? 0.08) also did
not differ from s/s, s/l individuals (1.98 ? 0.06).
Detecting gene effects with only small possible
impact on disease phenotype is still a difficult task.
Increasing sample size to increase power also
increases genetic heterogeneity,hampering the detec-
tion of possible small influence of a certain genetic
predisposition. The variety of publications reporting
contrasting results from association studies as well as
the obvious difficulty in replicating previous findings
is visible expressions of that dilemma.
Migraine,although a unique headache syndrome,
displays enormous clinical variability, regarding not
only pain intensity, attack duration, and frequency of
attacks but particularly its accompanying symptoma-
tology such as premonitory (prodromal) symptoms,
trigger factors, drug response rate, aura, and kind of
aura, as well as its comorbid traits and states. A
number of genetic loci have been implicated on chro-
mosomes 1q31, 4q24, 11q24, 15q11-13, 6p12.2-21.1,
5q21, 10q22-23, 14q21.2-22.3, Xq24-28, and 19p13.3
(for review see the study byWessman et al52),indicat-
ing a high degree of genetic heterogeneity.Although
genetic association studies are a valid tool to identify
disease relevant genes beyond family-based linkage
studies in complex genetic, multifactorial, and possi-
bly heterogenic diseases, pronounced genetic hetero-
geneity might prevent its ability to come up with
The present study, using a large cohort of head-
background regarding the serotonergic system is an
influencing factor on disease phenotype of either
migraine or depression. The functionally relevant
5-HT transporter gene polymorphism was not associ-
ated significantly either with migraine attack fre-
quency or with presence or absence of depression in
our patients.Sample size reached the numbers as cal-
validated as “true,” under the given uncertainties,
which are commonly accepted for this kind of
Table 3.—No Association of Any Genotype With Depression
or Attack Frequency
s/s (n = 48) l/s (n = 140)l/l (n = 104)
Depression, n (%)
Attacks per month
2.81 ? 2.22
3.51 ? 3.13
4.43 ? 4.68
The P value in the proportional odds regression analysis is
P = .53, indicating no statistically significant interaction in the
study population between genotype and depression.There was
even a negative association between the s/s genotype and
attack frequency, but failed to be significant (2-way ANOVA
P = .07).
Variance.—Increasing sample size is one approach to
achieve sufficient power in association studies; to
meet that goal,the cooperation of more than 1 center
for recruiting patients is often necessary and genetic
heterogeneity will be increased. In our study we
included patients from different parts of Europe;
careful comparison of all clinical and epidemiologic
characteristics failed to show differences that one
would expect relevant to the analysis.The most strik-
ing difference was, not unexpectedly, that patients
from the epidemiological study were markedly less
affected; this is easily explained because most
severely affected patients are more likely to seek help
from a highly specialized,university-based outpatient
department.Health providers requiring referral from
a general practitioner to the university-based clinics
add to this bias.
central serotonergic system is located in the raphe
stem. It is known to play an important role in pain
processing and pain modulation; yet, its exact role in
headache and specifically migraine is not fully under-
stood. Intravenous infusions of 5-HT can terminate
of trigeminal nucleus activity as could be experimen-
tally shown when this nucleus was activated by elec-
trical stimulation of the sagittal sinus,an experimental
model thought to reflect migraine mechanisms
closely.53Further evidence of the importance of the
central serotonergic system for migraine was pre-
sented recently by demonstrating, using a highly spe-
cific SERT radio ligand in a single photon emission
brainstem SERT protein availability in migraineurs
compared with controls,suggesting a dysregulation of
the brain stem serotonergic system in these patients.54
However,variation in transport capacity of 5-HT,
regulated by the polymorphism in the promoter of
the 5-HT transporter gene, does not appear to be a
mechanism with relevant consequences regarding the
phenotype as more recent, large studies fail to repli-
cate earlier results that had implicated this gene.30In
accordance with these findings, we were not able to
show genetic association of a SLC6A4 polymorphism
with the presence or absence of migraine compared
with controls. To avoid bias because of insufficiently
recruited for the epidemiological study for this suba-
nalysis, accepting a reduced power for this analysis
because of the reduced remaining sample size. Thus,
we were able to make use of a control group that was
carefully matched not only for sex and age, but also
with respect to recruitment. Using anonymous con-
trols such as blood donors or other clinical popula-
tions, as is often performed, the prevalence of the
phenotype in question is unknown, possibly influenc-
ing the results. A further strength in our approach is
that controls were all carefully phenotyped so that the
presence of the disease under investigation was
excluded, which is especially important when study-
ing a disease such as migraine with a high prevalence
in the general population.
Depression and the SLC6A4 Polymorphism.—The
SLC6A4 polymorphism was not associated with the
presence or absence of depression in our sample con-
firming results from numerous studies conducted on
this topic with mostly negative results.55-60As stated in
the introduction,however,the presence of the s-allele
seems to be a genetic risk for developing depression
in response to life events, which is one finding that
could be consistently replicated.23,32-35,61The probably
complex interaction that results in depression in
certain individuals with a risk allele in response to life
events, is obviously not relevant in chronic pain
patients as our results show.
The degree of depression increased with “head-
ache load”(ie,headache days and intensity/month) in
our sample. This is in line with previous findings,
showing association of “severe” headache (including
CM62-64) and major depression (with severe headache
being defined as high average pain intensity and long
duration [total lost time of activity] independent of
headache diagnosis). While this association is prima-
rily in only one direction, from severe headache to
major depression,42,65when looking at migraine alone,
it was shown that there is no direct causal relation of
migraine and depression but there seems to be a bidi-
The mechanism behind this bidirectional associa-
tion might be a genetic predisposition, for which the
selected only probands
5-HTTLPR is a plausible candidate. However, our
results do not support the 5-HTTLPR polymorphism
as a genetic factor acting to explain the presence or
absence of depression.
We further investigated an interrelation of occur-
rence and/or degree of depression and migraine
attack frequency depending on a specific genetic
depression in patients with a high headache load
could be caused by a common genetic denominator;
this model would explain the high comorbidity of
both disorders without a direct causal relationship.
Despite the serotonergic system being a most attrac-
tive candidate,66however, no such interaction could
be shown in the sample used in the present study.
Risk Factorsfor Chronification
Migraine.—The processes behind chronification of
pain in general and in migraine are not well under-
stood. Some risk factors for chronification have been
indentified such as obesity, hypertension, and stress-
ful life events; psychological factors like chronic dis-
tress in daily life, depression, pain-related cognition,
and coping behavior seem to play an important role,
too.67-69It is quite likely that genetic factors are also
involved in pain chronification. Heightened pain
sensitivity because of altered pain-related neu-
rotransmission pathways, differing sensitivity to
drugs, comorbidity, and behavioral peculiarities
regarding drug intake, drug dependence, and possi-
blypaincoping can be
Research to date has focused on genes involved
in serotonergic neurotransmission like SLC6A4,
COMT, MAOA, and 5-HT receptors, and also on
receptors, and deals largely with generalized pain
syndromes like chronic widespread pain and fibro-
myalgia. Although results in some studies were sig-
nificant, it could often not be confirmed and no
single gene gave convincing evidence for a signifi-
cant role in pain chronification.70
It was on this background that we were intrigued
to see Kotani reporting in their study of Japanese
migraine patients that there was also no association of
the 5-HTTLPR polymorphism with the presence of
migraine itself but that a certain genotype was asso-
ciated with high migraine attack frequency. In con-
mediators, and opioid
trast to other pain disorders, such as chronic back
pain,chronification in headache is defined not merely
by disease duration but by the frequency of the occur-
rence of headache (headache days per month). Our
results from the present study fail to show that a
certain genetic background acts on migraine attack
frequency (expressed as headache days or attack fre-
quency), and that the 5-HTTLPR polymorphism is
not a genetic risk factor for migraine chronification.
One reason for us not being able to replicate these
results might be that distribution of alleles in the par-
ticular Japanese sample was skewed in comparison
with our data with 60% of the s/s genotype present,in
contrast to our (16%) and other European samples
Genetically and clinically, migraine is a highly
complex syndromatic disease,with comorbid neurop-
sychiatric symptoms playing an important part not
only for the amount of the individual patients suffer-
ing but also for therapeutic strategies and,eventually,
anxiety disorders are detected in up to 80% of
migraineurs; unravelling the complex interaction of
the two would improve patient care enormously.
Among many neurotransmitters in the brain, the
serotonergic system has been most convincingly
implicated in migraine and depression pathophysiol-
ogy; 5-HT neurotransmission is genetically regulated
at the level of both its biosynthesis and reup-
take.66Numerous studies indicated a role of the 5-
HTTLPR polymorphism in the pathophysiology of
migraine.24,25,29,71However, in our large sample of
migraineurs, we could demonstrate that the 5-HT
transporter 5-HTTLPR functional polymorphism
does not play a significant role in this system influ-
encing migraine phenomenology. Further studies
using large and homogeneous samples are required to
provide evidence for other genetic factors, possibly
other genes involved in neurotransmitter metabolism
and regulation, playing a role both in migraine, its
comorbidity, and chronification.
Acknowledgment: The provision of DNA samples
and clinical data from patients of the DMKG epidemio-
logical study is greatly appreciated.
STATEMENT OF AUTHORSHIP
(a) Conception and Design
Thomas Wieser; Dale Nyholt;Thomas Deufel
(b) Acquisition of Data
Kathrin Dresler; Klaus Berger; Stefan Evers;
Charly Gaul;Thomas Wieser
(c) Analysis and Interpretation of Data
Dale Nyholt; Daniela Hölzl; Dorothea König;
(a) Drafting the Article
(b) Revising It for Intellectual Content
Thomas Deufel; Dale Nyholt; Stefan Evers;
Charly Gaul; Kathrin Dresler
(a) Final Approval of the Completed Article
Thomas Wieser; Kathrin Dresler; Stefan Evers;
Charly Gaul; Dorothea König; Daniela Hölzl;
Klaus Berger; Dale Nyholt;Thomas Deufel
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