A relevant part of the social and personal burden caused by Bipolar Disorder (BD) is related to depressive phases. Authors investigated the genetic impact of a set of variations located in CRY1, a gene involved in the control of the circadian rhythms, towards depressive episodes in a sample of bipolar patients from the STEP-BD sample. As a secondary analysis, CYR1 variations were analyzed as predictors of sleep disruption.
654 bipolar patients were included in the analysis. Data were available genome-wide. The part of the genome coding for the CRY1 was imputed and pruned according to standards in the field. 7 SNPs were available for the analysis. A correction for multitesting was applied and we had sufficient power (0.80) to detect a small-medium effect size (0.22) between two allelic frequencies each one represented by at least 300 subjects.
Intronic rs10861688 was associated with the number of depressive events corrected for the times patients were assessed during the period of observation. In particular, AA subjects (n=21) had 4.46±3.15 events, AG (n=141) had 3.08±3.17 and GG (n=342) 2.65±2.97 (p=0.0048, beta=-0.22). No other significant associations were reported.
We bring further evidence that genes involved in the regulation of circadian rhythms may be relevant to depressive bipolar phases. Independent confirmation analyses are mandatory.
Bipolar Disorder (BD) is a severe chronic disease with periods of remission and relapses. The hallmark of the disorder is a pathological mood swing between depressed and elated mood. Prevalence worldwide is estimated to be about 1%,
The sample under investigation was retrieved from the public available STEP-BD protocol.
The ratio between the times patients were found to be definitively depressed and the times patients were observed during the phase of the study under analysis was the outcome of choice. This phenotype was designed to include all the observed depressed phases, in order to include as many patients as possible to increase the power of the study. Care was taken to control for a possible clinical bias: more severe patients might have been seen more often compared to less severe ones. In order to do so, the correlations between the phenotype of choice and a set of other phenotypes calculated at standard timepoints (number of depressive phases from 30-90-120 and so forth days from the beginning of the study)-a more classical approach to this kind of studies-were calculated. We had confirmation that the phenotype under analyses significantly correlated with almost all the phenotypes at different timepoints, with the advantage of having 0% of missing values. The only timepoint at which the correlation was not significant was after 30 days from the beginning of the study. Nevertheless, the number of missing information for this timepoint (94%) may be held accountable for the lack of association.
Sleep disruption was measured according to the item of the MADRS scale. In particular, the times that a sleep disruption was recorded was corrected for the times patients were assessed.
The sociodemographic and clinical variables were investigated as possible stratification factors. A story of treatment for alcohol related problems resulted to be significantly associated with the outcome (F=2.54, df=4, p-value=0.038) as was included in the analysis as a covariate. Treatment (combination of treatments) correlated with the number of depressive episodes during the period of observation (combination of antipsychotics and antidepressants throughout the study F=18.28; p=2.07e-05; combination of mood stabilizers and antidepressants during the study F=39.82; p=4.07e-10; combination of mood stabilizers and antipsychotics during the study F=26.72; p=2.8e-07; combination of mood stabilizers, antipsychotics and antidepressants during the study F=28.2; p=1.33e-07) and was included in the analysis as covariate. The administration of antidepressant alone did not correlate with the number of depressive events (F=2.019; p=0.156), consistent with literature and guidelines in the field.
Age at the first depression episode negatively correlated with the secondary outcome (t=-3.2, df=638, p-value=0.001, r=-0.12) and was included in the analysis as a covariate. An history of legal problems was significantly associated with sleep disruption (sleep disruption frequency in subjects with legal problems was 2.35±1.8, and 1.81±1.71 in subjects without a story of legal problems) (F=4.7, df=2, p=0.008). This latter variable was not included in the analysis because it was classified as a psychopathological stratification factor.
We had sufficient power (0.80) to detect a small-medium effect size (0.22) between two allelic frequencies each one represented by at least 300 subjects (R-cran
CRY1 was the candidate gene for the analysis. Variations located in its genomic frame were imputed and pruned, please refer to the following paragraph. Moreover, the entire CYR1 molecular pathway was investigated as a secondary analysis. Candidates were selected according to the Cytoskape (
Imputation was run for the genes that belong to the pathway under analysis in order to decrease the computational effort. The CEU HapMap 1000 genomes served for the analysis. From the original (not pruned) set of 11 SNPs harbored by CRY1 we obtained 7 SNPs that passed the imputation quality control (info>0.9) and pruning (r2>0.2). Pruning was undertaken after imputation.
The p value for a significant result was set at 0.05/7=0.007 (Bonferroni correction). 7 was the number of SNPs available for analysis after imputation and pruning.
Covariated linear regression was the statistical model for the analysis. Plink served for the analysis.
We had evidence for an association between rs10861688 - located in an intronic region in CRY1-and the number of depressive events corrected for the times patients were assessed during the period of observation. In particular, AA subjects (n=21) had 4.46±3.15 events, AG (n=141) had 3.08±3.17 and GG (n=342) 2.65±2.97 (p=0.0048, beta=-0.22). The entire molecular pathway was not found to be significantly enriched after the permutation analysis.
CRY1 did not harbor variations significantly associated with the sleep disruptions, nor the CRY1 pathway was found to be enriched in bipolar patients presenting with sleep disruption. Within the pathway a trend for a significant association was found for rs707472 (p=0.006, beta=0.27) harbored by PER3. Rs10861688 harbored by PER3 displayed a trend of association with sleep disruption (p=0.47, beta=0.07), along with two other SNPs located in that gene (rs6539299 and rs7303842 respectively p=0.07, beta=-0.6 and p=0.08, beta=-0.06).
Many common psychiatric conditions are associated with disrupted sleep, indicative of imbalanced circadian timing in these disorders. Circadian rhythm hypotheses have proposed for the explanation of major depressive disorder (MDD) and bipolar disorder (BD), as many data support the association between circadian rhythm dysfunction and mood disorder (reviewed by
Circadian clock gene variants, including CRY1, have been previously associated with depression. In particular, the genetic variants of CRY1 (rs2287161), as well as of RORA (rs2028122), have been associate with depressive disorder, while those of RORB (rs7022435, rs3750420, rs1157358, rs3903529) and NR1D1 (rs2314339) with bipolar disorder, and those of NPAS2 (rs11541353) and CRY2 (rs10838524) with seasonal affective disorder or winter depression.
In conclusion, the data here reported further support the role of genes controlling circadian rhythm in bipolar depression and sleep disturbance, demonstrating the need to deeply study the genetic variants of all clock genes in the different aspects of these psychiatric diseases, from the identification of new genetic markers to predict the risk of mood disorders to the opportunity of new safe and inexpensive potential approaches to treat these disorders.
Data and biomaterials were collected for the Systematic Treatment Enhancement Program for Bipolar Disorder (STEP-BD), a multi-center, longitudinal (5-8 years) project selected from responses to RFP #NIMH-98-DS-0001, "Treatment for Bipolar Disorder." The project was led by Gary Sachs, M.D., and coordinated by Massachusetts General Hospital in Boston, MA. The NIMH grant number was 2N01MH080001-001. Given the major public health implications of identifying genes responsible for severe neuropsychiatric disorders, the National Institute of Mental Health (NIMH) has funded a Human Genetics Initiative. The goal of this Initiative is to establish a national resource of clinical data and biomaterials that are collected from individuals with Alzheimer disease, schizophrenia, or bipolar I disorder (BP), in order to aid researchers in understanding the genetic bases of these disorders. The NIMH Bipolar Disorder Genetics Initiative is supported by the Office of Human Genetics & Genomic Resources in NIMH's Division of Neuroscience and Basic Behavioral Science (DNBBS). Since 1996, data and biomaterials (cell lines and DNA samples) have been available to qualified investigators who study the genetics of BP, and may be accessed by following a set of instructions. We gratefully thank Samuel Mexcur for his help in editing the final version of the article.
Refer to the attached file. DARS2: aspartyl-tRNA synthetase 2, NPAS2: neuronal PAS domain protein 2, PER2: period circadian clock 2, CRY2: cryptochrome circadian clock 2, ARNTL: aryl hydrocarbon receptor nuclear translocator-like, PER1: period circadian clock 1, CLOCK: clock circadian regulator, PER3: period circadian clock 3, KDM5B: lysine (K)-specific demethylase 5B, CEP70: centrosomal protein 70 kDa, CSNK1E: casein kinase 1, epsilon, TIMELESS: timeless circadian clock, ADO: 2-aminoethanethiol (cysteamine) dioxygenase, HERC5: HECT and RLD domain containing E3 ubiquitin protein ligase 5, SMNDC1: survival motor neuron domain containing 1, FBXL3: F-box and leucine-rich repeat protein 3, ARFGAP3: ADP-ribosylation factor GTPase activating protein 3, CSNK1A1: casein kinase 1, alpha 1, MAP4K5: mitogen-activated protein kinase kinase kinase kinase 5, RBBP4: retinoblastoma binding protein 4.
Sample description