Juliane Kopf

Cross-disorder analysis of bipolar risk genes: further evidence of DGKH as a risk gene for bipolar disorder, but also unipolar depression and adult ADHD.

Recently, several genome-wide association studies (GWAS) on bipolar disorder (BPD) suggested novel risk genes. However, only few of them were followed up and further, the specificity of these genes is even more elusive. To address these issues, we genotyped SNPs in ANK3, CACNA1C, CMTM8, DGKH, EGFR, and NPAS3, which were significantly associated with BPD in previous GWAS, in a sample of 380 BPD patients. Replicated SNPs were then followed up in patients suffering from unipolar depression (UPD; n=387) or adult attention-deficit/hyperactivity disorder (aADHD; n=535). While we could not confirm an association of ANK3, CACNA1C, and EGFR with BPD, 10 SNPs in DGKH, CMTM8, and NPAS3 were nominally associated with disease, with two DGKH markers surviving correction for multiple testing. When these were followed up in UPD and aADHD, seven DGKH SNPs were also associated with UPD, while one SNP each in NPAS3 and CMTM8 and four in DGKH were linked to aADHD. Furthermore, a DGKH haplotype consisting of rs994856/rs9525580/rs9525584 GAT was associated with all disorders tested, while the complementary AGC haplotype was protective. The corresponding haploblock spans a 27-kb region covering exons coding for amino acids 65–243, and thus might include functional variants yet to be identified. We demonstrate an association of DGKH with BPD, UPD, and aADHD by applying a two-stage design. These disorders share the feature of mood instability, so that this phenotype might be associated with genetic variation in DGKH.

Progranulin Gene Variability and Plasma Levels in Bipolar Disorder and Schizophrenia

Basing on the assumption that frontotemporal lobar degeneration (FTLD), schizophrenia and bipolar disorder (BPD) might share common aetiological mechanisms, we analyzed genetic variation in the FTLD risk gene progranulin (GRN) in a German population of patients with schizophrenia (n = 271) or BPD (n = 237) as compared with 574 age-, gender- and ethnicity-matched controls. Furthermore, we measured plasma progranulin levels in 26 German BPD patients as well as in 61 Italian BPD patients and 29 matched controls. A significantly decreased allelic frequency of the minor versus the wild-type allele was observed for rs2879096 (23.2 versus 34.2%, P<0.001, OR:0.63, 95%CI:0.49–0.80), rs4792938 (30.7 versus 39.7%, P = 0.005, OR: 0.70, 95%CI: 0.55–0.89) and rs5848 (30.3 versus 36.8, P = 0.007, OR: 0.71, 95%CI: 0.56–0.91). Mean±SEM progranulin plasma levels were significantly decreased in BPD patients, either Germans or Italians, as compared with controls (89.69±3.97 and 116.14±5.80 ng/ml, respectively, versus 180.81±18.39 ng/ml P<0.001) and were not correlated with age. In conclusion, GRN variability decreases the risk to develop BPD and schizophrenia, and progranulin plasma levels are significantly lower in BPD patients than in controls. Nevertheless, a larger replication analysis would be needed to confirm these preliminary results.

The genetic contribution of the NO system at the glutamatergic post-synapse to schizophrenia : further evidence and meta-analysis

NO is a pleiotropic signaling molecule and has an important role in cognition and emotion. In the brain, NO is produced by neuronal nitric oxide synthase (NOS-I, encoded by NOS1) coupled to the NMDA receptor via PDZ interactions; this protein-protein interaction is disrupted upon binding of NOS1 adapter protein (encoded by NOS1AP) to NOS-I. As both NOS1 and NOS1AP were associated with schizophrenia, we here investigated these genes in greater detail by genotyping new samples and conducting a meta-analysis of our own and published data. In doing so, we confirmed association of both genes with schizophrenia and found evidence for their interaction in increasing risk towards disease. Our strongest finding was the NOS1 promoter SNP rs41279104, yielding an odds ratio of 1.29 in the meta-analysis. As findings from heterologous cell systems have suggested that the risk allele decreases gene expression, we studied the effect of the variant on NOS1 expression in human post-mortem brain samples and found that the risk allele significantly decreases expression of NOS1 in the prefrontal cortex. Bioinformatic analyses suggest that this might be due the replacement of six transcription factor binding sites by two new binding sites as a consequence of proxy SNPs. Taken together, our data argue that genetic variance in NOS1 resulting in lower prefrontal brain expression of this gene contributes to schizophrenia liability, and that NOS1 interacts with NOS1AP in doing so. The NOS1-NOS1AP PDZ interface may thus well constitute a novel target for small molecules in at least some forms of schizophrenia.

NOS1 ex1f-VNTR polymorphism influences prefrontal brain oxygenation during a working memory task.

Nitric oxide (NO) synthase produces NO, which serves as first and second messenger in neurons, where the protein is encoded by the NOS1 gene. A functional variable number of tandem repeats (VNTR) polymorphism in the promoter region of the alternative first exon 1f of NOS1 is associated with various functions of human behavior, for example increased impulsivity, while another, non-functional variant was linked to decreased verbal working memory and a heightened risk for schizophrenia. We therefore investigated the influence of NOS1 ex 1f-VNTR on working memory function as reflected by both behavioral measures and prefrontal oxygenation. We hypothesized that homozygous short allele carriers exhibit altered brain oxygenation in task-related areas, namely the dorsolateral and ventrolateral prefrontal cortex and the parietal cortex. To this end, 56 healthy subjects were stratified into a homozygous long allele group and a homozygous short allele group comparable for age, sex and intelligence. All subjects completed a letter n-back task (one-, two-, and three-back), while concentration changes of oxygenated (O(2)Hb) hemoglobin in the prefrontal cortex were measured with functional near-infrared spectroscopy (fNIRS). We found load-associated O(2)Hb increases in the prefrontal and parts of the parietal cortex. Significant load-associated oxygenation differences between the two genotype groups could be shown for the dorsolateral prefrontal cortex and the parietal cortex. Specifically, short allele carriers showed a significantly larger increase in oxygenation in all three n-back tasks. This suggests a potential compensatory mechanism, with task-related brain regions being more active in short allele carriers to compensate for reduced NOS1 expression.

Further evidence for plasma progranulin as a biomarker in bipolar disorder

BACKGROUND A recent study suggested that progranulin (encoded by the fronto-temporal dementia risk gene GRN) plasma levels are decreased in bipolar disorder (BD). Replication of this finding is however lacking. METHODS Progranulin plasma levels of bipolar patients (n=104) and healthy controls (n=80) were measured by enzyme-linked immunosorbent assay (ELISA). Participants were also genotyped for three single nucleotide polymorphisms (SNPs) in the GRN gene (rs2879096, rs4792938 and rs5848), and the effect of genetic variation on progranulin levels was examined. RESULTS Plasma progranulin levels were decreased in BD (ANCOVA, p=0.001). Furthermore, age was significantly and positively correlated with plasma progranulin (Pearson׳s correlation, r=0.269, p<0.001). Also, lithium treatment but no other medication had a significant effect on progranulin plasma levels (ANCOVA, p=0.007). Specifically in BD, the GRN SNP rs5848 was associated with progranulin plasma levels (Kruskal-Wallis test, p<0.005). LIMITATIONS Subgroup analysis regarding bipolar I vs. bipolar II subtype and polarity of the episode at sampling (manic vs. depressed vs. mixed vs. rapid cycling vs. euthymic) could only be performed with limited validity due to the relatively small sample size. The suitability of peripheral progranulin as a biomarker for BD is limited due to the overlap between patients and controls. CONCLUSION The findings strengthen the evidence for progranulin being involved in pathomechanisms of bipolar disorder, and suggest a genetic determinant of progranulin concentrations that is relevant specifically in bipolar patients.

The Effect of Emotional Content on Brain Activation and the Late Positive Potential in a Word n-back Task

Introduction There is mounting evidence for the influence of emotional content on working memory performance. This is particularly important in light of the emotion processing that needs to take place when emotional content interferes with executive functions. In this study, we used emotional words of different valence but with similar arousal levels in an n-back task. Methods We examined the effects on activation in the prefrontal cortex by means of functional near-infrared spectroscopy (fNIRS) and on the late positive potential (LPP). FNIRS and LPP data were examined in 30 healthy subjects. Results Behavioral results show an influence of valence on the error rate depending on the difficulty of the task: more errors were made when the valence was negative and the task difficult. Brain activation was dependent both on the difficulty of the task and on the valence: negative valence of a word diminished the increase in activation, whereas positive valence did not influence the increase in activation, while difficulty levels increased. The LPP also differentiated between the different valences, and in addition was influenced by the task difficulty, the more difficult the task, the less differentiation could be observed. Conclusions Summarized, this study shows the influence of valence on a verbal working memory task. When a word contained a negative valence, the emotional content seemed to take precedence in contrast to words containing a positive valence. Working memory and emotion processing sites seemed to overlap and compete for resources even when words are carriers of the emotional content.

NOS1 ex1f-VNTR polymorphism affects prefrontal oxygenation during response inhibition tasks

Impulsivity is a trait shared by many psychiatric disorders and therefore a suitable intermediate phenotype for their underlying biological mechanisms. One of the molecular determinants involved is the NOS1 ex1f‐VNTR, whose short variants are associated with a variety of impulsive behaviors. Fifty‐six healthy controls were stratified into homozygous long (LL) (30 probands) and short (SS) (26 probands) allele groups. Subjects completed a combined stop‐signal go/nogo task, while the oxygenation in the prefrontal cortex was measured with functional near‐infrared spectroscopy. Electromyography was recorded to control for differences in muscle activity in the two inhibition tasks. Two questionnaires on impulsive traits were completed. Differences between the two tasks are shown by distinct activation patterns within the prefrontal cortex. The nogo task resulted mainly in the activation of the dorsolateral prefrontal cortex (dlPFC), whereas successful and unsuccessful inhibition in the stop‐signal task elicited the predicted activity in the inferior frontal cortex (IFC). Although significant differences were found in neither the scores obtained on impulsivity‐related questionnaires nor the behavioral data, the LL group displayed increased dlPFC activity during nogo trials and the predicted activation in the IFC during successful inhibition in the stop‐signal task, while no significant activation was found in the SS group. Our data confirm an influence of NOS1 ex1f‐VNTR on impulsivity, as carriers of the short risk allele exhibited diminished activity of (pre‐)frontal brain regions during the inhibition in a stop‐signal task. Impairment of prefrontal control with consecutive failure of inhibitory processes might underlie association findings reported previously. Hum Brain Mapp, 2012.

Multi-level biomarker analysis of nitric oxide synthase isoforms in bipolar disorder and adult ADHD

Introduction: Several studies have shown altered levels of nitric oxide (NO) and its stable metabolites (NOx-) in blood and cerebrospinal fluid of psychiatric patients. The aim of our study was to replicate previous findings and investigate the influence of the nitrinergic system in bipolar disorder and adult attention-deficit/hyperactivity disorder (aADHD) in particular. Methods: The concentrations of NO2- and NO3- in peripheral blood in a sample of aADHD, bipolar disorder (BPD) and controls were analysed. The sample was genotyped for a three marker haplotype in the NOS3 gene (rs2070744, rs1799983 and Intron 4 VNTR) and for genetic variants of the NOS1 gene (NOS1 ex 1c, NOS1 ex 1f). Finally, qRT PCR was performed. Results: We found significantly lower NOx- levels in BPD (p<0.001). rs2070744 T/T-carriers of the whole sample showed increased mRNA expression of NOS3 (p=0.05). Only in BPD an influence of rs2070744 was seen regarding NO metabolite levels; C/C carriers displayed lower NOx- levels (p=0.05). Conclusion: We could replicate and extend previous findings showing altered NOx- levels in BPD and an influence of NOS3 rs2070744 on NOS3 expression and NOx- concentration. Together, these data point to a role of the nitrinergic pathway in BPD.

Neuropeptide S receptor gene variation and neural correlates of cognitive emotion regulation

The neuropeptide S (NPS) and its receptor NPSR have captured attention in the pathogenesis of anxiety disorders. Here, a functional polymorphism in the NPSR1 gene has been linked to deviant cortico-limbic interactions in response to negative stimuli. While healthy T allele carriers exhibited increased amygdala and prefrontal cortex activity, panic disorder patients carrying the T risk allele displayed hypofrontality possibly reflecting insufficient prefrontal inhibition of limbic reactivity. In order to study multi-level effects of genotype and anxiety, prefrontal cortex activity during an emotional n-back task was measured in 66 volunteers genotyped for the NPSR1 rs324981 A/T variant (AA homozygotes vs. T allele carriers) by means of functional near-infrared spectroscopy. For a high working memory load (3-back), T allele carriers showed a signal increase to negative pictures in the dorsolateral and medial prefrontal cortex while AA homozygotes displayed a signal decrease. Since groups did not differ on skin conductance level and behavioral parameters, this effect in the risk group in line with results from fMRI studies is speculated to represent an adaptive mechanism to compensate for presumably increased subcortical activity driven by an overactive NPS system. However, anxiety sensitivity correlated negatively with prefrontal activity in T allele carriers possibly suggesting a decompensation of the adaptive compensatory upregulation.

Predominant polarity in bipolar disorder and validation of the polarity index in a German sample

BackgroundA large number of patients with bipolar disorder (BD) can be characterized by predominant polarity (PP), which has important implications for relapse prevention. Recently, Popovic et al. (EUR NEUROPSYCHOPHARM 22(5): 339-346, 2012) proposed the Polarity Index (PI) as a helpful tool in the maintenance treatment of BD. As a numeric expression, it reflects the efficacy of drugs used in treatment of BD. In the present retrospective study, we aimed to validate this Index in a large and well characterized German bipolar sample.MethodsWe investigated 336 bipolar patients (BP) according to their PP and calculated the PI for each patient in order to prove if maintenance treatment differs according to their PP. Furthermore, we analysed whether PP is associated with demographic and clinical characteristics of BP.ResultsIn our sample, 63.9% of patients fulfilled criteria of PP: 169 patients were classified as depressive predominant polarity (DPP), 46 patients as manic predominant polarity (MPP). The two groups differed significantly in their drug regime: Patients with DPP were more often medicated with lamotrigine and antidepressants, patients with MPP were more often treated with lithium, valproate, carbamazepine and first generation antipsychotics. However, patients with DPP and MPP did not differ significantly with respect to the PI, although they received evidence-based and guideline-driven treatment.ConclusionThe reason for this negative finding might well be that for several drugs, which were used frequently, no PI value is available. Nevertheless we suggest PP as an important concept in the planning of BD maintenance treatment.