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Aydoğan Avşar P, Kara T, Kocaman O, Akkuş M. The relationship between digit ratio (2D:4D) and intelligence levels in specific learning disorders. Early Hum Dev 2024; 196:106085. [PMID: 39084185 DOI: 10.1016/j.earlhumdev.2024.106085] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/26/2024] [Revised: 07/25/2024] [Accepted: 07/26/2024] [Indexed: 08/02/2024]
Abstract
BACKGROUND Higher prenatal testosterone exposure regulates brain development and affects learning and intelligence directly. The digit ratio (2D:4D) is regarded as an indicator of prenatal testosterone exposure. This study aims to investigate the 2D:4D ratios and intelligence levels in individuals with specific learning disorders (SLD) and compare the ratios with healthy subjects. METHODS The study included a total of 117 patients diagnosed with SLD and 67 healthy controls. We measured the 2D:4D ratios and administered the Wechsler-Intelligence Scale for Children-Revised to assess intelligence quotient (IQ) scores in the SLD group. Sociodemographic data was obtained for both patients and healthy subjects and compared in both groups, as well as 2D:4D ratios. RESULTS Compared to healthy controls, both-hand 2D:4D ratios were found to be lower in the SLD group. In addition, male and female participants with SLD showed lower 2D:4D ratios in both hands than controls. The total scores on the WISC-R were found to decrease as the right-hand 2D:4D ratios and the age increased in the SLD group. CONCLUSION Our findings add to the literature examining the influence of prenatal testosterone exposure on learning and intelligence in the SLD sample. Further research in this domain may yield valuable insights into the underlying mechanisms and potential clinical implications for the management of SLDs examining additional variables that could potentially impact alongside the impact of sex hormones on brain development.
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Affiliation(s)
- Pınar Aydoğan Avşar
- Department of Child and Adolescent Psychiatry, Alanya Education and Research Hospital, Antalya 07425, Turkey.
| | - Tayfun Kara
- Department of Child and Adolescent Psychiatry, Alanya Alaaddin Keykubat University Faculty of Medicine, Antalya 07425, Turkey
| | - Orhan Kocaman
- Department of Child and Adolescent Psychiatry, Alanya Alaaddin Keykubat University Faculty of Medicine, Antalya 07425, Turkey
| | - Merve Akkuş
- Department of Psychiatry, Faculty of Medicine, Kütahya Health Sciences University, Kütahya 43100, Turkey
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2
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Bitsko RH, Holbrook JR, O'Masta B, Maher B, Cerles A, Saadeh K, Mahmooth Z, MacMillan LM, Rush M, Kaminski JW. A Systematic Review and Meta-analysis of Prenatal, Birth, and Postnatal Factors Associated with Attention-Deficit/Hyperactivity Disorder in Children. PREVENTION SCIENCE : THE OFFICIAL JOURNAL OF THE SOCIETY FOR PREVENTION RESEARCH 2024; 25:203-224. [PMID: 35303250 PMCID: PMC9482663 DOI: 10.1007/s11121-022-01359-3] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/17/2022] [Indexed: 12/17/2022]
Abstract
Previous studies have shown mixed results on the relationship between prenatal, birth, and postnatal ("pregnancy-related") risk factors and attention-deficit/hyperactivity disorder (ADHD). We conducted meta-analyses to identify potentially modifiable pregnancy-related factors associated with ADHD. A comprehensive search of PubMed, Web of Science, and EMBASE in 2014, followed by an updated search in January 2021, identified 69 articles published in English on pregnancy-related risk factors and ADHD for inclusion. Risk factors were included in the meta-analysis if at least three effect sizes with clear pregnancy-related risk factor exposure were identified. Pooled effect sizes were calculated for ADHD overall, ADHD diagnosis, inattention, and hyperactivity/impulsivity. Odds ratios (OR) were calculated for dichotomous measures and correlation coefficients (CC) for continuous measures. Prenatal factors (pre-pregnancy weight, preeclampsia, pregnancy complications, elevated testosterone exposure), and postnatal factors (Apgar score, neonatal illness, no breastfeeding) were positively associated with ADHD overall; the findings for ADHD diagnosis were similar with the exception that there were too few effect sizes available to examine pre-pregnancy weight and lack of breastfeeding. Prenatal testosterone was significantly associated with inattention and hyperactivity/impulsivity. Effect sizes were generally small (range 1.1-1.6 ORs, -0.16-0.11 CCs). Risk factors occurring at the time of birth (perinatal asphyxia, labor complications, mode of delivery) were not significantly associated with ADHD. A better understanding of factors that are consistently associated with ADHD may inform future prevention strategies. The findings reported here suggest that prenatal and postnatal factors may serve as potential targets for preventing or mitigating the symptoms of ADHD.
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Affiliation(s)
- Rebecca H Bitsko
- Division of Human Development and Disability, National Center On Birth Defects and Developmental Disabilities Centers for Disease Control and Prevention, Atlanta, GA, USA.
| | - Joseph R Holbrook
- Division of Human Development and Disability, National Center On Birth Defects and Developmental Disabilities Centers for Disease Control and Prevention, Atlanta, GA, USA
| | | | - Brion Maher
- Department of Mental Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, USA
| | | | | | | | | | | | - Jennifer W Kaminski
- Division of Human Development and Disability, National Center On Birth Defects and Developmental Disabilities Centers for Disease Control and Prevention, Atlanta, GA, USA
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3
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Maleki A, Bashirian S, Soltanian AR, Jenabi E, Farhadinasab A. Association between polycystic ovary syndrome and risk of attention-deficit/hyperactivity disorder in offspring: a meta-analysis. Clin Exp Pediatr 2022; 65:85-89. [PMID: 33872487 PMCID: PMC8841975 DOI: 10.3345/cep.2021.00178] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/13/2021] [Accepted: 03/31/2021] [Indexed: 11/27/2022] Open
Abstract
BACKGROUND There is evidence of a relationship between prenatal excess androgen exposure and central nervous developmental problems and attention-deficit/hyperactivity disorder (ADHD) in the offspring of mothers with polycystic ovary syndrome (PCOS). PURPOSE Here we aimed to use a meta-analysis to investigate whether the offspring of mothers with PCOS are at an increased chance of developing ADHD. METHODS Three main English databases were searched for articles published through December 2020. The NewcastleOttawa Scale was used to assess study quality. Study heterogeneity was determined using <italic>I</italic>2 statistics and publication bias was assessed using Begg and Egger tests. The results are presented as odds ratio (OR) and relative ratio (RR) estimates with 95% confidence intervals (CIs) using a random-effects model. RESULTS Six articles (3 cohort and 3 case-control studies; 401,413 total ADHD cases) met the study criteria. Maternal PCOS was associated with an increased risk of ADHD in the offspring based on OR and RR (OR, 1.42; 95% CI, 1.27-1.57) and (RR, 1.43; 95% CI, 1.35-1.51), respectively. There was no heterogeneity among the included articles based on OR (<italic>I</italic>2=0.0%, P=0.588) and RR (<italic>I</italic>2=0.0%, P=0.878). CONCLUSION Our study showed that maternal PCOS is a risk factor for ADHD. Therefore, screening their offspring for ADHD should be considered part of the comprehensive clinical care of women with PCOS.
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Affiliation(s)
- Azam Maleki
- Social Determinants of Health Research Center, Zanjan University of Medical Sciences, Zanjan, Iran
| | - Saeid Bashirian
- Social Determinants of Health Research Center, Hamadan University of Medical Sciences, Hamadan, Iran
| | - Ali Reza Soltanian
- Modeling of Non communicable Diseases Research Center, School of Public Health, Hamadan University of Medical Sciences, Hamadan, Iran
| | - Ensiyeh Jenabi
- Autism Spectrum Disorders Research Center, Hamadan University of Medical Sciences, Hamadan, Iran
| | - Abdollah Farhadinasab
- Department of Psychiatry, Shahid Beheshti University of Medical Sciences, Tehran, Iran
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Fusar-Poli L, Rodolico A, Sturiale S, Carotenuto B, Natale A, Arillotta D, Siafis S, Signorelli MS, Aguglia E. Second-to-Fourth Digit Ratio (2D:4D) in Psychiatric Disorders: A Systematic Review of Case-control Studies. CLINICAL PSYCHOPHARMACOLOGY AND NEUROSCIENCE : THE OFFICIAL SCIENTIFIC JOURNAL OF THE KOREAN COLLEGE OF NEUROPSYCHOPHARMACOLOGY 2021; 19:26-45. [PMID: 33508786 PMCID: PMC7851454 DOI: 10.9758/cpn.2021.19.1.26] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/07/2020] [Revised: 07/24/2020] [Accepted: 07/26/2020] [Indexed: 12/22/2022]
Abstract
The second-to-fourth digit ratio (2D:4D) is an indirect, retrospective, non-invasive measure that correlates negatively with intrauterine exposure to testosterone. The present meta-analysis aimed to evaluate if 2D:4D differs between patients with psychiatric disorders and controls. In September 2019, we searched in Web of Knowledge, PsycINFO, Embase, and CINHAL, and retrieved 619 papers. We finally included 43 case-control studies which compared the 2D:4D ratio of patients with autism spectrum disorder (ASD) (n = 16), schizophrenia (n = 8), gender non-conformity (n = 7), addictions (n = 5), attention deficit-hyperactivity disorder (ADHD) (n = 4), mood disorders (n = 2), and intellectual disability (n = 1) to non-clinical controls. Meta-analyses showed that, overall, psychiatric patients had lower 2D:4D than healthy controls (n = 43, overall sample = 9,484, mean difference = -0.0056, 95% confidence interval from -0.0093 to -0.002, I2 = 74%), with more pronounced differences in the right hand, males, and children. Considering psychiatric disorders individually, significant differences were found in the ASD, ADHD, and addictions groups, in which 2D:4D was significantly lower than healthy controls. Conversely, the right hand of males with schizophrenia showed higher 2D:4D than healthy controls. No other significant differences were detected. Although our results need to be cautiously interpreted and find limited applications in clinical practice, they may suggest that 2D:4D is altered in some psychopathological conditions, underlining the role of prenatal exposure to sex steroids in the etiology of psychiatric disorders.
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Affiliation(s)
- Laura Fusar-Poli
- Department of Clinical and Experimental Medicine, Psychiatry Unit, University of Catania, Catania, Italy
| | - Alessandro Rodolico
- Department of Clinical and Experimental Medicine, Psychiatry Unit, University of Catania, Catania, Italy
| | - Serena Sturiale
- Department of Clinical and Experimental Medicine, Psychiatry Unit, University of Catania, Catania, Italy
| | - Bianca Carotenuto
- Department of Clinical and Experimental Medicine, Psychiatry Unit, University of Catania, Catania, Italy
| | - Antimo Natale
- Department of Clinical and Experimental Medicine, Psychiatry Unit, University of Catania, Catania, Italy
| | - Davide Arillotta
- Department of Clinical and Experimental Medicine, Psychiatry Unit, University of Catania, Catania, Italy
| | - Spyridon Siafis
- Department of Psychiatry and Psychotherapy, School of Medicine, Technical University of Munich, Munich, Germany
| | - Maria Salvina Signorelli
- Department of Clinical and Experimental Medicine, Psychiatry Unit, University of Catania, Catania, Italy
| | - Eugenio Aguglia
- Department of Clinical and Experimental Medicine, Psychiatry Unit, University of Catania, Catania, Italy
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Işık Ü, Kılıç F, Aktepe E, Tanrıtanır B. The Relationship between Second-to-Fourth Digit Ratios, Attention-Deficit/Hyperactivity Disorder Symptoms, Aggression, and Intelligence Levels in Boys with Attention-Deficit/Hyperactivity Disorder. Psychiatry Investig 2020; 17:596-602. [PMID: 32517417 PMCID: PMC7324736 DOI: 10.30773/pi.2020.0003] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/05/2020] [Accepted: 04/15/2020] [Indexed: 01/21/2023] Open
Abstract
OBJECTIVE Observations of sex differences have led some scientists to doubt whether the neuroendocrine system is involved in attentiondeficit/hyperactivity disorder (ADHD) etiology. One of the interesting study subjects in this context is prenatal steroid hormone exposure. The aim of the present study was to replicate and extend previous work by addressing two research questions: 1) Are second-tofourth digit (2D:4D) ratios lower in ADHD than in controls? 2) Is there a correlation between 2D:4D ratios and symptoms of ADHD, aggression and intelligence scores in boys with ADHD? METHODS The study included 100 treatment-naive male children diagnosed with ADHD and 55 healthy male children. We measured the ratios of 2D:4D and administered a Wechsler Intelligence Scale for Children-Revised to assess IQ scores, as well as behavioral rating scales, in children with ADHD and comparison individuals. RESULTS We observed lower 2D:4D ratios in the right hand in ADHD in comparison to the control group. The left-hand ratios of 2D:4D, however, did not differ between ADHD and control groups. There were negative correlations between the left-hand 2D:4D ratios and the hyperactivity scores. However, no significant correlation was detected between right-hand 2D:4D ratios and the psychological questionnaire scores. CONCLUSION These results provide further evidence that fetal androgen exposure may contribute to the pathophysiology of ADHD, at least in boys.
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Affiliation(s)
- Ümit Işık
- Department of Child and Adolescent Psychiatry, Suleyman Demirel University Faculty of Medicine, Isparta, Turkey
| | - Faruk Kılıç
- Department of Psychiatry, Suleyman Demirel University Faculty of Medicine, Isparta, Turkey
| | - Evrim Aktepe
- Department of Child and Adolescent Psychiatry, Suleyman Demirel University Faculty of Medicine, Isparta, Turkey
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Wernicke J, Zabel JT, Zhang Y, Becker B, Montag C. Association between tendencies for attention-deficit/hyperactivity disorder (ADHD) and the 2D:4D digit ratio: a cross-cultural replication in Germany and China. Early Hum Dev 2020; 143:104943. [PMID: 32126477 DOI: 10.1016/j.earlhumdev.2019.104943] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/06/2019] [Revised: 12/16/2019] [Accepted: 12/17/2019] [Indexed: 12/19/2022]
Abstract
Prenatal testosterone is considered to be a possible factor contributing to the development of attention-deficit/hyperactivity disorder (ADHD) symptomatology, but findings regarding the connection between individual variations in prenatal testosterone exposure as (indirectly) indexed by the second-to-fourth digit (2D:4D) ratio and ADHD remain inconsistent. To clarify the inconsistent findings and to facilitate generalization on the association between subclinical variations in ADHD tendencies and lower 2D:4D ratios the current study applied a cross-cultural replication approach employing independent healthy adult cohorts from Germany and China. Samples from Germany and China were matched for gender and age (in each sample nmales = 96, nfemales = 96; ageGermany: M = 21.47, SD = 2.55; ageChina: M = 21.36, SD = 2.28). All participants filled in the Adult ADHD Self-Report Scale Symptom Checklist (ASRS) and provided hand scans to measure 2D:4D ratios. The German sample had significantly higher 2D:4D ratios than the Chinese sample but in both samples males had significantly lower 2D:4D ratios than females. The hypothesised negative association between 2D:4D ratios and ADHD tendencies was observed on a descriptive level in German and Chinese males and with one exception in Chinese females. But only in German males correlations gained significance (range: r = -0.198 to r = -0.177). The observed effect sizes are in line with former research that was conducted in samples from different cultures. In future research on the connection between testosterone and ADHD not only prenatal but also postnatal testosterone as well as possible moderators like childhood maltreatment should be taken into account.
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Affiliation(s)
- Jennifer Wernicke
- Department of Molecular Psychology, Institute of Psychology and Education, Ulm University, Ulm, Germany.
| | - Julia Tamara Zabel
- Department of Molecular Psychology, Institute of Psychology and Education, Ulm University, Ulm, Germany
| | - Yingying Zhang
- Department of Molecular Psychology, Institute of Psychology and Education, Ulm University, Ulm, Germany
| | - Benjamin Becker
- The Clinical Hospital of Chengdu Brain Science Institute, MOE Key Laboratory for Neuroinformation, University of Electronic Science and Technology of China, Chengdu, China
| | - Christian Montag
- Department of Molecular Psychology, Institute of Psychology and Education, Ulm University, Ulm, Germany; The Clinical Hospital of Chengdu Brain Science Institute, MOE Key Laboratory for Neuroinformation, University of Electronic Science and Technology of China, Chengdu, China
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7
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Yuksel T, Sizer E, Durak H. 2D:4D ratios as an indicator of intrauterine androgen exposure in children who stutter. Early Hum Dev 2019; 135:27-31. [PMID: 31228858 DOI: 10.1016/j.earlhumdev.2019.06.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/13/2019] [Revised: 06/01/2019] [Accepted: 06/04/2019] [Indexed: 11/15/2022]
Abstract
AIM We aimed to explore whether there is a relationship between stuttering and digit ratio (2D:4D), which is thought to be a marker of prenatal testosterone exposure. METHODS We evaluated a total of 90 children who stutter (CWS; n = 40 mild-to-moderate and n = 50 severe stutters) and 40 healthy peers (CWNS) as controls. We used the Clinical Global Impression-Severity (CGIS) scale to measure the severity of stuttering. We measured the lengths of index finger (2D) and ring finger (4D) of both hands directly and divided to calculate 2D:4D ratio. The difference between the right and the left hand 2D:4D ratio (DR-L) was also calculated. RESULT Significant difference was found in right 2D:4D and the mean DR-L between the CWS and CWNS groups. Right 2D:4D was significantly lower in stuttering boys than in control boys, and in stuttering girls than control girls. Also, DR-L was significantly lower in stuttering boys than control boys. In ANOVA, there were significant differences between the mild-to-moderate, severe stuttering and control groups in terms of right 2D:4D and DR-L. Right hand 2D:4D and DR-L decreased from controls to severe stutterers. CONCLUSION Our results suggest that lower right 2D:4D and DR-L were related to the presence and severity of stuttering in children, i.e. CWS had lower 2D:4D and DR-L than CWNS. Further large-scale prospective studies are needed to clarify the reliability of 2D:4D ratio as an indicator of fetal sex hormone exposure level and its relation with the presence and severity of stuttering in children.
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Affiliation(s)
- Tugba Yuksel
- Dicle University School of Medicine, Department of Child and Adolescent Psychiatry, Diyarbakir, Turkey.
| | - Esra Sizer
- Dicle University School of Medicine, Department of Child and Adolescent Psychiatry, Diyarbakir, Turkey
| | - Hasan Durak
- Dicle University School of Medicine, Department of Child and Adolescent Psychiatry, Diyarbakir, Turkey
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8
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Nguyen TV, Jutras B, Monnier P, Muckle G, Velez M, Arbuckle TE, Saint-Amour D. Prenatal masculinization of the auditory system in infants: The MIREC-ID study. Psychoneuroendocrinology 2019; 104:33-41. [PMID: 30784903 DOI: 10.1016/j.psyneuen.2019.02.015] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/12/2018] [Revised: 02/05/2019] [Accepted: 02/13/2019] [Indexed: 11/30/2022]
Abstract
Sex differences in inner-ear function are detectable in infants, notably through the measurement of otoacoustic emissions (OAEs). Prevailing theories posit that prenatal exposure to high levels of androgens in boys may weaken OAEs, and that this phenomenon may predominantly affect the right ear/left hemisphere (Geschwind-Galaburda (GG) hypothesis). Yet, actual tests of these models have been difficult to implement in humans. Here we examined the relationship between markers of fetal androgen exposure collected at birth (anogenital distances (AGD); penile length/width, areolar/scrotal/vulvar pigmentation) and at 6 months of age (2nd to 4th digit ratio (2D:4D)) with two types of OAEs, click-evoked OAEs (CEOAEs) and distortion-product OAEs (DPOAEs) (n = 49; 25 boys; 24 girls). We found that, in boys, scrotal pigmentation was inversely associated with the amplitude and reproducibility of CEOAEs in the right ear at 4 kHz, with trends also present in the same ear for mean CEOAE amplitude and CEOAE amplitude at 2 kHz. Penile length was inversely associated with the mean amplitude of DPOAEs in both the right and left ears, as well as with DPOAE amplitude in the right ear at 2 kHz and the reproducibility of CEOAEs in the left ear at 2.8 kHz. Finally, AGD-scrotum in boys was positively associated in boys with the amplitude of DPOAEs in the left ear at 2.8 kHz. Unexpectedly, there were no sex differences in the amplitude or reproducibility of OAEs, nor, in girls, any associations between androgenic markers and auditory function. Nonetheless, these findings, reported for the first time in a sample of human infants, support both the prenatal-androgen-exposure and GG models as explanations for the masculinization of auditory function in male infants.
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Affiliation(s)
- Tuong-Vi Nguyen
- Department of Psychiatry, McGill University, Royal Victoria Hospital, Montreal, Canada; Department of Obstetrics & Gynecology McGill University, Royal Victoria Hospital, Montreal, Canada; Research Institute of the McGill University Health Centre [RI-MUHC), Royal Victoria Hospital, Montreal, Canada.
| | - Benoît Jutras
- Research Center, CHU Sainte-Justine, Montreal, Canada; School of Speech Language Pathology and Audiology, Université de Montréal, Montréal, Canada
| | - Patricia Monnier
- Department of Obstetrics & Gynecology McGill University, Royal Victoria Hospital, Montreal, Canada; Research Institute of the McGill University Health Centre [RI-MUHC), Royal Victoria Hospital, Montreal, Canada
| | - Gina Muckle
- School of Psychology, Laval University, Quebec CHU Research Centre, Quebec City, Canada
| | - Maria Velez
- Department of Obstetrics & Gynecology, Queen's University, Kingston, Ontario, Canada
| | - Tye E Arbuckle
- Population Studies Division, Environmental Health Science and Research Bureau, Health Canada, Ottawa Canada
| | - Dave Saint-Amour
- Research Center, CHU Sainte-Justine, Montreal, Canada; Department of Psychology, Université du Québec à Montréal, Montréal, Canada
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9
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Fisher AD, Ristori J, Morelli G, Maggi M. The molecular mechanisms of sexual orientation and gender identity. Mol Cell Endocrinol 2018; 467:3-13. [PMID: 28847741 DOI: 10.1016/j.mce.2017.08.008] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/28/2017] [Revised: 08/02/2017] [Accepted: 08/15/2017] [Indexed: 12/21/2022]
Abstract
Differences between males and females are widely represented in nature. There are gender differences in phenotypes, personality traits, behaviors and interests, cognitive performance, and proneness to specific diseases. The most marked difference in humans is represented by sexual orientation and core gender identity, the origins of which are still controversial and far from being understood. Debates continue on whether sexual behavior and gender identity are a result of biological (nature) or cultural (nurture) factors, with biology possibly playing a major role. The main goal of this review is to summarize the studies available to date on the biological factors involved in the development of both sexual orientation and gender identity. A systematic search of published evidence was performed using Medline (from January 1948 to June 2017). Review of the relevant literature was based on authors' expertise. Indeed, different studies have documented the possible role and interaction of neuroanatomic, hormonal and genetic factors. The sexual dimorphic brain is considered the anatomical substrate of psychosexual development, on which genes and gonadal hormones may have a shaping effect. In particular, growing evidence shows that prenatal and pubertal sex hormones permanently affect human behavior. In addition, heritability studies have demonstrated a role of genetic components. However, a convincing candidate gene has not been identified. Future studies (e.i. genome wide studies) are needed to better clarify the complex interaction between genes, anatomy and hormonal influences on psychosexual development.
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Affiliation(s)
- Alessandra D Fisher
- Department of Experimental, Clinical and Biomedical Sciences, Careggi University Hospital, Florence, Italy
| | - Jiska Ristori
- Department of Experimental, Clinical and Biomedical Sciences, Careggi University Hospital, Florence, Italy
| | - Girolamo Morelli
- Department of Surgical, Medical, Molecular and of the Critical Area Pathology, University of Pisa, Pisa, Italy
| | - Mario Maggi
- Department of Experimental, Clinical and Biomedical Sciences, Careggi University Hospital, Florence, Italy.
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10
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Roberts B, Eisenlohr-Moul T, Martel MM. Reproductive steroids and ADHD symptoms across the menstrual cycle. Psychoneuroendocrinology 2018; 88:105-114. [PMID: 29197795 PMCID: PMC5803442 DOI: 10.1016/j.psyneuen.2017.11.015] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/10/2017] [Revised: 11/25/2017] [Accepted: 11/27/2017] [Indexed: 11/18/2022]
Abstract
Although Attention-Deficit/Hyperactivity Disorder shows (ADHD) male predominance, females are significantly impaired and exhibit additional comorbid disorders during adolescence. However, no empirical work has examined the influence of cyclical fluctuating steroids on ADHD symptoms in women. The present study examined estradiol (E2), progesterone (P4), and testosterone (T) associations with ADHD symptoms across the menstrual cycle in regularly-cycling young women (N=32), examining trait impulsivity as a moderator. Women completed a baseline measure of trait impulsivity, provided saliva samples each morning, and completed an ADHD symptom checklist every evening for 35days. Results indicated decreased levels of E2 in the context of increased levels of either P4 or T was associated with higher ADHD symptoms on the following day, particularly for those with high trait impulsivity. Phase analyses suggested both an early follicular and early luteal, or post-ovulatory, increase in ADHD symptoms. Therefore, ADHD symptoms may change across the menstrual cycle in response to endogenous steroid changes.
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Affiliation(s)
- Bethan Roberts
- Department of Psychology, University of Kentucky, Lexington, KY 40506, United States.
| | - Tory Eisenlohr-Moul
- Department of Psychiatry, University of North Carolina at Chapel Hill, 2218 Nelson Highway, Suite 3, Chapel Hill, NC 27517, United States.
| | - Michelle M Martel
- Department of Psychology, University of Kentucky, 207C Kastle Hall, Lexington, KY 40506, United States.
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11
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Millet K, Buehler F. A Context Dependent Interpretation of Inconsistencies in 2D:4D Findings: The Moderating Role of Status Relevance. Front Behav Neurosci 2018; 11:254. [PMID: 29403365 PMCID: PMC5785725 DOI: 10.3389/fnbeh.2017.00254] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2017] [Accepted: 12/14/2017] [Indexed: 12/16/2022] Open
Abstract
Whereas direct relationships between 2D:4D and dominance related attitudes or behavior often turn out to be weak, some literature suggests that the relation between 2D:4D and dominance is context-specific. That is, especially in status-challenging situations 2D:4D may be related to dominant behavior and its correlates. Based on this perspective, we interpret inconsistencies in the literature on the relation between 2D:4D and risk taking, aggression and dominance related outcomes and investigate in our empirical study how attitudes in low 2D:4D men may change as a function of the status relevance of the context. We provide evidence for the idea that status relevance of the particular situation at hand influences the attitude towards performance-enhancing means for low 2D:4D men, but not for high 2D:4D men. We argue that 2D:4D may be related to any behavior that is functional to attain status in a specific context. Implications for (economic) decision making are discussed.
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Affiliation(s)
- Kobe Millet
- Department of Marketing, Vrije Universiteit Amsterdam, Amsterdam, Netherlands
| | - Florian Buehler
- Department of Marketing, Vrije Universiteit Amsterdam, Amsterdam, Netherlands
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12
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Redmond SM, Ash AC. Associations Between the 2D:4D Proxy Biomarker for Prenatal Hormone Exposures and Symptoms of Developmental Language Disorder. JOURNAL OF SPEECH, LANGUAGE, AND HEARING RESEARCH : JSLHR 2017; 60:3226-3236. [PMID: 29086795 PMCID: PMC5945080 DOI: 10.1044/2017_jslhr-l-17-0143] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/17/2017] [Revised: 05/26/2017] [Accepted: 06/22/2017] [Indexed: 06/07/2023]
Abstract
PURPOSE Relative lengths of the index (2D) and ring (4D) fingers in humans represent a retrospective biomarker of prenatal hormonal exposures. For this reason, the 2D:4D digit ratio can be used to investigate potential hormonal contributions to the etiology of neurodevelopmental disorders. This study tested potential group differences in 2D:4D digit ratios in a sample of boys with and without developmental language disorder (DLD) and examined the strength of associations between 2D:4D digit ratio and a battery of verbal and nonverbal measures. METHOD A group of 29 boys affected by DLD and a group of 76 boys with typical language abilities participated (age range = 5;6-11;0 years). Scanned images were used to measure finger lengths. Language measures included the core language subtests from the Clinical Evaluation of Language Fundamentals-Fourth Edition (Semel, Wiig, & Secord, 2003), a nonword repetition task, a sentence recall task, and the Test of Early Grammatical Impairment (Rice & Wexler, 2001). RESULTS Significant group differences indicated lower 2D:4D digit ratios in the group with DLD. Modest associations were found between 2D:4D digit ratios and some Clinical Evaluation of Language Fundamentals-Fourth Edition subtests. CONCLUSIONS Prenatal hormone exposures may play a role in the etiology of some language symptoms.
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Cicek IE, Cicek E, Demirel B, Ayhan MG, Varsak N, Özbek SY, Selçuk M, Eren I. Digit ratio (2D:4D), impulsiveness and aggression in male heroin addicts: A prospective controlled study. PERSONALITY AND INDIVIDUAL DIFFERENCES 2017. [DOI: 10.1016/j.paid.2017.05.031] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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Romero-Martínez Á, Polderman TJC, González-Bono E, Moya-Albiol L. Masculinization in Parents of Offspring With Autism Spectrum Disorders Could Be Involved in Comorbid ADHD Symptoms. J Atten Disord 2017; 21:938-943. [PMID: 23569156 DOI: 10.1177/1087054713482685] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
OBJECTIVE People with autism spectrum disorders (ASD) often have comorbid ADHD symptoms. ASD and ADHD are both associated with high intrauterine testosterone (T) levels. This study aims to investigate whether masculinization predicts inattention symptoms in parents, and in their ASD-affected offspring. METHOD The sample consisted of 32 parents with ASD-affected children (13 male, 19 female) and 32 offspring individuals (28 male, 4 female). Masculinization of parents was measured by 2D:4D finger ratio, and current T levels. Inattention in both parents and in their offspring was measured with behavior questionnaires. RESULTS The results indicated that masculinized 2D:4D explains inattentive ADHD symptoms in ASD parents and in their offspring. These predictions are mediated by T and inattention symptoms of ASD parents, respectively. CONCLUSION These findings suggest the existence of a masculinized endophenotype in ASD parents, which may be characterized by high attentional sensitivity to T effects.
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Voracek M, Offenmuller D. Digit Ratios (2D:4D and other) and Relative Thumb Length: A Test of Developmental Stability. Percept Mot Skills 2016; 105:143-52. [DOI: 10.2466/pms.105.1.143-152] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Sex and side differences in relative thumb length of children and adolescents have been reported by prior researchers. These findings mirror those reported for the second-to-fourth digit ratio (2D:4D), a likely biomarker for the organizational (permanent) effects of prenatal androgens on the human brain and body. The present study investigated relative thumb length, in particular, its associations with all possible digit ratios (2D:3D, 2D:4D, 2D:5D, 3D:4D, 3D:5D, and 4D:5D), in a sample of young adults (60 men and 64 women). Relative thumb length was less precisely measurable than direct or image-based finger-length measurements, as used in digit ratio research. There were no significant sex or side differences in relative thumb length. Contrary to expectation, thumb size was not positively correlated with any digit ratios. Relative thumb length appears to be developmentally unstable (decreases during childhood and adolescence). Additional findings, such as the magnitude ranking of sex differences in digit ratios and the comparability of direct versus image-based finger-length measurements, are also discussed.
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Mouridsen SE, Rich B, Isager T. The Sex Ratio of Full and Half Siblings of People Diagnosed With ADHD in Childhood and Adolescence: A Danish Nationwide Register-Based Cohort Study. J Atten Disord 2016; 20:1017-1022. [PMID: 24752665 DOI: 10.1177/1087054714529817] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
OBJECTIVE It has been suggested that high levels of prenatal testosterone exposure are implied in the etiology of male preponderance disorders such as autism spectrum disorder and ADHD. Within this scope, we studied the sex ratio (proportion of males) in siblings of individuals diagnosed with ADHD in childhood and adolescence. METHOD We did a nationwide, register-based cohort study of the sex ratio in siblings of the 16,381 patients in Denmark diagnosed with ADHD at age 17 years and younger and registered in the nationwide Danish Psychiatric Central Register between January 1, 1994 and May 28, 2013. RESULTS Among the 33,151 siblings, 17,041 were males and 16,110 females. This yields a sex ratio of 0.514, which is not statistically significant different from the Danish live birth sex ratio of 0.513 during the relevant years (p = .70). CONCLUSION These findings provide no support for the hypothesis that the sex ratio is elevated among the siblings of people with ADHD.
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Affiliation(s)
| | - Bente Rich
- Hødersvej 5, Roskilde, Denmark.,International Rehabilitation Council for Torture Victims, Copenhagen, Denmark
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Stolten M, Ledet E, Dotiwala A, Luk E, Sartor O. Alternative Digit Ratios and Their Relationship to Prostate Cancer. Clin Genitourin Cancer 2016; 14:149-52. [DOI: 10.1016/j.clgc.2015.11.005] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2015] [Revised: 11/01/2015] [Accepted: 11/04/2015] [Indexed: 10/22/2022]
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Van Damme R, Wijnrocx K, Boeye J, Huyghe K, Van Dongen S. Digit ratios in two lacertid lizards: sexual dimorphism and morphological and physiological correlates. ZOOMORPHOLOGY 2015. [DOI: 10.1007/s00435-015-0275-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
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Martel MM, Roberts BA. Prenatal testosterone increases sensitivity to prenatal stressors in males with disruptive behavior disorders. Neurotoxicol Teratol 2014; 44:11-7. [PMID: 24819590 PMCID: PMC4295486 DOI: 10.1016/j.ntt.2014.05.001] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2013] [Revised: 04/28/2014] [Accepted: 05/01/2014] [Indexed: 12/24/2022]
Abstract
Disruptive Behavior Disorders (DBD) exhibit a sex-biased prevalence rate favoring boys, and prenatal testosterone exposure appears to be part of the complex etiology of these disorders. The current study examines whether high prenatal testosterone exposure may heighten the risk for DBD symptoms in males by increasing susceptibility to negative environmental conditions such as maternal nicotine and alcohol use during pregnancy. Participants were 109 three- to six-year-olds (64% male; 72% with DBD) and their 109 primary caregivers and 55 daycare providers/teachers who completed a multi-informant diagnostic procedure. A proxy of prenatal testosterone exposure, finger-length ratios, interacted with maternal report of prenatal nicotine use to predict teacher-rated hyperactivity-impulsivity during preschool, for boys, but not girls, although the three-way interaction was not significant. Prenatal testosterone interacted with prenatal alcohol exposure to predict teacher-rated hyperactivity-impulsivity and ODD symptoms differentially based on child sex (significant three-way interaction). Boys with higher levels of prenatal testosterone who were also exposed to higher levels of nicotine and alcohol during pregnancy exhibited increased hyperactivity-impulsivity during early childhood, but girls did not exhibit this same pattern. Thus, high prenatal testosterone exposure seems to increase risk for DBD symptoms particularly in males by increasing susceptibility to prenatal environmental stressors.
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Abstract
Disruptive Behaviors Disorders (DBD), including Oppositional-Defiant Disorder (ODD) and Attention-Deficit/Hyperactivity Disorder (ADHD), are fairly common and highly impairing childhood behavior disorders that can be diagnosed as early as preschool. Prenatal exposure to testosterone may be particularly relevant to these early-emerging DBDs that exhibit a sex-biased prevalence rate favoring males. The current study examined associations between preschool DBD symptom domains and prenatal exposure to testosterone measured indirectly via right 2D:4D finger-length ratios. The study sample consisted of 109 preschool-age children between ages 3 and 6 (64% males;72% with DBD) and their primary caregivers. Primary caregivers completed a semi-structured interview (i.e., Kiddie Disruptive Behavior Disorder Schedule), as well as symptom questionnaires (i.e., Disruptive Behavior Rating Scale, Peer Conflict Scale); teachers and/or daycare providers completed symptom questionnaires and children provided measures of prenatal testosterone exposure, measured indirectly via finger-length ratios (i.e., right 2D:4D). Study results indicated a significant association of high prenatal testosterone (i.e., smaller right 2D:4D) with high hyperactive-impulsive ADHD symptoms in girls but not boys, suggesting that the effect may be driven by, or might only exist in, girls. The present study suggests that prenatal exposure to testosterone may increase risk for early ADHD, particularly hyperactivity-impulsivity, in preschool girls.
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A review on the relationship between testosterone and life-course persistent antisocial behavior. Psychiatry Res 2012; 200:984-1010. [PMID: 22925371 DOI: 10.1016/j.psychres.2012.07.044] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/16/2011] [Revised: 07/18/2012] [Accepted: 07/28/2012] [Indexed: 12/11/2022]
Abstract
Life-course persistent antisocial behavior is 10 to 14 times more prevalent in males and it has been suggested that testosterone levels could account for this gender bias. Preliminary studies with measures of fetal testosterone find inconsistent associations with antisocial behavior, especially studies that use the 2D:4D ratio as a proxy for fetal testosterone. However, circulating testosterone consistently shows positive associations with antisocial behaviors throughout childhood, adolescence, and adulthood, particularly in males. It is suggested that high fetal/circulating testosterone interactively influence the maturation and functionality of mesolimbic dopaminergic circuitry, right orbitofrontal cortex, and cortico-subcortical connectivity, resulting in a strong reward motivation, low social sensitivity, and dampened regulation of strong motivational/emotional processes. The link between these testosterone induced endophenotypes and actual display of antisocial behavior is strongly modulated by different social (e.g., social rejection, low SES) and genetic (e.g., MAOA, 5HTT) risk factors that can disturb socio-, psycho-, and biological development and interact with testosterone in shaping behavior. When these additional risk factors are present, the testosterone induced endophenotypes may increase the risk for a chronic antisocial lifestyle. However, behavioral endophenotypes induced by testosterone can also predispose towards socially adaptive traits such as a strong achievement motivation, leadership, fair bargaining behaviors, and social assertiveness. These adaptive traits are more likely to emerge when the high testosterone individual has positive social experiences that promote prosocial behaviors such as strong and secure attachments with his caregivers, affiliation with prosocial peers, and sufficient socioeconomic resources. A theoretical model is presented, various hypotheses are examined, and future venues for research are discussed.
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Medland SE, Loehlin JC. Multivariate Genetic Analyses of the 2D:4D Ratio: Examining the Effects of Hand and Measurement Technique in Data from 757 Twin Families. Twin Res Hum Genet 2012; 11:335-41. [DOI: 10.1375/twin.11.3.335] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
AbstractThe ratio of the lengths of the second to fourth digits of the hand (2D:4D) is a sexually dimorphic trait that has been proposed as a measure of prenatal testosterone exposure and a putative correlate of a variety of later behavioral and physiological outcomes including personality, fitness and sexual orientation. We present analyses of 2D:4D ratios collected from twins (1413 individuals) and their nontwin siblings (328 individuals) from 757 families. In this sample 2D:4D was measured from photocopies using digital calipers, and for a subset of participants, computer-aided measurement. Multivariate modeling of the left- and right-hand measurements revealed significant genetic and environmental covariation between hands. The two methods yielded very similar results, and the majority of variance was explained by factors shared by both measurement methods. Neither common environmental nor dominant genetic effects were found, and the covariation between siblings could be accounted for by additive genetic effects accounting for 80% and 71% of the variance for the left and right hands, respectively. There was no evidence of sex differences in the total variance, nor in the magnitude or source of genetic and environmental influences, suggesting that X-linked effects (such as the previously identified association with the Androgen receptor) are likely to be small. However, there were also nonshared environmental effects specific to each hand, which, in addition to measurement error, may in part explain why some studies within in the literature find effects for the 2D:4D ratio of one hand but not the other.
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Snihur AW, Hampson E. Individual differences in 2D:4D digit-ratios and otoacoustic emissions: Do they share a common developmental origin? PERSONALITY AND INDIVIDUAL DIFFERENCES 2011. [DOI: 10.1016/j.paid.2010.11.001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Baron-Cohen S, Lombardo MV, Auyeung B, Ashwin E, Chakrabarti B, Knickmeyer R. Why are autism spectrum conditions more prevalent in males? PLoS Biol 2011; 9:e1001081. [PMID: 21695109 PMCID: PMC3114757 DOI: 10.1371/journal.pbio.1001081] [Citation(s) in RCA: 435] [Impact Index Per Article: 33.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Autism Spectrum Conditions (ASC) are much more common in males, a bias that may offer clues to the etiology of this condition. Although the cause of this bias remains a mystery, we argue that it occurs because ASC is an extreme manifestation of the male brain. The extreme male brain (EMB) theory, first proposed in 1997, is an extension of the Empathizing-Systemizing (E-S) theory of typical sex differences that proposes that females on average have a stronger drive to empathize while males on average have a stronger drive to systemize. In this first major update since 2005, we describe some of the evidence relating to the EMB theory of ASC and consider how typical sex differences in brain structure may be relevant to ASC. One possible biological mechanism to account for the male bias is the effect of fetal testosterone (fT). We also consider alternative biological theories, the X and Y chromosome theories, and the reduced autosomal penetrance theory. None of these theories has yet been fully confirmed or refuted, though the weight of evidence in favor of the fT theory is growing from converging sources (longitudinal amniocentesis studies from pregnancy to age 10 years old, current hormone studies, and genetic association studies of SNPs in the sex steroid pathways). Ultimately, as these theories are not mutually exclusive and ASC is multi-factorial, they may help explain the male prevalence of ASC.
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Affiliation(s)
- Simon Baron-Cohen
- Autism Research Centre, Department of Psychiatry, University of Cambridge, Cambridge, United Kingdom.
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Hönekopp J, Watson S. Meta-analysis of digit ratio 2D:4D shows greater sex difference in the right hand. Am J Hum Biol 2011; 22:619-30. [PMID: 20737609 DOI: 10.1002/ajhb.21054] [Citation(s) in RCA: 323] [Impact Index Per Article: 24.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
OBJECTIVES Our aims are, first, to describe the sex difference in the length ratio of the second and fourth digits (2D:4D), which likely reflects prenatal testosterone levels in humans. Second, to infer the loss of reliability observed in 2D:4D based on self-measured finger lengths. METHODS We used random-effects meta-analysis of 2D:4D based on expert-measured finger lengths (116 samples with 13,260 females and 11,789 males). RESULTS We find a moderate sex difference (with lower 2D:4D for males), which shows substantial heterogeneity (which is unrelated to age). The sex difference is moderated by the type of finger length measurement and by hand. Measurement involving the distortion of soft tissue leads to a significantly larger sex difference than finger length measurement avoiding this. The sex difference in 2D:4D is larger in the right hand than in the left. The reliability of self-measured 2D:4D in the BBC internet study, by far the largest study on 2D:4D, is estimated to be 46% of that of expert-measured 2D:4D. CONCLUSIONS Right-hand 2D:4D might be a better indicator of prenatal androgenisation than left-hand 2D:4D. The view that 2D:4D has allometric properties (Kratochvil L, Flegr J. 2009. Differences in 2nd to 4th digit length ratio in humans reflect shifts along the common allometric line. Biol Lett 5:643-646.) is not supported. Bone lengths contribute to the sex difference in 2D:4D. In addition, there might be a sex difference in fingers' soft tissue, which should be investigated. Because of measurement unreliability, correlations between 2D:4D and variables of interest are about one-third smaller in the BBC internet study than in studies in which 2D:4D is based on expert-measured finger lengths.
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Affiliation(s)
- Johannes Hönekopp
- Department of Psychology, Northumbria University, Newcastle upon Tyne NE1 8ST, United Kingdom.
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Lemiere J, Boets B, Danckaerts M. No association between the 2D:4D fetal testosterone marker and multidimensional attentional abilities in children with ADHD. Dev Med Child Neurol 2010; 52:e202-8. [PMID: 20491856 DOI: 10.1111/j.1469-8749.2010.03684.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
AIM It has been suggested that high levels of prenatal testosterone exposure are implied in the aetiology of attention-deficit-hyperactivity disorder (ADHD). This study examined the association between the ratio of the length of the second and fourth digits (2D:4D ratio), a marker of fetal testosterone exposure, and the presence of ADHD-related cognitive and behavioural problems in children with ADHD and in typically developing comparison individuals. METHOD A clinically referred group of 64 children who fulfilled DSM-IV-TR criteria for ADHD (47 males, 17 females; mean age 8 y 8 mo, SD 1 y 8 mo, range 7-12 y) and 46 comparison children (25 males, 21 females; mean age 9 y 2 mo; SD 1 y 10 mo, range 7-12 y) were included in the study. The length of the second and fourth digits was measured by two independent raters. The Child Behaviour Checklist (CBCL) and the Test of Everyday Attention for Children (TEA-Ch) were used to assess behavioural problems and different aspects of attention. RESULTS No group differences in 2D:4D ratio were observed between children with (combined, inattentive, or hyperactive-impulsive subtype of) ADHD and comparison children. The ratio did not show the postulated relation with cognitive and behavioural aspects of ADHD. INTERPRETATION These findings challenge the hypothesis that fetal testosterone exposure plays a prominent role in the aetiology of ADHD.
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Affiliation(s)
- Jurgen Lemiere
- Department of Child and Adolescent Psychiatry, UPC-KULeuven, Leuven, Belgium.
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Abstract
There is now compelling evidence that the ratio of the length of the second digit divided by the length of the fourth digit (2D:4D) is affected by prenatal androgens in humans. This ratio is greater in females than males from fetal life through adulthood, correlates with polymorphism in the androgen receptor gene in men, is feminine in XY androgen insensitivity syndrome, and masculinized in congenital adrenal hyperplasia. Using 2D:4D as a correlate, researchers have found evidence that prenatal androgens affect many sexually differentiated human behaviors, including sexual orientation in women (but not in men), attention deficit disorder, autism, eating disorders, aggression, and risk-taking. In each case, lower 2D:4D, indicative of greater prenatal androgen stimulation, is associated with behavior more commonly displayed by males than females. The correlation between 2D:4D and prenatal androgen stimulation is too imperfect to accurately predict the phenotype of a particular individual, even in terms of sex. However, digit ratio is the best available retrospective marker of average differences in prenatal androgen stimulation between groups of people, and/or correlations of prenatal androgen stimulation with particular behaviors and characteristics within a group. Thus digit ratios offer a valid test of the organizational hypothesis that androgens act early in life to masculinize various human behaviors.
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Affiliation(s)
- S Marc Breedlove
- Neuroscience Program and Department of Psychology, 108 Giltner Hall, Michigan State University, East Lansing, Michigan 48824-1101, USA.
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Galis F, Ten Broek CMA, Van Dongen S, Wijnaendts LCD. Sexual dimorphism in the prenatal digit ratio (2D:4D). ARCHIVES OF SEXUAL BEHAVIOR 2010; 39:57-62. [PMID: 19301112 PMCID: PMC2811245 DOI: 10.1007/s10508-009-9485-7] [Citation(s) in RCA: 164] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/11/2008] [Revised: 01/28/2009] [Accepted: 01/30/2009] [Indexed: 05/06/2023]
Abstract
The second to fourth digit ratio (2D:4D) is smaller in human males than in females and hence this trait is sexually dimorphic. The digit ratio is thought to be established during early prenatal development under the influence of prenatal sex hormones. However, the general assumption of early establishment has hardly been studied. In our study, we analyzed the 2D:4D ratio in 327 deceased human fetuses. We measured digit lengths in 169 male and 158 female fetuses ranging from 14 to 42 weeks old. Our results showed a slight, but significant, sexual dimorphism in the expected direction, i.e., females had, on average, a ratio of 0.924 and males a ratio of 0.916. There was no significant relationship with the presence or absence of minor and major or single and multiple congenital abnormalities. There was a minimal, but significant difference between digit ratios based on digit lengths including and excluding the non-bony fingertip with the values being strongly correlated (r = .98). The prenatal 2D:4D ratio was lower than has thus far been reported for children and adults both for males and females. The extent of the sexual dimorphism in fetuses was similar to that found for children, but lower than for adults. The 2D:4D ratio, thus, seems to increase after birth in both men and women, with the second digit growing faster than the fourth digit (positive allometric growth of digit two) and perhaps more so in women than in men. Therefore, the sexual dimorphism is probably determined by prenatal as well as by postnatal developmental processes.
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Affiliation(s)
- Frietson Galis
- Institute of Biology, Leiden University, PO Box 9516, 2300 RA Leiden, The Netherlands.
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Voracek M, Loibl LM. Scientometric analysis and bibliography of digit ratio (2D:4D) research, 1998-2008. Psychol Rep 2009; 104:922-56. [PMID: 19708418 DOI: 10.2466/pr0.104.3.922-956] [Citation(s) in RCA: 95] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
A scientometric analysis of modern research on the second-to-fourth digit ratio (2D:4D), a widely studied putative marker for prenatal androgen action, is presented. In early 2009, this literature totalled more than 300 publications and, since its initiation in 1998, has grown at a rate slightly faster than linear. Key findings included evidence of publication bias and citation bias, incomplete coverage and outdatedness of existing reviews, and a dearth of meta-analyses in this field. 2D:4D research clusters noticeably in terms of researchers, institutions, countries, and journals involved. Although 2D:4D is an anthropometric trait, most of the research has been conducted at psychology departments, not anthropology departments. However, 2D:4D research has not been predominantly published in core and specialized journals of psychology, but rather in more broadly scoped journals of the behavioral sciences, biomedical social sciences, and neurosciences. Total citation numbers of 2D:4D papers for the most part were not larger than their citation counts within 2D:4D research, indicating that until now, only a few 2D:4D studies have attained broader interest outside this specific field. Comparative citation analyses show that 2D:4D research presently is commensurate in size and importance to evolutionary psychological jealousy research, but has grown faster than the latter field. In contrast, it is much smaller and has spread more slowly than research about the Implicit Association Test Fifteen conjectures about anticipated trends in 2D:4D research are outlined, appendixed by a first-time bibliography of the entirety of the published 2D:4D literature.
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Affiliation(s)
- Martin Voracek
- Department of Basic Psychological Research, School of Psychology, University of Vienna, Liebiggasse 5, Rm 03-46, A-1010 Vienna, Austria.
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Martel MM. Conscientiousness as a mediator of the association between masculinized finger-length ratios and attention-deficit/hyperactivity disorder (ADHD). J Child Psychol Psychiatry 2009; 50:790-8. [PMID: 19298468 PMCID: PMC4311552 DOI: 10.1111/j.1469-7610.2009.02065.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
BACKGROUND One often-overlooked biological risk factor that may help explain sex-biased prevalence rates in psychopathology is sex hormones. Personality traits, which also show sex differences, may mediate relations between biological risk factors like hormones and childhood psychopathology such as ADHD (or, alternatively, be independent risk factors). METHODS Three hundred and twelve children/adolescents (178 boys, 134 girls) between the ages of 8 and 17 completed a comprehensive, multistage, clinical diagnostic procedure; 168 children were diagnosed with ADHD and 144 were classified as non-ADHD comparison controls. Primary caregivers completed the California Q-sort in order to provide a measure of conscientiousness. Finger-length ratios (specifically right 2D:4D) served as a proxy of prenatal testosterone exposure (relative to estrogen). RESULTS Lower levels of conscientiousness statistically mediated the relationship between more masculine right 2D:4D (i.e., increased prenatal testosterone exposure) and increased ADHD inattentive symptoms. CONCLUSION More masculinized finger-length ratios show associations with ADHD symptoms, possibly acting through the trait mechanism of conscientiousness.
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Affiliation(s)
- Michelle M Martel
- Psychology Department, University of New Orleans, 2005 Geology & Psychology Building, 2000 Lakeshore Drive, New Orleans, LA 70148, USA.
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Evardone M, Alexander GM. Anxiety, sex-linked behaviors, and digit ratios (2D:4D). ARCHIVES OF SEXUAL BEHAVIOR 2009; 38:442-455. [PMID: 17943431 PMCID: PMC2768336 DOI: 10.1007/s10508-007-9260-6] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/12/2006] [Revised: 07/24/2007] [Accepted: 07/28/2007] [Indexed: 05/25/2023]
Abstract
The second to fourth (2D:4D) digit ratio, a sexually dimorphic, phenotypic characteristic putatively associated with perinatal androgen action, has been used to evaluate the hypothesized relation between prenatal hormonal factors and a variety of sexually dimorphic behaviors, including sex-linked psychopathology. Smaller digit ratios, suggestive of stronger perinatal androgen action, have been associated with male-linked disorders (e.g., autism), and larger digit ratios, suggestive of weaker perinatal androgen action, have been associated with female-linked disorders (e.g., depression and eating disorders). To evaluate the possible relation between digit ratio and another traditionally female-linked disorder, anxiety, 2D:4D ratios were measured in a non-clinical sample (58 men, 52 women). Participants also completed a battery of anxiety and gender role measures and performed two spatial/cognitive tasks typically showing a male advantage (mental rotation and targeting) and two tasks typically showing a female advantage (location memory and spatial working memory). Men with a more feminine pattern of sex-linked traits and behaviors (including digit ratios) reported greater anxiety. In contrast, greater anxiety in women was associated with both female-typical and male-typical traits and behaviors, but and no significant association between digit ratio and anxiety was found. This pattern of results suggests that the development of anxiety is multiply determined, with contributing factors varying by sex.
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Affiliation(s)
- Milagros Evardone
- Department of Psychology, Texas A & M University, College Station, Texas
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Martel MM, Klump K, Nigg JT, Breedlove SM, Sisk CL. Potential hormonal mechanisms of attention-deficit/hyperactivity disorder and major depressive disorder: a new perspective. Horm Behav 2009; 55:465-79. [PMID: 19265696 PMCID: PMC3616481 DOI: 10.1016/j.yhbeh.2009.02.004] [Citation(s) in RCA: 84] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/12/2008] [Revised: 01/09/2009] [Accepted: 02/10/2009] [Indexed: 11/17/2022]
Abstract
Hormonal influences on the organization of behavior are apparent to neuroendocrinologists but under-examined in relation to childhood and adolescent mental disorders. A central mystery in the field of developmental psychopathology is the preferential male vulnerability to behavior disorders in childhood and female vulnerability to emotional disorders in adolescence. Relative neglect of a hormonal explanation may be due to lack of simple or unifying conceptual paradigms to guide studies. This paper seeks to stimulate research in this area by drawing upon clinical psychology and neuroscience literatures to offer a heuristic paradigm for clinical research. Two syndromes are selected here for illustration: Attention-Deficit/Hyperactivity Disorder (ADHD) and Major Depressive Disorder (MDD), because they have opposite gender risk profiles. Two guiding theories are evaluated. First, prenatal organizational effects of testosterone may modulate striatally-based dopaminergic circuits in such a way as to place boys at greater risk for early developing inattention and disruptive behavioral disorders. Second, activational effects of estradiol at puberty may modulate amygdalar and other circuitry, with particular effects on serotonergic pathways, in such a way as to place girls at greater risk for internalizing and mood disorders. Hypotheses from these theories are evaluated based on the current available literature, and limitations of, and future directions for, this literature are discussed.
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Loehlin JC, Medland SE, Martin NG. Relative finger lengths, sex differences, and psychological traits. ARCHIVES OF SEXUAL BEHAVIOR 2009; 38:298-305. [PMID: 18340520 DOI: 10.1007/s10508-007-9303-z] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/01/2006] [Revised: 04/18/2007] [Accepted: 07/20/2007] [Indexed: 05/26/2023]
Abstract
Various finger length and personality and ability measures were obtained for a sample of Australian adolescent twins (306 boys and 397 girls). A new measure of relative finger length (the length of a given finger relative to the sum of all four fingers) was investigated, and shown to be superior to the traditional 2D:4D for discriminating between the sexes. It also had the advantage of permitting a more analytic approach: for example, the 2nd finger-length contributed much more than the 4th finger length to the sex difference in 2D:4D, and a smooth gradient of sex differences across the hand was evident. Sex differences on right hands were greater than those for left hands. Within-sex correlations were obtained between the various finger-length measures and a personality and an ability scale that showed relatively large sex differences (Eysenck's Psychoticism scale and the spatial subscale from Jackson's Multidimensional Aptitude Battery). The correlations were low, but on the whole consistent with the between-sex differences for the girls. For the boys, this was so for Psychoticism, but spatial ability was, if anything, correlated in the opposite direction.
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Affiliation(s)
- John C Loehlin
- Department of Psychology, University of Texas, 1 University Station A8000, Austin, TX 78712-0187, USA.
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McFadden D, Bracht MS. Sex and race differences in the relative lengths of metacarpals and metatarsals in human skeletons. Early Hum Dev 2009; 85:117-24. [PMID: 18789613 PMCID: PMC2649659 DOI: 10.1016/j.earlhumdev.2008.07.001] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/29/2008] [Revised: 06/20/2008] [Accepted: 07/01/2008] [Indexed: 10/21/2022]
Abstract
BACKGROUND Previous research has revealed that the ratios of the lengths of various pairs of human fingers differ in males and females. METHOD In an attempt to determine whether parallel sex differences also exist in the relative lengths of human metacarpals and metatarsals, the lengths of the metapodials for both hands and both feet were measured in a collection of human skeletons. For each hand and each foot, all of the 10 possible pairwise ratios for length of the five metapodials were calculated. RESULTS For the skeletons of European/Caucasian extraction (Ns=89 males, 50 females), there were substantial sex differences for several of the metacarpal-length ratios, but the pattern was not identical with the pattern previously reported for human fingers. Namely, the largest sex differences were for the three ratios involving metacarpal 5 on the left hand, while the sex difference for the ratio comparing the second and fourth metacarpals (the comparison commonly showing the largest sex difference for fingers) was small and non-significant for both hands in these European-Americans. For the skeletons of African extraction (Ns=65 males, 55 females), no sex differences were found in any of the 20 metacarpal-length ratios. This outcome was unexpected because past research had shown sex differences in finger-length ratios for people of African extraction. For metatarsals, none of the 20 ratios exhibited a substantial sex difference for either group of skeletons. CONCLUSIONS A discrepancy apparently exists between the length ratios based on fingers and those based on metacarpals.
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Affiliation(s)
- Dennis McFadden
- Department of Psychology and Center for Perceptual Systems, University of Texas, Austin, Texas, 78712-0187, USA.
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McFadden D. Masculinization of the mammalian cochlea. Hear Res 2009; 252:37-48. [PMID: 19272340 DOI: 10.1016/j.heares.2009.01.002] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/05/2008] [Revised: 01/08/2009] [Accepted: 01/12/2009] [Indexed: 11/30/2022]
Abstract
Otoacoustic emissions (OAEs) differ between the sexes in humans, rhesus and marmoset monkeys, and sheep. OAEs also are different in a number of special populations of humans. Those basic findings are reviewed and discussed in the context of possible prenatal-androgen effects on the auditory system. A parsimonious explanation for several outcomes is that prenatal exposure to high levels of androgens can weaken the cochlear amplifiers and thereby weaken otoacoustic emissions (OAEs). Prenatal androgen exposure apparently also can alter auditory evoked potentials (AEPs). Some non-hormonal factors possibly capable of producing sex and group differences are discussed, and some speculations are offered about specific cochlear structures that might differ between the two sexes.
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Affiliation(s)
- Dennis McFadden
- Department of Psychology and Center for Perceptual Systems, University of Texas at Austin, Seay Building, 1 University Station, A8000, Austin, TX 78712-0187, USA.
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McFadden D. What Do Sex, Twins, Spotted Hyenas, ADHD, and Sexual Orientation Have in Common? PERSPECTIVES ON PSYCHOLOGICAL SCIENCE 2008; 3:309-23. [DOI: 10.1111/j.1745-6924.2008.00082.x] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The otoacoustic emissions (OAEs) measured in a collection of special populations of humans and certain nonhuman species suggest that OAEs may provide a window into some processes of human prenatal development and sexual differentiation. For reasons that are unclear, OAEs appear to be highly sensitive to events occurring during prenatal development that seem to be related to the degree of exposure to androgens a fetus receives. The (largely circumstantial) evidence for a relationship between androgen exposure and OAE strength comes from a series of studies of twins, children with attention-deficit/hyperactivity disorder, people of differing sexual orientations, and spotted hyenas, among others. Some conclusions are bolstered by parallel studies using auditory evoked potentials (AEPs). OAEs and AEPs are simple, objective, noninvasive measures that appear to have potential as tools of value to researchers working on a wide variety of basic and applied topics beyond audition.
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Affiliation(s)
- Dennis McFadden
- Department of Psychology and Center for Perceptual Systems, University of Texas
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Digit ratio (2D:4D) as a marker for mental disorders: Low (masculinized) 2D:4D in autism-spectrum disorders, high (feminized) 2D:4D in schizophrenic-spectrum disorders. Behav Brain Sci 2008. [DOI: 10.1017/s0140525x08004445] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
AbstractAugmenting and supplementing the arguments of Crespi & Badcock (C&B), I show that digit ratio (2D:4D), a putative marker of prenatal androgen action, indeed appears differentially altered in autism-spectrum disorders (lower/masculinized) versus schizophrenic-spectrum disorders (higher/feminized). Consistent with C&B's framework, some evidence (substantial heritability, assortative mating, sex-specific familial transmission) points to possible sex chromosome and imprinted genes effects on 2D:4D expression.
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Gobrogge KL, Breedlove SM, Klump KL. Genetic and environmental influences on 2D:4D finger length ratios: a study of monozygotic and dizygotic male and female twins. ARCHIVES OF SEXUAL BEHAVIOR 2008; 37:112-8. [PMID: 18074216 DOI: 10.1007/s10508-007-9272-2] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Recent studies have shown significant sex differences in the pattern of 2D:4D finger length ratios in humans and several other mammalian species. In humans, these ratios are suggested to be negatively correlated with prenatal exposure to testosterone, positively correlated with prenatal estrogen, and exhibit sex specific patterns of association with sexually dimorphic clinical phenotypes. However, the relative contributions of genetic and environmental influences on digit ratios in men and women are currently unknown. Therefore, the purpose of the current study was to examine genetic and environmental influences on 2D:4D ratios in twins. Participants included 146 monozygotic (MZ) and 154 dizygotic (DZ) adult male and female twins participating in the Michigan State University Twin Study of Behavioral Adjustment and Development. Overall, biometric model-fitting analyses indicated significant additive genetic and nonshared environmental influences on digit ratios. Findings suggest greater similarity between 2D:4D ratios in MZ relative to DZ twins that can be accounted for by genetic and nonshared environmental factors.
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Affiliation(s)
- Kyle L Gobrogge
- Department of Psychology, Florida State University, Tallahassee, FL, USA
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Stevenson JC, Everson PM, Williams DC, Hipskind G, Grimes M, Mahoney ER. Attention deficit/hyperactivity disorder (ADHD) symptoms and digit ratios in a college sample. Am J Hum Biol 2007; 19:41-50. [PMID: 17160985 DOI: 10.1002/ajhb.20571] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
Abstract
Diagnosticians recognize three subtypes of attention deficit/hyperactivity disorder (ADHD) if there are developmentally inappropriate levels (six or more symptoms) of Hyperactive-Impulsive behavior, or Inattentive behavior, or both (Combined), respectively. ADHD may partly reflect androgen dysfunction, and an arguable proxy for prenatal androgen exposure is the 2D:4D finger ratio set at least as early as week 9 in the fetus; this is lower in men than in women. We examined the relationship between digit ratios and ADHD symptoms representing the three phenotypes: ADHD/Combined as measured by "summarized" (Rasched) scales, i.e., 1) the short version of the Wender Utah Rating Scale (WURS) and a total symptom list derived from the DSM IV, and the subdivided DSM IV into 2) ADHD/Inattentive and 3) ADHD/Hyperactive-Impulsive inventories, in a sample of European-descent college students (135 female, 52 male) not selected for ADHD. All digit ratios were calculated excluding the thumb. There were significant sex differences for the 2D:4D digit ratios of both hands (RH and LH), and between the RH 3D:4D and between the LH 2D:3D ratio. In females, the more masculine the LH 2D:4D ratio, the more the ADHD/Combined symptoms (both WURS and DSM) and the more the ADHD/Inattentive symptoms and ADHD/Hyperactive-Impulsive symptoms. More masculine ratios also correlated between the total WURS and RH 2D:3D, RH 2D:4D, and LH 2D:3D; and between the inattentive DSM symptoms and LH 2D:5D, and between the ADHD/Hyperactive and Impulsive symptoms and RH 3D:4D.
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Affiliation(s)
- J C Stevenson
- Department of Anthropology, Western Washington University, Bellingham, Washington 98225, USA.
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VORACEK MARTIN. DIGIT RATIOS (2D:4D AND OTHER) AND RELATIVE THUMB LENGTH: A TEST OF DEVELOPMENTAL STABILITY. Percept Mot Skills 2007. [DOI: 10.2466/pms.105.5.143-152] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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McFadden D, Pasanen EG, Raper J, Lange HS, Wallen K. Sex differences in otoacoustic emissions measured in rhesus monkeys (Macaca mulatta). Horm Behav 2006; 50:274-84. [PMID: 16678823 DOI: 10.1016/j.yhbeh.2006.03.012] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/13/2005] [Revised: 03/22/2006] [Accepted: 03/23/2006] [Indexed: 11/25/2022]
Abstract
Click-evoked otoacoustic emissions (CEOAEs) and distortion-product OAEs (DPOAEs) were measured in about 60 rhesus monkeys. CEOAE strength was substantially greater in females than in males, just as in humans. DPOAE strength was generally slightly stronger in females, just as in humans. In males, CEOAEs were weaker (more masculine) in the fall breeding season and in winter than in the summer. In females, CEOAEs were slightly stronger (more feminine) in the fall, when sex steroids are elevated in females (and males), than in the summer when rhesus monkeys are reproductively quiescent. Thus, the sex differences in CEOAEs were greater in the fall than in the summer. We presume that the seasonal fluctuations in OAEs reflect activational hormonal effects, while the basic sex differences in OAEs likely reflect organizational effects of prenatal androgen exposure. Some monkeys of both sexes had been treated with additional testosterone or the anti-androgen flutamide during prenatal development. In accord with expectations, prenatal androgen treatment weakened CEOAEs in females, and prenatal flutamide treatment strengthened CEOAEs in males. For DPOAEs, the differences between treated and untreated groups were mostly small and often inconsistent. Taken as a whole, the data from both rhesus monkeys and humans suggest that the linear, reflection-based mechanism of OAE production that underlies CEOAEs is more sensitive to prenatal androgenic processes than is the nonlinear distortion mechanism that underlies DPOAEs.
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Affiliation(s)
- Dennis McFadden
- Department of Psychology and Center for Perceptual Systems, University of Texas, 1 University Station A8000, Austin, TX 78712-0187, USA.
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McFadden D, Loehlin JC, Breedlove SM, Lippa RA, Manning JT, Rahman Q. A reanalysis of five studies on sexual orientation and the relative length of the 2nd and 4th fingers (the 2D:4D ratio). ARCHIVES OF SEXUAL BEHAVIOR 2005; 34:341-56. [PMID: 15971017 DOI: 10.1007/s10508-005-3123-9] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/03/2004] [Revised: 08/16/2004] [Accepted: 08/17/2004] [Indexed: 05/03/2023]
Abstract
Five studies have examined the relationship between sexual orientation and the relative lengths of the 2nd and 4th fingers (the 2D:4D ratio). Although differences have commonly been found between heterosexuals and homosexuals, the direction of the difference has not been consistent across studies. The original data from all five studies were reanalyzed in a search for possible explanations of the discrepancies. Because ethnicity is known to affect the 2D:4D ratio, the reanalysis focused on participants who identified themselves as White or Caucasian, the ethnic group that was most numerous in all of the studies. Age differences did not account for the discrepancies. Differences in variability within different groups were minor. One interesting result to emerge from the reanalysis was that the 2D:4D ratios for the homosexual groups were relatively similar across studies. It was the 2D:4D values for the heterosexual participants that varied most, particularly between the USA and the British studies, and these were responsible for many of the discrepancies in the conclusions across studies. The constancy of the 2D:4D ratio for the White homosexuals did not appear to extend to homosexuals of three other ethnicities, and there were also subpopulation differences related to right or left hands.
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Affiliation(s)
- Dennis McFadden
- Department of Psychology and Center for Perceptual Systems, University of Texas, Austin, Texas 78712-0187, USA.
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