New research reveals why animals don’t get schizophrenia and humans do

While many animal species suffer from psychiatric symptoms, schizophrenia is specifically human. A new study has revealed that human speech and language play a role in the disease.

New research led by Dr. Joel Dudley from Mount Sinai hospital in New York has shown that psychosis in humans may be due to the fact that our brains have evolved to be larger and more complex than those of non-human species.

Schizophrenia affects one percent of adults and can be potentially lethal. It is also known to be heavily genetic.

The study examined a segment of the human genome called human accelerated regions, or HAR’s. HARs are short stretches of DNA that underwent fast evolution in humans when we split from chimpanzees. HARs often help regulate neighboring genes.

In order to determine whether there is a link between schizophrenia and HARs, Dudley and his team culled data from the Psychiatric Genomics Consortium, which had previously conducted a study identifying genetic variants associated with schizophrenia. They found that HARS play a role in regulating the genes associated with the disease.

The scientists then turned to gene expression profiles, which reveal where and when in the body certain genes are active. HAR-associated schizophrenia genes are found in areas of the genome that influence genes in the prefrontal cortex (PFC), a part of the brain involved in higher order thinking. When the functions of the PFC are impaired, it is thought to contribute to psychosis.

These genes are also crucial in the synaptic transmission of the neurotransmitter GABA, which is an inhibitor or regulator of neuronal activity by suppressing dopamine, which is thought to be involved in schizophrenia. When GABA malfunctions, dopamine runs wild. This contributes to hallucinations and delusions, which are symptoms of psychosis.

“The ultimate goal of the study was to see if evolution may help provide additional insights into the genetic architecture of schizophrenia so we can better understand and diagnose the disease,” said Dudley to Scientific American.

The research also shows how schizophrenia arose in humans in the first place; with higher cognition, there is more that can go wrong in the brain.

“The emergence of human speech and language bears a relationship with schizophrenia genetics, and incidentally also autism. Indeed, language dysfunction is a feature of schizophrenia, and GABA is critical to speech, language and many other aspects of higher-order cognition,” Dudley said.

The researchers pointed out that they still haven’t found any “smoking gun genes” that definitively cause the disease, as the genetics behind schizophrenia is highly complex.