Chronobiology International, Early Online: 1–5, (2015) ! Informa Healthcare USA, Inc. ISSN: 0742-0528 print / 1525-6073 online DOI: 10.3109/07420528.2015.1014096
ORIGINAL ARTICLE
Differences in planning performance, a neurocognitive endophenotype, are associated with a functional variant in PER3 gene
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Yeimy Gonza´lez-Giraldo1, Rodrigo E. Gonza´lez-Reyes1, Shane T. Mueller2, Brian J. Piper3, Ana Adan4,5, and Diego A. Forero1 1
Laboratory of NeuroPsychiatric Genetics, Biomedical Sciences Research Group, School of Medicine, Universidad Antonio Narin˜o, Bogota´, Colombia, 2Department of Cognitive and Learning Sciences, Michigan Technological University, Houghton, MI, USA, 3School of Pharmacy, Husson University, Bangor, ME, USA, 4Department of Psychiatry and Clinical Psychobiology, University of Barcelona, Barcelona, Spain, and 5Institute for Brain, Cognition and Behavior (IR3C), Barcelona, Spain
Performance alterations in executive function have been studied as potential endophenotypes for several neuropsychiatric diseases. Planning is an important component of executive function and has been shown to be affected in diseases such as attention deficit hyperactivity disorder, schizophrenia, obsessive–compulsive disorder and Parkinson’s disease. Several genes related to dopaminergic systems, such as COMT, have been explored as candidates for influencing planning performance. The circadian clock gene PERIOD3 (PER3) has been shown to be associated with several complex behaviors in humans and could be involved in different signaling mechanisms. In this study, we evaluated the possible association between a functional polymorphism in the PER3 gene (PER3-VNTR, rs57875989) and performance in a commonly used test of planning (Tower of London, TOL) in 229 healthy subjects from Bogota´, Colombia. PER3-VNTR genotyping was carried out with conventional PCR and all participants completed the TOL test using the computerized Psychology Experiment Building Language (PEBL) battery. A linear regression model was used for the analysis of association with the SNPStats program. We found that 4/4 genotype carriers showed a better performance and made fewer moves, in comparison to 4/5 and 5/5 genotype carriers (p ¼ 0.003). These results appear to be independent from effects of this polymorphism on self-reported average hours of sleep during work days in our sample. This is the first evidence of an association between PER3-VNTR and planning performance in a sample of healthy subjects and our results are consistent from previous findings for alterations in other cognitive domains. Future studies examining additional genes could lead to the identification of novel molecular underpinnings of planning in healthy subjects and in patients with neuropsychiatric disorders. Keywords: Candidate gene, chronobiology, cognition, neurogenetics, psychiatric genetics
INTRODUCTION
pegs are moved individually from an initial state to match a goal state (Piper et al., 2012). It has been shown that genetic factors account for about 40% of the variance in TOL performance (Kremen et al., 2009). Previous genetic association studies for TOL have been focused on genes of the dopaminergic system, mainly Catechol-O-MethylTransferase (COMT), with conflicting results (Table 1) (Roussos et al., 2008; Taerk et al., 2004). Exploration of additional candidate genes could help to elucidate the molecular correlates of planning performance. The circadian clock gene PERIOD3 (PER3) is located on chromosome 1p36.23 and has been shown to be associated with several complex behaviors in humans, such as the delayed sleep phase syndrome and individual differences in extreme
Performance alterations in executive functions have been studied as potential endophenotypes for several neuropsychiatric diseases (Piper et al., 2012). Planning is an important aspect of executive function and has been shown to be affected in diseases such as attention deficit hyperactivity disorder (ADHD), schizophrenia, obsessive–compulsive disorder and Parkinson’s disease (Sullivan et al., 2009). The Tower of London (TOL) (Shallice, 1982) task is a commonly used test that measures planning and problem solving ability (Sullivan et al., 2009). It mainly involves forming, retaining and implementing a plan to make as few moves as possible. In this task, colored disks or balls on
Submitted November 28, 2014, Returned for revision January 27, 2015, Accepted January 28, 2015
Correspondence: Prof. Dr. Diego Forero, Laboratory of NeuroPsychiatric Genetics, School of Medicine, Universidad Antonio Narin˜o, Bogota´, Colombia. Tel: +57 313 2610427. E-mail: [email protected]
1
6–12 65.3 65.3 64.9 18–35 6–12 28–61 37.1/37.2 6–12 ADHD patients Parkinson’s patients Parkinson’s patients Parkinson’s patients Healthy subjects ADHD patients Healthy subjects Schizophrenia patients and controls ADHD patients COMT/Val158Met COMT/Val158Met BDNF/Val66Met COMT/Val158Met COMT/C/G 4818 SLC6A3/VNTR COMT/Val158Met COMT/Val158Met COMT/Val158Met Taerk, 2004 Foltynie, 2004 Foltynie, 2005 Williams-Gray, 2007 Roussos, 2008 Karama, 2008 Stokes, 2011 Tsuchimine, 2013 Choudhry, 2014
Canada United Kingdom United Kingdom United Kingdom United Kingdom Canada United Kingdom Japan United Kingdom
118 288 291 32 107 223 65 118/149 445
Age (range or mean) Sample size Subjects Country Gene Author, Year
TABLE 1. Previous candidate gene studies of planning performance, using the TOL task.
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No significant differences Val carriers: better performance Met carriers: better performance Val carriers: longer response times C/C carriers: better performance 9/10 carriers: poorer performance No significant differences Val/Val carriers-higher score (controls) No significant differences
Y. Gonza´lez-Giraldo et al.
Association
2
diurnal preference, daytime sleepiness and sleep structure (Archer et al., 2003; Jones et al., 2007; Lazar et al., 2012; Pereira et al., 2005; Viola et al., 2007; von Schantz, 2008) and could be involved in different signaling mechanisms (Dijk & Archer, 2010). A variable-number tandem repeat (VNTR, rs57875989) polymorphism in the exon 18 of PER3 gene has been identified, with two main alleles (4 and 5) which correspond to 4 or 5 repeats of 54 nucleotides (18 amino acids) (Archer et al., 2003; Ebisawa et al., 2001). This functional VNTR has been shown to be associated with differences in performance in several cognitive domains, such as the Psychomotor Vigilance Task, mainly on healthy individuals exposed to sleep deprivation (Lo et al., 2012; Viola et al., 2007). In order to investigate the possible role of PER3 gene on planning in healthy individuals, we evaluated the association of TOL performance and PER3-VNTR polymorphism in a sample of young Colombian participants.
MATERIALS AND METHODS Participants Two-hundred and twenty-nine healthy young subjects were included in this study, 130 female (56.8%) and 99 male (43.2%), with age range 18–34 years (mean 21.2, SD 3.3). Subjects had all four grandparents born in Colombia, were unrelated and recruited from a private ˜ o) in Bogota´, University (Universidad Antonio Narin Colombia. The population living in Bogota´ is composed of a European genetic background with some historical admixture with Amerindians (Ojeda et al., 2013). Participants with self-reported history of neuropsychiatric diseases, such as depression or anxiety disorders, were excluded. All participants provided written informed consent (Beskow et al., 2001). This study was approved by the respective Institutional Ethics Committee and followed the international ethical standards and the recommendations of Chronobiology International (Portaluppi et al., 2010). Phenotypic measurements Participants completed a self-administered questionnaire, which was used to collect socio-demographic variables (age, sex, personal and familial history of neuropsychiatric disorders and the average number of hours of sleep during work days). We applied to all participants a computerized test version of TOL to analyze quantitative and objective measures of planning performance, using the Psychology Experiment Building Language (PEBL) platform version 0.13, which is freely available at http://pebl.sourceforge.net/ and has been described and used previously (Gonzalez-Giraldo et al., 2014; Mueller & Piper, 2014). Testing was carried out in a distraction-free room (Clinical Simulation Laboratory, Universidad Antonio Narin˜o), on a schedule between 9 am and 11 am. The specific TOL test from the PEBL battery that was used comprised 24 trials of increasing difficulty (eight trials per 3, 4 and 5 discs) and it did not Chronobiology International
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PER3 gene and planning performance
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Statistical analysis Identification of outliers in TOL scores was carried out using a z transformation and those values with an absolute value greater than 3 were excluded for each variable analyzed. Kolmogorov–Smirnov test for normality was applied in the PASW Statistics 18 program to TOL data and it was identified as a non-normal distribution (p50.0005). Original data were transformed using a logarithmic operation obtaining a normal distribution (p40.05, Kolmogorov–Smirnov test). SNPStats program was used for calculation of allele and genotype frequencies, Hardy–Weinberg equilibrium analysis (with a 2 test) and for exploration of the association of PER3 genotypes with quantitative measures of planning performance (transformed TOL scores), using a linear regression model, corrected for age and sex (Ojeda et al., 2014). A p value50.05 was considered as statistically significant. FIGURE 1. Illustration of the Tower of London Task, PEBL battery (four discs).
have limits on maximum number of moves or maximum time. Source code was modified to allow its application in the Spanish language, using laptops (Latitude E6530, Dell Inc., Round Rock, TX) running the Windows 8 operating system. Subjects used a generic optical computer mouse (JT-DMS057, Jetion International, Guangzhou, China) to move the discs between the three piles and complete the task (Figure 1). Output of the program gave the scores used to measure the performance of the subjects in the TOL test: number of total moves and average number of moves for trials of 3, 4 and 5 discs; these performance variables have been widely used (Sullivan et al., 2009).
Genotyping Genomic DNA was extracted from peripheral blood using a QIAamp DNA Blood Mini kit (Qiagen, Hilden, Germany) (Morales et al., 2009). Genotyping of PER3 VNTR (rs57875989) was performed by touchdown PCR, following a previously described protocol (Perea et al., 2014). PCRs (annealing temperature of 56 C) were performed in a Labnet MultiGene 96-well thermal cycler (Labnet International Inc., Edison, NJ) and PCR products were separated in a 2% agarose gel at 9.3 V/cm and visualized with ultraviolet light after SYBRÕ -safe (Invitrogen, Carlsbad, CA) staining. It involved two primers (F: AGG CAA CAA TGG CAG TGA G and R: AAT GTC TGG CAT TGG AGT TTG) and 2 ml of genomic DNA (50 ng). Alleles and genotypes were assigned as follows: 310 bp for 4 allele and 364 bp for 5 allele. To assure consistency in the genotyping results, a random subsample (10% of subjects) was reanalyzed. Two different investigators checked all genotypes, in order to confirm and validate the results. !
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RESULTS Relative frequencies for 4 and 5 alleles in our sample were 0.76 and 0.24, respectively. PER3-VNTR showed a genotypic distribution that was in Hardy–Weinberg equilibrium (p ¼ 0.59). Genotype frequencies were: 4/4 ¼ 0.58 (n ¼ 134), 4/5 ¼ 0.35 (n ¼ 80) and 5/5 ¼ 0.06 (n ¼ 15). Median score for the total number of TOL moves was 166, the median of average number of moves in trials for 3, 4 and 5 discs were 4.3, 6.8 and 9.6, respectively. A linear regression model correcting for sex and age showed a significant association between genotype and the number of total moves for TOL task (p ¼ 0.003, for a dominant model, using log transformed data) (Table 2). PER3-VNTR 4/5–5/5 genotype carriers took an average of seven additional moves to complete the 24 trials, compared with 4/4 genotype carriers (165 versus 172 moves), who showed better performance (i.e. fewer moves). In a detailed subanalysis, we found that the significant differences between genotypes, under a dominant model, are mainly related to average number of moves for the trials with four discs (Table 2). The average numbers of moves in the trials of 3 and 5 discs for the PER3 genotypes were: 4.2 and 9.6 moves for 4/4 carriers and 4.3 and 9.8 moves for 4/5–5/5 carriers, respectively. There were no significant differences between PER3-VNTR genotypes in the number of self-reported average hours of sleep during work days: 4/4 carriers slept a mean (±SE) of 5.7 (0.1) h and for 4/5 and 5/5 carriers it was 6.0 (0.1) (p ¼ 0.14).
DISCUSSION Planning is an important endophenotype for several neuropsychiatric disorders, such as ADHD, Parkinson’s disease, schizophrenia and obsessive compulsive disorder (Sullivan et al., 2009). Previous genetic studies for planning performance, using smaller sample sizes, have
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Y. Gonza´lez-Giraldo et al.
TABLE 2. Associations between PER3-VNTR and Tower of London performance, under a dominant model. Genotype
n
Mean (S.E)a
p Value
Average of total moves
4/4 4/5–5/5
134 95
165.4 (1.0) 172.4 (1.0)
0.0033
Average for four discs
4/4 4/5–5/5
134 95
6.5 (1.0) 7.1 (1.0)
0.0007
Variable
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a
Results from SNPStats program, carried out log transformed data, were back-transformed to facilitate a better understanding of results.
been focused on the dopaminergic pathway (mainly COMT gene), in patients with neuropsychiatric disorders and healthy subjects, obtaining conflicting results (Table 1) (Choudhry et al., 2014; Foltynie et al., 2004, 2005; Karama et al., 2008; Roussos et al., 2008; Stokes et al., 2011; Taerk et al., 2004; Tsuchimine et al., 2013; Williams-Gray et al., 2007). It highlights the need for the study of novel candidate genes involved in planning performance. In this study, we found a significant association between a functional polymorphism in the PER3 gene and performance in the TOL task, a commonly used test for assessing planning. Individuals carrying the 4/4 genotype showed better performance in the TOL test, making fewer moves when compared with 4/5 and 5/5 subjects. These results are consistent with findings from previous studies in sleep-deprived subjects (using smaller sample sizes), where carriers of 5/5 genotype had worse performance in measures of working memory (such as n-back) and lower reaction times in Psychomotor Vigilance Tasks (Groeger et al., 2008; Lo et al., 2012; Rupp et al., 2013). A smaller previous study in sleep-deprived subjects did not find association with TOL performance (Goel et al., 2009). In subjects under normal conditions, Lazar et al. found lower scores of nonverbal fluid intelligence and an increase in time in bed during rest days in PER3 5/5 subjects (Lazar et al., 2012). Our current results seem to be independent from the effects on sleep length during work days, as we did not find significant differences in self-reported average hours of sleep during work days between PER3-VNTR genotypes. Recently, no association was found between PER3-VNTR and chronotype in a sample from the Colombian population (Perea et al., 2014). Therefore, we present additional evidence suggesting that PER3VNTR could have an effect on cognitive function in healthy individuals under normal conditions (not exposed to sleep deprivation). The mid-dorsolateral prefrontal cortex has been shown to be involved in planning and interestingly presents changes in activity in males and females and also during life, varying from postadolescence to adulthood (Kaller et al., 2012, 2013). PER3 gene is expressed in the dorsolateral prefrontal cortex (Lim et al., 2013) and could participate in the function of some elements of the complex cognitive
components, such as planning, observed in these pathways. There is initial evidence that PER3 gene could regulate the expression of downstream genes (Wang et al., 2012) and future studies in cell and animal models are needed to understand the specific role of PER3 gene in neurosignaling pathways and mechanisms (Dijk & Archer, 2010; Kyriacou & Hastings, 2010). In the context of the genetic analysis of human cognitive abilities, such as planning, use of a computerized neuropsychological battery (such as PEBL) allows a quantitative and detailed assessment of multiple cognitive abilities for a large number of subjects (Mueller & Piper, 2014). As PEBL is free, it easily enables implementation of studies in developing countries, allowing for genetic analyses of cognitive performance in different ethnic groups (Forero et al., 2014; Gonzalez-Giraldo et al., 2014). Our findings of an association between PER3-VNTR and TOL should be replicated in an independent sample in a future study, which should control for history of shift work and transmeridian travel, as well as sleep timing and intake of caffeinated beverages during several hours prior to the testing. A future analysis of polymorphisms and epigenetic variants in other genes related to circadian rhythms and neural and synaptic plasticity could be helpful to understand in further detail the molecular correlates of planning abilities (Bhatti et al., 2014; Cheng et al., 2007; Strazisar et al., 2014), which could contribute to a more complete knowledge about normal cognitive functions and related neuropsychiatric disorders (Alaerts et al., 2009; Forero et al., 2009).
ACKNOWLEDGEMENTS We thank the collaboration of the staff of the Clinical ˜ o. Simulation Laboratory, Universidad Antonio Narin
DECLARATION OF INTEREST Authors declare that there is no conflict of interest. This study was supported by a research grant from ˜ o (VCTI-UAN, project # Universidad Antonio Narin 20131079). YG-G was supported by a fellowship from VCTI-UAN (Young Scientists Program).
REFERENCES Alaerts M, Ceulemans S, Forero D, et al. (2009). Detailed analysis of the serotonin transporter gene (SLC6A4) shows no association with bipolar disorder in the Northern Swedish population. Am J Med Genet B Neuropsychiatr Genet. 150B:585–92. Archer SN, Robilliard DL, Skene DJ, et al. (2003). A length polymorphism in the circadian clock gene Per3 is linked to delayed sleep phase syndrome and extreme diurnal preference. Sleep. 26:413–5. Beskow LM, Burke W, Merz JF, et al. (2001). Informed consent for population-based research involving genetics. JAMA. 286: 2315–21. Chronobiology International
Chronobiol Int Downloaded from informahealthcare.com by Oregon Health Sciences University on 03/27/15 For personal use only.
PER3 gene and planning performance Bhatti P, Zhang Y, Song X, et al. (2014). Nightshift work and genome-wide DNA methylation. Chronobiol Intl. 32:103–12. Cheng HY, Papp JW, Varlamova O, et al. (2007). microRNA modulation of circadian-clock period and entrainment. Neuron. 54:813–29. Choudhry Z, Sengupta S, Thakur G, et al. (2014). Catecholo-methyltransferase gene and executive function in children with ADHD. J Atten Disord. 18:202–11. Dijk DJ, Archer SN. (2010). PERIOD3, circadian phenotypes, and sleep homeostasis. Sleep Med Rev. 14:151–60. Ebisawa T, Uchiyama M, Kajimura N, et al. (2001). Association of structural polymorphisms in the human period3 gene with delayed sleep phase syndrome. EMBO Rep. 2:342–6. Foltynie T, Goldberg TE, Lewis SG, et al. (2004). Planning ability in Parkinson’s disease is influenced by the COMT val158met polymorphism. Mov Disord. 19:885–91. Foltynie T, Lewis SG, Goldberg TE, et al. (2005). The BDNF Val66Met polymorphism has a gender specific influence on planning ability in Parkinson’s disease. J Neurol. 252:833–8. Forero DA, Arboleda GH, Vasquez R, Arboleda H. (2009). Candidate genes involved in neural plasticity and the risk for attentiondeficit hyperactivity disorder: A meta-analysis of 8 common variants. J Psychiatry Neurosci. 34:361–6. Forero DA, Velez-van-Meerbeke A, Deshpande SN, et al. (2014). Neuropsychiatric genetics in developing countries: Current challenges. World J Psychiatry. 4:69–71. Goel N, Banks S, Mignot E, Dinges DF. (2009). PER3 polymorphism predicts cumulative sleep homeostatic but not neurobehavioral changes to chronic partial sleep deprivation. PLoS One. 4:e5874. Gonzalez-Giraldo Y, Rojas J, Novoa P, et al. (2014). Functional polymorphisms in BDNF and COMT genes are associated with objective differences in arithmetical functioning in a sample of young adults. Neuropsychobiology. 70:152–7. Groeger JA, Viola AU, Lo JC, et al. (2008). Early morning executive functioning during sleep deprivation is compromised by a PERIOD3 polymorphism. Sleep. 31:1159–67. Jones KH, Ellis J, von Schantz M, et al. (2007). Age-related change in the association between a polymorphism in the PER3 gene and preferred timing of sleep and waking activities. J Sleep Res. 16:12–6. Kaller CP, Heinze K, Mader I, et al. (2012). Linking planning performance and gray matter density in mid-dorsolateral prefrontal cortex: Moderating effects of age and sex. Neuroimage. 63:1454–63. Kaller CP, Reisert M, Katzev M, et al. (2013). Predicting planning performance from structural connectivity between left and right mid-dorsolateral prefrontal cortex: Moderating effects of age during postadolescence and midadulthood. Cereb Cortex. [Epub ahead of print]. doi: 10.1093/cercor/bht276. Karama S, Grizenko N, Sonuga-Barke E, et al. (2008). Dopamine transporter 3’UTR VNTR genotype is a marker of performance on executive function tasks in children with ADHD. BMC Psychiatry. 8:45. Kremen WS, Jacobson KC, Panizzon MS, et al. (2009). Factor structure of planning and problem-solving: A behavioral genetic analysis of the Tower of London task in middle-aged twins. Behav Genet. 39:133–44. Kyriacou CP, Hastings MH. (2010). Circadian clocks: Genes, sleep, and cognition. Trends Cogn Sci. 14:259–67. Lazar AS, Slak A, Lo JC, et al. (2012). Sleep, diurnal preference, health, and psychological well-being: A prospective singleallelic-variation study. Chronobiol Int. 29:131–46. Lim AS, Myers AJ, Yu L, et al. (2013). Sex difference in daily rhythms of clock gene expression in the aged human cerebral cortex. J Biol Rhythms. 28:117–29. Lo JC, Groeger JA, Santhi N, et al. (2012). Effects of partial and acute total sleep deprivation on performance across cognitive domains, individuals and circadian phase. PLoS One. 7:e45987.
!
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Morales LC, Arboleda G, Rodriguez Y, et al. (2009). Absence of Lamin A/C gene mutations in four Wiedemann–Rautenstrauch syndrome patients. Am J Med Genet A. 149A:2695–9. Mueller ST, Piper BJ. (2014). The Psychology Experiment Building Language (PEBL) and PEBL test battery. J Neurosci Methods. 222:250–9. Ojeda DA, Perea CS, Nino CL, et al. (2013). A novel association of two non-synonymous polymorphisms in PER2 and PER3 genes with specific diurnal preference subscales. Neurosci Lett. 553: 52–6. Ojeda DA, Perea CS, Suarez A, et al. (2014). Common functional polymorphisms in SLC6A4 and COMT genes are associated with circadian phenotypes in a South American sample. Neurol Sci. 35:41–7. Perea CS, Nino CL, Lopez-Leon S, et al. (2014). Study of a functional polymorphism in the PER3 gene and diurnal preference in a colombian sample. Open Neurol J. 8:7–10. Pereira DS, Tufik S, Louzada FM, et al. (2005). Association of the length polymorphism in the human Per3 gene with the delayed sleep-phase syndrome: Does latitude have an influence upon it? Sleep. 28:29–32. Piper BJ, Li V, Eiwaz MA, et al. (2012). Executive function on the Psychology Experiment Building Language tests. Behav Res Methods. 44:110–23. Portaluppi F, Smolensky MH, Touitou Y. (2010). Ethics and methods for biological rhythm research on animals and human beings. Chronobiol Int. 27:1911–29. Roussos P, Giakoumaki SG, Pavlakis S, Bitsios P. (2008). Planning, decision-making and the COMT rs4818 polymorphism in healthy males. Neuropsychologia. 46:757–63. Rupp TL, Wesensten NJ, Newman R, Balkin TJ. (2013). PER3 and ADORA2A polymorphisms impact neurobehavioral performance during sleep restriction. J Sleep Res. 22:160–5. Shallice T. (1982). Specific impairments of planning. Philos Trans Roy Soc Lond B Biol Sci. 298:199–209. Stokes PR, Rhodes RA, Grasby PM, Mehta MA. (2011). The effects of the COMT Val108/158Met polymorphism on BOLD activation during working memory, planning, and response inhibition: A role for the posterior cingulate cortex? Neuropsychopharmacology. 36:763–71. Strazisar M, Cammaerts S, van der Ven K, et al. (2014). MIR137 variants identified in psychiatric patients affect synaptogenesis and neuronal transmission gene sets. Mol Psychiatry. doi:10.1038/mp.2014.53. Sullivan JR, Riccio CA, Castillo CL. (2009). Concurrent validity of the tower tasks as measures of executive function in adults: A meta-analysis. Appl Neuropsychol. 16:62–75. Taerk E, Grizenko N, Ben Amor L, et al. (2004). Catechol-Omethyltransferase (COMT) Val108/158 Met polymorphism does not modulate executive function in children with ADHD. BMC Med Genet. 5:30. Tsuchimine S, Yasui-Furukori N, Kaneda A, Kaneko S. (2013). Differential effects of the catechol-O-methyltransferase Val158Met genotype on the cognitive function of schizophrenia patients and healthy Japanese individuals. PLoS One. 8:e76763. Viola AU, Archer SN, James LM, et al. (2007). PER3 polymorphism predicts sleep structure and waking performance. Curr Biol. 17: 613–8. von Schantz M. (2008). Phenotypic effects of genetic variability in human clock genes on circadian and sleep parameters. J Genet. 87:513–9. Wang X, Mozhui K, Li Z, et al. (2012). A promoter polymorphism in the Per3 gene is associated with alcohol and stress response. Transl Psychiatry. 2:e73. Williams-Gray CH, Hampshire A, Robbins TW, et al. (2007). Catechol O-methyltransferase Val158Met genotype influences frontoparietal activity during planning in patients with Parkinson’s disease. J Neurosci. 27:4832–8.
ORIGINAL ARTICLE
Differences in planning performance, a neurocognitive endophenotype, are associated with a functional variant in PER3 gene
Chronobiol Int Downloaded from informahealthcare.com by Oregon Health Sciences University on 03/27/15 For personal use only.
Yeimy Gonza´lez-Giraldo1, Rodrigo E. Gonza´lez-Reyes1, Shane T. Mueller2, Brian J. Piper3, Ana Adan4,5, and Diego A. Forero1 1
Laboratory of NeuroPsychiatric Genetics, Biomedical Sciences Research Group, School of Medicine, Universidad Antonio Narin˜o, Bogota´, Colombia, 2Department of Cognitive and Learning Sciences, Michigan Technological University, Houghton, MI, USA, 3School of Pharmacy, Husson University, Bangor, ME, USA, 4Department of Psychiatry and Clinical Psychobiology, University of Barcelona, Barcelona, Spain, and 5Institute for Brain, Cognition and Behavior (IR3C), Barcelona, Spain
Performance alterations in executive function have been studied as potential endophenotypes for several neuropsychiatric diseases. Planning is an important component of executive function and has been shown to be affected in diseases such as attention deficit hyperactivity disorder, schizophrenia, obsessive–compulsive disorder and Parkinson’s disease. Several genes related to dopaminergic systems, such as COMT, have been explored as candidates for influencing planning performance. The circadian clock gene PERIOD3 (PER3) has been shown to be associated with several complex behaviors in humans and could be involved in different signaling mechanisms. In this study, we evaluated the possible association between a functional polymorphism in the PER3 gene (PER3-VNTR, rs57875989) and performance in a commonly used test of planning (Tower of London, TOL) in 229 healthy subjects from Bogota´, Colombia. PER3-VNTR genotyping was carried out with conventional PCR and all participants completed the TOL test using the computerized Psychology Experiment Building Language (PEBL) battery. A linear regression model was used for the analysis of association with the SNPStats program. We found that 4/4 genotype carriers showed a better performance and made fewer moves, in comparison to 4/5 and 5/5 genotype carriers (p ¼ 0.003). These results appear to be independent from effects of this polymorphism on self-reported average hours of sleep during work days in our sample. This is the first evidence of an association between PER3-VNTR and planning performance in a sample of healthy subjects and our results are consistent from previous findings for alterations in other cognitive domains. Future studies examining additional genes could lead to the identification of novel molecular underpinnings of planning in healthy subjects and in patients with neuropsychiatric disorders. Keywords: Candidate gene, chronobiology, cognition, neurogenetics, psychiatric genetics
INTRODUCTION
pegs are moved individually from an initial state to match a goal state (Piper et al., 2012). It has been shown that genetic factors account for about 40% of the variance in TOL performance (Kremen et al., 2009). Previous genetic association studies for TOL have been focused on genes of the dopaminergic system, mainly Catechol-O-MethylTransferase (COMT), with conflicting results (Table 1) (Roussos et al., 2008; Taerk et al., 2004). Exploration of additional candidate genes could help to elucidate the molecular correlates of planning performance. The circadian clock gene PERIOD3 (PER3) is located on chromosome 1p36.23 and has been shown to be associated with several complex behaviors in humans, such as the delayed sleep phase syndrome and individual differences in extreme
Performance alterations in executive functions have been studied as potential endophenotypes for several neuropsychiatric diseases (Piper et al., 2012). Planning is an important aspect of executive function and has been shown to be affected in diseases such as attention deficit hyperactivity disorder (ADHD), schizophrenia, obsessive–compulsive disorder and Parkinson’s disease (Sullivan et al., 2009). The Tower of London (TOL) (Shallice, 1982) task is a commonly used test that measures planning and problem solving ability (Sullivan et al., 2009). It mainly involves forming, retaining and implementing a plan to make as few moves as possible. In this task, colored disks or balls on
Submitted November 28, 2014, Returned for revision January 27, 2015, Accepted January 28, 2015
Correspondence: Prof. Dr. Diego Forero, Laboratory of NeuroPsychiatric Genetics, School of Medicine, Universidad Antonio Narin˜o, Bogota´, Colombia. Tel: +57 313 2610427. E-mail: [email protected]
1
6–12 65.3 65.3 64.9 18–35 6–12 28–61 37.1/37.2 6–12 ADHD patients Parkinson’s patients Parkinson’s patients Parkinson’s patients Healthy subjects ADHD patients Healthy subjects Schizophrenia patients and controls ADHD patients COMT/Val158Met COMT/Val158Met BDNF/Val66Met COMT/Val158Met COMT/C/G 4818 SLC6A3/VNTR COMT/Val158Met COMT/Val158Met COMT/Val158Met Taerk, 2004 Foltynie, 2004 Foltynie, 2005 Williams-Gray, 2007 Roussos, 2008 Karama, 2008 Stokes, 2011 Tsuchimine, 2013 Choudhry, 2014
Canada United Kingdom United Kingdom United Kingdom United Kingdom Canada United Kingdom Japan United Kingdom
118 288 291 32 107 223 65 118/149 445
Age (range or mean) Sample size Subjects Country Gene Author, Year
TABLE 1. Previous candidate gene studies of planning performance, using the TOL task.
Chronobiol Int Downloaded from informahealthcare.com by Oregon Health Sciences University on 03/27/15 For personal use only.
No significant differences Val carriers: better performance Met carriers: better performance Val carriers: longer response times C/C carriers: better performance 9/10 carriers: poorer performance No significant differences Val/Val carriers-higher score (controls) No significant differences
Y. Gonza´lez-Giraldo et al.
Association
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diurnal preference, daytime sleepiness and sleep structure (Archer et al., 2003; Jones et al., 2007; Lazar et al., 2012; Pereira et al., 2005; Viola et al., 2007; von Schantz, 2008) and could be involved in different signaling mechanisms (Dijk & Archer, 2010). A variable-number tandem repeat (VNTR, rs57875989) polymorphism in the exon 18 of PER3 gene has been identified, with two main alleles (4 and 5) which correspond to 4 or 5 repeats of 54 nucleotides (18 amino acids) (Archer et al., 2003; Ebisawa et al., 2001). This functional VNTR has been shown to be associated with differences in performance in several cognitive domains, such as the Psychomotor Vigilance Task, mainly on healthy individuals exposed to sleep deprivation (Lo et al., 2012; Viola et al., 2007). In order to investigate the possible role of PER3 gene on planning in healthy individuals, we evaluated the association of TOL performance and PER3-VNTR polymorphism in a sample of young Colombian participants.
MATERIALS AND METHODS Participants Two-hundred and twenty-nine healthy young subjects were included in this study, 130 female (56.8%) and 99 male (43.2%), with age range 18–34 years (mean 21.2, SD 3.3). Subjects had all four grandparents born in Colombia, were unrelated and recruited from a private ˜ o) in Bogota´, University (Universidad Antonio Narin Colombia. The population living in Bogota´ is composed of a European genetic background with some historical admixture with Amerindians (Ojeda et al., 2013). Participants with self-reported history of neuropsychiatric diseases, such as depression or anxiety disorders, were excluded. All participants provided written informed consent (Beskow et al., 2001). This study was approved by the respective Institutional Ethics Committee and followed the international ethical standards and the recommendations of Chronobiology International (Portaluppi et al., 2010). Phenotypic measurements Participants completed a self-administered questionnaire, which was used to collect socio-demographic variables (age, sex, personal and familial history of neuropsychiatric disorders and the average number of hours of sleep during work days). We applied to all participants a computerized test version of TOL to analyze quantitative and objective measures of planning performance, using the Psychology Experiment Building Language (PEBL) platform version 0.13, which is freely available at http://pebl.sourceforge.net/ and has been described and used previously (Gonzalez-Giraldo et al., 2014; Mueller & Piper, 2014). Testing was carried out in a distraction-free room (Clinical Simulation Laboratory, Universidad Antonio Narin˜o), on a schedule between 9 am and 11 am. The specific TOL test from the PEBL battery that was used comprised 24 trials of increasing difficulty (eight trials per 3, 4 and 5 discs) and it did not Chronobiology International
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PER3 gene and planning performance
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Statistical analysis Identification of outliers in TOL scores was carried out using a z transformation and those values with an absolute value greater than 3 were excluded for each variable analyzed. Kolmogorov–Smirnov test for normality was applied in the PASW Statistics 18 program to TOL data and it was identified as a non-normal distribution (p50.0005). Original data were transformed using a logarithmic operation obtaining a normal distribution (p40.05, Kolmogorov–Smirnov test). SNPStats program was used for calculation of allele and genotype frequencies, Hardy–Weinberg equilibrium analysis (with a 2 test) and for exploration of the association of PER3 genotypes with quantitative measures of planning performance (transformed TOL scores), using a linear regression model, corrected for age and sex (Ojeda et al., 2014). A p value50.05 was considered as statistically significant. FIGURE 1. Illustration of the Tower of London Task, PEBL battery (four discs).
have limits on maximum number of moves or maximum time. Source code was modified to allow its application in the Spanish language, using laptops (Latitude E6530, Dell Inc., Round Rock, TX) running the Windows 8 operating system. Subjects used a generic optical computer mouse (JT-DMS057, Jetion International, Guangzhou, China) to move the discs between the three piles and complete the task (Figure 1). Output of the program gave the scores used to measure the performance of the subjects in the TOL test: number of total moves and average number of moves for trials of 3, 4 and 5 discs; these performance variables have been widely used (Sullivan et al., 2009).
Genotyping Genomic DNA was extracted from peripheral blood using a QIAamp DNA Blood Mini kit (Qiagen, Hilden, Germany) (Morales et al., 2009). Genotyping of PER3 VNTR (rs57875989) was performed by touchdown PCR, following a previously described protocol (Perea et al., 2014). PCRs (annealing temperature of 56 C) were performed in a Labnet MultiGene 96-well thermal cycler (Labnet International Inc., Edison, NJ) and PCR products were separated in a 2% agarose gel at 9.3 V/cm and visualized with ultraviolet light after SYBRÕ -safe (Invitrogen, Carlsbad, CA) staining. It involved two primers (F: AGG CAA CAA TGG CAG TGA G and R: AAT GTC TGG CAT TGG AGT TTG) and 2 ml of genomic DNA (50 ng). Alleles and genotypes were assigned as follows: 310 bp for 4 allele and 364 bp for 5 allele. To assure consistency in the genotyping results, a random subsample (10% of subjects) was reanalyzed. Two different investigators checked all genotypes, in order to confirm and validate the results. !
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RESULTS Relative frequencies for 4 and 5 alleles in our sample were 0.76 and 0.24, respectively. PER3-VNTR showed a genotypic distribution that was in Hardy–Weinberg equilibrium (p ¼ 0.59). Genotype frequencies were: 4/4 ¼ 0.58 (n ¼ 134), 4/5 ¼ 0.35 (n ¼ 80) and 5/5 ¼ 0.06 (n ¼ 15). Median score for the total number of TOL moves was 166, the median of average number of moves in trials for 3, 4 and 5 discs were 4.3, 6.8 and 9.6, respectively. A linear regression model correcting for sex and age showed a significant association between genotype and the number of total moves for TOL task (p ¼ 0.003, for a dominant model, using log transformed data) (Table 2). PER3-VNTR 4/5–5/5 genotype carriers took an average of seven additional moves to complete the 24 trials, compared with 4/4 genotype carriers (165 versus 172 moves), who showed better performance (i.e. fewer moves). In a detailed subanalysis, we found that the significant differences between genotypes, under a dominant model, are mainly related to average number of moves for the trials with four discs (Table 2). The average numbers of moves in the trials of 3 and 5 discs for the PER3 genotypes were: 4.2 and 9.6 moves for 4/4 carriers and 4.3 and 9.8 moves for 4/5–5/5 carriers, respectively. There were no significant differences between PER3-VNTR genotypes in the number of self-reported average hours of sleep during work days: 4/4 carriers slept a mean (±SE) of 5.7 (0.1) h and for 4/5 and 5/5 carriers it was 6.0 (0.1) (p ¼ 0.14).
DISCUSSION Planning is an important endophenotype for several neuropsychiatric disorders, such as ADHD, Parkinson’s disease, schizophrenia and obsessive compulsive disorder (Sullivan et al., 2009). Previous genetic studies for planning performance, using smaller sample sizes, have
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Y. Gonza´lez-Giraldo et al.
TABLE 2. Associations between PER3-VNTR and Tower of London performance, under a dominant model. Genotype
n
Mean (S.E)a
p Value
Average of total moves
4/4 4/5–5/5
134 95
165.4 (1.0) 172.4 (1.0)
0.0033
Average for four discs
4/4 4/5–5/5
134 95
6.5 (1.0) 7.1 (1.0)
0.0007
Variable
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a
Results from SNPStats program, carried out log transformed data, were back-transformed to facilitate a better understanding of results.
been focused on the dopaminergic pathway (mainly COMT gene), in patients with neuropsychiatric disorders and healthy subjects, obtaining conflicting results (Table 1) (Choudhry et al., 2014; Foltynie et al., 2004, 2005; Karama et al., 2008; Roussos et al., 2008; Stokes et al., 2011; Taerk et al., 2004; Tsuchimine et al., 2013; Williams-Gray et al., 2007). It highlights the need for the study of novel candidate genes involved in planning performance. In this study, we found a significant association between a functional polymorphism in the PER3 gene and performance in the TOL task, a commonly used test for assessing planning. Individuals carrying the 4/4 genotype showed better performance in the TOL test, making fewer moves when compared with 4/5 and 5/5 subjects. These results are consistent with findings from previous studies in sleep-deprived subjects (using smaller sample sizes), where carriers of 5/5 genotype had worse performance in measures of working memory (such as n-back) and lower reaction times in Psychomotor Vigilance Tasks (Groeger et al., 2008; Lo et al., 2012; Rupp et al., 2013). A smaller previous study in sleep-deprived subjects did not find association with TOL performance (Goel et al., 2009). In subjects under normal conditions, Lazar et al. found lower scores of nonverbal fluid intelligence and an increase in time in bed during rest days in PER3 5/5 subjects (Lazar et al., 2012). Our current results seem to be independent from the effects on sleep length during work days, as we did not find significant differences in self-reported average hours of sleep during work days between PER3-VNTR genotypes. Recently, no association was found between PER3-VNTR and chronotype in a sample from the Colombian population (Perea et al., 2014). Therefore, we present additional evidence suggesting that PER3VNTR could have an effect on cognitive function in healthy individuals under normal conditions (not exposed to sleep deprivation). The mid-dorsolateral prefrontal cortex has been shown to be involved in planning and interestingly presents changes in activity in males and females and also during life, varying from postadolescence to adulthood (Kaller et al., 2012, 2013). PER3 gene is expressed in the dorsolateral prefrontal cortex (Lim et al., 2013) and could participate in the function of some elements of the complex cognitive
components, such as planning, observed in these pathways. There is initial evidence that PER3 gene could regulate the expression of downstream genes (Wang et al., 2012) and future studies in cell and animal models are needed to understand the specific role of PER3 gene in neurosignaling pathways and mechanisms (Dijk & Archer, 2010; Kyriacou & Hastings, 2010). In the context of the genetic analysis of human cognitive abilities, such as planning, use of a computerized neuropsychological battery (such as PEBL) allows a quantitative and detailed assessment of multiple cognitive abilities for a large number of subjects (Mueller & Piper, 2014). As PEBL is free, it easily enables implementation of studies in developing countries, allowing for genetic analyses of cognitive performance in different ethnic groups (Forero et al., 2014; Gonzalez-Giraldo et al., 2014). Our findings of an association between PER3-VNTR and TOL should be replicated in an independent sample in a future study, which should control for history of shift work and transmeridian travel, as well as sleep timing and intake of caffeinated beverages during several hours prior to the testing. A future analysis of polymorphisms and epigenetic variants in other genes related to circadian rhythms and neural and synaptic plasticity could be helpful to understand in further detail the molecular correlates of planning abilities (Bhatti et al., 2014; Cheng et al., 2007; Strazisar et al., 2014), which could contribute to a more complete knowledge about normal cognitive functions and related neuropsychiatric disorders (Alaerts et al., 2009; Forero et al., 2009).
ACKNOWLEDGEMENTS We thank the collaboration of the staff of the Clinical ˜ o. Simulation Laboratory, Universidad Antonio Narin
DECLARATION OF INTEREST Authors declare that there is no conflict of interest. This study was supported by a research grant from ˜ o (VCTI-UAN, project # Universidad Antonio Narin 20131079). YG-G was supported by a fellowship from VCTI-UAN (Young Scientists Program).
REFERENCES Alaerts M, Ceulemans S, Forero D, et al. (2009). Detailed analysis of the serotonin transporter gene (SLC6A4) shows no association with bipolar disorder in the Northern Swedish population. Am J Med Genet B Neuropsychiatr Genet. 150B:585–92. Archer SN, Robilliard DL, Skene DJ, et al. (2003). A length polymorphism in the circadian clock gene Per3 is linked to delayed sleep phase syndrome and extreme diurnal preference. Sleep. 26:413–5. Beskow LM, Burke W, Merz JF, et al. (2001). Informed consent for population-based research involving genetics. JAMA. 286: 2315–21. Chronobiology International
Chronobiol Int Downloaded from informahealthcare.com by Oregon Health Sciences University on 03/27/15 For personal use only.
PER3 gene and planning performance Bhatti P, Zhang Y, Song X, et al. (2014). Nightshift work and genome-wide DNA methylation. Chronobiol Intl. 32:103–12. Cheng HY, Papp JW, Varlamova O, et al. (2007). microRNA modulation of circadian-clock period and entrainment. Neuron. 54:813–29. Choudhry Z, Sengupta S, Thakur G, et al. (2014). Catecholo-methyltransferase gene and executive function in children with ADHD. J Atten Disord. 18:202–11. Dijk DJ, Archer SN. (2010). PERIOD3, circadian phenotypes, and sleep homeostasis. Sleep Med Rev. 14:151–60. Ebisawa T, Uchiyama M, Kajimura N, et al. (2001). Association of structural polymorphisms in the human period3 gene with delayed sleep phase syndrome. EMBO Rep. 2:342–6. Foltynie T, Goldberg TE, Lewis SG, et al. (2004). Planning ability in Parkinson’s disease is influenced by the COMT val158met polymorphism. Mov Disord. 19:885–91. Foltynie T, Lewis SG, Goldberg TE, et al. (2005). The BDNF Val66Met polymorphism has a gender specific influence on planning ability in Parkinson’s disease. J Neurol. 252:833–8. Forero DA, Arboleda GH, Vasquez R, Arboleda H. (2009). Candidate genes involved in neural plasticity and the risk for attentiondeficit hyperactivity disorder: A meta-analysis of 8 common variants. J Psychiatry Neurosci. 34:361–6. Forero DA, Velez-van-Meerbeke A, Deshpande SN, et al. (2014). Neuropsychiatric genetics in developing countries: Current challenges. World J Psychiatry. 4:69–71. Goel N, Banks S, Mignot E, Dinges DF. (2009). PER3 polymorphism predicts cumulative sleep homeostatic but not neurobehavioral changes to chronic partial sleep deprivation. PLoS One. 4:e5874. Gonzalez-Giraldo Y, Rojas J, Novoa P, et al. (2014). Functional polymorphisms in BDNF and COMT genes are associated with objective differences in arithmetical functioning in a sample of young adults. Neuropsychobiology. 70:152–7. Groeger JA, Viola AU, Lo JC, et al. (2008). Early morning executive functioning during sleep deprivation is compromised by a PERIOD3 polymorphism. Sleep. 31:1159–67. Jones KH, Ellis J, von Schantz M, et al. (2007). Age-related change in the association between a polymorphism in the PER3 gene and preferred timing of sleep and waking activities. J Sleep Res. 16:12–6. Kaller CP, Heinze K, Mader I, et al. (2012). Linking planning performance and gray matter density in mid-dorsolateral prefrontal cortex: Moderating effects of age and sex. Neuroimage. 63:1454–63. Kaller CP, Reisert M, Katzev M, et al. (2013). Predicting planning performance from structural connectivity between left and right mid-dorsolateral prefrontal cortex: Moderating effects of age during postadolescence and midadulthood. Cereb Cortex. [Epub ahead of print]. doi: 10.1093/cercor/bht276. Karama S, Grizenko N, Sonuga-Barke E, et al. (2008). Dopamine transporter 3’UTR VNTR genotype is a marker of performance on executive function tasks in children with ADHD. BMC Psychiatry. 8:45. Kremen WS, Jacobson KC, Panizzon MS, et al. (2009). Factor structure of planning and problem-solving: A behavioral genetic analysis of the Tower of London task in middle-aged twins. Behav Genet. 39:133–44. Kyriacou CP, Hastings MH. (2010). Circadian clocks: Genes, sleep, and cognition. Trends Cogn Sci. 14:259–67. Lazar AS, Slak A, Lo JC, et al. (2012). Sleep, diurnal preference, health, and psychological well-being: A prospective singleallelic-variation study. Chronobiol Int. 29:131–46. Lim AS, Myers AJ, Yu L, et al. (2013). Sex difference in daily rhythms of clock gene expression in the aged human cerebral cortex. J Biol Rhythms. 28:117–29. Lo JC, Groeger JA, Santhi N, et al. (2012). Effects of partial and acute total sleep deprivation on performance across cognitive domains, individuals and circadian phase. PLoS One. 7:e45987.
!
Informa Healthcare USA, Inc.
5
Morales LC, Arboleda G, Rodriguez Y, et al. (2009). Absence of Lamin A/C gene mutations in four Wiedemann–Rautenstrauch syndrome patients. Am J Med Genet A. 149A:2695–9. Mueller ST, Piper BJ. (2014). The Psychology Experiment Building Language (PEBL) and PEBL test battery. J Neurosci Methods. 222:250–9. Ojeda DA, Perea CS, Nino CL, et al. (2013). A novel association of two non-synonymous polymorphisms in PER2 and PER3 genes with specific diurnal preference subscales. Neurosci Lett. 553: 52–6. Ojeda DA, Perea CS, Suarez A, et al. (2014). Common functional polymorphisms in SLC6A4 and COMT genes are associated with circadian phenotypes in a South American sample. Neurol Sci. 35:41–7. Perea CS, Nino CL, Lopez-Leon S, et al. (2014). Study of a functional polymorphism in the PER3 gene and diurnal preference in a colombian sample. Open Neurol J. 8:7–10. Pereira DS, Tufik S, Louzada FM, et al. (2005). Association of the length polymorphism in the human Per3 gene with the delayed sleep-phase syndrome: Does latitude have an influence upon it? Sleep. 28:29–32. Piper BJ, Li V, Eiwaz MA, et al. (2012). Executive function on the Psychology Experiment Building Language tests. Behav Res Methods. 44:110–23. Portaluppi F, Smolensky MH, Touitou Y. (2010). Ethics and methods for biological rhythm research on animals and human beings. Chronobiol Int. 27:1911–29. Roussos P, Giakoumaki SG, Pavlakis S, Bitsios P. (2008). Planning, decision-making and the COMT rs4818 polymorphism in healthy males. Neuropsychologia. 46:757–63. Rupp TL, Wesensten NJ, Newman R, Balkin TJ. (2013). PER3 and ADORA2A polymorphisms impact neurobehavioral performance during sleep restriction. J Sleep Res. 22:160–5. Shallice T. (1982). Specific impairments of planning. Philos Trans Roy Soc Lond B Biol Sci. 298:199–209. Stokes PR, Rhodes RA, Grasby PM, Mehta MA. (2011). The effects of the COMT Val108/158Met polymorphism on BOLD activation during working memory, planning, and response inhibition: A role for the posterior cingulate cortex? Neuropsychopharmacology. 36:763–71. Strazisar M, Cammaerts S, van der Ven K, et al. (2014). MIR137 variants identified in psychiatric patients affect synaptogenesis and neuronal transmission gene sets. Mol Psychiatry. doi:10.1038/mp.2014.53. Sullivan JR, Riccio CA, Castillo CL. (2009). Concurrent validity of the tower tasks as measures of executive function in adults: A meta-analysis. Appl Neuropsychol. 16:62–75. Taerk E, Grizenko N, Ben Amor L, et al. (2004). Catechol-Omethyltransferase (COMT) Val108/158 Met polymorphism does not modulate executive function in children with ADHD. BMC Med Genet. 5:30. Tsuchimine S, Yasui-Furukori N, Kaneda A, Kaneko S. (2013). Differential effects of the catechol-O-methyltransferase Val158Met genotype on the cognitive function of schizophrenia patients and healthy Japanese individuals. PLoS One. 8:e76763. Viola AU, Archer SN, James LM, et al. (2007). PER3 polymorphism predicts sleep structure and waking performance. Curr Biol. 17: 613–8. von Schantz M. (2008). Phenotypic effects of genetic variability in human clock genes on circadian and sleep parameters. J Genet. 87:513–9. Wang X, Mozhui K, Li Z, et al. (2012). A promoter polymorphism in the Per3 gene is associated with alcohol and stress response. Transl Psychiatry. 2:e73. Williams-Gray CH, Hampshire A, Robbins TW, et al. (2007). Catechol O-methyltransferase Val158Met genotype influences frontoparietal activity during planning in patients with Parkinson’s disease. J Neurosci. 27:4832–8.
