Genetic explanation of Schizophrenia CLINICAL: CONTENT

Genetic inheritance schizophrenia is a heritable condition that passes down from one generation to the next Twin, adoption and familial studies clearly points to a genetic component in schizophrenia this explanation looks at how genes affect brain development and may be partly responsible for symptoms of schizophrenia.

No one gene for schizophrenia Specific genes have not been shown to directly cause schizophrenia, BUT, numerous studies have shown a variety of chromosomes to be involved in the inheritance of schizophrenia

Which Chromosomes? chromosomes thought to contain these genes associated with increased risk of schizophrenia: 22, 1, 18, 15, 14, 13, 12, 11, 10, 8, 6, 5, 3 many specific regions on these chromosomes have also been identified Some of the strongest evidence to date suggests the importance of chromosomes 13 and 6.

700 genes associated with schizophrenia Numerous individual genes are thought to increase the chance of an individual developing schizophrenia These include genes that regulate neurochemicals such as dopamine and serotonin Currently, research suggests around 700 genes that are associated with schizophrenia, (Write, 2014).

Chromosome 22 and DiGeorge Syndrome Potentially there may be subsets of schizophrenia, where specific symptoms are triggered by different gene abnormalities the deletion of a specific region of chromosome 22, containing around 30-40 genes, causes a syndrome known as DiGeorge as many as 1 in 4 people with DiGeorge develop schizophrenia.

The COMT gene A specific gene called ‘COMT’ found on region 22q11.21) provides instructions for the creation of the enzyme (catechol-O-methyltransferase) which breaks down neurotransmitters such as dopamine

COMT deletions deletion of the COMT gene would mean dopamine levels are not controlled effectively If this happens in regions such as the frontal lobes, hallucinations and the characteristic loss of reality associated with psychosis can result

DISC1 Abnormality the gene “Disrupted-in-Schizophrenia 1” or DISC1 is important for brain development and the neurotransmitter GABA People with DISC 1 abnormalities are 1.4 times more likely to develop schizophrenia than people without this abnormality Remember GABA is important in regulating dopamine levels in the meso-limbic pathways and links to positive symptoms

Liability not certainty schizophrenia certainly seems to have a heritable component But what is inherited is a liability rather than a certainty of developing the condition e.g. the person has heightened chance (predisposition) IF, in addition, they are exposed to a certain set of environmental risk factors