Schizophrenia genetics is an interesting subject. When someone is diagnosed with schizophrenia, one of the first things people want to know is how they got it – did they get it from their parents; is schizophrenia hereditary?
It’s natural to ask these questions, but the answers may be unsettling. Scientists believe that schizophrenia involves genes and the environment but no single gene, or even known combination of genes, causes schizophrenia.
Schizophrenia and Genetics
For decades researchers have been looking at families to try to determine if schizophrenia was hereditary and if they could identify one or more schizophrenia genes. What researchers have found is that schizophrenia does indeed run in families, but this does not completely account for the cause of schizophrenia.
For example, parents and children share 50% of their genes but the risk of getting schizophrenia if one has a schizophrenic parent is only 6%. The following is your risk of developing schizophrenia based on a known relative with schizophrenia:1
- General population – 1%
- First cousins / uncles / aunts – 2%
- Nephews / nieces – 4%
- Grandchildren – 5%
- Half-sibling – 6%
- Sibling – 9%
- Children – 13%
- Fraternal twins – 17%
- Identical twins – 48%
Notably, identical twins share 100% of genes, yet their risk is only 48% if their twin has schizophrenia. This indicates that there is more than just genetics at work in schizophrenia.
Schizophrenia, Genes and the Environment
It’s thought that the difference then, is the environment. It is likely that a complex network of genes puts a person at risk for schizophrenia, but then environmental factors may be the deciding factor as to whether a person gets the illness. Similarly, a person may be at less risk of schizophrenia genetically, but due to greater environmental factors, they develop schizophrenia.
Environmental factors that are thought to increase the risk of schizophrenia include:
- Lead exposure during pregnancy
- Birth complications
- Extremely high stress experiences
- Drug use as a teenager
Specific Schizophrenia Genes
Scientists are working hard to identify which genes increase the heritability of schizophrenia. Unfortunately, scientists estimate that there are between 100 and 10,000 genes with brain-damaging mutations but how these genes work depends on the individual. There are over 280 genes currently identified as having been linked to schizophrenia.
Schizophrenia genes are sought after by population studies. Some studies look for common genes between large numbers of people, while others look for shared rare combinations of genes. Both types of studies, however, have only been successful at accounting for a tiny part of schizophrenia’s heredity. As Nicholas Wade of The New York Times put it,2
"Schizophrenia too seems to be not a single disease, but the end point of 10,000 different disruptions to the delicate architecture of the human brain."