PLoS ONEplosplosonePLoS ONE1932-6203Public Library of ScienceSan Francisco, USAPONE-D-11-0125510.1371/journal.pone.0019332Research ArticleBiologyAnatomy and physiologyEndocrine systemEndocrine physiologyMedicineAnatomy and physiologyEndocrine systemEndocrine physiologyEndocrinologyEndocrine physiologyMental healthPsychiatryNeuropsychiatric disordersSubstance abusePublic healthAlcoholDiabetes and EndocrinologyPublic Health and EpidemiologyMental HealthPhysiologyLow Digit Ratio 2D∶4D in Alcohol Dependent
PatientsLow 2D∶4D in Alcohol Dependent
PatientsKornhuberJohannes1*ErhardGabriele1LenzBernd1KrausThomas12SperlingWolfgang1BayerleinKristina1BiermannTeresa1StoesselChristina1Department of Psychiatry and Psychotherapy,
Friedrich-Alexander University of Erlangen-Nuremberg, Erlangen,
GermanyDepartment of Psychiatry and Psychotherapy,
Frankenalbklinik Engelthal, Engelthal, GermanyZhangXiang YangEditorBaylor College of Medicine, United States of America* E-mail: Johannes.kornhuber@uk-erlangen.de
Conceived and designed the experiments: JK GE CS. Performed the experiments:
GE CS. Analyzed the data: JK GE CS. Contributed reagents/materials/analysis
tools: JK. Wrote the paper: JK CS GE BL. Provided intellectual input: KB TB
TK WS.
The authors have declared that no competing interests exist.
2011254201164e1933261201126320112011Kornhuber et alThis is an open-access article distributed under
the terms of the Creative Commons Attribution License, which permits unrestricted
use, distribution, and reproduction in any medium, provided the original author and
source are credited.
The ratio of the lengths of the second and fourth finger (2D∶4D) has been
described as reflecting the degree of prenatal androgen exposure in humans.
2D∶4D is smaller for males than females and is associated with traits such
as left-handedness, physical aggression, attention-deficit-hyperactivity
disorder and a genetic polymorphism of the androgen receptor. All of these
traits are known to be correlated to the vulnerability for alcohol dependency.
We therefore hypothesized low 2D∶4D in patients with alcohol dependency.
In the present study on 131 patients suffering from alcohol dependency and 185
healthy volunteers, we found that alcohol dependent patients had smaller
2D∶4D ratios compared to controls with preserved sexual dimorphism but
with reduced right-left differences. The detection of alcohol dependency based
on 2D∶4D ratios was most accurate using the right hand of males
(ROC-analysis: AUC 0.725, sensitivity 0.667, specificity 0.723). These findings
provide novel insights into the role of prenatal androgen exposure in the
development of alcohol dependency and for the use of 2D∶4D as a possible
trait marker in identifying patients with alcohol dependency.
Funding for this study was provided by intramural grants of the University
Hospital of the Friedrich-Alexander University Erlangen-Nuremberg. The funders
had no role in study design, data collection and analysis, decision to publish,
or preparation of the manuscript.Introduction
The lengths of the second digit (2D) and fourth digit (4D) and their ratio have
received attention because of sex differences [1]. The ratio of 2D to 4D is
smaller for males than females. Those differences are generally larger for the right
hand than for the left in humans [2]–[4]. Sexual dimorphism is already seen in the 9th
week of the foetal period [3]. Low 2D∶4D values probably result from high prenatal
testosterone exposure [1], [4], [5]. Evidence supporting this hypothesis has recently been
reviewed [6],
but for an alternative critical view see Forstmeier et al., 2010 [7].
Several of the phenomena that are observed in persons with low 2D∶4D ratio have
also been found in patients with alcohol dependency. Men have lower 2D∶4D
ratios and consume more alcohol [8], [9]. Left-handedness is associated with altered 2D∶4D
measures [10]–[13], and is also more frequent in patients with alcohol
dependency [14]
(however, see also [15]). Low 2D∶4D is associated with
attention-deficit-hyperactivity disorder [16], which is also associated
with alcohol dependency [17]. Low 2D∶4D correlates with psychological traits
such as physical aggression, novelty seeking and higher dominance [18]–[20]. These
features have also been reported as predictors of substance abuse [8], [21], [22]. Finally, a
CAGn trinucleotide repeat within the coding region of the androgen receptor has been
shown to correlate with variation in 2D∶4D ratio. Thus, men with shorter
alleles ( = more sensitive androgen receptors) possess more
masculinized right hand 2D∶4D ratios relative to their left 2D∶4D, and
this correlation was driven by a positive association between right 2D∶4D and
CAGn [23].
However, while Hurd et al. [18] found a similar association between right
2D∶4D-left 2D∶4D (Dr-l) and CAGn, in this case the correlation was
driven by a positive association between left 2D∶4D and CAGn. This
polymorphism is associated with craving for alcohol of male patients during
withdrawal [24]. We
therefore hypothesized that patients with alcohol dependency have been exposed to
high prenatal testosterone levels, as indicated by the proxy 2D∶4D.
Methods
This study is part of the FLIP-project (Finger-Length In Psychiatry). Between
February 2009 and March 2010 we recruited 131 patients (87 males and 44 females; age
between 24 and 77 years, median age 46.4) who were treated as inpatients in the
Department of Psychiatry in the Frankenalbklinik Engelthal. All patients suffered
from alcohol dependency according to ICD-10-criteria. Controls consisted of 185
volunteers (83 males and 102 females; age between 19 and 64 years; median age 37.5)
recruited predominantly from among employees of the University of Erlangen-Nuremberg
via direct personal contact. Written informed consent was obtained after complete
description of the study to the subjects. The study was approved by the local Ethics
Committee (Ethik-Kommission der Medizinischen Fakultät der Friedrich-Alexander
Universität Erlangen-Nürnberg).
Scanning was conducted prior to examining or analyzing questionnaires scores. A HP
scan-jet G4050 was used to scan participants' hands. To increase accuracy,
small marks were drawn on the basal creases of the index and ring fingers before
scanning. Both hands were scanned at the same time, palms down. We used the GNU
Image Manipulation Program (GIMP, version 2.6.8 p1; www.gimp.org) to measure the index
(2D) and ring (4D) fingers from the hand scans. This technique provides good
reliability [19].
The total length of the second and fourth digit of the fight and left hands was
measured from the middle of the basal crease to the tip of the finger and was
determined in units of pixels, using the GIMP “measure” tool. The
measurements were performed by three independent persons, first by one experimenter
(GE) and also by two untrained persons blind to the hypothesis and blind to the
diagnostic category. Each of the three persons had to perform 1264 measurements (131
patients and 185 controls, two digits, two hands). Mean values of the three
measurements were calculated for the second and fourth digit.
The reliability of the three measurements was calculated for each finger separately
for the right and left hand using the two-way random intra-class correlation
coefficient (ICC) [25]. ICCs were also calculated for 2D∶4D ratios and
Dr-l values. Deviation from normal distribution was tested by
Kolmogorof-Smirnov-Test. 2D∶4D ratios of the subjects were analyzed by a 2
(diagnosis)×2 (sex)×2 (hand) factorial ANCOVA with repeated measurement
on the factor hand and age as covariate. Dr-l values were analyzed by a 2
(diagnosis)×2 (sex) factorial ANCOVA with age as covariate. The effect size of
the main factors or interactions was estimated by partial η2-values.
Partial η2-values, in contrast to classical
η2-values, are defined as the proportion of total variation
attributable to the experimental factor partialling out other factors from the total
nonerror variation [26]. To estimate the value of 2D∶4D ratio as a
diagnostic test for discrimination of alcohol dependent patients from controls, we
used a ROC-analysis to calculate AUC values (ranging from
0.5 = random prediction to 1 = perfect
prediction), as well as sensitivity and specificity at the Youden-point (the point
on the ROC-curve, where the sum of sensitivity and specificity is maximized). A
p-value<0.05 (two-tailed) was regarded as significant. All statistical analyses
were computed using PASW (Version 18, Chicago, Illinois).
Results
Reliability of the three raters was high for both the right hand (2D:
ICC = 1.000; 4D: ICC = 0.998; 2D∶4D:
ICC = 0.988) and the left hand (2D:
ICC = 0.991; 4D: ICC = 0.998; 2D∶4D:
ICC = 0.951). Reliability of the Dr-l values were also high
(ICC = 0.898). The mean 2D∶4D and Dr-l values are
presented in Table 1.
2D∶4D and Dr-l values did not deviate from normal distribution.
10.1371/journal.pone.0019332.t001
2D∶4D and Dr-l values in patients and controls.
Patients
Controls
Males (n = 87)
Females (n = 44)
Males (n = 83)
Females (n = 102)
2D∶4D right hand
0.952±0.031
0.967±0.030
0.976±0.029
0.983±0.032
2D∶4D left hand
0.949±0.034
0.967±0.031
0.967±0.029
0.976±0.030
Dr-l
0.0029±0.0278
0.0003±0.0218
0.0086±0.0251
0.0067±0.0241
Values are means ± standard deviation (SD).
Dr-l = right 2D∶4D - left 2D∶4D.
2D∶4D ratio was most associated, in descending order, with diagnosis
(F = 16.0, df = 1, p<0.001, partial
η2 = 0.049), sex
(F = 13.2, df = 1, p<0.001, partial
η2 = 0.041), hand*diagnosis-interaction
(F = 4.4, df = 1,
p = 0.038, partial
η2 = 0.014) and age
(F = 4.2, df = 1,
p = 0.041, partial
η2 = 0.013). There were no further significant
main or interaction effects. The interaction line plots for 2D∶4D ratios for
male and female subjects are shown in figure 1. Diagnosis was significantly associated with Dr-l values
(F = 4.4, df = 1,
p = 0.038, partial
η2 = 0.014) with no further main or interaction
effects. Together, these results indicate that alcohol dependent patients have
smaller 2D∶4D ratios with preserved sexual dimorphism but with reduced
right-left differences. The ROC analysis indicates highest diagnostic accuracy of
the 2D∶4D ratio of the right hand in males (AUC 0.725, sensitivity 0.667,
specificity 0.723), followed by males' left hand (AUC 0.667, sensitivity 0.529,
specificity 0.759), females' right hand (AUC 0.650, sensitivity 0.864,
specificity 0.392) and females' left hand (AUC 0.570, sensitivity 0.886,
specificity 0.265).
10.1371/journal.pone.0019332.g001
Interaction line plots.
A 2 (diagnosis)×2 (sex)×2 (hand) factorial ANCOVA with repeated
measurement on the factor hand with age as a covariate shows a reduced
2D∶4D ratio in alcohol dependent patients with preserved sexual
dimorphism and reduced right-left difference.
Discussion
This is the first study investigating prenatal testosterone exposure, as assessed by
the proxy 2D∶4D, in alcohol dependent patients. Patients with alcohol
dependency have low 2D∶4D ratios with preserved sexual dimorphism and reduced
right-left differences. These findings are remarkable for several reasons. (1) As
2D∶4D is fixed before birth [3] and remains relatively constant during life, 2D∶4D
is a novel and easily-accessible trait marker for alcohol dependency. (2) The low
2D∶4D ratio in alcohol dependent patients suggests that several phenomena that
have largely been investigated independently before share a common
pathophysiological basis. These phenomena include a higher life-time risk of males
to develop alcohol dependency, increased prevalence of left-handedness, higher
comorbidity of attention-deficit-hyperactivity disorder, higher prevalence of
personality traits such as aggression, novelty seeking and higher dominance, and
shorter CAGn trinucleotide repeat alleles of the androgen receptor. Sex steroids
have an important organizing effect on the brain during the foetal period with
subsequent long-term effects on behaviour [6]. There is considerable
evidence suggesting that prenatal testosterone exposure causes masculinization of
physiology, anatomy, and behaviour. The findings presented here provide a novel
insight into the etiopathogenesis of alcohol dependency. High prenatal testosterone
exposure, as assessed by its proxy 2D∶4D, probably presents a risk factor for
the development of alcohol dependency via mechanisms to be investigated. (3) It is
known that right hand 2D∶4D is a better indicator of prenatal androgenization
than left hand 2D∶4D [4]. Furthermore, the difference in 2D∶4D between
controls and persons with congenital adrenal hyperplasia, a condition that causes
excessive androgen production during gestation, is larger on the right hand than the
left hand [4]. It
is therefore plausible that right hand 2D∶4D is a better predictor of alcohol
dependency than left hand 2D∶4D, as shown here. Low Dr-l values have been
associated with high prenatal testosterone load (Manning, 2002, pp 21–22,
[27]). The
significantly lower Dr-l values in alcohol dependent patients shown here support the
hypothesis of high prenatal testosterone load being a risk factor for later
development of alcohol dependency. (4) This study shows that right hand 2D∶4D
alone provides a reasonable sensitivity and specificity in the diagnosis of alcohol
dependency, comparable to state markers such as GGT [28]. However, the sensitivity
and specificity of 2D∶4D as a single marker is too low to support an
individual diagnosis, and possessing a low 2D∶4D ratio is neither necessary
nor sufficient to develop alcohol dependency. Furthermore, the diagnostic value of
2D∶4D presented here may be overoptimistic, since we used a mono-centric
design and did not apply cross-validation or external validation during data
analysis [29].
The diagnostic and prognostic value of 2D∶4D as a single trait marker or in
combination with other trait as well as state markers has to be investigated in
future studies under clinical routine conditions using internal and external
validation. (5) Our results are supported by a very recent study reporting on a
negative association between 2D∶4D and alcohol consumption in the general
population [30].
We used a case control design without a matched sample approach. (1) There were
differences in age between the patient and control groups. In agreement with Manning
et al. 2010 [31],
age had a marginal significant negative effect on 2D∶4D in the present study.
However, alcohol dependency was clearly associated with both small 2D∶4D and
small Dr-l values, even when controlling for age effects. Furthermore, Manning and
Fink [30]
observed a negative relationship between alcohol consumption and 2D∶4D in the
general population that was also independent of age. Therefore, it is unlikely that
age had an impact on the results presented here. (2) Previous studies have shown
that the educational level and the academic abilities are related to 2D∶4D.
For instance, 2D∶4D was positively related to the examination marks of
three-year degree courses in male, but not in female university students [32]. Women in
academia have lower, more masculine 2D∶4D values [33] which explains a reduced
2D∶4D gender difference in academic populations [33], [34]. Assuming that our control
sample from a university hospital environment has a higher mean level of education
would possibly result in reduced female 2D∶4D ratios and would thus result in
an underestimation of the difference between alcohol dependent patients and
controls. (3) We did not evaluate alcohol consumption in the control group.
Therefore, volunteers with moderate to heavy alcohol consumption may have been part
of the control group, which might also result in an underestimation of the
difference in 2D∶4D between alcohol dependent patients and control persons
with low alcohol consumption.
May prolonged alcohol consumption have induced changes in 2D∶4D in later life?
This appears unlikely, because (1) the differences in 2D∶4D between control
subjects and alcohol dependent patients observed in our study are large. (2)
Furthermore, it would be hard to explain, why alcohol should have different effects
on the index finger compared to the ring finger. (3) In addition, duration of
alcohol use disorder (range: 0.5–44 years) was not related to 2D∶4D in
the patients investigated here when controlling for age (data not shown). However,
in order to definitely answer this question would require a longitudinal study with
individual tracking of changes of 2D∶4D due to heavy alcohol consumption. Such
data are currently not available.
Alcohol consumption of the mother may have an impact on finger length ratios of the
offspring, as has been shown in rodents. Maternal alcohol consumption results in
reduced testosterone levels and more female finger length ratios [35] and,
therefore, does also not explain the results presented here.
In conclusion, we were able to demonstrate that alcohol dependent patients have small
2D∶4D ratios. Prenatal androgen exposure might be a missing link between
several well-known findings in alcohol research. Further studies are needed to
clarify the value of 2D∶4D as a diagnostic or prognostic marker for alcohol
dependency.
The authors thank Friedrich Lösel for administrative support, Werner Erhard for
writing a software tool for random order evaluation of the scans by the raters and
the team of the Frankenalb Klinik Engelthal for their assistance with the collection
of the data. We thank the anonymous referees for valuable suggestions, and for
pointing our attention to a study, which was in an in-press-status, on the
association between alcohol consumption and 2D∶4D in a general population.
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