One of the myths surrounding schizophrenia is that it is largely considered a genetic disease and several genetics studies have been funded over the years. However, recent scientific findings challenge this theory.

In the 60s, the genetics basis of schizophrenia was listed among other potential causes, such as family interactions, and textbooks noted that “the relative importance of genetic factors still is far from clear”.² By the early 21st century, though, these theories had dominated and it was believed that schizophrenia “is an undoubtedly genetic disorder”. Geneticists in the 90s had even suggested that “a strong possibility that most or all of the remaining small proportion of variance can be explained by non-transmissible changes in gene structure or expression”, meaning that schizophrenia might be 100% genetic with environmental factors playing little or no role.¹ However, studies in the following years, starting with the Human Genome Project in 2003, followed by genome-wide association studies (GWAS) did not yield the results expected with regards to the genetic basis of schizophrenia.² Therefore, research indicated that although genes do appear to play a role in schizophrenia, they are not entirely accountable for it.

Dr Torrey and Dr Yolken, from the Stanley Medical Research Institute and the Johns Hopkins Medical Center in the USA, respectively, have recently published a review article pointing out that the involvement of genetics in schizophrenia has been overestimated.² The researchers analysed heritability data from population-based studies in twins, and found that the heritability of schizophrenia, meaning how much of the variability of a particular trait is due to genetics as compared to environmental factors, is much lower than genetic researchers claimed. In particular, they estimated the heritability of schizophrenia to be 28%, much less than the 80-85% previously assumed.

The two researchers have worked on understanding the causes of schizophrenia for many years. Their work identified that toxoplasmosis, an infection by the parasite Toxoplasma gondii, is related to the onset of the disease.³ Notably, they reported that the association of toxoplasmosis with schizophrenia may have contributed to the theory about the genetic basis of schizophrenia, because toxoplasmosis clusters in families, thus giving rise to pseudo-genetic characteristics of the illness.

In conclusion, genetic factors may play a role in schizophrenia, but they are not as significant as previously anticipated. According to the data, genetics appear to play approximately the same role as in other mental disorders and physical diseases. Through the pioneering work of Dr Torrey, Dr Yolken and others there is hope that the focus will shift to environmental and other factors that may be accountable for the disease, beyond genetic theories, thus opening new avenues for the development of schizophrenia therapeutics.