Blood Gene Expression Correlated with Tic Severity in Medicated and Unmedicated Patients with Tourette Syndrome
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RESEARCH ARTICLE For reprint orders, please contact: [email protected] Blood gene expression correlated with tic severity in medicated and unmedicated patients with Tourette Syndrome Background: Tourette Syndrome (TS) has been linked to both genetic and environmental factors. Gene- expression studies provide valuable insight into the causes of TS; however, many studies of gene expression in TS do not account for the effects of medication. Materials & methods: To investigate the effects of medication on gene expression in TS patients, RNA was isolated from the peripheral blood of 20 medicated TS subjects (MED) and 23 unmedicated TS subjects (UNMED), and quantified using whole-genome Affymetrix microarrays. Results: D2 dopamine receptor expression correlated positively with tic severity in MED but not UNMED. GABAA receptor e subunit expression negatively correlated with tic severity in UNMED but not MED. Phenylethanolamine N-methyltransferase expression positively correlated with tic severity in UNMED but not MED. Conclusion: Modulation of tics by TS medication is associated with changes in dopamine, norepinephrine and GABA pathways. †1 KEYWORDS: GABRE n gene expression n microarray n NPAS4 n phenylethanolamine Isaac H Liao , N-methyltransferase n PNMT n Tourette Syndrome Blythe A Corbett1, Donald L Gilbert2, Silvia A Bunge3 Tourette Syndrome (TS) is a developmen- into this complex disorder. Ideally, tic severity & Frank R Sharp1 tal neuropsychiatric disorder characterized should be examined in relation to gene expres- 1University of California, Davis, MIND by the presence of patterned movements or sion in brain tissue, but this is not feasible Institute & Department of Neurology, sounds performed involuntarily or in response using the current technology. The advantage 2805 50th St, Sacramento, CA 9581, USA to urges. Clinic-based TS cohorts show of studying blood gene expression is the ability 2Cincinnati Children’s Hospital Medical extremely high rates of obsessive compulsive to characterize the relationship between genes, Center, Department of Pediatric behaviors and attention deficit hyperactivity environmental factors and disease symptoms Neurology Cincinnati, OH, USA 3University of California, Berkeley, disorder (ADHD) symptoms. Currently, there in a noninvasive manner. As such, blood gene Department of Psychology & Helen is no biological marker for this disorder and its expression could provide accessible biomarkers Wills Neuroscience Institute, CA, USA †Author for correspondence: pathophysiology is poorly understood. Despite for TS subgroups, prognosis, pathophysiology Tel.: +1 916 703 0384 high apparent heritability, sometimes in an and treatment efficacy. [email protected] autosomal dominant fashion with increased Our previous study comparing gene expres- penetrance of tics in males and obsessive com- sion of TS subjects to controls found several pulsive behaviors in females, no dominant gene interesting differences [5]. Notably, a subgroup effect has been identified. The current standard of TS subjects overexpressed natural killer cell for diagnosis is based on the observed presence genes. However, one limitation of this patient of tics, codified in Diagnostic and Statistical sample was medication exposure; patients Manual, Fourth Edition, Text Revision (DSM taking medication were grouped with patients IV-TR) [1] as: that were medication-free. Patients with severe tics and comorbidities are often treated Multiple motor and one or more vocal tics pharmacologically using antipsychotics and Tics that occur daily or intermittently but a2-adrenergic agonists, which act upon dopa- must be present for at least 1 year minergic and adrenergic signaling pathways. We hypothesized that these treatments might Onset before 18 years of age influence gene expression and that the degree to The severity and frequency of tics wax and which this occurrs might be associated with tic wane, tend to peak in adolescence and often severity. Therefore, in this study, we evaluated improve by the end of adolescence or early the gene expression of medicated (MED) and adulthood (for reviews, see [2–4]). unmedicated (UNMED) TS subjects in rela- Our research group has used gene-expression tion to medication status and symptom sever- profiling, through the quantification of RNA ity, specifically focusing on the genes involved levels, in peripheral blood to glean insights in catecholamine signaling and metabolism. 10.2217/PGS.10.160 © 2010 Future Medicine Ltd Pharmacogenomics (2010) 11(12), 1733–1741 ISSN 1462-2416 1733 RESEARCH ARTICLE Liao, Corbett, Gilbert, Bunge & Sharp Materials & methods using the Agilent 2100 Bioanalyzer (Agilent n Subject recruitment & assessment Technologies Inc., Foster City, CA, USA) and Medicated subjects were recruited from the quantified by fiberoptic spectrophotometry Tourette Syndrome Clinic at Cincinnati using the Nanodrop ND-1000 (Nanodrop Inc., Children’s Hospital Medical Center (Ohio, Wilmington, DE, USA). Samples were excluded USA). UNMED subjects were recruited via if purified RNA did not have both an A260:A280 the Tourette Syndrome Association, clinical absorbance ratio greater than 2.0 and a 28s:18s referrals, local advertisements, physician refer- rRNA ratio equal to or exceeding 1.8. rals and through the University of California at Davis (CA, USA). UNMED subjects were n Gene expression measurement excluded if their estimated IQ was less than Biotin-labeled cDNA was synthesized from 75, if they had taken medication to treat tics, 50 ng of RNA from each sample using the or if they had serious neurological, psychiatric Ovation Whole Blood Solution (NuGEN or medical conditions other than TS, comor- Technologies, Inc., San Carlos, CA, USA) bid ADHD or comorbid obsessive compulsive according to the manufacturer’s protocol. cDNA disorder (OCD). Most UNMED subjects was hybridized with probes on Affymetrix also participated in a functional neuroimag- Human Genome U133 Plus 2.0 microarrays ing study of tic severity and cognitive control (Affymetrix Inc., CA, USA). Microarrays were conducted by Bunge et al. [6]. UNMED sub- washed and stained on a Fluidics Station 450 jects were medication naive as per parental (Affymetrix) and were scanned on a GeneChip® reports, except for two subjects that had previ- Scanner 3000 (Affymetrix). ously taken atomoxetine (Strattera™; Eli Lilly, IN, USA) to treat ADHD symptoms. One of n Data analysis these subjects ended medication approximately Scanned microarray images in the form of 1 month before participation in the study; the Affymetrix CEL files were imported into Partek other stopped taking medication 40 h before Genomics Suite 6.4 (Partek Inc., St Louis, participation. Behavioral measures and princi- MO, USA) using Partek default settings (GC pal component analysis of gene-expression data content adjustment, robust multichip average indicate that these two subjects are not outliers. background correction, log base 2 normaliza- Informed consent was obtained from tion). An analysis of variance using the model each participant, parent or legal guardian. ‘expression = YGTSS’ was performed with age, Recruitment, interview and sample collection gender and scan date (i.e., microarray batch) as proceeded according to established institu- covariates of no interest. tional review board protocols. TS diagnosis was Within Partek, the batch remover algorithm based on Diagnostic and Statistical Manual was used to remove the effects of age, gender of Mental Disorders criteria [1]. Tic severity and batch, and the resulting expression data was assessed via direct child and parent inter- were plotted against tic severity for each gene. view using the Yale Global Tic Severity Scale However, because MED and UNMED micro- (YGTSS) [7]. arrays were processed separately, it is not pos- sible to completely remove the batch effect. n Sample collection Thus, MED and UNMED data cannot be A total of 15 ml of whole blood was collected compared directly. Accordingly, Pearson cor- from each subject via antecubital fossa venipunc- relation coefficients were chosen as a within- ture into six PAXgene Vacutainer tubes (Qiagen, group metric and calculated separately for Hilden, Germany). These tubes contain a solu- MED and UNMED. For each gene, the cor- tion that immediately lyses all of the cells in relation between gene expression and tic sever- whole blood and stabilizes the RNA without ity was measured, and the associated p-value measurable degradation. The RNA represents of each correlation was calculated (with a null genes expressed in all white blood cells, imma- hypothesis of no correlation, or r: 0). ture red blood cells and immature platelets. To test whether gene expression values Blood samples were frozen at -70°C for storage. and YGTSS were normally distributed, a one-sample Kolmogorov–Smirnov test was n RNA isolation from whole blood performed within Partek on each probeset Total RNA was isolated using the PAXgene and on the YGTSS. The null hypothesis was Blood RNA Kit (Qiagen) according to the manu- that the observed values were from a normal facturer’s protocol. RNA quality was assessed distribution. Of the UNMED data, 47 of 1734 Pharmacogenomics (2010) 11(12) future science group Blood gene expression correlated with tic severity RESEARCH ARTICLE 54,683 probesets were not normally distrib- MED uted (p < 0.05), and of the MED data, 23 of 6.61 54,679 probesets were not normally distributed (p < 0.05). Given the null hypothesis, the prob- 6.554 ability of obtaining the observed YGTSS