Even as the genetic studies on schizophrenia released this week illustrate our progress toward the ultimate goal of personalized medicine, they also bring to mind the challenges that still lie ahead.
All three studies focus on identifying the genetic bases of schizophrenia, a mental disorder characterized by hallucinations, delusions and the decreased ability to plan and organize. These symptoms typically manifest during a patient’s late teens or early 20s.
One study led by Cardiff University researcher Michael O’Donovan identified single nucleotide gene variants (SNPs) associated with schizophrenia. As detailed in the journal Nature Genetics, the researchers started with 12 variants, narrowed the list to six after replicating the tests on several thousand study participants and finally identified three SNPs associated with the disease.
Unfortunately, the variant ultimately found to have the strongest association with schizophrenia – rs1344706 – is not included in 23andMe’s database. Yet the SNP’s effects are so small – it increases the chances of schizophrenia by only about 12 percent among people who have the higher risk version – that it offers limited information.
The other studies – one from the International Schizophrenic Consortium and one from deCODE and the SGENE Consortium – which appear in the journal Nature opted to look for genetic associations by checking copy number variants, DNA segments with deletions or duplications that can be inherited.
One group found three deletions – one on chromosome 1 and two on chromosome 15 – that showed up in a few dozen people out of thousands sampled and were more common among people with schizophrenia. The other group identified two of those three deletions. They also found that people with schizophrenia tend to have more rare copy number variants – both duplications and deletions – in their genomes compared to people without the disease.
“This work opens up an entirely new way to think about schizophrenia and eventually will suggest new avenues for researching effective therapies for the sake of patients and families suffering from this terrible disorder,” said International Schizophrenic Consortium member and study co-author Pamela Sklar in a statement.
One of the frustrations schizophrenia researchers have encountered is that while the disease is fairly common – affecting one percent of Americans – the genetic basis of schizophrenia has been difficult to pinpoint. One as-yet unsolved mystery is how the disease, which has a high degree of heritability, is as prevalent as it is when correlated with the fact that people who have schizophrenia and other similar mental disorders have fewer offspring.
These studies suggest that very rare gene mutations might play more of a role in the disease than had previously been supposed. That’s valuable information for scientists, and may explain why the genetics of schizophrenia have been so difficult to figure out. But it also suggests that it will take much more research to understand the genetic risk factors underlying schizophrenia than many other diseases.