Identical twins study provides rare insight into schizophrenia

A Western University study on identical twins is uncovering just how genetically different schizophrenia can be — a discovery that could possibly help doctors diagnose and treat the devastating mental disorder more effectively.

Over two decades, Western researchers studied two very rare sets of identical twins. In each pair, one twin had schizophrenia and the other did not.

“These are the exceptional cases,” said Shiva Singh, a Western science professor and one of the study’s authors.

The findings have “a lot of potential,” he said.

The two sets of twins were in their 20s when they started participating and are now 42 and 53 years old. Singh and his team chose the two pairs from 73 sets of twins.

The researchers mapped out the complete genetic roadmap of each twin and their biological parents to compare the results, a costly and labour-intensive undertaking.

Scientists found the twins’ genomes weren’t exactly identical. The siblings with schizophrenia had several different gene mutations.

“The bottom line is no two patients affected with schizophrenia have identical mutations,” Singh said. “Therefore, the same medication could not be used to treat these patients.”

The study by Singh, Western researcher Richard O’Reilly and Christina Castellani from Johns Hopkins University in Baltimore was carried out at the London campus.

The researchers say the schizophrenia-contributing genetic abnormalities happen independently in individuals as they grow and age.

“The challenge was finding what mutations are making one individual have the disease and the other individual unaffected,” Singh said.

Schizophrenia isn’t caused by any single DNA abnormality, but the combination of mutations across more than 100 different genes — making almost every case genetically unique.

Singh said scanning a patient’s genome sequence will help doctors detect the mutations that are contributing to the mental disorder that affects more than 21 million people worldwide.

“Diagnosis of schizophrenia is not easy, and it is all based on the behaviour patterns,” Singh said.

“If we have this, then based on the mutations, you can say that a person has schizophrenia. Biologically, a clinical diagnosis.”

In the future, doctors could also tailor treatment and medication based on the results of the genetic screening.

“Now the treatment is really hit and miss. You try medication number one and if it doesn’t work, then you try medicine number two, then number three,” Singh said.

“It’s really frustrating for the patient and physician because they’re shooting in the dark.”

The study was published in the November edition of Clinical and Translational Medicine.