Schizophrenia is actually eight distinct disorders, say scientists after genome study

Schizophrenia might in fact be a group of related but distinct genetic disorders - a study has
identified specific gene clusters that can be linked to eight clinically different
types of the psychiatric illness.

The findings could have implications for better targeted diagnosis and
treatment for the condition.

'Genes don't operate by themselves', said Professor
Robert Cloninger, one of the study's senior investigators. 'They function
in concert much like an orchestra, and to understand how they're working, you
have to know not just who the members of the orchestra are but how they
interact'.

The researchers at Washington University School of Medicine in the USA compared
the DNA of 4,200 people with and 3,800 people without schizophrenia. They
looked at areas of the genome where the DNA differed by one simple unit, these
changes being known as single nucleotide polymorphisms (SNPs).

Taking a new approach, the researchers first identified sets
of interacting SNPs that occur within individuals, not taking clinical status
into account. They then looked at the risk of schizophrenia associated with
each of these SNP sets and replicated their findings using two independent
samples. Ultimately, they were able to test whether specific SNP sets were
associated with distinct sets of clinical symptoms.

Surprisingly, they found that the symptom groups they
created consisted of eight distinct schizophrenic disorders that were
characterised by specific underlying genetic conditions.

For example, patients who displayed disorganised speech and
behaviour were specifically associated with a set of genetic variations that carry, the researchers claim, 'a 100 percent risk of schizophrenia'.

'In the past, scientists had been looking for associations
between individual genes and schizophrenia', said Dr
Dragan Svrakic, who co-authored the study. 'When one study would identify
an association, no one else could replicate it. What was missing was the idea
that these genes don't act independently. They work in concert to disrupt the
brain's structure and function, and that results in the illness'.

The idea that schizophrenia is a wholly or even predominantly genetic condition does not have universal support among psychiatrists. All the same, the
researchers hope that one day schizophrenia will be regarded in much the same
way as breast cancer is today - as not one disease but several, driven by
different genes.

'Doctors today have tests to predict a
woman's risk of some types of breast cancer, and other tests that help them select
the most effective drugs', said a report in USA Today, paraphrasing Professor Cloninger.

'Those
sorts of tests could be extremely helpful for people with schizophrenia, who
often try two or three drugs before finding one that's effective'.

The study was published in The American Journal of
Psychiatry.