Endophenotype properties of niacin sensitivity as marker of impaired prostaglandin signalling in schizophrenia

Attenuated niacin response is associated with a subtype of first-episode drug-naïve psychosis characterized as serious negative symptoms

Although the phenomenon of attenuated niacin response (ANR) has been widely replicated in some patients with first-episode psychosis (FEP), its relevance to the negative symptoms (NS) of psychosis remains unclear. Total of 240 patients with drug-naïve FEP and 101 healthy controls (HCs) were recruited, and 209 were followed up for 1 year. Psychotic symptoms were assessed using the Positive and Negative Syndrome Scale (PANSS), and niacin-induced responses were measured using laser Doppler flowmetry. We calculated the log-transform EC50 [concentration of methyl nicotinate required to elicit a half-maximal blood flow (MBF) response] and MBF values. Core-NS was generated by factor analysis of the PANSS-NS subscale and cluster analysis to produce subtypes. Significant differences were found in the log10 (EC50) values between the FEP and HC groups (p < 0.001), supporting the ANR in patients with FEP. A higher NS severity was found in the ANR subgroup than that in other patients. Factor analysis determined that a two-dimensional model included core NS and rigidity of thinking. The log10 (EC50) value was significantly associated with only the core NS. Cluster analysis revealed three subtypes-36.7% (cluster-1, n = 88), 16.7% (cluster-2, n = 40), and 46.7% (cluster-3, n = 112). Cluster-2 characterized by extensive NS appeared to have a more remarkable ANR and less symptomatic improvement than those with other clusters during follow-up. No significant changes were found in the niacin response trajectories between the baseline and follow-up. Our findings indicate a significant correlation between ANR and core NS in patients with FEP. ANR may be a potential biomarker for certain subtypes with NS-dominated characteristics and poor symptomatic remission.

The Inflammatory Signals Associated with Psychosis: Impact of Comorbid Drug Abuse

Psychosis and substance use disorders are two diagnostic categories whose association has been studied for decades. In addition, both psychosis spectrum disorders and drug abuse have recently been linked to multiple pro-inflammatory changes in the central nervous system. We have carried out a narrative review of the literature through a holistic approach. We used PubMed as our search engine. We included in the review all relevant studies looking at pro-inflammatory changes in psychotic disorders and substance use disorders. We found that there are multiple studies that relate various pro-inflammatory lipids and proteins with psychosis and substance use disorders, with an overlap between the two. The main findings involve inflammatory mediators such as cytokines, chemokines, endocannabinoids, eicosanoids, lysophospholipds and/or bacterial products. Many of these findings are present in different phases of psychosis and in substance use disorders such as cannabis, cocaine, methamphetamines, alcohol and nicotine. Psychosis and substance use disorders may have a common origin in an abnormal neurodevelopment caused, among other factors, by a neuroinflammatory process. A possible convergent pathway is that which interrelates the transcriptional factors NFκB and PPARγ. This may have future clinical implications.

Niacin skin flush and membrane polyunsaturated fatty acids in schizophrenia from the acute state to partial remission: a dynamic relationship

Despite the consistent finding of an attenuated niacin-induced flush response in schizophrenia, its long-term stability and relationship to the membrane polyunsaturated fatty acid (PUFA) levels remain unknown. We conducted niacin skin tests and measured the membrane PUFAs using gas chromatography among 46 schizophrenia inpatients and 37 healthy controls at the baseline and the 2-month follow-up. Attenuated flush responses were persistently observed in schizophrenia patients in both acute and partial remission states, whereas an increased flush response was found in the controls. A persistent decrease in both dihomo-gamma-linolenic acid and docosahexaenoic acid and an increased turnover of arachidonic acid (ARA) via endogenous biosynthesis were found in schizophrenia patients. A composite niacin flush score by combining those with a control-to-case ratio of >1.4 (i.e., scores at 5 min of 0.1 M, 0.01 M, and 0.001 M + 10 min of 0.01 M and 0.001 M + 15 min of 0.001 M) at the baseline was correlated positively with ARA levels among controls but not among schizophrenia patients, whereas the flush score at the 2-month follow-up was correlated positively with ARA levels among patients. The 2-month persistence of attenuated niacin-induced flush response in schizophrenia patients implies that the niacin skin test might tap a long-term vulnerability to schizophrenia beyond acute exacerbation.

Replication of the abnormal niacin response in first episode psychosis measured using laser Doppler flowmeter

INTRODUCTION

Impaired sensitivity of the skin flush response to niacin is found in approximately 30% of patients with schizophrenia. Although the niacin response abnormality (NRA) may serve as a useful endophenotype for schizophrenia, few studies have directly replicated NRA in patients with first-episode psychosis (FEP).

METHODS

In total, 204 patients with FEP, 16 with psychotic mood disorder (PMD), and 68 healthy controls (HC) were included. The log₁₀ (EC₅₀ ) values represent the concentration of methyl nicotinate required to elicit a half-maximal blood flow (MBF) response, and the MBF value was calculated. The NRA was defined as having log₁₀ (EC₅₀ ) molar value above the 90% and an MBF value below the 60% of those in the HC group.

RESULTS

In total, 13.7% of the FEP, 12.5% of the PMD, and 7.4% of the HC group met the definition of NRA. Significant differences were found in the log₁₀ (EC₅₀ ) values between the FEP and HC groups (p = .014) and in the MBF between the FEP and PMD groups (p = .011). Patients with FEP and NRA had more severe negative symptoms than those with a normal niacin response.

DISCUSSION

These data represent the NRA in patients with FEP, defining a small subgroup of patients with early-phase psychosis possessing a clinically significant phospholipid-signaling defect.

A potential objective marker in first-episode schizophrenia based on abnormal niacin response

The lack of objective diagnostic markers has long been a challenge in the clinical management of schizophrenia (SZ). The current bivariate cut-offs method is an objective quantification of niacin skin flush abnormality (NFA) for identifying the SZ subgroup. However, the sensitivity of approximately 30% limits the application of NFA as a marker for detecting SZ. A laser Doppler flowmeter was employed to test the niacin skin-flushing response in 123 patients with first-episode psychosis including first-episode SZ (FES, n = 82) and psychotic bipolar disorders (PBP, n = 41), and non-psychiatric comparisons (NPC, n = 80). We modified the bivariate cut-offs using a combination of the niacin concentration corresponding to the half-maximal blood flow response (EC₅₀) and a new quantitative indicator called the overall trend area (OTA). The NFA used this study method predicted FES in the NPC group with 57% sensitivity, 89% specificity, and 73% accuracy compared to the 28% sensitivity, 91% specificity, and 59% accuracy of the existing method. This novel method could discern FES from the PBP group with an accuracy of 62%, compared with the 45% of the old method. In addition, we also discuss whether the bivariate cut-offs were occasional by adjusting the cut-offs threshold. The experimental results showed that the sensitivity and specificity were most stable when using the study method. The study indicates that NFA using modified bivariate cut-offs may be a potential objective marker in FES, and the niacin skin test could be feasible for early diagnosis and treatment of SZ.

Attenuated and delayed niacin skin flushing in schizophrenia and affective disorders: A potential clinical auxiliary diagnostic marker

AIM

Schizophrenia and affective disorders all show high heterogeneity in clinical manifestations. A lack of objective biomarkers has long been a challenge in the clinical diagnosis of these diseases. In this study, we aimed to investigate the performance of niacin skin flushing in schizophrenia and affective disorders and determine its clinical potential as an auxiliary diagnostic marker.

METHODS

In this case-control study, niacin skin-flushing tests were conducted in 613 patients (including 307 schizophrenia patients, 179 bipolar disorder patients, and 127 unipolar depression patients) and 148 healthy controls (HCs) with a modified method. Differences in niacin skin-flushing responses were compared with adjustment for gender, BMI, age, nicotine dependence, alcohol consumption and educational status. A diagnostic model was established based on a bivariate cut-off.

RESULTS

Schizophrenia and affective disorders showed similar performance of niacin bluntness, characterized by attenuated flushing extent and reduced flushing rate. An innovative bivariate cut-off was established according to these two features, by which we could identify -patients with either schizophrenia or affective disorders from HCs with a sensitivity of 55.28%, a specificity of 83.56% and a positive predictive value of 93.66%.

CONCLUSIONS

The niacin-induced skin flushing was prevalently blunted in patients with schizophrenia or affective disorders, indicating a promising potential as an auxiliary diagnostic marker in risk prediction and clinical management of these disorders. Additionally, the niacin-blunted subgroup implies a common biological basis in the investigated disorders, which provokes new thoughts in elucidating the pathological mechanisms.

An investigation of calcium-independent phospholipase A2 (iPLA2) and cytosolic phospholipase A2 (cPLA2) in schizophrenia

Evidence indicates that abnormal phospholipase A2 (PLA2) levels and niacin insensitivity are present in individuals with schizophrenia. This study was designed to determine whether differences in plasma calcium-independent phospholipase A2 (iPLA2) and cytosolic phospholipase A2 (cPLA2) exist between those with schizophrenia and healthy controls, and to explore the correlation between PLA2s and the niacin skin reaction in schizophrenic patients. We performed ELISA experiments to measure the concentrations of plasma iPLA2 and cPLA2 and we conducted a series of niacin skin tests on schizophrenic patients from the Chinese Han population. In addition, a meta-analysis of the relationship between PLA2 and schizophrenia was conducted. The plasma concentration of iPLA2 in patients with schizophrenia was significantly higher than that in healthy controls while the plasma concentration of cPLA2 did not differ. The meta-analysis also revealed that the activity level of iPLA2 in individuals with schizophrenia was higher than that in healthy controls, whereas that of cPLA2 was not. Furthermore, a significant positive correlation was found between the concentration of iPLA2 and the score for the skin flushing response within 20 min. The abnormal plasma iPLA2 concentration and its relationship with the niacin skin test in schizophrenic patients has contributed to a deeper understanding of the pathology of schizophrenia, which may in turn provide new insights into the clinical diagnoses and treatment of schizophrenia.

The niacin response biomarker as a schizophrenia endophenotype: A status update

Increasingly, it is recognized that the behavioral syndrome of schizophrenia is not a unitary disease with a single underlying cause. Rather, it may have several possible etiologies, and its symptoms may arise from multiple causes. Such heterogeneity could account for some of the difficulties in elucidating its genetics, and may also explain clinical observations of variable medication response in schizophrenia. The ability to categorize schizophrenia using objectively recognizable, physiologically-based subtypes promises to make our understanding of schizophrenia more comprehensive and could provide some clues for more personalized treatment. This paper will review the extent to which an abnormally blunted skin flush response to niacin satisfies the criteria for a schizophrenia endophenotype.

State marker properties of niacin skin sensitivity in ultra-high risk groups for psychosis - An optical reflection spectroscopy study

Impaired niacin sensitivity (NS) is one of the most replicated findings in untreated schizophrenia, and reflects a disturbance of prostaglandin-mediated pathways in association with deregulated arachidonic acid metabolism, pro-inflammatory activation, and vasomotor function. In ultra-high risk individuals (UHR) increased NS was reported recently, pointing towards dynamic alterations of the underlying pathomechanisms in the period preceding psychosis. However, these characteristics are still unresolved in the diverse UHR groups. We tested the hypothesis that NS is attenuated in patients who have transitioned to psychosis and in the Brief Limited Intermittent Psychotic Symptoms (BLIPS, UHR-B) and/or the attenuated symptoms (UHR-A) groups, while it is unchanged or increased in the genetic risk group (UHR-G). Sensitivity to three concentrations (0.1-0.001M) of aqueous methylnicotinate was tested in 84 UHR patients, 105 first-episode psychosis patients (FEP) and 180 healthy individuals (HC), using optical reflection spectroscopy (ORS). The UHR subgroup and transition/non-transition outcomes were assessed according to PACE criteria using the CAARMS. Psychopathology was assessed using SANS, SAPS, and BPRS or SCL-90-R self-ratings. In 0.001M data, decreased NS was found in the UHR-B (n=12), UHR-A (n=45) and the transition groups (n=13), similar to the result in FEP. NS in the UHR-G (n=27) and HC groups did not differ. In the UHR-B and FEP groups, NS and positive symptom scores were inversely correlated. These state marker properties could be used to characterize the intensity of the underlying pathomechanisms during the onset of psychosis or to identify UHR individuals that might benefit from related indicated prevention strategies.

A Role for the Transcription Factor Nk2 Homeobox 1 in Schizophrenia: Convergent Evidence from Animal and Human Studies

Schizophrenia is a highly heritable disorder with diverse mental and somatic symptoms. The molecular mechanisms leading from genes to disease pathology in schizophrenia remain largely unknown. Genome-wide association studies (GWASs) have shown that common single-nucleotide polymorphisms associated with specific diseases are enriched in the recognition sequences of transcription factors that regulate physiological processes relevant to the disease. We have used a “bottom-up” approach and tracked a developmental trajectory from embryology to physiological processes and behavior and recognized that the transcription factor NK2 homeobox 1 (NKX2-1) possesses properties of particular interest for schizophrenia. NKX2-1 is selectively expressed from prenatal development to adulthood in the brain, thyroid gland, parathyroid gland, lungs, skin, and enteric ganglia, and has key functions at the interface of the brain, the endocrine-, and the immune system. In the developing brain, NKX2-1-expressing progenitor cells differentiate into distinct subclasses of forebrain GABAergic and cholinergic neurons, astrocytes, and oligodendrocytes. The transcription factor is highly expressed in mature limbic circuits related to context-dependent goal-directed patterns of behavior, social interaction and reproduction, fear responses, responses to light, and other homeostatic processes. It is essential for development and mature function of the thyroid gland and the respiratory system, and is involved in calcium metabolism and immune responses. NKX2-1 interacts with a number of genes identified as susceptibility genes for schizophrenia. We suggest that NKX2-1 may lie at the core of several dose dependent pathways that are dysregulated in schizophrenia. We correlate the symptoms seen in schizophrenia with the temporal and spatial activities of NKX2-1 in order to highlight promising future research areas.

Prevalence and Specificity of the Abnormal Niacin Response: A Potential Endophenotype Marker in Schizophrenia

The skin flush response to niacin is abnormally blunted among a subset of patients with schizophrenia (SZ), preferentially associates with SZ compared to other mental illnesses, occurs frequently in nonpsychotic members of SZ-affected families, appears heritable, and shows evidence of genetic association. The niacin response abnormality (NRA) may prove to be a useful SZ endophenotype. Using a laser Doppler flowmeter, we undertook this study to estimate the prevalence of NRA in SZ (n = 70), bipolar disorder (BP, n = 59), and healthy control (HC, n = 87) groups, and to estimate its specificity for the illness. From the dose-response curves, we calculated the concentration of methylnicotinate required to elicit a half-maximal blood flow (MBF) response (EC50 value) and MBF value for each subject. The median log10EC50 of the SZ was above the third quartile of log10EC50 of either the HC or BP groups, whereas the MBF was significantly lower in the SZ than in the HC or BP groups. With a definition of NRA of having both EC50 above the ninetieth percentile of the control samples and MBF response below the sixtieth percentile for the control range, the NRA predicted SZ with 31% sensitivity and 97% specificity. Moreover, the NRA was not influenced by age, gender, race, and cigarette smoking. In summary, the NRA may define a SZ subtype with a clinically significant phospholipid signaling defect. Understanding its molecular origins may shed light on the pathophysiology of SZ and suggest new tools for its early diagnosis and treatment.

Niacin Skin Sensitivity Is Increased in Adolescents at Ultra-High Risk for Psychosis

Background

Most studies provide evidence that the skin flush response to nicotinic acid (niacin) stimulation is impaired in schizophrenia. However, only little is known about niacin sensitivity in the ultra-high risk (UHR) phase of psychotic disorders.

Methods

We compared visual ratings of niacin sensitivity between adolescents at UHR for psychosis according to the one year transition outcome (UHR-T n = 11; UHR-NT n = 55) with healthy controls (HC n = 25) and first episode schizophrenia patients (FEP n = 25) treated with atypical antipsychotics.

Results

Contrary to our hypothesis niacin sensitivity of the entire UHR group was not attenuated, but significantly increased compared to the HC group, whereas no difference could be found between the UHR-T and UHR-NT groups. As expected, niacin sensitivity of FEP was attenuated compared to HC group. In UHR individuals niacin sensitivity was inversely correlated with omega-6 and -9 fatty acids (FA), but positively correlated with phospholipase A₂ (inPLA₂) activity, a marker of membrane lipid repair/remodelling.

Conclusions

Increased niacin sensitivity in UHR states likely indicates an impaired balance of eicosanoids and omega-6/-9 FA at a membrane level. Our findings suggest that the emergence of psychosis is associated with an increased mobilisation of eicosanoids prior to the transition to psychosis possibly reflecting a “pro-inflammatory state”, whereas thereafter eicosanoid mobilisation seems to be attenuated. Potential treatment implications for the UHR state should be further investigated.

Does tobacco use cause psychosis? Systematic review and meta-analysis

BACKGROUND

Although the association between psychotic illness and cigarette smoking is well known, the reasons are unclear why people with psychosis are more likely to smoke than are the general population. We aimed to test several hypotheses. First, that daily tobacco use is associated with an increased risk of psychotic illness in both case-control and prospective studies. Second, that smoking is associated with an earlier age at onset of psychotic illness. Finally, that an earlier age at initiation of smoking is associated with an increased risk of psychosis. We also aimed to derive an estimate of the prevalence of smoking in patients presenting with their first episode of psychosis.

METHODS

We searched Embase, Medline, and PsycINFO and selected observational studies in which rates of smoking were reported in people with psychotic disorders, compared with controls. We calculated the weighted mean difference for age at onset of psychosis and age at initiation of smoking. For categorical outcomes, we calculated odds ratios from cross-sectional studies and risk ratios from prospective studies.

FINDINGS

Of 3717 citations retrieved, 61 studies comprising 72 samples met inclusion criteria. The overall sample included 14 555 tobacco users and 273 162 non-users. The prevalence of smoking in patients presenting with their first episode of psychosis was 0·57 (95% CI 0·52-0·62; p<0·0001). In case-control studies, the overall odds ratio for the first episode of psychosis in smokers versus non-smokers was 3·22 (95% CI 1·63-6·33), with some evidence of publication bias (Egger's test p=0·018, Begg's test p=0·007). For prospective studies, we calculated an overall relative risk of new psychotic disorders in daily smokers versus non-smokers of 2·18 (95% CI 1·23-3·85). Daily smokers developed psychotic illness at an earlier age than did non-smokers (weighted mean difference -1·04 years, 95% CI -1·82 to -0·26). Those with psychosis started smoking at a non-significantly earlier age than did healthy controls (-0·44 years, 95% CI -1·21 to 0·34).

INTERPRETATION

Daily tobacco use is associated with increased risk of psychosis and an earlier age at onset of psychotic illness. The possibility of a causal link between tobacco use and psychosis merits further examination.

FUNDING

NIHR Maudsley Biomedical Research Centre.

Skin ceramide alterations in first-episode schizophrenia indicate abnormal sphingolipid metabolism

There is considerable evidence for specific pathology of lipid metabolism in schizophrenia, affecting polyunsaturated fatty acids and in particular sphingolipids. These deficits are assumed to interfere with neuronal membrane functioning and the development and maintenance of myelin sheaths. Recent studies suggest that some of these lipid pathologies might also be detected in peripheral skin tests. In this study, we examined different skin lipids and their relation to schizophrenia. We assessed epidermal lipid profiles in 22 first-episode antipsychotic-naïve schizophrenia patients and 22 healthy controls matched for age and gender using a hexan/ethanol extraction technique and combined high-performance thin-layer chromatography/gas-chromatography. We found highly significant increase of ceramide AH and NH/AS classes in patients and decrease of EOS and NP ceramide classes. This is the first demonstration of specific peripheral sphingolipid alterations in schizophrenia. The results support recent models of systemic lipid pathology and in particular of specific sphingolipids, which are crucial in neuronal membrane integrity. Given recent findings showing amelioration of psychopathology using fatty acid supplementation, our findings also bear relevance for sphingolipids as potential biomarkers of the disease.

A genome-wide quantitative linkage scan of niacin skin flush response in families with schizophrenia

Schizophrenia patients frequently display reduced niacin flush responses, and similar characteristics are also observed in their nonpsychotic relatives. This study aimed to identify loci influencing flush response to niacin in schizophrenia using genome-wide quantitative linkage scan. In a nationwide sample of families with at least 2 siblings affected with schizophrenia in each family, 115 families that had at least 2 affected siblings with information on the niacin skin test were subjected to quantitative trait loci linkage analysis, either involving affected individuals only or the whole family. Nonparametric linkage z (NPL-Z) scores were calculated for each of 386 microsatellite markers spaced at an average of 9-cM intervals. Niacin patches of 3 concentrations (0.001 M, 0.01, and 0.1 M) were applied to forearm skin, and the flush response was rated at 5, 10, and 15 minutes, respectively, with a 4-point scale. Determination of genome-wide empirical significance was implemented using 1000 simulated genome scans. One linkage peak attaining genome-wide significance was identified at chromosomal region 14q32.12 for 0.01 M concentration at 5 minutes (NPL-Z scores = 3.39, genome-wide empirical P = .03) in affected individuals, and the corresponding linkage signal remained strong (NPL-Z scores = 2.87) for the analyses of the whole family. This locus is distinct from the chromosomal region identified in the previous genome-wide scan for the diagnosis of schizophrenia, and the signal was higher than the peak linkage signal in that study. These findings indicate that there might be modifier or susceptibility-modifier genes at 14q32.12 for schizophrenia-related attenuation of flush response to niacin.

Constructing endophenotypes of complex diseases using non-negative matrix factorization and adjusted rand index

Complex diseases are typically caused by combinations of molecular disturbances that vary widely among different patients. Endophenotypes, a combination of genetic factors associated with a disease, offer a simplified approach to dissect complex trait by reducing genetic heterogeneity. Because molecular dissimilarities often exist between patients with indistinguishable disease symptoms, these unique molecular features may reflect pathogenic heterogeneity. To detect molecular dissimilarities among patients and reduce the complexity of high-dimension data, we have explored an endophenotype-identification analytical procedure that combines non-negative matrix factorization (NMF) and adjusted rand index (ARI), a measure of the similarity of two clusterings of a data set. To evaluate this procedure, we compared it with a commonly used method, principal component analysis with k-means clustering (PCA-K). A simulation study with gene expression dataset and genotype information was conducted to examine the performance of our procedure and PCA-K. The results showed that NMF mostly outperformed PCA-K. Additionally, we applied our endophenotype-identification analytical procedure to a publicly available dataset containing data derived from patients with late-onset Alzheimer's disease (LOAD). NMF distilled information associated with 1,116 transcripts into three metagenes and three molecular subtypes (MS) for patients in the LOAD dataset: MS1 (n1=80), MS2 (n2=73), and MS3 (n3=23). ARI was then used to determine the most representative transcripts for each metagene; 123, 89, and 71 metagene-specific transcripts were identified for MS1, MS2, and MS3, respectively. These metagene-specific transcripts were identified as the endophenotypes. Our results showed that 14, 38, 0, and 28 candidate susceptibility genes listed in AlzGene database were found by all patients, MS1, MS2, and MS3, respectively. Moreover, we found that MS2 might be a normal-like subtype. Our proposed procedure provides an alternative approach to investigate the pathogenic mechanism of disease and better understand the relationship between phenotype and genotype.

Niacin subsensitivity is associated with functional impairment in schizophrenia

OBJECTIVE

Sensitivity to the skin flush effect of niacin is reduced in a portion of patients with schizophrenia. Though this peripheral physiological abnormality has been widely replicated, its relevance to neuropsychiatric manifestations of the illness has been unclear. The goal of this study was to determine if the niacin response abnormality in schizophrenia is associated with functional impairment.

METHODS

Following psychiatric assessment, a Global Assessment of Functioning (GAF) score was assigned to each of 40 volunteers with schizophrenia. For each subject, the blood flow responses to several concentrations of topical methylnicotinate were recorded. Blood flow was measured objectively, using laser Doppler flowmetry. From the dose-response data, EC(50) values were derived. GAF scores were assigned without knowledge of the participants' niacin response data.

RESULTS

There was a significant negative correlation between GAF scores and EC(50) values for methylnicotinate (Pearson r=-0.42; p=0.007).

CONCLUSIONS

Reduced niacin sensitivity is associated with greater functional impairment among patients with schizophrenia. These findings raise the possibility that a subset of schizophrenia patients possesses a biochemical abnormality that reduces niacin sensitivity in the skin and contributes to functional impairment from the disease.

Identification of a biological signature for schizophrenia in serum

Biomarkers are now used in many areas of medicine but are still lacking for psychiatric conditions such as schizophrenia (SCZ). We have used a multiplex molecular profiling approach to measure serum concentrations of 181 proteins and small molecules in 250 first and recent onset SCZ, 35 major depressive disorder (MDD), 32 euthymic bipolar disorder (BPD), 45 Asperger syndrome and 280 control subjects. Preliminary analysis resulted in identification of a signature comprised of 34 analytes in a cohort of closely matched SCZ (n=71) and control (n=59) subjects. Partial least squares discriminant analysis using this signature gave a separation of 60-75% of SCZ subjects from controls across five independent cohorts. The same analysis also gave a separation of ~50% of MDD patients and 10-20% of BPD and Asperger syndrome subjects from controls. These results demonstrate for the first time that a biological signature for SCZ can be identified in blood serum. This study lays the groundwork for development of a diagnostic test that can be used as an aid for distinguishing SCZ subjects from healthy controls and from those affected by related psychiatric illnesses with overlapping symptoms.

Alterations of niacin skin sensitivity in recurrent unipolar depressive disorder

INTRODUCTION

Skin flushing after niacin (methylnicotinate, vitamin B(3)) stimulation is a biological marker of availability of polyunsaturated fatty acids (PUFA). Decreased PUFA levels have been reported in depressive disorder, while add-on supplementation of omega-3 PUFA has been suggested to improve depressive symptoms. This study aimed to clarify whether a disturbance of niacin skin flushing occurs also in depression, and to identify patient characteristics for those who might benefit from PUFA supplementation.

METHOD

We studied 30 patients with recurrent unipolar depressive disorder during a major depressive episode (treated with antidepressants), and 30 healthy volunteers matched for age and gender. Aqueous methylnicotinate was applied in three dilution steps (0.001M, 0.01M, and 0.1M) onto the inner forearm skin. Skin flushing was assessed in three-minute intervals over 15min using optical reflection spectroscopy.

RESULTS

While there was no overall difference in skin flushing between patients and controls, niacin sensitivity was inversely correlated with severity of symptoms, and flush deficits were significantly associated with depressed mood, feelings of anxiety and somatic symptoms (loss of appetite and weight loss).

CONCLUSION

Results are suggestive of a subgroup of depressive patients characterised by a specific symptom cluster and disturbed niacin skin flushing.

Test-retest stability of the oral niacin test and electrodermal activity in patients with schizophrenia

In schizophrenia, well-replicated findings support an attenuated niacin skin-flush response. We have previously reported a delayed skin-flush after niacin ingestion and also an association between niacin non-responding and electrodermal non-responding in schizophrenia. The stability of the niacin and electrodermal tests was now studied in a test-retest design. An additional aim was to assess the association previously found. Twenty-three patients with schizophrenia underwent two sessions 3 months apart during which an oral niacin test was conducted and electrodermal activity was measured. Despite similar values for niacin outcome variables at the group level, there was high intraindividual variation. Test-retest stability for the oral niacin test was thus low, although a trend toward correlation for the dichotomous response criterion was found. Most electrodermal measures correlated between baseline and retest. A significant association between the tests was again found; niacin non-responding implied electrodermal non-responding, providing further support for a common underlying aberration in schizophrenia.

Evaluation of behavioral impulsivity and aggression tasks as endophenotypes for borderline personality disorder

Borderline personality disorder (BPD) is marked by aggression and impulsive, often self-destructive behavior. Despite the severe risks associated with BPD, relatively little is known about the disorder's etiology. Identification of genetic correlates (endophenotypes) of BPD would improve the prospects of targeted interventions for more homogeneous subsets of borderline patients characterized by specific genetic vulnerabilities. The current study evaluated behavioral measures of aggression and impulsivity as potential endophenotypes for BPD. Subjects with BPD (N=127), a non cluster B personality disorder (OPD N=122), or healthy volunteers (HV N=112) completed self report and behavioral measures of aggression, motor impulsivity and cognitive impulsivity. Results showed that BPD subjects demonstrated more aggression and motor impulsivity than HV (but not OPD) subjects on behavioral tasks. In contrast, BPD subjects self-reported more impulsivity and aggression than either comparison group. Subsequent analyses showed that among BPD subjects behavioral aggression was associated with self-reported aggression, while behavioral and self-report impulsivity measures were more modestly associated. Overall, the results provide partial support for the use of behavioral measures of aggression and motor impulsivity as endophenotypes for BPD, with stronger support for behavioral aggression measures as an endophenotype for aggression within BPD samples.