Lack of support for the inability to taste phenylthiocarbamide as an endophenotypic marker in patients with schizophrenia and their first-degree relatives

Decrease in olfactory and taste receptor expression in the dorsolateral prefrontal cortex in chronic schizophrenia

We have recently identified up- or down-regulation of the olfactory (OR) and taste (TASR) chemoreceptors in the human cortex in several neurodegenerative diseases, raising the possibility of a general deregulation of these genes in neuropsychiatric disorders. In this study, we explore the possible deregulation of OR and TASR gene expression in the dorsolateral prefrontal cortex in schizophrenia. We used quantitative polymerase chain reaction on extracts from postmortem dorsolateral prefrontal cortex of subjects with chronic schizophrenia (n = 15) compared to control individuals (n = 14). Negative symptoms were evaluated premortem by the Positive and Negative Syndrome and the Clinical Global Impression Schizophrenia Scales. We report that ORs and TASRs are deregulated in the dorsolateral prefrontal cortex in schizophrenia. Seven out of eleven ORs and four out of six TASRs were down-regulated in schizophrenia, the most prominent changes of which were found in genes from the 11p15.4 locus. The expression did not associate with negative symptom clinical scores or the duration of the illness. However, most ORs and all TASRs inversely associated with the daily chlorpromazine dose. This study identifies for the first time a decrease in brain ORs and TASRs in schizophrenia, a neuropsychiatric disease not linked to abnormal protein aggregates, suggesting that the deregulation of these receptors is associated with altered cognition of these disorders. In addition, the influence of antipsychotics on the expression of ORs and TASRs in schizophrenia suggests that these receptors could be involved in the mechanism of action or side effects of antipsychotics.

An examination of associations between the inability to taste phenylthiocarbamide (PTC) and clinical characteristics and trait markers in first-episode, nonaffective psychotic disorders

Research findings are mixed as to whether or not the inability to taste phenylthiocarbamide (PTC) might represent an endophenotypic trait marker for schizophrenia. We hypothesized associations between PTC-tasting status and select clinical characteristics and trait markers in patients with psychotic disorders that, if present, would provide support for the inability to taste PTC as a trait marker. In a first-episode psychosis sample (n=93), we measured PTC tasting, family history of psychosis, age at onset of prodrome and psychosis, severity of positive and negative symptoms, global impairment in functioning, neurological soft signs, and four neurocognitive domains (verbal learning/memory, visual learning/memory, verbal working memory, and spatial working memory). Associations between PTC-non-tasting and clinical/neurocognitive variables were examined with χ(2) tests and independent samples t tests. Among participants, 67.7% tasted PTC in comparison to a strip of control paper, and 25.8% were non-tasters. Tasters and non-tasters did not show statistically significant differences with respect to family history, age at onset, severity of symptoms, neurological soft signs, or the four neurocognitive domains. In conjunction with other findings, it is unlikely that PTC-non-tasting is a trait marker of schizophrenia, though a conclusive study is warranted.

Phenylthiocarbamide (PTC) perception in ultra-high risk for psychosis participants who develop schizophrenia: testing the evidence for an endophenotypic marker

Reports suggesting that schizophrenia participants are more likely to be phenylthiocarbamide (PTC) non-tasters when compared to controls have recently been controversial. If supported, a genetic-based phenotypic variation in PTC taster status is implicated, suggesting a greater illness risk for those participants with recessive alleles for the TAS2R38 receptor. Should PTC insensitivity be a schizophrenia endophenotype, then it would be expected in follow-up of ultra high-risk for psychosis participants who later develop schizophrenia (UHR-S). UHR-S was hypothesised to show reduced PTC sensitivity compared to those who were previously at risk, but did not transition (UHR-NP). PTC perception was assessed in 219 UHR participants at long-term follow-up, of whom 53 had transitioned to psychosis (UHR-P) during the follow-up period. Fifteen of the 219 participants were diagnosed with schizophrenia. Seventy-eight had a family history of psychotic disorder. No differences in PTC taster status were found in UHR participants based upon transition to psychosis status, schizophrenia diagnosis, or family history of schizophrenia. This report indicates that schizophrenia development among UHR participants is not associated with PTC tasting deficits and fails to support previous findings that inability to detect the bitter taste of PTC is a schizophrenia endophenotype.