healthHealth and Medicine

Almost 80% Of Schizophrenia Risk Is Down To Just One Factor


Robin Andrews

Science & Policy Writer

It's (almost) all in the genes. Konstantin Faraktinov/Shutterstock

Schizophrenia, a type of psychosis, is something that can be as debilitating as it’s poorly understood. At present, it’s uncertain how much of it is down to genetics, and how much is down to environmental factors.

A new study, published in the journal Biological Psychiatry, has now claimed that nearly 80 percent of the risk factor for schizophrenia is genetic. Science, of course, is decided by consensus, not just a single study, so it’s important not to blow these results out of proportion. So what’re the facts behind the scary-sounding headlines?


The study, which was carried out by researchers from the Center for Neuropsychiatric Schizophrenia Research at Copenhagen University Hospital, took an interesting approach to identifying the causes of this condition: it used twins, along with a database on psychiatric patients. Known as a twin cohort study, this piece of research actually used both identical twins and non-identical twins.

As marvelously explained by the NHS, these studies provide unique comparisons when it comes to genetics. Identical twins have 100 percent of their genome in common, whereas non-identical twins share roughly 50 percent of their genes.

If – assuming their lifestyles are similar enough – identical twins are shown to have more similar health statuses than non-identical twins, this suggests that their genetics are having a powerful influence over their lives, compared to environmental factors.

Indeed, when it comes to schizophrenia, it’s previously been shown that it affects both members of an identical twin pair in 41 to 61 percent of cases. This drops to 0 to 28 percent in non-identical twin cases. Overall, based on multiple genetic analyses, it appears that schizophrenia is 81 percent down to heritable genes.

Schizophrenia is a complex disorder with multiple symptoms, including delusions and hallucinations. pathdoc/Shutterstock

This new study performed a cutting-edge statistical analysis on nearly 32,000 twin pairs born up to the year 2000 – some identical, some not. They found that roughly 1 percent of them had developed schizophrenia, and 2.5 percent had schizophrenia-like disorders.

In terms of identical twins, if one was afflicted, then there was a 33 percent chance the other would be too. For non-identical twins, this probability plunged to between 7 and 9 percent. Based on this – and without identifying the genes responsible – the team calculated that 73 percent of schizophrenia-like disorders, and 78 percent of schizophrenia cases, were down to genetics.

One major problem with this study, and others like it, is that environmental factors are assumed to be insignificant, and do not impact on the genetic makeup of a person. This means that the role of genes is being overestimated, but it’s not clear by how much.

Ultimately, though, this research looks to confirm what was already known: conditions that manifest mentally tend to have a genetic (or neurological) basis more than one may assume.


[H/T: NHS]


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