br Material and methods br Discussion
Material and methods
Discussion First, we investigated cannabis use, and results showed that the lifetime prevalence of cannabis use in our sample was 29.63%, with a significant difference between males (73.8% of the abusers) and females (26.2%). Moreover, the mean age and age at onset were significantly lower in patients with a history of cannabis use, compared to patients without history of cannabis use. These results are consistent with the previously reported socio-demographic characteristics of cannabis abuse or dependence in schizophrenia, suggesting that cannabis using patients are younger and more likely males (Dervaux et al., 2003; Large et al., 2011), as well as an association between cannabis use and earlier onset (Arseneault et al., 2002; Arseneault et al., 2004). No other significant differences between patients who reported cannabis use and those who did not use cannabis were observed for the other clinical and demographic variables analyzed. Moreover, when examining the relationship between cannabis use and cognitive measures, no significant differences emerged between the two groups. This finding is in line with other studies in patients with schizophrenia, showing no differences in cognitive abilities between cannabis users and non-users (Bahorik et al., 2014; Scholes and Martin-Iverson, 2009). However, it is to notice that contrasting results have also been reported, suggesting a negative effect of cannabis on cognition (Ringen et al., 2010). Still, it is to notice that this result may depend on the small and unbalanced sample, as well as on other factors mediating the relationship between cannabis and neurocognition. Among these, the interaction with COMT Val158Met polymorphism, which is the focus of this study, may have contributed. Interestingly, we found a significant interaction effect of COMT Cathepsin K Activity Fluorometric Assay Kit australia and cannabis use for two core cognitive domains, namely verbal fluency and processing speed. In details, the analysis on verbal fluency showed a significant difference between COMT Val/Val homozygous and Met carriers with cannabis use, the latter performing significantly better. A similar finding was also observed for processing speed, with a significantly higher performance among COMT Met carriers compared to Val/Val, more pronounced in patients with history of cannabis use. These results, while supporting previous literature (Prata et al., 2009) concerning the influence of COMT genotype on prefrontal cognition, innovatively highlight a significant interaction between COMT genotype and cannabis use on two key domains: verbal fluency and processing speed. Indeed, semantic and phonological fluency tasks are the most suitable tests for verbal skills in schizophrenia, eliciting associative exploration and retrieval of words based on certain conceptual categories and phonological characteristics, respectively. These measures depend upon comparable demands on executive or supervisory processes, as both require efficient organization of verbal retrieval and recall, effortful self-initiation, self-monitoring aspects of cognition, and inhibition of responses when appropriate (Henry and Crawford, 2005). The “Symbol Coding” subtest, used to assess processing speed, involves integration of multiple component operations, relying mostly on effective connectivity among distributed brain networks, rather than specific subprocesses (Dickinson et al., 2007). Symbol coding yields the largest impairment documented in the schizophrenia clinical neuropsychology literature. Digit symbol coding tasks are useful tools in quantifying a form of cognitive impairment that is a central, reliable feature of the illness, and are more discriminating of diagnostic group status than other cognitive measures that have been the focus of the recent schizophrenia literature. Coding task performance distinguished individuals who would go on to develop schizophrenia years later from their own siblings who would not develop the disease. This measure has also a graded relationship with illness risk, severity, and disability in schizophrenia and it appears to index poor prognosis and functional disability within the patient group (Dickinson et al., 2007).