The Association of the 2nd to 4th Digit Ratio with the Age of Onset and Metabolic Factors in Korean Patients with Schizophrenia

OBJECTIVES: The ratio of second to fourth digit length (2D : 4D) could be a potential epigenetic marker of sexual dimorphism reflecting prenatal testosterone exposure. Testosterone is known to affect the development of the brain through an epigenetic mechanism. The purpose of this study was to investigate the effects of exposure to fetal testosterone on the metabolic syndrome based on 2D : 4D of schizophrenia patients and the relationship with the age of onset of schizophrenia. METHODS: A total of 214 schizophrenia patients participated in this study. The participant's physical and blood tests were performed according to the American National Cholesterol Education Program's Third Amendment of the Metabolic Syndrome Diagnostic Criteria, and the 2D : 4D was measured by the method designed by McFadden. Data were statistically analyzed by t-test, Pearson's correlation analysis and multiple regression model analysis. RESULTS: 2D : 4D was significantly higher in female than male in both hands, and there was a statistically significant negative correlation between 2D : 4D and the age of onset of schizophrenia in male. However, 2D : 4D did not show statistically significant correlation with metabolic factors. CONCLUSIONS: Fetal testosterone suggests the possibility of affecting the age of onset of schizophrenia through the epigenetic mechanism, but there is no clear relationship with metabolic factors.

Change of Second to Fourth Digit Ratio according to Age in Korean Children / 체질인류학회지

The 2nd to 4th digit ratio (2D : 4D) reflects exposure level of sex hormones in fetal period. The aim of this study is to identify a change of digit ratio according to age and a critical age showing gender difference in Korean children. This study was done on 1,182 children (588 males, 594 females). Data were collected by measuring index and ring finger length on both hands by photocopy. The data were analyzed using SPSS win 21.0. This study showed that the 2nd and 4th finger length and digit ratio of both hands increased with age both male and female. There was no differences in 2nd to 4th digit ratio between males and females until they were 3 years old. However, there were significant differences in 2nd to 4th digit ratio between males and females from the age of four. The results suggest that digit ratio in Korean children increases with age and a critical age showing gender difference is from the age of four.

The Sex-Related Differences of Relationships between 2D : 4D Ratio and Electroencephalographic Coherence in Patients with Schizophrenia Compared with Controls

OBJECTIVES: Prenatal testosterone is known to influence both cerebral laterality and 2nd to 4th digit ratio (2D : 4D). Epigenetic changes are thought to play some role in it. We studied sex-related differences between 2D : 4D and cerebral laterality in patients with schizophrenia and controls to examine the effects of prenatal testosterone in the development of schizophrenia. METHODS: Forty one men (18 schizophrenic patients and 23 controls) and 40 women (17 schizophrenic patients and 23 controls) were recruited from one psychiatric hospital in Korea. The 2D : 4D and electroencephalographic (EEG) coherence in 19 channels (66 pairs of interhemispheric coherence and 54 pairs of intrahemispheric coherence) were measured. The sex-related statistical analyses between 2D : 4D and EEG coherence in controls and patients with schizophrenia were performed using multiple regression. RESULTS: In male patients, the relationship between 2D : 4D and right intrahemispheric EEG coherence showed mainly positive correlation in delta and theta frequency bands, while it showed negative correlation in male controls. In female patients, the relationship between 2D : 4D and interhemispheric EEG coherence showed stronger positive correlation in alpha and beta frequency bands, while it showed weaker positive correlation in female controls. CONCLUSIONS: Low prenatal testosterone may play certain roles in altered correlation between 2D : 4D and cerebral laterality in schizophrenia and the development of schizophrenia by epigenetic mechanism.

Difference of Second to Fourth Digit Ratio according to the Methods of Measuring Length / 체질인류학회지

The 2nd to 4th digit ratio (2D : 4D) reflects exposure level of sex hormones in fetal period and there are various methods for finger length measurement. The aim of this study is to identify an accurate and effective method for finger length measurement. This study was done on 272 individuals (115 males, 157 females). Data were collected by measuring index and ring finger length on both hands by calipers, ruler, photocopy, and radiography. The data were analyzed through independent t-test, paired t-test, Pearson correlation analysis using SPSS win 19.0. This study showed that the 2nd and 4th finger measured by radiography were the longest finger both of males and females and revealed the largest length difference between 2nd and 4th finger. There were significant sex differences all of 4 measurement methods in 2D : 4D, especially remarkable sex difference by radiography and photography. The 2D : 4D by indirect measurement was lower than that of direct measurement. Correlation between digit ratio by radiography and by photocopy was 0.590 and correlation between digit ratio by radiography and by calipers was 0.586. The results of this study suggest that indirect measurement by radiography can be alternated by photocopy primarily and by calipers secondarily.

Second to Fourth Digit Ratio as a Sex Determinant in Korean / 체질인류학회지

The 2nd to 4th digit ratio (2D : 4D) as a predictor of the degree of expression of sexually dimorphic and other sex-hormone-mediated traits differs between the sexes, ethnics and race. The aim of this study is to identify characteristics and role of 2nd to 4th digit ratio as a sex determinant in Korean. This study was done on 664 individuals (332 males, 332 females). Data were collected by measuring index and ring finger length on both hands with digital callipers. The data were analyzed through the frequency, descriptive statistics, X2 test, independent t-test, paired t-test, Pearson correlation analysis using SPSS win 19.0. This study showed that the 2nd to 4th digit ratio (2D : 4D) in Korean men (0.96) was significantly lower than that of women (0.97). There was a significant difference in the types of 2nd and 4th finger length according to sex. There was a significant difference between right 2D : 4D and left 2D : 4D both of Korean men and women. Correlation between right and left hand digit ratio was .530 in men and .556 in women. The 2nd to 4th digit ratio accurately determinated sex in 89.1% males and 89.2% females for the left hand, and in 91.8% males and 91.9% females for the right hand. The results of this study suggest that 2nd to 4th digit ratio in Korean differs between males and females, moreover, it will be able to perform a role as a sex determinant.

A Relationship between 2nd to 4th Digit Length Ratio and Aggression Related-Sports Entries Characteristics in Female Athletics of Korean National Teams

OBJECTIVES: The 2nd to 4th digit length ratio(2D : 4D) is a sexually dimorphic trait regardless of ethnicity and shows sex differences. According to previous research, men usually have a relatively shorter 2nd digit than 4th digit. There is tendency that men with lower 2D : 4D are perceived as being more masculine and tend to perform better in some physical sports. Furthermore, 2D : 4D is negatively associated with trait aggression. In this study, we examine gender difference of 2D : 4D and compare 2D : 4D of female Korean national team members to 2D : 4D of control subjects. Besides that, we also compare 2D : 4D of female Korean national team members according to their sports entries. METHODS: The sample of this study is 396 people, 67 female Korean national team member, 216 control women and 113 control men. We measured 2nd to 4th digit length of their right hand. In addition, we collected demographic information of female Korean national team members using a self-report questionnaire. RESULTS: The mean 2D : 4D of female Korean national team members is 0.96(SD=0.04), smaller than control women's 2D : 4D(0.97, SD=0.03) and significantly higher than control men's 2D : 4D(0.95, SD=0.03). We also found differences between control men and women. Non-martial arts related sports athletes have significant difference with control men in 2D : 4D. However, martial arts related sports athletes' 2D : 4D is not significantly different from other groups, including control men. CONCLUSION: These results are consistent with the findings of previous research that there is a significant difference between men and women in their 2D : 4D. Furthermore, 2D : 4D of martial arts related sports athletes have not shown any difference from the 2D : 4D of control men that 2D : 4D of non-martial arts related athletes have shown. This fact is important in consideration of masculine characteristics. For further research, it is necessary to examine 2D : 4D difference according to sport ability and gender differences.

The Differences of 2nd to 4th Digit Length Ratio between Schizophrenia Patients and Normal Controls / 신경정신의학

OBJECTIVES: The length ratio of the second to the fourth finger (2D : 4D) is a known indirect measure of prenatal sex hormone exposure. Sex hormones influence brain development through structural and epigenetic modifications of neurons. We examined the 2D : 4D in schizophrenia patients and normal controls to investigate the relationship between prenatal sex hormone exposure and the genesis of schizophrenia. METHODS: The participants were 187 schizophrenia patients (94 male, 93 female) and 190 normal controls (95 male, 95 female). We determined handedness via the Edinburgh Handedness Inventory and age of onset of schizophrenia via clinical records or directly questioning the patients. We measure digit length using vernier caliper and performed T-tests, ANOVA, and ANCOVA to analyze the data. RESULTS: There were no significant 2D : 4D differences between schizophrenic participants and normal controls. Also, there was no significant correlation between the 2D : 4D and the age of onset of schizophrenia. Among the controls, the 2D : 4D was significantly higher (more "feminized") in females than in males (F=4.937, p=.027). But, there were no significant 2D : 4D sex differences among the schizophrenia patients (F=3.429, p=.066). CONCLUSION: These results imply that sex hormone changes during fetal development might play some role in the development of schizophrenia.