genetic variants of dopamine receptor d4 and psychopathology · by alessandro serretti, fabio...
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Genetic Variants of Dopamine Receptor D4and Psychopathology
by ALessandro Serretti, Fabio Macciardi, Marco Catalano, Laura Bettodi,and Enrico Smeraldi
AbstractThere is much evidence to indicate that the dopaminereceptor D4 (DRD4) gene is involved in psychiatricdisorders. We investigated the correlation betweenDRD4 gene polymorphism and the psychopathology ofmajor psychoses, independently of diagnoses. Some461 inpatients affected by major psychoses wereassessed by the Operational Criteria checklist for psy-chotic illness and typed for DRD4 variants. The foursymptomatologic factors—mania, depression, delu-sion, and disorganization—were used as phenotypedefinitions. DRD4 Exon 3 long allele variants wereassociated with high delusional scores, with the mostsignificant difference between alleles 2 and 7 (p -0.004). DRD4 variants may, therefore, constitute a lia-bility factor for development of delusional symptoma-tology in patients with major psychoses.
Key words: Psychopathology, DRD4, psychiatricgenetics, mood disorders, schizophrenia.
Schizophrenia Bulletin, 25(3):609-618,1999.
Major psychiatric disorders tend to aggregate in families.Clinical practice supports this observation to the extentthat ill relatives constitute the only accepted risk factor.Familial aggregation suggests that genetic factors play arole in the etiopathogenesis of major psychoses. Butdespite the fact that twin and family studies have con-firmed the existence of genetic factors, no exact model oftransmission has yet been established (Risch 1990).Beyond formal genetics, recent molecular geneticapproaches permit investigation of specific genetic sus-ceptibilities through both candidate genes and genomescans. Those approaches have produced some positiveresults, but they are still far from producing ultimate find-ings (Risch and Botstein 1996).
A possible explanation for the lack of conclusiveresults could lie in the definition of the phenotype, whichat present is mainly based on psychiatric diagnoses. These
are derived from operational criteria (AmericanPsychiatric Association 1994), and their main achieve-ment pertains to the reliability of the diagnostic process,not to its validity. In addition, family studies do not univo-cally validate diagnoses (Maier et al. 1992, 1993; Taylor1992; Heun and Maier 1993; Taylor et al. 1993; Winokuret al. 1993, 1995). Existing diagnoses guarantee partialclinical similarity, not biological homogeneity. In fact, nosymptom or biological marker has ever revealed sufficientdiscriminating power among psychiatric diagnoses(Elliott 1992; Koyama and Yamashita 1992; Cannon andMarco 1994; Claridge 1994; Csernansky and Newcomer1994), and even drug response shows a strong degree ofvariation within the same diagnosis. Thus, psychiatricdiagnoses do not guarantee any biological homogeneity;moreover, the use of psychiatric clinical diagnoses hasbeen considered to be reductive of the amount of informa-tion available from the whole symptomatologic presenta-tion of patients (Tsuang and Faraone 1990; Cloninger1994; Ginsburg et al. 1996; Vollenweider et al. 1997).
This is a troublesome issue for genetic research,where biologically homogeneous samples are needed. Theproblem is usually addressed using multiple diagnosticlevels from narrow to broad, but that solution can fre-quently and spuriously increase result significance(Cloninger 1994). Our working approach is to use psy-chopathology independently of clinical diagnoses. Thus,our search for candidate genes may be directed towardintermediate psychopathological structures that do notoverlap with psychiatric diagnoses, but that are moreclosely related to the underlying biologic and geneticbackground. Because genetic liability may be expressedas psychopathological traits shared by several psychiatricdisorders (Cloninger 1994; Serretti et al. 1996), we have
Reprint requests should be sent to Dr. Enrico Smeraldi, Department ofNeuroscience, Istituto Scientifico H. San Raffaele, University of MilanoSchool of Medicine, Via Luigi Prinetti 29, 20127 Milano, Italy.
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Schizophrenia Bulletin, Vol. 25, No. 3, 1999 A. Serretti et al.
developed a phenotypic definition based on the observedsymptomatology independently of the clinical diagnosis(Serretti et al. 1996). A few other studies have adoptedthis strategy with promising results in both Alzheimer'sdisease and psychiatric disorders (Weisgraber et al. 1994;Ginsburg et al. 1996; Bellivier et al. 1997; Gottesman1997;Yaffeetal. 1997).
Dopamine pathways are involved in the pathophysi-ology of schizophrenia and mood disorders (Kahn andDavis 1995; Willner 1995). Since the dopamine D4 recep-tor gene (DRD4) was cloned (Van Tol et al. 1991), it hasreceived considerable interest because of its many inter-esting properties. The DRD4 mRNA distribution profilediffers from other dopamine receptors in having elevatedvalues in limbic areas, such as the frontal cortex andamygdala, involved in the pathophysiology of major psy-choses (Van Tol et al. 1991; Matsumoto et al. 1995;Murray et al. 1995). Postmortem studies of schizophreniapatients detected a sixfold elevation of D4 sites (Seemanet al. 1993; Sumiyoshi et al. 1995).
The DRD4 gene is extremely polymorphic. It has onepolymorphism located in the third exon coding for thethird cytoplasmatic loop of the receptor (Van Tol et al.1991, 1992) and consisting of a variable number of copiesof a 48 base pair (bp) sequence, from 2 to 10. A secondpolymorphism is characterized by a polymorphic 12 bprepeat in exon 1 and codes for a sequence of four aminoacids in the extracellular N-terminal part of the receptor(Catalano et al. 1993). Other known DRD4 gene polymor-phisms include a T -* G substitution in nucleotide posi-tion + 581 (Seeman et al. 1994), and the presence of anonsense 13 bp deletion in exon 1 (Nothen et al. 1994).Furthermore, two novel polymorphisms and a rare dele-tion variant were recently reported (Cichon et al. 1995).
The 48 bp variation exhibited different pharmacologi-cal activities. Dopamine stimulation of the DRD4 recep-tors decreases cAMP formation. The potency ofdopamine's inhibition of cAMP formation was reducedabout twofold for the 7 allele compared with the shortallele variants (Asghari et al. 1995). DRD4 also shows ahigh affinity for clozapine, an antipsychotic used forschizophrenia and manic states. Moreover, a different dis-sociation constant for clozapine in the absence of sodiumwas demonstrated between short and long alleles of the 48bp polymorphism (Van Tol et al. 1992; Calabrese et al.1996; Marder 1996).
In conclusion, variants of the DRD4 gene may pro-duce functionally different receptor proteins with a poten-tial influence on the psychopathology of major psychoses.The aim of this study was to investigate the association ofexon 1 and exon 3 polymorphisms of the DRD4 gene withmajor psychoses symptomatology, within basic psy-chopathological areas.
Methods
Sample. Some 461 psychiatric inpatients (females =244, males = 217; mean age = 42.93 years, standard devi-ation [SD] = 14.41; mean age at onset = 29.48 years,SD — 13.25) consecutively admitted to the Department ofNeuropsychiatry at the Institute H. San Raffaele wereincluded in this study. All the patients were evaluatedusing the Operational Criteria (OPCRIT) checklist forpsychotic illness (McGuffin et al. 1991). Lifetime diag-noses were assigned by two independent psychiatrists onthe basis of interviews and medical records, according toDSM-III—R criteria (American Psychiatric Association1987). We included all subjects affected by major psy-choses. However, the presence of concomitant diagnosesof mental retardation and drug dependence, together withsomatic or neurological illnesses that impaired psychiatricevaluation (e.g., hypothyroidism mimicking a depressivestate) represented exclusion criteria. The subjects includedwere affected by schizophrenia, including all subtypes(n - 162), major depressive disorder (n = 83, including 26obsessive-compulsive comorbid subjects), bipolar disor-der (n = 152), delusional disorder (n = 56), and psychoticdisorder not otherwise specified (NOS) (n = 8). Informedconsent was obtained from all probands, who were unre-lated and of Italian descent with antecedents from all partsof Italy.
DNA Analysis. Genomic DNA was extracted from anti-coagulated thawed blood according to the method ofLahiri and Nurnberger (1991). For the D4 exon 3 typing,a polymerase chain reaction (PCR) was carried out withprimers and conditions as described elsewhere (Macciardiet al. 1994). This PCR polymorphism is particularly com-plex and detects a 7 allele system (A2 = 0.1, A3 = 0.03,A4 = 0.7, A5 = 0.01, A6 = 0.01, A7 = 0.15, A8 = 0.01).For exon 1, PCR conditions were also as described else-where (Catalano et al. 1993) and 446 subjects were typed.
Statistical Analysis. In a previous article we describedthe factoring process of the OPCRIT checklist in a sampleof patients affected by major psychoses (Serretti et al.1996). We identified four factors:1. Excitement: excessive activity, reduced need for sleep,pressured speech, elevated mood, thoughts racing, in-creased sociability, increased self esteem, irritable mood,distractibility, agitated activity, dysphoria, grandiose delu-sions, reckless activity2. Depression: loss of pleasure, loss of energy/tiredness,diminished libido, excessive self reproach, slowed activ-ity, poor appetite, poor concentration, suicidal ideation,weight loss, diurnal variation, early morning waking,delusions of guilt
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Genetic Variants of Dopamine Receptor D4 Schizophrenia Bulletin, Vol. 25, No. 3,1999
3. Delusion: persecutory delusions, well-organized delu-sions, delusions of influence, widespread delusions, pri-mary delusional perception, delusions and hallucinationslasting for 1 week, persecutory/jealous delusions and hal-lucinations, thought insertion, thought withdrawal,thought broadcast, third-person auditory hallucinations4. Disorganization: speech difficult to understand, inco-herent, positive formal thought disorder, inappropriateaffect, bizarre behavior, bizarre delusions, blunted affect,negative formal thought disorder, deterioration from pre-morbid level of function
These factors explain 50 percent of the variance ofthe selected OPCRIT items and were confirmed in anindependent sample. The factors were present, in variousdegrees, in all the clinical diagnoses considered.Standardized factor scores have been derived from thesefactors and were considered to be dependent variableswhen investigating their distribution across DRD4 allelesand genotypes. Of the original 461 subjects, factor scorescould be calculated only for 446 subjects due to missingitems. For all calculations we excluded variants 3, 5, 6,and 8 because in our sample they were poorly represented(their cumulative prevalence was only 0.06).
Differences were assessed using t test or one-wayanalysis of variance (ANOVA), with Newman-Keul(N-K) test to evaluate post hoc comparisons; frequenciewere compared by chi-square test. The power of our sampie was tested considering an alpha value of 5 percenttwo tailed. Our sample featured mixed mood and schizcphrenia spectrum disorders, which could introduce a biain the analysis of the genetic effect. The diagnostic composition of our sample was not established a priori, and imust be considered as randomly extracted from all possible sets of samples. To control for this bias, we repeatethe analysis using a mixed effect two-factor ANOVA iwhich D4 typing was considered the fixed effect and diagnostic status a random effect. For this calculation we useBMDP 3V program with restricted maximum likelihoomethod (Dixon 1990).
Results
The association between DRD4 variants and excitement,depressive, disorganized, and delusional symptomatologywas estimated using one-way ANOVA (table 1). TheANOVA on factor scores showed a significant differenceon delusion factor (F = 5.52, df = 2,840, p = 0.004; mixedmodel F = 5.37, df = 2,840, p = 0.005), with a post hocsignificant difference between the 2 and the 7 bp repeatsO = 0.0006; N-K p < 0.01) (see figure 1). The 7 bprepeats groups had the highest scores on this factor whilethe 4 bp repeats group had intermediate scores betweenthe 7 and the 2 repeats. The power of detection for theobserved difference in the delusional factor was 0.83 inour sample. Subgroups considering sex and diagnoses didnot show any significant deviation from the observedresults.
The genotype analysis is summarized in table 2.Overall ANOVA did not show significant differences, but
Figure 1. Distribution of Delusion score accord-ing to alleles at DRD4 exon 3
DRD4 Exon 3 Alleles
Table 1. Factor Scores and DRD4 exon 3 aileles
DRD4 exon3 alleles
2 repeat
4 repeat
7 repeat
Total
Excitement
Mean
0.050-0.051
0.108-0.013
SD
1.044
1.0111.052
1.023
Depression
Mean
0.1950.152
0.0530.146
SD
1.121
1.146
1.0031.052
Delusion
Mean
-0.049
0.1050.3821
• 0.117
SD
1.037
1.057
0.934
1.043
Disorganization
Mean
-0.0810.006
-0.091-0.083
SD
0.962
1.051
1.030
1.015
n
138
591114
843
Note.—Rare alleles are not displayed. SD = standard deviation.1 High delusional scores are significantly associated with long exon 3 alleles (F = 5.52, df = 2,840, p = 0.004).
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Schizophrenia Bulletin, Vol. 25, No. 3, 1999 A. Serretti et al.
Table 2. Factor scores and DRD4 exon 3 genotypes
DRD4 exon 3genotypes
2/2
2/42/7
4/4
4/7
7/7
Total
Excitement
Mean
0.2590.084
-0.567
-0.103
0.25
0.109
0.005
SD
1.0931.072
0.528
0.998
1.070
1.1651.032
Depression
Mean
-0.0910.311
0.176
0.180
0.0430.064
0.165
SD
1.017
1.150
1.076
1.0311.012
1.032
1.052
Delusion
Mean
-O.043-0.077
0.174
0.066
0.400
0.3730.107
SD
1.0251.044
1.2091.087
0.892
0.887
1.048
Disorganization
Mean
0.314
-0.267
-0.118
0.0400.054
-0.728
-0.031
SD
0.917
0.866
1.2001.076
1.020
0.609
1.026
n
18
81
16200
779
401
Note.—Rare genotypes are not displayed. SD = standard deviation.
a significant post hoc comparison on the delusion factorwas detected between the 2/4 and the 4/7 genotypes (p =0.004; N-K p < 0.05). Variants of DRD4 gene showed apharmacological activity related to the number of repeats;in our sample we observed a linear increase in delusionalscores with the number of 48 bp repeats on the DRD4genotype (figure 2). We then performed a linear regres-sion of delusional score on genotypes considered as a
Figure 2. Distribution of Delusion score accord-ing to genotypes at DRD4 exon 3
DRD4 Exon 3 Genotypes
variable ranging from 1 (corresponding to genotype 2/2)to 6 (corresponding to genotype 7/7). We observed a sig-nificant linear regression for the number of 48 bp variantson delusional scores (r = 0.111, F = 5.53, df = 1,444, p =0.019). DRD4 exon 1 variants were not related to any fac-tor (table 3), even when subjects were stratified for sexand diagnoses.
A possible interaction between exon 1 and exon 3was hypothesized and an haplotype analysis was per-formed stratifying exon 3 on exon 1 variants, but no sig-nificant interaction was detected.
Diagnostic group could constitute a stratification biasbut the mixed model ANOVA formally excluded thisissue. Table 4 reports the delusion factor scores distribu-tion on DRD4 exon 3 stratified for diagnostic group. TheDRD4 exon 3 variants difference remained significantonly for the bipolar group, but delusional values were alsohigher for the 7 allele for schizophrenia, major depressive,and NOS psychoses.
Discussion
In our sample, the intensity of delusional symptomatologyincreased linearly from short to long alleles of DRD4exon 3, producing a significant linear regression on delu-sional scores. Because delusional scores are the weightedsum of OPCRIT items, we also cross-tabulated exon 3variants with any of the 11 items that constitute the delu-
Table 3. Factor Scores and DRD4 exon 1 alleles
DRD4 exon1 alleles
1
2
Total
Excitement
Mean
0.010-0.289-0.012
SD
1.0310.7801.018
Depression
Mean
0.129-0.002
0.119
SD
1.0500.9741.045
Delusion
Mean
0.0780.1170.081
SD
1.0081.1921.022
Disorganization
Mean
-0.0330.018
-0.030
SD
1.037
1.021
1.035
n
82864
892
Note.—Scores are not associated with DRD4 exon 1 alleles and genotypes (data not shown); SD = standard deviation.
612
Tabl
e 4.
D
elu
sio
n f
acto
r sc
ore
s an
d D
RD
4 ex
on
3 a
llele
s an
d g
eno
typ
es s
trat
ifie
d f
or
dia
gn
ose
so
I—*
DR
D4
exo
n2 4 7 T
otal
DR
D4
exo
n2/
22/
4
2/7
4/4
4/7
in Tot
al
Sch
izo
ph
ren
ia
Mea
n
3 al
lele
s0.
845
0.96
9
1.11
6
0.97
3
SD
1.00
1 (3
9)0.
912(
204)
0.74
8(41
)
0.90
3 (2
84)
3 g
eno
typ
es0.
442
1.08
2
1.25
4
0.94
91.
096
0.84
90.
985
1.11
4(7)
0.92
6(18
)
0.79
5 (6
)0.
954
(70)
0.72
9 (2
9)
1.30
1 (2
)0.
906(
132)
Del
usi
on
al
Mea
n
0.31
6
0.21
3
0.30
50.
237
0.73
90.
083
-0.3
61
0.21
90.
245
0.87
50.
234
SD
0.61
6(15
)0.
691
(80)
0.57
7(11
)
0.66
5(10
6)
0.24
0 (3
)0.
667
(8)
0.00
0(1)
0.73
8 (3
0)0.
561
(8)
0.00
0(1)
0.67
7(51
)
Bip
olar
Mea
n
-0.4
67
-0.4
23
-0.0
22
-0.3
69
(F=
6.1
6
-0.6
97
-0.4
06
0.23
3
-0.5
19
-0.1
12
0.21
5-0
.37
4
SD
0.70
5 (4
9)0.
720(
190)
0.71
3(44
)
0.73
0 (2
83)
, df
= 2
,280
, p
0.64
3 (7
)
0.73
5 (3
3)
0.00
0(1)
0.69
9 (6
0)0.
677
(32)
0.91
4(5)
0.72
7(13
8)
Maj
or
Mea
n
-0.3
38
-0.4
69
-0.1
89
-0.4
07
= 0
.002
4)
-1.2
09
-0.2
89
-0.1
88
-0.5
94
-0.1
50
-0.2
89
-0.4
26
Dep
ress
ive
SD
0.98
8 (2
2)0.
937
(66)
0.91
9(12
)
0.94
1 (1
00)
0.00
0(1)
1.0
70
(13
)
1.11
5(5)
0.93
1 (2
2)1
.03
5(5
)0.
000(
1)0.
971
(47)
Maj
or
Mea
n
-1.1
92
-1.0
12
-1.2
10
-1.0
55
—
-1.1
85
-1.2
10
-0.9
57
— —
-1.0
46
Dep
ress
ive
+ d
oc
SD
0.04
9(11
)0.
594
(42)
0.01
5(2)
0.52
4 (5
5)
—
0.05
6 (8
)
0.01
5(2)
0.68
4(16
)— —
0.54
3 (2
6)
Psy
cho
tic
NO
S
Mea
n
-0.4
83
0.11
9
0.03
3
0.01
6
— 0.28
5
-1.2
50
-0.1
83
0.46
1— 0.00
7
SD
1.08
5 (2
)
0.50
5 (9
)
0.98
3 (4
)
0.69
2(15
)
—
0.00
0(1)
0.00
0(1)
0.54
4 (2
)
0.59
3 (3
)—
0.74
7 (7
)
netii < | O >-ti 1 n •8 2
Not
e.—
The
num
ber o
f sub
ject
s is
dis
play
ed in
par
enth
eses
. SD
= s
tand
ard
devi
atio
n; N
OS
= n
ot o
ther
wis
e sp
ecifi
ed; d
oc =
obs
essi
ve c
ompu
lsiv
e di
sord
er.
! si S' I £ o
Schizophrenia Bulletin, Vol. 25, No. 3, 1999 A. Serretti et al.
sion factor. The allele 7 variant of DRD4 was significantlyassociated with four delusion factor items: persecutorydelusions, delusions of influence, widespread delusions,and persecutory/jealous delusions and hallucinations. Forthe remaining items, the association was present but notsignificant.
In the present study, we used a mixed sample ofpatients affected by mood, schizophrenia, and delusionaldisorders. This heterogeneity might indicate that theobserved differences on the delusional factor are simplythe result of a spurious correlation (e.g., an excess ofdelusional subjects with allele 7). However, delusionaldisorder was not associated with DRD4 exon 3 variants(Serretti et al., in press); moreover, the same associationof delusional symptomatology with allele 7 was observedfor all the diagnoses. A formal demonstration of this lastpoint was achieved by considering diagnoses through amixed model ANOVA and observing the substantial sta-bility of the results. Thus, the reported association couldbe considered an extended effect of long alleles on delu-sional symptoms among psychotic patients. DRD4 exon 1variants did not show any association with symptom fac-tors. We hypothesized that exon 1 might interact withexon 3 on symptoms, but, among subjects with exon 1deletion, exon 3 variants did not differ significantly intheir symptom scores.
Recently, an association of DRD4 with the noveltyseeking personality trait has been demonstrated in normalsubjects (Benjamin et al. 1996; Ebstein et al. 1996;Ebstein and Belmaker 1997), although no univocal confir-mations followed (Jonsson et al. 1997; Ono et al. 1997;Sander et al. 1997; Vandenbergh et al. 1997). Dopaminetransmission is involved both in the individual variationsin novelty seeking (Cloninger et al. 1996) and in thedevelopment of delusion (Kahn and Davis 1995). It mightbe hypothesized that there is a broad effect of the altereddopamine receptor D4 on the dopaminergic system, pro-ducing an increase of the novelty seeking personality traitand, among psychiatric patients, an increase in delusionalsymptoms independently of diagnosis. The relevance oflong alleles for psychopathology is also indicated by arecent article (LaHoste et al. 1996) describing an associa-tion of long DRD4 alleles with attention deficit hyperac-tivity disorder. DRD4 gene has been investigated in majorpsychiatric disorders and associations have been reported(Catalano et al. 1993; Lim et al. 1993; Manki et al. 1996).Previous findings reported an excess of 7 allele in personswith bipolar disorder (Lim et al. 1993) that subsequentlywas not confirmed (Lim et al. 1994) and reported noresults in persons with schizophrenia (Shaikh et al. 1993,1994; Petronis et al. 1995). A recent article reported anassociation between DRD4 gene (allele 2) and unipolardisorder in a Japanese population (Manki et al. 1996). Our
findings may suggest a sampling effect: High frequenciesof subjects with delusional symptoms may increase theallele 7 frequency. When using psychiatric diagnoses asthe phenotype definition, it would also be useful toinclude a symptomatologic description of subjects.
However, the extent of variance in symptomsexplained was low. The DRD4 48 bp polymorphism onlyexplained about 2 percent (effect size 0.1) of the variationin delusional symptomatology, an observation that is inagreement with a supposedly minor effect of the genecoding for the D4 receptor in the development of delu-sional symptomatology. While the variance explained isstatistically informative, we were also interested in theepidemiological influence of DRD4 on delusional symp-tomatology. To accomplish this task we split the delu-sional factor into the original 11 OPCRIT items. Theincrease in risk of having at least one delusional item,given the presence of the DRD4 7 allele, was 2.24 (oddsratio [OR],/? = 0.016). When using the items most associ-ated with DRD4 long alleles (persecutory delusions, delu-sions of influence, widespread delusions, persecutory/jeal-ous delusions and hallucinations), the risk wassignificantly higher (OR = 2.9l,p = 0.0004). In the lattercase, we calculated the attributable fraction, that is, theproportion of subjects that would not present those delu-sional symptoms in the absence of the risk factor. In otherwords, the attributable fraction reveals the extent to whichthe risk factor contributes to the delusional symptoms.The attributable fraction was 3.4 percent; that means thatin the absence of allele 7 we would observe 3.4 percentfewer subjects with delusional symptoms.
To our knowledge, our sample is the largest in anypublished study, and the small effect observed would nothave been detectable in smaller samples. We scored sub-jects with a lifetime prospect of ever-present symptoms;that should partially circumvent any bias derived from thecross-sectional nature of the study. This sample does notinclude control subjects, because our objective was to testthe effect of liability factors on psychopathological traitsamong affected individuals, not on the development of dis-ease. Thus, a mixed psychiatric sample constitutes the bestmeans to verify this hypothesis. However, it might be ofinterest to compare DRD4 exon 3 allele frequencies in sub-jects with high delusional scores with those of controls. Tothis end, ill subjects are compared to a sample of controlsubjects currently analyzed for a companion paper (Serrettiet al., in press). DRD4 alleles 7 and 2 for subjects with highdelusional scores differ from those for subjects with lowdelusional scores, but not from controls (see table 5).
Ethnic origin is frequently a cause of stratificationbias; however, our sample is composed of subjects withItalian antecedents back to grandparents and no other ori-gin was allowed. Most studies, including the present one,
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Genetic Variants of Dopamine Receptor D4 Schizophrenia Bulletin, Vol. 25, No. 3,1999
Table 5. DRD4 exon 3 alleles and genotype frequencies among patients and controls
DRD4 alleles2345678Total
Genotypes2/22/42/74/44/77/7Total
Controls
n
9826
65587
1435
942
125714
229102
12426
%
0.100.030.700.010.010.150.01
0.030.120.030.490.220.03
High
n
5614
29473
751
450
831
89454
5200
delusion
%
, 0.120.030.650.020.010.170.01
0.040.160.040.470.270.03
Very highdelusion
n
437
21353
530
324
723
670374
147
%
0.130.020.660.020.010.160.00
0.050.160.040.480.250.03
Patients
Low delusion
n
8215
29743
392
442
1050
810623
4201
%
0.191
0.030.670.010.010.091
0.01
0.050.251
0.040.530.111
0.02
n
13829
591116
1143
892
188116
20077
9401
All
%
0.160.30.660.010.010.130.01
0.050.200.040.500.190.02
Note.—High delusional subjects (delusional factor scores > 0.0) did not show higher frequencies of 7 allele compared to controls.Subjects with extreme delusion scores (> 0.5) were not different from controls. Subjects presenting low delusion scores were significantlydifferent from both controls and the remaining subjects.1 p < 0.001 versus controls and high delusion score subjects.
use multiple statistical testing. Therefore, significance lev-els would be unlikely to survive correction in many cases.However, analyses of candidate genes have high a prioriprobabilities of association, and multiple correction couldnot demonstrate the best choice (Carey 1994; Levinson1997). Replication using independent samples or family-based association designs should be considered more suit-able strategies.
In conclusion, DRD4 variants were related to psy-chopathology: long DRD4 exon 3 alleles may constitute aliability factor for delusional symptoms in major psy-choses. The use of a symptomatological definition of phe-notype complements the usual genetic research strategies.
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The Authors
Alessandro Serretti, M.D., is Researcher; FabioMacciardi, M.D., Ph.D., and Marco Catalano, M.D., areLecturer of Psychiatry and Vice Psychiatrist-in-Chief;Laura Bellodi, M.D., is Associate Professor of Psychiatryand Psychiatrist-in-Chief; Enrico Smeraldi, M.D., isProfessor of Psychiatry and Head of the Department ofPsychiatry, Istituto Scientifico H. San Raffaele, Universityof Milano School of Medicine, Milano, Italy.
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