Brain-specific epigenetic markers of schizophrenia.

Epigenetics plays a crucial role in schizophrenia susceptibility. In a previous study, we identified over 4500 differentially methylated sites in prefrontal cortex (PFC) samples from schizophrenia patients. We believe this was the first genome-wide methylation study performed on human brain tissue using the Illumina Infinium HumanMethylation450 Bead Chip. To understand the biological significance of these results, we sought to identify a smaller number of differentially methylated regions (DMRs) of more functional relevance compared with individual differentially methylated sites. Since our schizophrenia whole genome methylation study was performed, another study analysing two separate data sets of post-mortem tissue in the PFC from schizophrenia patients has been published. We analysed all three data sets using the bumphunter function found in the Bioconductor package minfi to identify regions that are consistently differentially methylated across distinct cohorts. We identified seven regions that are consistently differentially methylated in schizophrenia, despite considerable heterogeneity in the methylation profiles of patients with schizophrenia. The regions were near CERS3, DPPA5, PRDM9, DDX43, REC8, LY6G5C and a region on chromosome 10. Of particular interest is PRDM9 which encodes a histone methyltransferase that is essential for meiotic recombination and is known to tag genes for epigenetic transcriptional activation. These seven DMRs are likely to be key epigenetic factors in the aetiology of schizophrenia and normal brain neurodevelopment.

Dysbindin (DTNBP1) variants are associated with hallucinations in schizophrenia.

BACKGROUND: Dystrobrevin binding protein 1 (DTNBP1) is a schizophrenia susceptibility gene involved with neurotransmission regulation (especially dopamine and glutamate) and neurodevelopment. The gene is known to be associated with cognitive deficit phenotypes within schizophrenia. In our previous studies, DTNBP1 was found associated not only with schizophrenia but with other psychiatric disorders including psychotic depression, post-traumatic stress disorder, nicotine dependence and opiate dependence. These findings suggest that DNTBP1 may be involved in pathways that lead to multiple psychiatric phenotypes. In this study, we explored the association between DTNBP1 SNPs (single nucleotide polymorphisms) and multiple psychiatric phenotypes included in the Diagnostic Interview of Psychosis (DIP). METHODS: Five DTNBP1 SNPs, rs17470454, rs1997679, rs4236167, rs9370822 and rs9370823, were genotyped in 235 schizophrenia subjects screened for various phenotypes in the domains of depression, mania, hallucinations, delusions, subjective thought disorder, behaviour and affect, and speech disorder. SNP-phenotype association was determined with ANOVA under general, dominant/recessive and over-dominance models. RESULTS: Post hoc tests determined that SNP rs1997679 was associated with visual hallucination; SNP rs4236167 was associated with general auditory hallucination as well as specific features including non-verbal, abusive and third-person form auditory hallucinations; and SNP rs9370822 was associated with visual and olfactory hallucinations. SNPs that survived correction for multiple testing were rs4236167 for third-person and abusive form auditory hallucinations; and rs9370822 for olfactory hallucinations. CONCLUSION: These data suggest that DTNBP1 is likely to play a role in development of auditory related, visual and olfactory hallucinations which is consistent with evidence of DTNBP1 activity in the auditory processing regions, in visual processing and in the regulation of glutamate and dopamine activity.

Genome-wide DNA methylation analysis of human brain tissue from schizophrenia patients.

Recent studies suggest that genetic and environmental factors do not account for all the schizophrenia risk, and epigenetics also has a role in disease susceptibility. DNA methylation is a heritable epigenetic modification that can regulate gene expression. Genome-wide DNA methylation analysis was performed on post-mortem human brain tissue from 24 patients with schizophrenia and 24 unaffected controls. DNA methylation was assessed at over 485,000 CpG sites using the Illumina Infinium HumanMethylation450 Bead Chip. After adjusting for age and post-mortem interval, 4641 probes corresponding to 2929 unique genes were found to be differentially methylated. Of those genes, 1291 were located in a CpG island and 817 were in a promoter region. These include NOS1, AKT1, DTNBP1, DNMT1, PPP3CC and SOX10, which have previously been associated with schizophrenia. More than 100 of these genes overlap with a previous DNA methylation study of peripheral blood from schizophrenia patients in which 27,000 CpG sites were analysed. Unsupervised clustering analysis of the top 3000 most variable probes revealed two distinct groups with significantly more people with schizophrenia in cluster one compared with controls (P=1.74 × 10(-4)). The first cluster composed of 88% of patients with schizophrenia and only 12% controls, whereas the second cluster composed of 27% of patients with schizophrenia and 73% controls. These results strongly suggest that differential DNA methylation is important in schizophrenia etiology and add support for the use of DNA methylation profiles as a future prognostic indicator of schizophrenia.

DRD2/ANKK1 Taq1A (rs 1800497 C>T) genotypes are associated with susceptibility to second generation antipsychotic-induced akathisia.

Although the advent of atypical, second-generation antipsychotics (SGAs) has resulted in reduced likelihood of akathisia, this adverse effect remains a problem. It is known that extrapyramidal adverse effects are associated with increased drug occupancy of the dopamine 2 receptors (DRD2). The A1 allele of the DRD2/ANKK1, rs1800497, is associated with decreased striatal DRD2 density. The aim of this study was to identify whether the A1(T) allele of DRD2/ANKK1 was associated with akathisia (as measured by Barnes Akathisia Rating Scale) in a clinical sample of 234 patients who were treated with antipsychotic drugs. Definite akathisia (a score ≥ 2 in the global clinical assessment of akathisia) was significantly less common in subjects who were prescribed SGAs (16.8%) than those prescribed FGAs (47.6%), p < 0.0001. Overall, 24.1% of A1+ patients (A1A2/A1A1) who were treated with SGAs had akathisia, compared to 10.8% of A1- (thus, A2A2) patients. A1+ patients who were administered SGAs also had higher global clinical assessment of akathisia scores than the A1- subjects (p = 0.01). SGAs maintained their advantage over FGAs regarding akathisia, even in A1+ patients who were treated with SGAs. These results strongly suggested that A1+ variants of the DRD2/ANKK1 Taq1A allele do confer an associated risk for akathisia in patients who were treated with SGAs, and these variants may explain inconsistencies found across prior studies, when comparing FGAs and SGAs.

HapMap tag-SNP analysis confirms a role for COMT in schizophrenia risk and reveals a novel association.

Catechol-O-methyl transferase (COMT) encodes an enzyme involved in the metabolism of dopamine and maps to a commonly deleted region that increases schizophrenia risk. A non-synonymous polymorphism (rs4680) in COMT has been previously found to be associated with schizophrenia and results in altered activity levels of COMT. Using a haplotype block-based gene-tagging approach we conducted an association study of seven COMT single nucleotide polymorphisms (SNPs) in 160 patients with a DSM-IV diagnosis of schizophrenia and 250 controls in an Australian population. Two polymorphisms including rs4680 and rs165774 were found to be significantly associated with schizophrenia. The rs4680 results in a Val/Met substitution but the strongest association was shown by the novel SNP, rs165774, which may still be functional even though it is located in intron five. Individuals with schizophrenia were more than twice as likely to carry the GG genotype compared to the AA genotype for both the rs165774 and rs4680 SNPs. This association was slightly improved when males were analysed separately possibly indicating a degree of sexual dimorphism. Our results confirm that COMT is a good candidate for schizophrenia risk, by replicating the association with rs4680 and identifying a novel SNP association.

Analysis of HapMap tag-SNPs in dysbindin (DTNBP1) reveals evidence of consistent association with schizophrenia.

Dystrobrevin binding protein 1 (DTNBP1), or dysbindin, is thought to be critical in regulating the glutamatergic system. While the dopamine pathway is known to be important in the aetiology of schizophrenia, it seems likely that glutamatergic dysfunction can lead to the development of schizophrenia. DTNBP1 is widely expressed in brain, levels are reduced in brains of schizophrenia patients and a DTNBP1 polymorphism has been associated with reduced brain expression. Despite numerous genetic studies no DTNBP1 polymorphism has been strongly implicated in schizophrenia aetiology. Using a haplotype block-based gene-tagging approach we genotyped 13 SNPs in DTNBP1 to investigate possible associations with DTNBP1 and schizophrenia. Four polymorphisms were found to be significantly associated with schizophrenia. The strongest association was found with an A/C SNP in intron 7 (rs9370822). Homozygotes for the C allele of rs9370822 were more than two and a half times as likely to have schizophrenia compared to controls. The other polymorphisms showed much weaker association and are less likely to be biologically significant. These results suggest that DTNBP1 is a good candidate for schizophrenia risk and rs9370822 is either functionally important or in disequilibrium with a functional SNP, although our observations should be viewed with caution until they are independently replicated.

Advances in molecular genetics and the prevention and treatment of substance misuse: Implications of association studies of the A1 allele of the D2 dopamine receptor gene.

Substance misuse is influenced by multiple genetic and environmental factors. Recent research has identified a number of potential genetic markers of risk and those associated with drug reward substrates show particular promise. The current study reexamines the extant published data of the association between the D2 dopamine receptor (DRD2) gene minor Taq 1A (A1) allele and substance misuse risk. A series of meta-analyses was performed on 64 studies examining DRD2 A1+ allelic status and substance misuse. In addition, personality was examined as a possible endophenotype. Significant association was found between the A1 allele and severe substance dependence in both Caucasian and non-Caucasian groups. The data did not support a significant association between the A1 allele and personality features. While the specific mechanism underlying these associations requires further elucidation, this genetic marker shows promise as a marker of brain reinforcement processes. Possible ways of utilising the A1 allele to inform prevention and treatment initiatives are discussed.

Harmful drinking in military veterans with post-traumatic stress disorder: association with the D2 dopamine receptor A1 allele.

AIMS: The frequency of the Taq I A alleles (A1 and A2) of the D2 dopamine receptor (DRD2) gene was examined in Caucasian post-traumatic stress disorder (PTSD) patients and controls. RESULTS: In 91 PTSD patients, the frequency of the A1 allele was higher (P = 6.12 x 10(-3)) than in the 51 controls. In the 38 PTSD harmful drinkers (>or=60 g alcohol/day), A1 allelic frequency was higher (P = 3.91 x 10(-2)) than in the 53 non-harmful drinkers (<60 g alcohol/day), the former being also higher (P = 3.76 x 10(-4)) than in controls. However, there was no difference between non-harmful drinkers and controls. Based on DRD2 allelic association, the 35 PTSD patients with the A1(+) (A1A1, A1A2) allele consumed more than twice the daily amount of alcohol than the 56 patients with the A1(-) (A2A2) allele (P = 1.94 x 10(-3)). When the hourly rate of alcohol consumed was compared, A1(+) allelic patients consumed twice the rate of the A1(-) allelic patients (P < 10(-7)). CONCLUSION: The DRD2 A1 allele was associated with PTSD. However, this association was found only in the harmful drinkers. PTSD patients with the A1(+) allele consumed more alcohol than patients with the A1(-) allele. The importance of determining alcohol consumption in DRD2 association studies with PTSD is suggested.

D(2) dopamine receptor (DRD2) polymorphism is associated with severity of alcohol dependence.

The A(1) allele of the D(2) dopamine receptor (DRD2) gene has been associated with alcohol dependence. However, the expression of this allele risk on the severity of drinking behavior in patients with alcohol dependence has not been systematically explored. The present study examines the association between DRD2 A(1)(+) (A(1)/A(1) and A(1)/A(2) genotypes) and A(1)- (A(2)/A(2) genotype) allele status and key drinking parameters in alcohol-dependent patients. A sample of Caucasian adults was recruited from an alcohol detoxification unit. A clinical interview and the Alcohol Dependence Scale (ADS) questionnaire provided data on consumption, dependence, chronology of drinking and prior detoxification. A(1)(+) allele compared to A(1)- allele patients consumed higher quantities of alcohol, commenced problem drinking at an earlier age, experienced a shorter latency between first introduction to alcohol to the onset of problem drinking and had higher ADS scores. Moreover, A(1)(+) allele patients had more detoxification attempts than their A(1)- allele counterparts. In sum, alcohol-dependent patients with the DRD2 A(1) allele compared to patients without this allele are characterized by greater severity of their disorder across a range of problem drinking indices. The implications of these findings are discussed.

Sertraline treatment of interferon-alfa-induced depressive disorder.

Interferon alfa therapy for chronic hepatitis C infection is commonly associated with neuropsychiatric symptoms, including depression. These side effects may necessitate reduction or even cessation of interferon alfa, but there is little information regarding the management of this important problem. We report 10 cases of interferon-alfa-induced depressive disorder treated with the selective serotonin reuptake inhibitor sertraline. All patients obtained rapid symptom relief without the need for reduction or cessation of interferon alfa.

The D(2) dopamine receptor A(1) allele and opioid dependence: association with heroin use and response to methadone treatment.

A total of 95 Caucasian opioid-dependent patients were followed over a one-year period in an outpatient methadone treatment program. The frequency of the TaqI A(1) allele of the D(2) dopamine receptor (DRD2) gene was 19.0% in these patients compared with 4.6% in controls free of past and current alcohol and other drug abuse and free of family history of alcohol and other drug abuse (p = 0.009). Twenty-two of these patients dropped out of the methadone program (Group A), 54 had a successful treatment (Group B), and 19 had a poor treatment (Group C) outcome. The frequency of the A(1) allele was highest in Group C (42.1%), followed by Group A (22.7%) and was lowest in Group B (9.3%). The more than fourfold higher frequency of the A(1) allele in the poor treatment outcome group compared with the successful treatment outcome group was significant (p = 0.00002). Moreover, the average use of heroin (grams/day) during the year prior to study entry was more than twice as great in patients with the A(1)(+) allele (A(1)/A(1) or A(1)/A(2) genotype) than those with the A(1)(-) allele (A(2)/A(2) genotype) (A(1)(+) allele = 0.55 +/- 0. 10, A(1)(-) allele = 0.25 +/- 0.05; p = 0.003). The results indicate that DRD2 variants are predictors of heroin use and subsequent methadone treatment outcome and suggest a pharmacogenetic approach to the treatment of opioid dependence.

D2 dopamine receptor and GABA(A) receptor beta3 subunit genes and alcoholism.

As the dopaminergic and GABAergic systems have been implicated in alcohol-related behaviors, variants of the D2 dopamine receptor (DRD2) and GABA(A) receptor beta3 subunit (GABRB3) genes were determined in a population-based association study of Caucasian non-alcoholic and alcoholic subjects. In severe alcoholics, compared to non-alcoholics, a significant increase was found in the prevalence (P = 1.7 x 10(-5)) and frequency (P = 1.6 x 10(-5)) of the DRD2 minor (A1) allele. Moreover, a significant progressive increase was observed in A1 allelic prevalence (P = 3.1 x 10(-6)) and frequency (P = 2.7 x 10(-6)) in the order of non-alcoholics, less severe and severe alcoholics. In severe alcoholics, compared to non-alcoholics, a significant decrease was found in the prevalence (P = 4.5 x 10(-3)) and frequency (P = 2.7 x 10(-2)) of the GABRB3 major (G1) allele. Furthermore, a significant progressive decrease was noted in G1 allelic prevalence (P = 2.4 x 10(-3)) and frequency (P = 1.9 x 10(-2)) in non-alcoholics, less severe and severe alcoholics, respectively. In sum, in the same population of non-alcoholics and alcoholics studied, variants of both the DRD2 and GABRB3 genes independently contribute to the risk for alcoholism, with the DRD2 variants revealing a stronger effect than the GABRB3 variants. However, when the DRD2 and the GABRB3 variants are combined, the risk for alcoholism is more robust than when these variants are considered separately.

Association of the D2 dopamine receptor A1 allele with alcoholism: medical severity of alcoholism and type of controls.

D2 dopamine receptor (DRD2) A1 allele frequency was determined in alcoholics of varying medical severity from three different inpatient settings and in various controls. A1 frequency was .15 in 68 alcoholics in a detoxification unit (group A), .19 in 90 alcoholics in a rehabilitation unit (group B), and .31 in 43 alcoholics in a gastroenterology unit (group C). Group C had a higher A1 frequency than group B (p = .045) or group A (p = .005) alcoholics. In 46 controls (group D), A1 frequency was .18. In subsets of these controls, A1 frequency was .14 in 39 subjects with a negative family history (FH-) of alcoholism (group E), .06 in 34 subjects without previous hazardous alcohol consumption (group F), and .05 in 30 subjects with FH- and without previous hazardous alcohol consumption (group G). A1 frequency was significantly higher in group C alcoholics than group F (p = .0002) or group G (p = .0002) controls; however, no A1 frequency difference was found among group A alcoholics and any of the control groups. The severity of alcoholism and the type of controls used are important determinants of DRD2 A1 allele association with alcoholism.

Bromocriptine in the treatment of alcoholics with the D2 dopamine receptor A1 allele.

Various types of alcoholics have been described and heredity has been shown to be involved in some of these types. An important role of the mesolimbic dopamine system has been suggested in the reinforcing effects of alcohol and recent molecular genetic studies are implicating the gene for the D2 dopamine receptor (DRD2) in alcoholism. In a double-blind study, bromocriptine, a DRD2 agonist, or placebo was administered to alcoholics with either the A1 (A1/A1 and A1/A2 genotypes) or only the A2 (A2/A2 genotype) allele of the DRD2 gene. The greatest improvement in craving and anxiety occurred in the bromocriptine-treated A1 alcoholics and attrition was highest in the placebo-treated A1 alcoholics. The feasibility of a pharmacogenetic approach in treating certain types of alcoholics is suggested.