Gene expression can be determined by methylation, histone modification and RNA regulators (see epigenetics) and is important as the stepping stone between the genome and proteome – what a gene codes for as opposed to what, and whether a protein is made as a result.
The brain, its development, activity and health are all subject to the effects of gene expression. Many studies have revealed these connections. For example, specific epigenetic markers on the brain were found in victims of child abuse who committed suicide compared to suicide victims who had not experienced child abuse. Another finding was higher methylation of genes responsible for rRNA (ribosomal RNA) which makes ribosomes which make proteins. This results in less protein being made in the hippocampus part of the brain of people who also committed suicide before a separate study.
60 epigenetic markers were identified in a sample of patients with psychiatric conditions compared to healthy controls. The genes with these markers are involved in the signalling between brain cells. In people with schizophrenia, a lower methylation of a gene was discovered compared to healthy controls. This gene is involved in the early development of the brain, affecting learning into adolescence and adulthood.
Drugs such as cocaine can cause immediate but also long term changes in the brain that extend to hundreds of genes. These effects have been linked with the drug abuse, addiction and relapse seen in people who use these drugs.
Therefore, gene expression in the brain has effects on its development, which carries later implications for behaviour as well as mental illness.