The first genetic analysis of schizophrenia in a black African population, which drew on DNA provided by South Africans of Xhosa descent, has found that people with the disorder are more likely to carry rare but damaging genetic mutations than those who are well.

The research sheds new light on the nature of schizophrenia, and scientists hope the knowledge will ultimately help develop new treatment for people all over the world, not just those of Xhosa descent.  Schizophrenia is a severe and potentially debilitating brain disorder, characterised by hallucinations and confused speech or behaviour. It affects 0.3%-0.7 % of the world’s population.

Ironically, although the genetic material of Africans is richer than that of other population groups, African populations are the least studied. Africans have the greatest genetic diversity because Africa is the ancestral home to all people. As small bands of people migrated out of Africa, they took only a subset of the available genetic diversity with them. Thus other population groups, such as Caucasians, today have less genetic diversity than people of African descent.

The greater the genetic diversity among people involved in studies into the links between genetics and disease, the greater the chance of identifying meaningful variations that affect the risk of developing a disease, or the way subjects respond to treatment. The fact that most studies examining the genetics of disease have been conducted with Caucasians means there are huge gaps in scientists’ understanding of the genetics of many diseases, including schizophrenia, said UCT head of psychiatry and mental health Dan Stein, and co-author of a paper describing the research, published in the peer review journal Science, on Thursday.

The researchers studied DNA sequences from more than 1,800 Xhosa people, half of whom had been diagnosed with schizophrenia. They found those who had schizophrenia had rare mutations that disrupt genes involved in the organisation and functioning of brain synapses, which are responsible for communication among neurons. The brain’s learning, memory and organisational functions all hinge on the way these synapses operate.

“We’ve known for some time now that genetic factors contribute to schizophrenia, but there has been debate about the nature of these genetic factors.  We found that rare mutations seen in only a few individuals in the whole population, but which severely impact brain function, are important.

“It is possible that by understanding these specific genes better we can develop new treatment targets down the line,” he said.

Stein said there was a pressing need to do more genetic research on African populations, particularly for mental disorders. “There are currently major health inequalities across the world, and as genetics starts to increasingly be used in clinical care, there is a risk that exclusion of African populations from genetics research will further increase health inequalities,” he said.


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