2023 Volume 72 Issue 4 Pages 487-491
Clock genes efficiently regulate circadian rhythms and also the biological environment rhythm and determine an efficient morning and night routine, acting as risk factors for psychosis. In this study, after obtaining informed consent, blood samples were obtained from male (n = 34) and female (n = 107) subjects. We performed NEO-FFI personality and STAI tests to determine whether or not clock gene polymorphisms are associated with reward personality-related traits, as assessed using the five-factor model. We used the unpaired T-test for statistical analysis, and the statistical significance level was defined as p < 0.025. As a result of the statistical analysis, significant differences were found in the allele frequencies of the rs3805151 polymorphism in terms of openness in the NEO-FFI personality test (p = 0.003 in all subjects; p = 0.0004 in female subjects). We conclude that the CLOCK polymorphic may affect openness, as measured by NEO-FFI. Further investigations involving personality questionnaires with more subjects are necessary to confirm the relationship between the clock gene and personality.
時計遺伝子は，概日リズムを調節する遺伝子であり，朝型や夜型といった24時間周期の生体リズムを効率的に調節することが知られているが，精神疾患の危険因子となりうることも確認されている。この研究ではインフォームドコンセントを得た被験者から血液検体を採取した（男性n = 34，女性n = 107）。NEO-FFIパーソナリティおよびSTAIテストを実施し，CLOCK多型が人格の特性に関連しているかどうかを測定した。統計分析には対応の無いT検定を使用し，統計的有意差はp = 0.025と定義した。統計解析の結果，多型rs3805151のNEO-FFI人格検査における開放性に有意な差異が認められた（すべての被験者群：p = 0.003，女性被験者群：p = 0.0004）。CLOCK多型rs3805151はNEO-FFI人格検査によって測定される開放性に影響を与える可能性が示唆された。今後は他の時計遺伝子にも着目し，人格特性と概日と概日時計遺伝子との関連についてより詳細に検討する必要がある。
The circadian rhythm is known as one of the biological rhythms at the molecular level, and includes the rhythm of each internal organ’s metabolism, body temperature, and hormone secretion.1) The clock genes regulate the circadian rhythms and also regulate the biological environment rhythms efficiently and have been said to determine the morning and night routine.2) Recent studies suggested psychosis may have been associated with abnormalities in circadian rhythms.3) Furthermore, it is considered mismatching between the circadian and social rhythms might be a risk factor for psychosis.4) In fact, it has been suggested that changes in the circadian clock gene are observed in the psychiatric disorder schizophrenia.5)
In this study, we focused on the CLOCK gene of the clock ones. CLOCK belongs to the core feedback group, and has been associated with the sleep and one waking cycle. It might be considered that the normal CLOCK allele shows morningness preference, while the altered CLOCK shows eveningness preference. This pattern is said to be the cause of circadian rhythm disturbance and prolongation. Such circadian abnormality cause not only sleep disorders and various physical disorders, but also mental disorders.4),6),7)
Personality traits have been suggested to be associated with various psychiatric disorders. However, a direct relationship between CLOCK and personality traits in Japanese are poorly understood. Therefore, we thought that clarifying a relationship between this gene and neo-ffi personality traits would lead to tailor-made medicine for individual mental disorders. In this study, we investigated the relationship between CLOCK polymorphism and characteristic personality traits. We hypothesized that CLOCK might influence characteristic personality traits.
This study was approved by the ethics committee of Azabu University, Japan (2660). Written informed consent was obtained from the subjects, 141 healthy students (male, n = 34; female, n = 107; mean age, 19.629 ± SD: 2.145 years). Blood samples were obtained from them, and extraction and purification of genomic DNA were performed using the phenol/chloroform method. CLOCK genotyping was performed by the polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP) method according to the method of Dai et al. (2011)6) and Yamaguchi et al. (2015).7) For rs3805151, the PCR primers used were as follows: forward: 5'-AAA AAC CAT CAA GAG CCT GAA A-3' and reverse: 5'-TTG TCC AAT AGA TGG CCA GA-3'. PCR was performed in a 20 μL reaction volume comprising 1 μL genomic DNA, 18.4 μL purified water, 2.5 μL 10 × ExTaq, 2.0 μL 2.5 M dNTP, 0.5 μL each primer, and 0.1 μL ExTaq. The PCR cycling conditions were: 95°C for 5 min, 40 cycles of 95°C for the 30 s, 57°C 40 s and 72°C 45 s, and final extension at 72°C for 10 min. Homozygous alleles of the TT genotype appeared as a 240-bp DNA band on the gel, and homozygous alleles of the CC genotype appeared as 155-bp and 85-bp DNA bands. These PCR products were digested with restriction enzymes and Hpy188I (New England BioLabs, Inc., Beverly, MA) overnight at 37°C. The resultant PCR products were separated by 2% agarose gel electrophoresis and visualized by staining of the gels with ethidium bromide (according to the method of Dai et al. 2011).6)
In the same manner, for rs1801260, the following primers were used: forward 5'-TCC AGC AGT TTC ATG AGA TGC-3' and reverse:5'-GAG GTC ATT TCA TAG CTG AGC-3'. For PCR, the reaction mixture composition and volume were the same as above. The PCR cycling conditions were: 94°C for 3 min, 40 cycles of 94°C for 30 s, 58°C for 30 s and 72°C for 1 min, and final extension at 72°C for 5 min. Homozygous alleles of the TT genotype appeared as a 221-bp DNA band on the gel, and homozygous alleles of the CC genotype appeared as a 125-bp and 96-bp DNA band. These PCR products were digested with Bsp1260I (New England BioLabs, Inc., Beverly, MA) overnight at 37°C. The resultant PCR products were separated by 1.5% agarose gels electrophoresis and visualized by staining the gel with ethidium bromide (according to the method of M. Yamaguchi et al. 2015).7)
In particular, we focused on two kinds of CLOCK polymorphisms, rs3805151, and rs1801260, as to personality trait score statistics.8),9)
In this study, the following psychometric tests were performed. The NEO Five-Factor Inventory (NEO-FFI) and State-Trait Anxiety Inventory (STAI) questionnaires were used to investigate the relationship between characteristic personality traits and CLOCK.10)
The NEO-FFI personality test is a Japanese standardized version of the Revised NEO Personality Inventory (NEO-PI-R), which is world-famous as a five-factor personality test, it is sufficiently reliable and valid.11),12)
The NEO-FFI personality test includes five components—Neuroticism, Extraversion, Openness, Agreeableness, and Conscientiousness, characteristic of personalities are determined by these five personality trends.13)
Moreover, the STAI test evaluates anxiety on two and four-point scales. The STAI measured anxiety two components, anxiety stats (A-state) and anxiety trait (A-trait). The A-state includes fear, discomfort, and arousal of the autonomic nervous system occurring temporarily unrelated to a particular situation. The A-trait may be described as a permanent and enduring disposition to experience stress, worries, and discomfort.10) In this study, we focused on the A-trait as an individual anxiety trait. The Japanese standardized version of the STAI is sufficiently reliable and valid.14)
Statistical analysis was performed by chi-square test to examine the comparison of genotype and allele frequency of CLOCK gene polymorphism. Hardy-Weinberg disequilibrium was assessed using the chi-square test. His NEO-FFI scores were compared between CLOCK polymorphisms by performing statistical analysis using the unpaired T-test. As few subjects were homozygous for the minor allele, subjects were divided into two groups for each polymorphism for statistical analysis. For rs1801260 and rs3805151 T/T + T/C, the p-value was set at 0.05 (two-saided). A p-value < 0.025 was considered significant for five comparisons (neuroticism, extroversion, openness, agreeableness, and conscientiousness).
Table 1 shows the genotype distributions and allele frequency of CLOCK polymorphisms rs3805151 and rs1801260 in the subjects. The genotype distributions of these polymorphisms in the subjects exhibited Hardy-Weinberg equilibrium when examined using the χ2 test. For the CLOCK rs3805151 polymorphism, there were no significant differences in the genotype or allele frequencies in the subjects (total genotypes: χ2 = 0.896, p = 0.343; female genotypes: χ2 = 0.677, p = 0.410). For the CLOCK rs1801260 polymorphism, there were also no significant differences in the genotype (or allele frequencies) in the subjects, total genotypes: χ2 = 1.000, p = 0.752; female genotypes: χ2 = 0.020 p = 0.886).
| SNP | Genotype (%) | p-value | Allele (%) | |||
|---|---|---|---|---|---|---|
| rs3805151 | TT | TC | CC | T | C | |
| All subjects (n = 141) | 27 (19.1%) | 63 (44.7%) | 51 (36.2%) | 0.344 | 117 (41.5%) | 165 (58.5%) |
| Female (n = 107) | 21 (19.6%) | 48 (44.9%) | 38 (35.5%) | 0.410 | 90 (42.1%) | 124 (57.9%) |
| rs1801260 | TT | TC | CC | T | C | |
| All subjects (n = 141) | 106 (75.2%) | 33 (23.4%) | 2 (1.4%) | 0.752 | 245 (86.9%) | 37 (13.1%) |
| Female (n = 107) | 81 (75.7%) | 24 (22.4%) | 2 (1.9%) | 0.886 | 186 (86.9%) | 28 (13.1%) |
We used the Unpaired T-test to examine for any relationship between personality test scores and genotypes. Table 2 shows the significant differences in the allele frequencies of the rs3805151 polymorphism in all subjects in terms of openness in the NEO-FFI personality test (Openness: p = 0.003, all subjects). In the same manner, there was a significant difference in female subjects (p = 0.0004, females). However, Table 3 shows there was no significant difference in rs1801260 polymorphism.
| Genotype rs3805151 | N | E | O | A | C |
|---|---|---|---|---|---|
| All subjects T/T | 29.44 ± 10.34 | 25 ± 7.71 | 31.30 ± 6.18 | 29.04 ± 6.75 | 28.07 ± 8.19 |
| All subjects T/C + C/C | 31.56 ± 8.36 | 24.82 ± 7.52 | 27.40 ± 6.075 | 28.75 ± 6.73 | 25.39 ± 6.24 |
| p-value | 0.261 | 0.914 | 0.003* | 0.84 | 0.06 |
| Female T/T | 29.52 ± 10.38 | 24.24 ± 8.05 | 32.52 ± 4.84 | 28.95 ± 7.45 | 28.14 ± 9.09 |
| Female T/C + C/C | 31.45 ± 8.39 | 25.38 ± 7.69 | 27.51 ± 5.822 | 28.97 ± 6.922 | 25.97 ± 6.14 |
| p-value | 0.37 | 0.546 | 0.0004* | 0.994 | 0.173 |
*p < 0.025
N: Neuroticism, E: Extraversion, O: Openness, A: Agreeableness, C: Conscientiousness
| Genotype rs1801260 | N | E | O | A | C |
|---|---|---|---|---|---|
| All subjects T/T | 31.40 ± 8.87 | 25.29 ± 7.37 | 28.34 ± 6.26 | 29.06 ± 6.76 | 25.81 ± 6.98 |
| All subjects T/C + C/C | 30.43 ± 8.57 | 23.54 ± 7.93 | 27.37 ± 6.17 | 28.029 ± 6.62 | 26.17 ± 5.90 |
| p-value | 0.057 | 0.234 | 0.428 | 0.434 | 0.784 |
| Female T/T | 31.65 ± 8.85 | 25.44 ± 7.70 | 28.68 ± 6.00 | 29.01 ± 7.16 | 26.14 ± 7.18 |
| Female T/C + C/C | 29.27 ± 8.53 | 24.269 ± 7.94 | 27.92 ± 5.92 | 28.80 ± 6.58 | 28.80 ± 6.58 |
| p-value | 0.23 | 0.503 | 0.577 | 0.897 | 0.095 |
N: Neuroticism, E: Extraversion, O: Openness, A: Agreeableness, C: Conscientiousness
Furthermore, Table 4 and Table 5 show there was no significant difference in either polymorphism in the STAI test.
| Genotype rs3805151 | Anxiety Inventory |
|---|---|
| All subjects T/T | 48.04 ± 12.45 |
| All subjects T/C + C/C | 49.98 ± 10.74 |
| p-value | 0.413 |
| Female T/T | 47.43 ± 11.63 |
| Female T/C + C/C | 49.49 ± 10.38 |
| p-value | 0.428 |
| Genotype 1801260 | Anxiety Inventory |
|---|---|
| All subjects T/T | 50.52 ± 11.18 |
| All subjects T/C + C/C | 46.85 ± 10.40 |
| p-value | 0.09 |
| Female T/T | 50.31 ± 10.78 |
| Female T/C + C/C | 45.27 ± 9.25 |
| p-value | 0.035 |
In this study, we investigated the association between CLOCK polymorphism and the result of two personality tests, NEO-FFI and STAI. We compared the NEO-FFI and STAI test scores of TT homo subjects and C allele carrier subjects for both the CLOCK rs3805151 and rs1801260 polymorphisms.
We found an association between openness and CLOCK rs3805151. This significant difference was found in both all subjects and the female subjects.
According to the results, it is considered that CLOCK might regulate the NEO-FFI personality trait of openness. This personality trait was found to show significant differences in both subject groups.
Therefore, it is suggested that CLOCK rs3805151 is likely to affect the openness personality trait assessed by the NEO-FFI personality test. The personality trait openness is a normally distributed personality trait reflecting the tendency to engage in imaginative, creative, and abstract cognitive processes.15) High openness scores have been reported for bipolar disorder.10),16) Therefore, these results suggest rs3805151 may be an indicator of bipolar disorder.
In this study, C allele carriers exhibit lower openness scores than TT homo carriers. Personality traits with low openness scores also include schizophrenia.17) Therefore, the results may be related to schizophrenia.
Moreover, the clock genes have been reported to be related not only to the genetic tendency of personality traits but also to circadian rhythm. The circadian systems affect the morningness-eveningness preference in humans.8)
Therefore, it could be considered that desynchronization between the internal chronotype and the external environment increases the risks of anxiety and some psychiatric disorders,9) because C alleles of the CLOCK rs3805151 polymorphism are factors that strengthen the tendency of an eveningness preference pattern.8) Some reports suggest that rs1801260 T/T subjects show higher morningness scores. While the C/C genotype is associated with delayed sleep timing and greater daytime sleepiness in the Japanese population.5),10) Therefore, we thought the circadian rhythm regulated by rs1801260 was considered to be related to personality traits involved in psychiatric disorders. In this study, CLOCK rs1801260 was no significant difference with openness personality traits. However, the relationship between lower openness scores with mental illnesses such as schizophrenia and sleep distribution be ruled out cannot deny.
In particular, the clock genes may affect personality traits, and they could be considered to be associated with the sleep pattern, internal chronotype, and external environment. Consequently, we have to consider not only the genotype but also these factors.
If genes involved in the development of psychiatric disorders are revealed in future studies, with a tailor-made medical procedure, early prevention and treatment based on features of the genetic background of an individual may be possible.
Several studies of the above polymorphisms and characteristic personality traits have been conducted recently, but consistent results have not yet been obtained. Therefore, thi is considered necessary to conduct a large-scale study considering sample bias and to confirm the reproducibility of the results of this study.
There is no potential conflict of interest to disclose.
This research was supported by a research project grant from Azabu University. Special thanks to Ms. Teruko Honda (Azabu University) for her helpful advice.
