Second-to-fourth digit length ratio is associated with negative and affective symptoms in schizophrenia patients

Androgen regulation of behavioral stress responses and the hypothalamic-pituitary-adrenal axis

Testosterone is a powerful steroid hormone that can impact the brain and behavior in various ways, including regulating behavioral and neuroendocrine (hypothalamic-pituitary-adrenal (HPA) axis) stress responses. Early in life androgens can act to alter development of brain regions associated with stress regulation, which ultimately impacts the display of stress responses later in life. Adult circulating androgens can also influence the expression of distinct genes and proteins that regulate stress responses. These changes in the brain are hypothesized to underlie the potent effects of androgens in regulating behaviors related to stress and stress-induced activation of the HPA axis. Androgens can induce alterations in these functions through direct binding to the androgen receptor (AR) or following conversion to estrogens and subsequent binding to estrogen receptors including estrogen receptor alpha (ERα), beta (ERβ), and G protein-coupled estrogen receptor 1 (GPER1). In this review, we focus on the role of androgens in regulating behavioral and neuroendocrine stress responses at different stages of the lifespan and the sex hormone receptors involved in regulating these effects. We also review the specific brain regions and cell phenotypes upon which androgens are proposed to act to regulate stress responses with an emphasis on hypothalamic and extended amygdala subregions. This knowledge of androgen effects on these neural systems is critical for understanding how sex hormones regulate stress responses.

An Exploratory Analysis on the 2D:4D Digit Ratio and Its Relationship with Social Responsiveness in Adults with Prader-Willi Syndrome

Prader-Willi syndrome (PWS) is a genetic disorder produced by a lack of expression of paternally derived genes in the 15q11-13 region. Research has generally focused on its genetic and behavioral expression, but only a few studies have examined epigenetic influences. Prenatal testosterone or the maternal testosterone-to-estradiol ratio (MaTtEr) has been suggested to play an important role in the development of the 'social brain' during pregnancy. Some studies propose the 2D:4D digit ratio of the hand as an indirect MaTtEr measure. The relationship between social performance and MaTtEr has been studied in other neurodevelopmental conditions such as Autism Spectrum Disorder (ASD), but to our best knowledge, it has never been studied in PWS. Therefore, our study aims to clarify the possible existence of a relationship between social performance-as measured using the Social Responsiveness Scale (SRS)-and MaTtEr levels using the 2D:4D ratio. We found that, as a group, PWS individuals have shorter index and ring fingers than the control group, but no significant difference in the 2D:4D ratios. The 2D:4D ratio showed a correlation only with Restricted Interests and Repetitive Behavior Subscale, where a positive correlation only for male individuals with PWS was found. Considering only PWS with previous GH treatment during childhood/adolescence (PWS-GH), index and ring fingers did not show differences in length with the control group, but the 2D:4D ratio was significantly higher in the right or dominant hand compared to controls.

Digit ratio as an endophenotype in a schizophrenia population

BACKGROUND

Schizophrenia is a debilitating mental health condition affecting the lives of many South Africans. The origins of the heterogeneity in the presentation of the illness remain uncertain.

AIM

This cross-sectional study performed a retrospective data analysis to determine the usefulness of digit ratio as an endophenotype in a South African schizophrenia population.

SETTING

A large genetic study in a South African schizophrenia population recruited patients from services in the Western and Eastern Cape.

METHODS

Complete clinical histories were captured for participants, including sets of images of the face and extremities. Software was utilised to measure the lengths of participants' digits from said images and digit ratios (2D:4D) were calculated. Descriptive analyses were performed on the ratios and statistical differences in digit ratio means were calculated between groups characterised by sex, age of onset and the presence vs absence of positive symptoms. Linear modelling was utilised to assess for correlates between 2D:4D and positive and negative symptom severity using scores obtained from the Positive and Negative Syndrome Scale (PANSS) and Scale for the Assessment of Negative Symptoms (SANS).

RESULTS

2D:4D in male participants did not significantly differ from female participants as in healthy populations. 2D:4D did not significantly correlate with the severity of positive or negative symptoms and 2D:4D means between groups did not significantly relate to age of onset.

CONCLUSION

2D:4D appears to be a possible endophenotype in schizophrenia in this population. 2D:4D, however, may not be as readily identifiable as certain minor physical anomalies and neurological soft signs significantly associated with schizophrenia in this population.

Second-to-Fourth Digit Ratio (2D:4D) in Psychiatric Disorders: A Systematic Review of Case-control Studies

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.

Sexual Dimorphism in Titi Monkeys' Digit (2D:4D) Ratio is Associated with Maternal Urinary Sex Hormones During Pregnancy

The second-to-fourth digit (2D:4D) ratio is a sexually-dimorphic biomarker for prenatal sex hormone exposure. We investigated whether titi monkeys (Plecturocebus cupreus) exhibit sexually-dimorphic 2D:4D ratio, and whether variation in 2D:4D ratio correlates with maternal testosterone and estrogen levels during early pregnancy. Subjects were 61 adult titi monkeys (32 males, 29 females). For 26 subjects, maternal urine samples were collected approximately 15-20 weeks before birth and assayed for testosterone and estrone conjugate (E1 C). Titi monkeys exhibited a human-like pattern of sexual dimorphism in right-hand 2D:4D ratio, with females exhibiting higher 2D:4D ratio than males (β = -0.29, p = 0.023). For left-hand 2D:4D ratio, high levels of maternal E1 C predicted low offspring 2D:4D ratio (β = -0.48, p = 0.009). For right-hand 2D:4D ratio, high levels of testosterone (β = -0.53, p = 0.005) and testosterone-to-E1 C ratio (β = -0.41, p = 0.028) predicted low offspring 2D:4D ratio. For 2D:4D ratio asymmetry (right-hand - left-hand), high levels of testosterone (β = -0.43, p = 0.03) and testosterone-to-E1 C ratio (β = -0.53, p = 0.003) predicted low (right-biased) asymmetry. This is the first report of sexually-dimorphic 2D:4D ratio in New World monkeys, and the results support a growing literature suggesting prenatal sex hormones may modulate offspring 2D:4D ratio.

Masculinized Second-to-Fourth Digit Ratio (2D:4D Ratio) Is Associated With Lower Cortisol Response in Infant Female Rhesus Monkeys (Macaca mulatta)

The second-to-fourth digit ratio (2D:4D ratio) is considered a postnatal proxy measure for the degree of prenatal androgen exposure (PAE), which is the primary factor responsible for masculinizing the brain of a developing fetus. Some studies suggest that the organizational effects of PAE may extend to the hypothalamic-pituitary-adrenal (HPA) axis response to stress. This study investigates the relationship between 2D:4D ratio and HPA axis functioning using a rhesus monkey (Macaca mulatta) model. Subjects were N = 268 (180 females, 88 males) rhesus monkey infants (3–4 months of age). Plasma cortisol concentrations were assayed from two blood samples obtained during a 25-h experimental social separation stressor at 2- and 7-h post-separation. Subjects’ 2D:4D ratio was measured later in life (M_age = 6.70 years). It was hypothesized that infant rhesus monkeys that exhibited a more masculine-like 2D:4D ratio would show lower levels of circulating cortisol after a social separation and relocation stressor. The results showed that there was a sex difference in the left-hand 2D:4D ratio. The results also showed that there was an overall sex difference in cortisol concentrations and that female, but not male, monkeys that exhibited a more masculine-like right- and left-hand 2D:4D ratio exhibited lower mean stress-induced cortisol concentrations early in life. These findings suggest that higher levels of prenatal androgens in females, as measured by 2D:4D ratio, may be related to an attenuated HPA axis stress-response, as measured by plasma cortisol levels. To the extent that these findings generalize to humans, they suggest that the organizational effects of PAE extend to the infant HPA axis, modulating the HPA axis response, particularly in females.

Evaluation of 2D:4D digit ratio in bipolar 1 disorder patients and its relationship with treatment response

BACKGROUND

The role of sex steroids in bipolar disorder (BD) has been demonstrated in adults. We aimed to evaluate the 2D:4D ratio, which indirectly reflects prenatal sex steroids, in BD. Another purpose of this study was to determine the relationship between clinical features, especially lithium response, and digit ratio.

METHODS

The study included 74 patients with bipolar 1 disorder and 74 healthy individuals matched according to age, gender, and educational status. The digit ratio was calculated by dividing the index finger (2D) length by the ring finger (4D) length in both hands. A lithium response scale was used to evaluate the lithium response history.

RESULTS

There was no difference in 2D:4D ratio between the patients and controls in either right or left hands. The digit ratio was not different between groups with and without suicide attempts. The 2D:4D ratio in the patient group was lower in individuals unresponsive to lithium therapy than in partial and good responders for both right and left hands.

DISCUSSION

According to the results of our study, the 2D:4D ratio in the BD group was not different from healthy controls but was lower in patients unresponsive to lithium. In this respect, the 2D:4D ratio can be considered as a biomarker for lithium response in BD. In large-sample studies, the 2D:4D ratio should be investigated for pathophysiology and treatment response of BD.

Classical Steroids in a New Fashion: Focus on Testosterone and Aldosterone

Several endocrine glands produce steroid hormones. Thanks to the work of chemists and biochemists, the main synthetic as well as metabolic pathways of steroid hormones were included in the textbooks more than 50 years ago and the classical endocrine gland functions were identified. Later on, evidence of steroid hormone effects beyond the classical endocrine gland function has been accumulating. Testosterone was shown to participate in the stress response and may influence coping with stressors. We have shown a decrease in testosterone concentrations in saliva in children undergoing a school exam compared to values on a non-exam school day. Testosterone has been associated with different cognitive functions in both adults and children. Circulating testosterone has been linked to negative symptoms of schizophrenia. Aldosterone is acting via mineralocorticoid receptors, which are thought to be fully occupied by glucocorticoids in the brain. Until now, an action of aldosterone in the brain has not been considered at all, because the enzyme 11-beta-hydroxysteroid dehydrogenase type 2, which would enable aldosterone to bind to receptors is absent in most of the brain areas. We have brought evidence that aldosterone can act in the brain and produce anxiogenic and depressogenic effects. To facilitate the translation of animal findings into clinical research, we have developed methodology for measurement of salivary aldosterone and obtained first data on a relationship between salivary aldosterone and trait anxiety. We have shown that salivary aldosterone concentrations reflect treatment outcome in patients with major depressive disorder.

Sex-Specific Associations of Androgen Receptor CAG Trinucleotide Repeat Length and of Raloxifene Treatment with Testosterone Levels and Perceived Stress in Schizophrenia

Lower testosterone levels are associated with greater negative symptoms in men with schizophrenia. Testosterone signals via androgen receptor (AR). A functional variant in the AR gene (CAG trinucleotide repeat polymorphism) is associated with circulating testosterone and mood-related symptoms in healthy people. Raloxifene increases testosterone in healthy males and reduces symptom severity and improves cognition in schizophrenia; however, whether raloxifene increases testosterone in men with schizophrenia is unknown. We assessed the interaction of a functional AR gene variant and adjunctive raloxifene on peripheral testosterone and symptom severity in schizophrenia. Patients with schizophrenia (59 males and 38 females) participated in a randomized, double-blind, placebo-controlled, crossover trial of adjunctive raloxifene (120 mg/day). Healthy adults (46 males and 41 females) were used for baseline comparison. Baseline circulating testosterone was decreased in male patients compared to male controls and positively correlated with CAG repeat length in male controls and female patients. Male patients with short, compared to long, CAG repeat length had higher stress scores. Raloxifene treatment increased testosterone in male patients, but was unrelated to AR CAG repeat length, suggesting that raloxifene's effects may not depend on AR activity. Sex-specific alterations of the relationship between AR CAG repeat length and testosterone suggest that altered AR activity may impact perceived stress in men with schizophrenia.

Sex Differences in Rhesus Monkeys' Digit Ratio (2D:4D Ratio) and Its Association With Maternal Social Dominance Rank

Prenatal androgen exposure (PAE) plays a pivotal role in masculinizing the developing body and brain, and extreme exposure may contribute to autism, anxiety disorder and schizophrenia. One commonly used biomarker for PAE is the pointer-to-ring-finger digit length (2D:4D) ratio. Although this biomarker is widely used in human studies, relatively few studies have investigated 2D:4D ratio in nonhuman primates, particularly rhesus macaques (Macaca mulatta), one of the most commonly used animals in biomedical research. Thus far, data suggest that sexual dimorphism in 2D:4D ratio may be in the opposite direction in some monkey species, when compared to the pattern exhibited by humans and great apes. Using a large sample size, we investigated whether rhesus monkeys' 2D:4D ratio shows the same sex-differentiated pattern present in other Old World monkey species. We also investigated whether individual differences in 2D:4D ratio are associated with the social dominance rank of subjects' mothers during pregnancy, and the social dominance rank the subjects attained as adults. Subjects were 335 rhesus monkeys between 3 years and 24 years of age (M = 6.6). Maternal dominance rank during pregnancy and subjects' adult dominance rank were categorized into tertiles (high, middle and low). Results showed that, across both hands, male rhesus monkeys exhibited higher 2D:4D ratio than females, a pattern consistent with other monkey species and a reversal from the pattern typically observed in humans and apes. This sex difference was modulated by maternal dominance rank, with female offspring of high-ranking and middle-ranking mothers exhibiting masculinized 2D:4D ratio, indicating that maternal dominance rank during pregnancy may influence levels of PAE. There was no association between subjects' 2D:4D ratio and the social dominance rank they attained as adults. These findings show a consistent sex difference in Old World monkeys' 2D:4D ratio that diverges from the pattern observed in apes and humans, and suggest maternal social dominance rank modulates PAE in rhesus monkeys.