The onset of psychosis is the consequence of complex interactions between genetic vulnerability to psychosis and response to environmental and/or maturational changes. Epigenetics is hypothesized to mediate the interplay between genes and environment leading to the onset of psychosis. We believe we performed the first longitudinal prospective study of genomic DNA methylation during psychotic transition in help-seeking young individuals referred to a specialized outpatient unit for early detection of psychosis and enrolled in a 1-year follow-up. We used Infinium HumanMethylation450 BeadChip array after bisulfite conversion and analyzed longitudinal variations in methylation at 411 947 cytosine-phosphate-guanine (CpG) sites. Conversion to psychosis was associated with specific methylation changes. Changes in DNA methylation were significantly different between converters and non-converters in two regions: one located in 1q21.1 and a cluster of six CpG located in GSTM5 gene promoter. Methylation data were confirmed by pyrosequencing in the same population. The 100 top CpGs associated with conversion to psychosis were subjected to exploratory analyses regarding the related gene networks and their capacity to distinguish between converters and non-converters. Cluster analysis showed that the top CpG sites correctly distinguished between converters and non-converters. In this first study of methylation during conversion to psychosis, we found that alterations preferentially occurred in gene promoters and pathways relevant for psychosis, including oxidative stress regulation, axon guidance and inflammatory pathways. Although independent replications are warranted to reach definitive conclusions, these results already support that longitudinal variations in DNA methylation may reflect the biological mechanisms that precipitate some prodromal individuals into full-blown psychosis, under the influence of environmental factors and maturational processes at adolescence.

Pharmacological, genetic and expression studies implicate N-methyl-D-aspartate (NMDA) receptor hypofunction in schizophrenia (SCZ). Similarly, several lines of evidence suggest that autism spectrum disorders (ASD) could be due to an imbalance between excitatory and inhibitory neurotransmission. As part of a project aimed at exploring rare and/or de novo mutations in neurodevelopmental disorders, we have sequenced the seven genes encoding for NMDA receptor subunits (NMDARs) in a large cohort of individuals affected with SCZ or ASD (n=429 and 428, respectively), parents of these subjects and controls (n=568). Here, we identified two de novo mutations in patients with sporadic SCZ in GRIN2A and one de novo mutation in GRIN2B in a patient with ASD. Truncating mutations in GRIN2C, GRIN3A and GRIN3B were identified in both subjects and controls, but no truncating mutations were found in the GRIN1, GRIN2A, GRIN2B and GRIN2D genes, both in patients and controls, suggesting that these subunits are critical for neurodevelopment. The present results support the hypothesis that rare de novo mutations in GRIN2A or GRIN2B can be associated with cases of sporadic SCZ or ASD, just as it has recently been described for the related neurodevelopmental disease intellectual disability. The influence of genetic variants appears different, depending on NMDAR subunits. Functional compensation could occur to counteract the loss of one allele in GRIN2C and GRIN3 family genes, whereas GRIN1, GRIN2A, GRIN2B and GRIN2D appear instrumental to normal brain development and function.