Niacin skin test response in dyslexia

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.

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.

The impact of PLA2G4A and PTGS2 gene polymorphisms, and red blood cell PUFAs deficit on niacin skin flush response in schizophrenia patients

We investigated the etiology of the attenuated niacin skin flush response in schizophrenia patients. Skin response to topical niacin of 0.1M, 0.01 M, 0.001 M, and 0.0001 M concentrations was rated using method of volumetric niacin response (VNR) and correlated to two functional A/G polymorphisms in genes: phospholipase A2 group IVA (BanI of the PLA2G4A), and rs689466 of the prostaglandin synthase-2 (PTGS2). We further tested the possible correlation between niacin response and fatty acid (FA) content of red blood cells (RBCs). We detected statistically significant but weak impact of both polymorphisms on niacin flush response in schizophrenia patients. The dosage of the G alleles of both polymorphisms was associated with higher VNR values, although each polymorphic variant accounted for only 1% of the overall flush response variability. Regarding FA content, both n-3 and n-6 polyunsaturated FAs (PUFAs) were significantly reduced in the patient group, but an association with niacin sensitivity was not detected.

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.