Poster presented at IMFAR 2011. The relationship between 2nd to 4th digit ratio (2D:4D) and autism severity in boys

1. 2D:4D Digit Ratio and Autism Severity in Boys
Green, C., Dissanayake, C., Loesch, D.Z.
Olga Tennison Autism Research Centre, La Trobe University, Australia
Background
It has been suggested that the digit ratio of the 2nd to 4th fingers (2D:4D) may be
negatively correlated with prenatal testosterone. Digit ratio can be viewed as an
index of testosterone level by the 14th week of pregnancy1, with a low 2D:4D Table 3
indicating longer 4th digits relative to 2nd digits. The lower the 2D:4D ratio, the
higher the prenatal testosterone level. In general, males have a low 2D:4D while
Differences in 2D:4D Ratios between Participants with ASD compared to
females have a higher 2D:4D, indicating a negative correlation between digit ratio
those with AD
and prenatal testosterone levels.
95% CI
Many studies have reported that prenatal levels of testosterone correlate with Classification
autistic traits during infancy and early childhood2-5, as well as with language n M (SD) t (df) P LL UL Cohen’s d
Cut-Offs
development6. Children with AD have been reported to have lower 2D:4D than SA ASD 15 0.934 (0.02) 0.36 (42)
0.80 -0.020 -0.026 0.09
children with HFA/AspD. Cognitive and psychological profiles have also been related AD 58 0.931 (0.04)
to 2D:4D, especially measures of systemising and empathising, although the results SA + RRB ASD 8 0.941 (0.03) 0.64 (57)
0.64 -0.023 0.037 0.20
have been mixed7-12. AD 51 0.934 (0.04)
Severity ASD 8 0.939 (0.02) 0.28 (59)
0.78 -0.025 -0.034 0.13
Inconsistencies in the literature are likely to be due to differences in measurement AD 53 0.935 (0.04)
method, as well as differences in operationalizing autistic traits and other variables
Note. ASD = Participants above the ASD cut-off; AD = Participants above the AD cut-off; CI =
of interest. To date, autistic characteristics have been defined by scores on a variety Confidence Interval; LL = Lower Limit; UL = Upper Limit.
of measures, including the Autism Quotient (AQ) and the Autism Diagnostic Table 1
Observation Schedule (ADOS), as well as other measures thought to reflect autistic
strengths and weaknesses. Correlations of Parental 2D:4D to Child 2D:4D Discussion
• This is the first study to compare 2D:4D ratio in individuals with AD and ASD as
Objectives 2D:4D Correlations determined by autism severity cut-offs across ADOS modules 1-3. The revised
The objective in the current study was to compare 2D:4D ratios between boys with ADOS algorithm severity score allows for comparison amongst individuals with
an Autism Spectrum Disorder (ASD) and typically developing (TD) boys to ascertain Mother Father Mother + Father ASD, regardless of age and verbal ability.
if boys with ASD have lower 2D:4D ratios, and presumably have had higher exposure • Consistent with previous research, the data indicated a lower 2D:4D ratio amongst
Diagnosis n r p n r p n r p
to prenatal testosterone. Associations between 2D:4D ratio and autism severity, as boys with an ASD, implying higher prenatal testosterone levels compared to TD
rated by the ADOS revised algorithms13, were also explored. TD 35 0.269 0.12 27 -0.133 0.51 37 0.056 0.74 boys.
• No associations were found between children’s and parents’ measurements,
ASD 67 -0.033 0.79 31 0.183 0.32 69 0.059 0.629 indicating that familial factors are not implicated in determining the digit ratios
Method
Participants comprised of 77 boys (4-16 years of age) with an ASD and 38 TD boys, TD +ASD 102 0.053 0.60 58 0.118 0.34 106 0.061 0.53 studied here.
along with their parents. DSM IV diagnosis of ASD was confirmed by administration • As with many autism measurements, there was more variability in 2D:4D ratios in
of the ADOS. Measurements of the second and fourth fingers were obtained by Note. Mother + Father = Average 2D:4D of Mother and Father for each participant.
the ASD group than in the TD group, possibly reflecting the increased
measuring from the metacarpophalangeal joint to the finger-tip to establish 2D:4D heterogeneity inherent in affected individuals.
ratios for all the boys and their parents. Measurements were collected as part of a References
larger, ongoing, longitudinal study; an average of 2D:4D ratios was calculated for Table 2 1. Galis, F., Ten Broeck, C., Van Dongen, S., & Wijnaendts, L. (2009). Sexual Dimoprhism in the Prenatal
Ratio (2D:4D). Archives of Sexual Behavior, 39, 57-62.
each participant based on the number of visits each participant had completed to 2. Knickmeyer, R., & Baron-Cohen, S. (2006). Fetal testosterone and sex differences. Early Human
Development, 82, 755-760.
date. In order to preserve the variability of the ASD group, outliers were adjusted Correlation between 2D:4D and ADOS Revised Algorithm Totals and Severity 3. Auyeung, B., Baron-Cohen, S., Chapman, E., Knickmeyer, R., Taylor, K., & Hackett, G. (2006). Foetal
testosterone and the child systemizing quotient. European Journal of Endocrinology, 155, 123-130.
according to the method recommended by Tabachnick and Fidell (2007)14. 4. Chapman, E., Baron-Cohen, S., Auyeung, B., Knickmeyer, R., Taylor, K., & Hackett, G. (2006). Fetal
Algorithm ADOS testosterone and empathy: Evidence from the Empathy Quotient (EQ) and the "Reading the Mind in
n r p the Eyes" test. Social Neuroscience, 1(2), 135-148.
Results Totals Module 5. Knickmeyer, R., Taylor, K., Raggatt, P., Hackett, G., & Baron-Cohen, S. (2006). Fetal testosterone and
empathy. Hormones and Behavior, 49(3), 282-292.
The 2D:4D ratio was significantly lower in boys with ASD (M = 0.931, SD = .04) 1 19 0.20 0.41 6. Manning, J. T., Baron-Cohen, S., Wheelwright, S., & Sanders, G. (2001). The 2nd to 4th digit ratio and
SA 2 11 0.28 0.41 autism. Developmental Medicine & Child Neurology, 43, 160-164.
compared to TD boys (M = 0.952, SD = 0.03), t(113) = 2.99, p = .003, d = .62, 95% 7. van Honk, J., Schutter, D., Bos, P., Kruijt, A., Lentjes, E., & Baron-Cohen, S. (2011). Testosterone
3 34 0.04 0.81 administration impairs cognitive empathy in women depending on second-to-fourth digit ratio.
CI = [0.01, 0.04] (Figure 1) Proceedings of the National Academy of Sciences of the United States of America, 108 (8), 3448-3452.
1 19 0.00 0.99 8. Putz, D., Gaulin, S., Sporter, R., & McBurney, D. (2004). Sex hormones and finger length: What does
The 2D:4D ratios of the mothers of boys with ASD (M = 0.958, SD = 0.04) and TD RRB 2 11 -0.00 0.99 2D:4D indicate? Evolution and Human Behavior, 25, 182-199.
(M = 0.962, SD = 0.04) and fathers of boys with ASD (M = 0.945, SD =0.03) and TD 3 34 0.00 0.99
9. Voracek, M., & Dressler, S. (2006). Lack of correlation between digit ratio (2D:4D) and Baron-Cohen’s
“Reading the Mind in the Eyes” test, empathy, systemising, and autism-spectrum quotients in a
(M = 0.955, SD = 0.03) did not differ significantly between, or within, groups. 1 19 0.15 0.53 general population sample. Personality and Individual Differences, 41, 1481-1491.
10. von Horn, A., Bäckman, L., Davidsson, T., & Hansen, S. (2010). Empathizing, systemizing and finger
Parental measures of 2D:4D did not correlate with child measures of 2D:4D SA + RRB 2 11 0.20 0.55 length ratio in a Swedish sample. Scandinavian Journal of Psychology, 51, 31–37.
11. Manning, J., Baron-Cohen, S., Wheelwright, S., & Fink, B. (2010) Is digit ratio (2D:4D) related to
(Table 1) 3 34 0.04 0.83 systemizing and empathizing? Evidence from direct finger measurements reported in the BBC internet
survey. Personality and Individual Differences, 48, 767-771.
There were no significant correlations between 2D:4D and autism severity, nor 12. Valla, J., & Ceci, S. (2011). Can sex differences be tied to the long reach of prenatal hormones?
between 2D:4D and algorithm totals (Table 2) Severity 1-3 64 0.09 0.46 Brain organization theory, digit ratio (2D/4D), and sex differences in preferences and cognition.
Perspectives on Psychological Science, 6, 134-146.
There were no significant differences between AD and ASD groups on 2D:4D 13. Gotham, K., Pickles, A., & Lord, C. (2009). Standardizing ADOS scores for a measure of severity in
Autism Spectrum Disorders. Journal of Autism and Developmental Disorders, 39 (5), 693-705.
ratios (as determined by the different ADOS algorithm classifications) (Table 3) Note. SA = Social Affect; RRB = Restricted Repetitive Behaviours.
14. Tabachnick, B., & Fidell, L. (2007). Using Multivariate Statistics (5th ed.). Pearson International
Edition.