Dopa decarboxylase genotypes may influence age at onset of schizophrenia

Synaptotagmin-11 deficiency mediates schizophrenia-like behaviors in mice via dopamine over-transmission

Schizophrenia is a severe neuropsychiatric disease, but the initiation mechanisms are unclear. Although antipsychotics are effective against positive symptoms, therapeutic interventions for negative symptoms are limited due to the lack of pathophysiological mechanisms. Here we identify synaptotagmin-11 (Syt11) as a potential genetic risk factor and dopamine over-transmission as a mechanism in the development of schizophrenia. Syt11 expression is reduced in individuals with schizophrenia but restored following the treatment with antipsychotics. Syt11 deficiency in dopamine neurons in early adolescence, but not in adults, leads to persistent social deficits and other schizophrenia-like behaviors by mediating dopamine over-transmission in mice. Accordingly, dopamine neuron over-excitation before late adolescence induces persistent schizophrenia-associated behavioral deficits, along with the structural and functional alternations in the mPFC. Notably, local intervention of D2R with clinical drugs presynaptically or postsynaptically exhibits both acute and long-lasting therapeutic effects on social deficits in schizophrenia mice models. These findings not only define Syt11 as a risk factor and DA over-transmission as a potential risk factor initiating schizophrenia, but also propose two D2R-targeting strategies for the comprehensive and long-term recovery of schizophrenia-associated social withdrawal.

Dopaminergic Epistases in Schizophrenia

Background: The dopaminergic theory, the oldest and most comprehensively analyzed neurotransmitter theory of schizophrenia, remains a focal point of research. Methods: This systematic review examines the association between combinations of 14 dopaminergic genes and the risk of schizophrenia. The selected genes include dopamine receptors (DRD1-5), metabolizing enzymes (COMT, MAOA, MAOB, DBH), synthesizing enzymes (TH, DDC), and dopamine transporters (DAT, VMAT1, and VMAT2). Results: Recurring functional patterns show combinations with either hyperdopaminergic effects in limbic and striatal regions or high striatal and low prefrontal dopamine levels. The protective statuses of certain alleles or genotypes are often maintained in epistatic effects; however, exceptions exist. This complexity could explain the inconsistent results in previous genetic studies. Investigating individual alleles may be insufficient due to the heterozygous advantage observed in some studies. Conclusions: Schizophrenia may not be a monolithic disease, but rather a sum of different phenotypes which respond uniquely to different treatment and prevention approaches.

[Association of polymorphic variants of DDC (AADC), AANAT and ASMT genes encoding enzymes for melatonin synthesis with the higher risk of neuropsychiatric disorders]

Melatonin is the most well-known regulator of the circadian rhythms of all living organisms and the main substrate synthesized at night. There are 4 stages in the synthesis of melatonin. This review focuses on the 2nd, 3rd, and 4th stages. The review is aimed at analyzing publications on molecular genetic association studies on the role of single nucleotide polymorphisms (SNPs) of the DDC (AADC), AANAT and ASMT genes encoding melatonin synthesis enzymes in the pathogenesis of socially significant neuropsychiatric disorders in humans. The authors analyzed the available full-text articles from several databases, as well as materials from electronic resources. Search depth was 15 years. The analysis of these studies over the past decade show the association of some SNPs of the studied genes with the risk of neuropsychiatric disorders such as delayed sleep phase disorder, attention deficit hyperactivity disorder, autism spectrum disorder, migraine, Parkinson's disease, depression, anxiety, bipolar-affective disorder, schizophrenia.

Genetic variability of serotonin pathway associated with schizophrenia onset, progression, and treatment

Schizophrenia (SZ) onset and treatment outcome have important genetic components, however individual genes do not have strong effects on SZ phenotype. Therefore, it is important to use the pathway-based approach and study metabolic and signaling pathways, such as dopaminergic and serotonergic. Serotonin pathway has an important role in brain signaling, nevertheless, its role in SZ is not as thoroughly examined as that of dopamine pathway. In this study, we reviewed serotonin pathway genes and genetic variations associated with SZ, including variations at DNA, RNA, and epigenetic level. We obtained 30 serotonin pathway genes from Kyoto encyclopedia of genes and genomes and used these genes for the literature review. We extracted 20 protein coding serotonin pathway genes with genetic variations associated with SZ onset, development, and treatment from 31 research papers. Genes associated with SZ are present on all levels of serotonin pathway: serotonin synthesis, transport, receptor binding, intracellular signaling, and reuptake; however, regulatory genes are poorly researched. We summarized common challenges of genetic association studies and presented some solutions. The analysis of reported serotonin pathway-SZ associations revealed lack of information about certain serotonin pathway genes potentially associated with SZ. Furthermore, it is becoming clear that interactions among serotonin pathway genes and their regulators may bring further knowledge about their involvement in SZ.

A Study for Therapeutic Treatment against Parkinson's Disease via Chou's 5-steps Rule

The enzyme L-DOPA decarboxylase (DDC), also called aromatic-L-amino-acid decarboxylase, catalyzes the biosynthesis of dopamine, serotonin, and trace amines. Its deficiency or perturbations in expression result in severe motor dysfunction or a range of neurodegenerative and psychiatric disorders. A DDC substrate, L-DOPA, combined with an inhibitor of the enzyme is still the most effective treatment for symptoms of Parkinson's disease. In this review, we provide an update regarding the structures, functions, and inhibitors of DDC, particularly with regards to the treatment of Parkinson's disease. This information will provide insight into the pharmacological treatment of Parkinson's disease.

Trace Amines and Their Receptors

Trace amines are endogenous compounds classically regarded as comprising β-phenylethyalmine, p-tyramine, tryptamine, p-octopamine, and some of their metabolites. They are also abundant in common foodstuffs and can be produced and degraded by the constitutive microbiota. The ability to use trace amines has arisen at least twice during evolution, with distinct receptor families present in invertebrates and vertebrates. The term "trace amine" was coined to reflect the low tissue levels in mammals; however, invertebrates have relatively high levels where they function like mammalian adrenergic systems, involved in "fight-or-flight" responses. Vertebrates express a family of receptors termed trace amine-associated receptors (TAARs). Humans possess six functional isoforms (TAAR1, TAAR2, TAAR5, TAAR6, TAAR8, and TAAR9), whereas some fish species express over 100. With the exception of TAAR1, TAARs are expressed in olfactory epithelium neurons, where they detect diverse ethological signals including predators, spoiled food, migratory cues, and pheromones. Outside the olfactory system, TAAR1 is the most thoroughly studied and has both central and peripheral roles. In the brain, TAAR1 acts as a rheostat of dopaminergic, glutamatergic, and serotonergic neurotransmission and has been identified as a novel therapeutic target for schizophrenia, depression, and addiction. In the periphery, TAAR1 regulates nutrient-induced hormone secretion, suggesting its potential as a novel therapeutic target for diabetes and obesity. TAAR1 may also regulate immune responses by regulating leukocyte differentiation and activation. This article provides a comprehensive review of the current state of knowledge of the evolution, physiologic functions, pharmacology, molecular mechanisms, and therapeutic potential of trace amines and their receptors in vertebrates and invertebrates.

Down-Regulation of Hippocampal Genes Regulating Dopaminergic, GABAergic, and Glutamatergic Function Following Combined Neonatal Phencyclidine and Post-Weaning Social Isolation of Rats as a Neurodevelopmental Model for Schizophrenia

BACKGROUND

Dysfunction of dopaminergic, GABAergic, and glutamatergic function underlies many core symptoms of schizophrenia. Combined neonatal injection of the N-methyl-D-aspartate (NMDA) receptor antagonist, phencyclidine (PCP), and post-weaning social isolation of rats produces a behavioral syndrome with translational relevance to several core symptoms of schizophrenia. This study uses DNA microarray to characterize alterations in hippocampal neurotransmitter-related gene expression and examines the ability of the sodium channel blocker, lamotrigine, to reverse behavioral changes in this model.

METHODS

Fifty-four male Lister-hooded rat pups either received phencyclidine (PCP, 10mg/kg, s.c.) on post-natal days (PND) 7, 9, and 11 before being weaned on PND 23 into separate cages (isolation; PCP-SI; n = 31) or received vehicle injection and group-housing (2-4 per cage; V-GH; n = 23) from weaning. The effect of lamotrigine on locomotor activity, novel object recognition, and prepulse inhibition of acoustic startle was examined (PND 60-75) and drug-free hippocampal gene expression on PND 70.

RESULTS

Acute lamotrigine (10-15mg/kg i.p.) reversed the hyperactivity and novel object recognition impairment induced by PCP-SI but had no effect on the prepulse inhibition deficit. Microarray revealed small but significant down-regulation of hippocampal genes involved in glutamate metabolism, dopamine neurotransmission, and GABA receptor signaling and in specific schizophrenia-linked genes, including parvalbumin (PVALB) and GAD67, in PCP-SI rats, which resemble changes reported in schizophrenia.

CONCLUSIONS

Findings indicate that alterations in dopamine neurotransmission, glutamate metabolism, and GABA signaling may contribute to some of the behavioral deficits observed following PCP-SI, and that lamotrigine may have some utility as an adjunctive therapy to improve certain cognitive deficits symptoms in schizophrenia.

Common Variation in the DOPA Decarboxylase (DDC) Gene and Human Striatal DDC Activity In Vivo

The synthesis of multiple amine neurotransmitters, such as dopamine, norepinephrine, serotonin, and trace amines, relies in part on DOPA decarboxylase (DDC, AADC), an enzyme that is required for normative neural operations. Because rare, loss-of-function mutations in the DDC gene result in severe enzymatic deficiency and devastating autonomic, motor, and cognitive impairment, DDC common genetic polymorphisms have been proposed as a source of more moderate, but clinically important, alterations in DDC function that may contribute to risk, course, or treatment response in complex, heritable neuropsychiatric illnesses. However, a direct link between common genetic variation in DDC and DDC activity in the living human brain has never been established. We therefore tested for this association by conducting extensive genotyping across the DDC gene in a large cohort of 120 healthy individuals, for whom DDC activity was then quantified with [(18)F]-FDOPA positron emission tomography (PET). The specific uptake constant, Ki, a measure of DDC activity, was estimated for striatal regions of interest and found to be predicted by one of five tested haplotypes, particularly in the ventral striatum. These data provide evidence for cis-acting, functional common polymorphisms in the DDC gene and support future work to determine whether such variation might meaningfully contribute to DDC-mediated neural processes relevant to neuropsychiatric illness and treatment.

A genetic locus in 7p12.2 associated with treatment resistant schizophrenia

Approximately 30% of patients with schizophrenia are treatment resistant (TRS), i.e. have persistent psychotic symptoms despite adequate trials of at least two antipsychotic drugs (APDs). Most TRS patients are candidates for clozapine treatment which is underutilized because of its side effects and difficulty in identifying TRS. We conducted a genome-wide association study (GWAS) of 79 TRS and 95 non-treatment resistant (NTRS) Caucasian schizophrenia patients to identify possible biomarkers for TRS, which might also provide insight into the pathobiology of TRS. The single nucleotide polymorphism, rs2237457, located in 7p12.2, a region reported to have imprinted inheritance, was found to have the lowest p value in an allelic association test (unadjusted p = 5.53 × 10(-6)). Haploview disclosed a 30 kb block flanking this SNP within GRB10, 70 kb upstream of l-dopa decarboxylase (DDC), an enzyme which is rate-limiting in the synthesis of trace amines and neurotransmitters implicated in schizophrenia and the action of APDs. This SNP or haplotype was identified as an exclusive cis-acting eQTL for DDC in human dorsolateral prefrontal cortex by BrainCloud®. A replication sample genotyped for this SNP produced a weaker result, but in the same direction. After combining the two samples, rs2237457 remained significantly associated with TRS (unadjusted p = 5.66 × 10(-7) in recessive mode; 9.42 × 10(-5) in allelic association). If replicated in an independent sample, rs2237457 may provide a biomarker to identify a significant proportion of Caucasian TRS. The results implicate trace amines and their synthesis in the pathophysiology of TRS.

Polymorphisms in genes implicated in dopamine, serotonin and noradrenalin metabolism suggest association with cerebrospinal fluid monoamine metabolite concentrations in psychosis

BACKGROUND

Homovanillic acid (HVA), 5-hydroxyindoleacetic acid (5-HIAA) and 3-methoxy-4-hydroxyphenylglycol (MHPG) are the major monoamine metabolites in the central nervous system (CNS). Their cerebrospinal fluid (CSF) concentrations, reflecting the monoamine turnover rates in CNS, are partially under genetic influence and have been associated with schizophrenia. We have hypothesized that CSF monoamine metabolite concentrations represent intermediate steps between single nucleotide polymorphisms (SNPs) in genes implicated in monoaminergic pathways and psychosis.

METHODS

We have searched for association between 119 SNPs in genes implicated in monoaminergic pathways [tryptophan hydroxylase 1 (TPH1), TPH2, tyrosine hydroxylase (TH), DOPA decarboxylase (DDC), dopamine beta-hydroxylase (DBH), catechol-O-methyltransferase (COMT), monoamine oxidase A (MAOA) and MAOB] and monoamine metabolite concentrations in CSF in 74 patients with psychotic disorder.

RESULTS

There were 42 nominally significant associations between SNPs and CSF monoamine metabolite concentrations, which exceeded the expected number (20) of nominal associations given the total number of tests performed. The strongest association (p = 0.0004) was found between MAOB rs5905512, a SNP previously reported to be associated with schizophrenia in men, and MHPG concentrations in men with psychotic disorder. Further analyses in 111 healthy individuals revealed that 41 of the 42 nominal associations were restricted to patients with psychosis and were absent in healthy controls.

CONCLUSIONS

The present study suggests that altered monoamine turnover rates in CNS reflect intermediate steps in the associations between SNPs and psychosis.

Onset of schizophrenia at 100 years of age

Although generally regarded as a disease of young adults, schizophrenia does occur in older ages. Doubts have been raised about the validity of diagnosing schizophrenia in very old age. We have described herein a rare and unique case of a woman who had onset of "schizophrenia" as per ICD-10 and DSM-IV-TR criteria at the age of 100 years. We have discussed about the validity of diagnosing schizophrenia in older age.

Reversible infertility in a liver receptor homologue-1 (LRH-1)-knockdown mouse model

Liver receptor homologue-1 (LRH-1) is an orphan nuclear receptor that has been implicated in steroid hormone biosynthesis and fertility. Herein we describe a transgenic inducible short hairpin (sh) RNA mouse model that was used to study the effect of transient LRH-1 knockdown in vivo. Induction of expression of the shRNA directed against LRH-1 for 2–6 weeks resulted in 80% knockdown of LRH-1 protein in the ovary and complete infertility. Gonadotropin hyperstimulation could not rescue the observed defects in ovulation and corpus luteum formation in LRH-1-knockdown mice. The infertility phenotype was fully reversible because LRH-1-knockdown females became pregnant and delivered normal size litters and healthy pups after cessation of LRH-1 shRNA expression. Timed ovarian microarray analysis showed that, in line with the observed decrease in plasma progesterone levels, key steroid biosynthesis genes, namely Star, Cyp11a1, Hsd3b and Scarb1, were downregulated in LRH-1-knockdown ovaries. In contrast with what has been described previously, no clear effect was observed on oestrogenic activity in LRH-1-knockdown mice. Only Sult1e1 and, surprisingly, Hsd17b7 expression was modulated with potentially opposite effects on oestradiol bioavailability. In conclusion, the fully reversible infertility phenotype of LRH-1-knockdown mice shows the feasibility of an LRH-1 antagonist as new contraceptive therapy with a mechanism of action that most prominently affects cholesterol availability and progesterone production.

Memory deficits in late-onset schizophrenia

Late-onset schizophrenia (LOS) is a controversial diagnosis, mainly characterized by more positive symptoms and less deterioration. LOS could be considered as either an extreme of typical schizophrenia (but for old age patients, and short duration of the disorder), or an independent group of patients with a specific diagnosis, with no clear evidence in favor or against any of these hypotheses. The aim of the present study is to characterize the memory cognitive profile of LOS patients without related organic factors (N=25), compared to early-onset schizophrenic patients (EOS, N=44), matched for the duration of the disorder, and healthy controls (HC, N=23), matched for the age of patients. Lifetime clinical symptoms and functioning were collected using the DIGS and the PANSS, and components of memory capacity were assessed with the Forward and Backward Digit Span Tasks, Rey Complex Figure and Verbal Fluency Tests. LOS patients were performing significantly better than EOS patients on the digit span task, Rey's complex figure at T1 score and phonemic verbal fluency. However, LOS had significantly lower performances than healthy controls on the digit span task and on both verbal fluency tests. This study provides evidence that LOS had intermediate outcome compared to EOS and controls. LOS can therefore be in line with a dimensional clinical approach of schizophrenia, whereby it presents few memory deficits and few disorganization and negative symptoms with mostly positive symptoms and possibly etiopathogenic specificities. Further studies including more specific memory assessment tests and larger samples are needed to confirm the present finding.

The role of cerebellar genes in pathology of autism and schizophrenia

Schizophrenia and autism are neurodevelopmental diseases that have genetic as well as environmental etiologies. Both disorders have been associated with prenatal viral infection. Brain imaging and postmortem studies have found alterations in the structure of the cerebellum as well as changes in gene expression. Our laboratory has developed an animal model using prenatal infection of mice with human influenza virus that has demonstrated changes in behavior, pharmacology, structure, and gene expression in the brains of exposed offspring. In the current communication we describe altered expression of cerebellar genes associated with development of brain disorder in a mouse model for schizophrenia and autism and correlate these changes with those involved in the pathology of these two disorders.

Combining fMRI and SNP data to investigate connections between brain function and genetics using parallel ICA

There is current interest in understanding genetic influences on both healthy and disordered brain function. We assessed brain function with functional magnetic resonance imaging (fMRI) data collected during an auditory oddball task--detecting an infrequent sound within a series of frequent sounds. Then, task-related imaging findings were utilized as potential intermediate phenotypes (endophenotypes) to investigate genomic factors derived from a single nucleotide polymorphism (SNP) array. Our target is the linkage of these genomic factors to normal/abnormal brain functionality. We explored parallel independent component analysis (paraICA) as a new method for analyzing multimodal data. The method was aimed to identify simultaneously independent components of each modality and the relationships between them. When 43 healthy controls and 20 schizophrenia patients, all Caucasian, were studied, we found a correlation of 0.38 between one fMRI component and one SNP component. This fMRI component consisted mainly of parietal lobe activations. The relevant SNP component was contributed to significantly by 10 SNPs located in genes, including those coding for the nicotinic alpha-7 cholinergic receptor, aromatic amino acid decarboxylase, disrupted in schizophrenia 1, among others. Both fMRI and SNP components showed significant differences in loading parameters between the schizophrenia and control groups (P = 0.0006 for the fMRI component; P = 0.001 for the SNP component). In summary, we constructed a framework to identify interactions between brain functional and genetic information; our findings provide a proof-of-concept that genomic SNP factors can be investigated by using endophenotypic imaging findings in a multivariate format.

Dopamine genes and schizophrenia: case closed or evidence pending?

The dopamine hypothesis of schizophrenia (SZ) has motivated a large number of genetic association studies but few if any dopaminergic (DA) polymorphisms are accepted as credible risk factors at present. To evaluate whether dopamine-related genes have been investigated adequately, we surveyed public genetic databases and published SZ association studies with regard to 14 conventional DA genes and 7 selected dopamine-interacting proteins. We estimate that 325 polymorphisms would be required to evaluate the impact of common variation on SZ risk among Caucasian samples. To date, 98 polymorphisms have been analyzed in published association studies. We estimate that only 19 of these variations have been evaluated in samples with at least 50% power to detect an association of the effect size commonly found in genetically complex disorders. While it is possible that DA genes do not harbor genetic risk factors for SZ, our review suggests that satisfactory conclusions for most genes cannot be drawn at present. Whole-genome association studies have begun to fill this void, but additional analyses are likely to be needed. Recommendations for future association studies include analysis of adequately powered samples, judiciously selected polymorphisms, multiple ethnic groups, and concurrent evaluation of function at associated single-nucleotide polymorphisms.

Evidence implicating BRD1 with brain development and susceptibility to both schizophrenia and bipolar affective disorder

Linkage studies suggest that chromosome 22q12-13 may contain one or more shared susceptibility genes for schizophrenia (SZ) and bipolar affective disorder (BPD). In a Faeroese sample, we previously reported association between microsatellite markers located at 22q13.31-qtel and both disorders. The present study reports an association analysis across five genes (including 14 single nucleotide and two microsatellite polymorphisms) in this interval using a case-control sample of 162 BPD, 103 SZ patients and 200 controls. The bromodomain-containing 1 gene (BRD1), which encodes a putative regulator of transcription showed association with both disorders with minimal P-values of 0.0046 and 0.00001 for single marker and overall haplotype analysis, respectively. A specific BRD1 2-marker 'risk' haplotype showed a frequency of approximately 10% in the combined case group versus approximately 1% in controls (P-value 2.8 x 10(-7)). Expression analysis of BRD1 mRNA revealed widespread expression in mammalian brain tissue, which was substantiated by immunohistochemical detection of BRD1 protein in the nucleus, perikaryal cytosol and proximal dendrites of the neurons in the adult rat, rabbit and human CNS. Quantitative mRNA analysis in developing fetal pig brain revealed spatiotemporal differences with high expression at early embryonic stages, with intense nuclear and cytosolar immunohistochemical staining of the neuroepithelial layer and early neuroblasts, whilst more mature neurons at later embryonic stages had less nuclear staining. The results implicate BRD1 with SZ and BPD susceptibility and provide evidence that suggests a role for BRD1 in neurodevelopment.

Association analyses suggest GPR24 as a shared susceptibility gene for bipolar affective disorder and schizophrenia

Linkage analyses suggest that chromosome 22q12-13 may harbor a shared susceptibility locus for bipolar affective disorder (BPD) and schizophrenia (SZ). In a study of a sample from the Faeroe Islands we have previously reported association between both disorders and microsatellite markers in a 3.6 cM segment on 22q13. The present study investigated three candidate genes located in this segment: GPR24, ADSL, and ST13. Nine SNPs located in these genes and one microsatellite marker (D22S279) were applied in an association analysis of two samples: an extension of the previously analyzed Faeroese sample comprising 28 distantly related cases (17 BPD, 11 SZ subjects) and 44 controls, and a Scottish sample including 162 patients with BPD, 103 with SZ, and 200 controls. In both samples significant associations were observed in both disorders with predominantly GPR24 SNPs and haplotypes. In the Faeroese sample overall P-values of 0.0009, 0.0054, and 0.0023 were found for haplotypes in BPD, SZ, and combined cases, respectively, and in the Scottish sample overall P-values of 0.0003, 0.0005, and 0.016 were observed for similar groupings. Specific haplotypes showed associations with lowest P-values of 7 x 10(-5) and 0.0006 in the combined group of cases from the Faeroe Islands and Scotland, respectively. The G protein-coupled receptor 24 encoded by GPR24 binds melanin-concentrating hormone (MCH) and has been implicated with feeding behavior, energy metabolism, and regulation of stress and mood. To our knowledge this is the first study reporting association between GPR24 and BPD and SZ, suggesting that GPR24 variants may confer susceptibility to both disorders.

Intronic variants in the dopa decarboxylase ( DDC ) gene are associated with smoking behavior in European-Americans and African-Americans

We report here a study considering association of alleles and haplotypes at the DOPA decarboxylase (DDC) locus with the DSM-IV diagnosis of nicotine dependence (ND) or a quantitative measure for ND using the Fagerstrom Test for Nicotine Dependence (FTND). We genotyped 18 single nucleotide polymorphisms (SNPs) spanning a region of approximately 210 kb that includes DDC and the genes immediately flanking DDC in 1,590 individuals from 621 families of African-American (AA) or European-American (EA) ancestry. Evidence of association (family-based tests) was observed with several SNPs for both traits (0.0002<or=P<or=0.04). The most significant result was obtained for the relationship of FTND score to SNP rs12718541 (AA families: P=0.002; EA families: P=0.03; all families: P=0.0002) which is in the same intron as the splice site for a neuronal isoform of human DDC lacking exons 10-15. Haplotype analysis did not reveal any SNP combination with stronger evidence for association than rs12718541 alone. Although sequence analysis suggests that rs12718541 may be an intronic splicing enhancer, further studies are needed to determine whether a direct link exists between an alternatively spliced form of DDC and predisposition to ND. These findings confirm a previous report of association of DDC with ND, localize the causative variants to the 3' end of the coding region and extend the association to multiple population groups.

Multi-locus association study of schizophrenia susceptibility genes with a posterior probability method

Schizophrenia is a serious neuropsychiatric illness affecting about 1% of the world's population. It is considered a complex inheritance disorder. A number of genes are involved in combination in the etiology of the disorder. Evidence implicates the altered dopaminergic transmission in schizophrenia. In the present study, in order to identify susceptibility genes for schizophrenia in dopaminergic metabolism, we analyzed 59 single nucleotide polymorphisms (SNPs) in 24 genes of the dopaminergic pathway among 82 unrelated patients with schizophrenia and 108 matched normal controls. Considering that traditional single-locus association studies ignore the multigenic nature of complex diseases and do not take into account possible interactions between susceptibility genes, we proposed a multi-locus analysis method, using the posterior probability of morbidity as a measure of absolute disease risk for a multi-locus genotype combination, and developed an algorithm based on perturbation and average to detect the susceptibility multi-locus genotype combinations, as well as to repress noise and avoid false positive results at our best. A three-locus SNP genotype combination involved in the interactions of COMT and ALDH3B1 genes was detected to be significantly susceptible to schizophrenia.

Haplotype analysis indicates an association between the DOPA decarboxylase (DDC) gene and nicotine dependence

DOPA decarboxylase (DDC; also known as L-amino acid decarboxylase; AADC) is involved in the synthesis of dopamine, norepinephrine and serotonin. Because the mesolimbic dopaminergic system is implicated in the reinforcing effects of many drugs, including nicotine, the DDC gene is considered a plausible candidate for involvement in the development of vulnerability to nicotine dependence (ND). Further, this gene is located within the 7p11 region that showed a 'suggestive linkage' to ND in our previous genome-wide scan in the Framingham Heart Study population. In the present study, we tested eight single nucleotide polymorphisms (SNPs) within DDC for association with ND, which was assessed by smoking quantity (SQ), the heaviness of smoking index (HSI) and the Fagerstrom test for ND (FTND) score, in a total of 2037 smokers and non-smokers from 602 nuclear families of African- or European-American (AA or EA, respectively) ancestry. Association analysis for individual SNPs using the PBAT-GEE program indicated that SNP rs921451 was significantly associated with two of the three adjusted ND measures in the EA sample (P=0.01-0.04). Haplotype-based association analysis revealed a protective T-G-T-G haplotype for rs921451-rs3735273-rs1451371-rs2060762 in the AA sample, which was significantly associated with all three adjusted ND measures after correction for multiple testing (min Z=-2.78, P=0.006 for HSI). In contrast, we found a high-risk T-G-T-G haplotype for a different SNP combination in the EA sample, rs921451-rs3735273-rs1451371-rs3757472, which showed a significant association after Bonferroni correction with the SQ and FTND score (max Z=2.73, P=0.005 for FTND). In summary, our findings provide the first evidence for the involvement of DDC in the susceptibility to ND and, further, reveal the racial specificity of its impact.

No association between polymorphisms in the DDC gene and paranoid schizophrenia in a northern Chinese population

Several lines of evidence suggest that dysfunctions of neurotransmitters are associated with schizophrenia. DOPA decarboxylase (DDC) is an enzyme involved directly in the synthesis of dopamine and serotonin, and indirectly in the synthesis of noradrenaline. Therefore, the DDC gene can be considered a candidate gene for schizophrenia. We performed an association study between three single nucleotide polymorphisms in the DDC gene and paranoid schizophrenia. However, in our study no significant differences were found in the genotype distributions and allele frequencies between 80 paranoid schizophrenics and 108 controls for any of the polymorphisms. Neither did the haplotypes of the single nucleotide polymorphisms show any association with paranoid schizophrenia. Therefore, we conclude that the polymorphisms studied do not play a major role in paranoid schizophrenia pathogenesis in the population investigated.

Comparison of microarray-based mRNA profiling technologies for identification of psychiatric disease and drug signatures

The gene expression profiles of human postmortem parietal and prefrontal cortex samples of normal controls and patients with bipolar disease, or human neuroblastoma flat (NBFL) cells treated with the mood-stabilizing drug, valproate, were used to compare the performance of Affymetrix oligonucleotide U133A GeneChips and Agilent Human 1 cDNA microarrays. Among those genes represented on both platforms, the oligo array identified 26-53% more differentially expressed genes compared to the cDNA array in the three experiments, when identical fold change and t-test criteria were applied. The increased sensitivity was primarily the result of more robust fold changes measured by the oligonucleotide system. Essentially all gene changes overlapping between the two platforms were co-directional, and ranged from 4 to 19% depending upon the amount of biological variability within and between the comparison groups. Q-PCR validation rates were virtually identical for the two platforms, with 23-24% validation in the prefrontal cortex experiment, and 56% for both platforms in the cell culture experiment. Validated genes included dopa decarboxylase, dopamine beta-hydroxylase, and dihydropyrimidinase-related protein 3, which were decreased in NBFL cells exposed to valproate, and spinocerebellar ataxia 7, which was increased in bipolar disease. The modest overlap but similar validation rates show that each microarray system identifies a unique set of differentially expressed genes, and thus the greatest information is obtained from the use of both platforms.

Pharmacogenomics of psychiatric drug treatment

It is the goal of pharmacogenomics in psychiatry to establish predictive relationships between polymorphisms of candidate genes and therapeutic response to drug treatment. Polymorphisms of candidate genes related to drug mechanisms and pathophysiology of illness and defined clinical phenotype are the foundations for pharmacogenomic studies. Pharmacogenomic studies of antipsychotic response have focused on polymorphisms of genes for dopamine and serotonin receptors with most positive results reported for polymorphisms of genes of the 5HT2a and 5HT2c serotonin receptor subtypes. Although the goal of establishing individualized medicine predicated on an individual patient's genetic code has yet to be achieved, the fundamentals are now in place for second-generation investigation and more application to health care.

Possible parent-of-origin effect of Dopa decarboxylase in susceptibility to bipolar affective disorder

Dopa decarboxylase (DDC) catalyses the synthesis of both dopamine and serotonin as well as trace amines suggested to possess neuromodulating capabilities. We have previously reported evidence suggesting an association between DDC and bipolar affective disorder (BPAD) [Børglum et al., 1999]. To further investigate the possible role of DDC in BPAD, we analyzed a 1- and a 4-bp deletion variant-both of putative functional significance-in two new samples: a case-control sample with 140 cases and 204 controls, and 100 case-parents trios. We also tested for association in subjects with familial disease in both the new and the previously investigated samples. The previously reported association was not replicated in either of the new samples. However, a preponderance of the 1-bp deletion was increased by analysis of the familial cases separately for all case-control samples investigated, indicating a possible association with familial disease (combined analysis, P = 0.02). In the trio sample, a preferential paternal transmission of the 4-bp deletion was observed (P = 0.006). DDC is located next to the imprinted gene GRB10, which is expressed specifically from the paternal allele in fetal brains. Increased transmission of paternal DDC alleles has also been suggested in attention deficit hyperactivity disorder. We suggest that DDC might confer susceptibility to BPAD predominantly when paternally transmitted.