cytosine can induce rapid gene expression. Demethylation appears to occur by a DNA repair process involving the GADD45G protein. Psychiatric disorders Classification and diagnosis of neuropsychiatric illnesses are symptom-based, often exhibiting similar brain activity. Furthermore, the development of psychiatric illnesses is dependent of both genetics and environmental factors, as such, predictive risk assessment of diseases such as schizophrenia has lagged behind other prevalent illnesses. Using IEGs as a marker, animal models have identified altered levels of Arc,effecting synaptic activities, and EGR1, involved in memory trace encoding, in the case of depression. Similarly, other neuropsychiatric illnesses such as schizophrenia also exhibit altered IEG expression with recent studies showing a correlation of low expression of EGR3, a transcription factor downstream of NMDARs, in patients exhibiting schizophrenia. As such, IEGs are crucial markers in evaluating neuronal activity in the context of psychiatric illness with its expression pattern shaped by environmental and genetic factors. Potential therapeutic applications Human Cytomegalovirus (HCMV) Human Cytomegalovirus is a prevalent beta herpesvirus that remains in the latent state, going unnoticed in healthy individuals with serious consequences if the individual is immunocompromised. The virus cycles in and out of the latent state and is characterized by different gene expression regions: immediate-early (IE), early, and late. Conventional anti-viral treatments such as Ganciclovir use nucleoside analogs to target the early events of the viral replication cycles, however, these approaches are prone to developing resistance. Targeting IE1 and IE2 are thought to be crucial in regulating the pathogenesis of HCMV and retaining the virus in the latent state. Viral proteins derived from IE1 and IE2 regulate viral latency by controlling subsequent expression of early and late genes. Silencing of IE gene expression through antisense oligonucleotides, RNA interference, and gene-targeting ribosomes have been investigated for therapeutic applications. Alternatively, the rise of CRISPR technology allows for precise DNA editing that can knockout HCMV genes responsible for IE transcription. DNA targeting is more effective in latent infections, in which viral mRNA is absent or at a low concentration. Small molecule chemical inhibitors are also being investigated that target epigenetic factors and signaling proteins involved in IE expression. References External links Activation of Immediate Early Genes by Drugs of Abuse a monograph published by the National Institute on Drug Abuse Genes