Family history of schizophrenia: understanding the risk

The NHS describes schizophrenia as a long-term mental health condition that causes a range of different psychological symptoms, and says doctors often describe it as a type of psychosis, meaning the person may not always be able to distinguish their own thoughts and ideas from reality. It does not mean a split personality, and the NHS says it does not usually cause someone to be violent.

Symptoms can include hallucinations, such as hearing or seeing things that do not exist outside the mind, delusions, which are unusual beliefs not based on reality, muddled thoughts and speech, losing interest in everyday activities, not looking after yourself, wanting to avoid people and feeling disconnected from your feelings.

The NHS says schizophrenia tends to run in families, but no single gene is thought to be responsible. It is more likely that different combinations of genes make people vulnerable to it, and having these genes does not necessarily mean you will develop the condition.

The evidence that the condition is partly inherited comes from studies of twins. The NHS says that identical twins share the same genes and that when one develops schizophrenia the other has a 1 in 2 chance of developing it too, even if they were raised separately. In non-identical twins, who have different genetic make-ups, the figure is 1 in 8. The chance in the general population is about 1 in 100.

Those figures show two things at once. A shared genetic make-up clearly raises the chance, but even in identical twins the chance is only about half, which tells us genes are not the only factor.

The NHS describes several further things linked with a higher likelihood of schizophrenia. NHS inform groups them similarly under genetics, differences in brain structure and chemicals, complications in pregnancy or after birth, and trauma including sexual and emotional abuse and neglect.

• Subtle differences in brain development and structure, which are not seen in everyone with schizophrenia and can occur in people without a mental illness.

• Differences in neurotransmitters such as dopamine, which medicines that lower these levels can help in some people.

• Complications before and during birth, including low birthweight, premature labour and a lack of oxygen during birth.

The NHS says triggers are things that can cause schizophrenia to develop in people who are at risk. Stressful life events such as bereavement, losing a job or home, divorce, the end of a relationship, and physical, sexual or emotional abuse are listed as the main psychological triggers. The NHS stresses these experiences, although stressful, do not cause schizophrenia, but can trigger it in someone already vulnerable.

It also says studies show drug use, particularly cannabis, cocaine, LSD or amphetamines, can increase the risk of schizophrenia, psychosis or a similar illness. Teenagers and young adults who use cannabis regularly are more likely to develop schizophrenia in later adulthood, and the risk may be higher with stronger forms of cannabis. If someone has already had episodes of psychosis, drug use can cause a relapse or stop symptoms from getting better.

For someone with a relative who has schizophrenia, avoiding drug use, especially cannabis, is therefore a practical step linked in these sources to lower risk.

The NHS says there is no single test for schizophrenia. It is usually diagnosed after an assessment by a mental health care professional such as a psychiatrist. It is usually treated with a combination of medicine and therapy tailored to each individual, in most cases antipsychotic medicines and cognitive behavioural therapy, with help from a community mental health team.

Many people recover, although they may have periods when symptoms return. The NHS says that if schizophrenia is well managed it is possible to reduce the chance of severe relapses by recognising the signs of an acute episode, taking medicine as prescribed and talking to others about the condition.