The genetic origins of schizophrenia

An introduction to Schizophrenia

Schizophrenia is a mental disease, a group of psychotic disorders that interfere with thinking and responsiveness. It is a disease of the brain, like Alzheimer’s and Parkinson’s diseases. A person with schizophrenia has deteriorated occupational, interpersonal, and self-supportive abilities. Schizophrenia is known as one of the most disabling and emotionally devastating illnesses among mankind. But this disease has been misunderstood for so long that it has received relatively little attention and its victims have been undeservingly stigmatized. Schizophrenia is not a split personality, a common idea about what schizophrenia is, but it is a rare and very different disorder usually common among young people.

The word schizophrenia comes from Greek origins “schizein” and “frenos” meaning split mind. (Wikipedia contributors. “Schizophrenia.” Wikipedia, the Free Encyclopedia.)

Studies on the genetics of schizophrenia show that schizophrenia has a genetic component. While in general population its lifetime prevalence is %1, the risk of schizophrenia is higher in relatives of schizophrenic patients. Third-degree relatives (e.g. cousins) share their %12.5 genes and carry a %2 risk for schizophrenia. Second-degree relatives (e.g. half brothers) share their %25 genes and carry %6 risk for schizophrenia. Many First degree relatives (e.g. siblings, fraternal twins) share their %50 and carry %9 risk for disease.

But schizophrenia does not imply a split minded personality instead it describes a person who believes two different reality at the same time. While a normal person can only be able to believe in one reality, a schizophrenic person can adopt a second reality which can not be understood by a man in mental health. Genetics constitute a crucial risk factor to schizophrenia. In the last decade, molecular genetic research has produced novel findings, infusing optimism about discovering the biological roots of schizophrenia. However, the complexity of the object of inquiry makes it almost impossible for non-specialists in genetics (e.g., many clinicians and researchers) to get a proper understanding and appreciation of the genetic findings and their limitations. This study aims at facilitating such an understanding by providing a brief overview of some of the central methods and findings in schizophrenia genetics, from its historical origins to its current status, and also by addressing some limitations and challenges that confront this field of research. In short, the genetic architecture of schizophrenia has proven to be highly complex, heterogeneous and polygenic. The disease risk is constituted by numerous common genetic variants of only very small individual effect and by rare, highly penetrant genetic variants of larger effects. In spite of recent advances in molecular genetics, our knowledge of the etiopathogenesis of schizophrenia and the genotype-environment interactions remain limited.

The first genetic analysis of schizophrenia in an ancestral African population, the South African Xhosa, appears in the journal Science. The study was carried out in the Xhosa population because Africa is the birthplace of all humans, yet ancestral African populations have rarely been the focus of genetics research (There is no evidence that the Xhosa have an unusually high risk of schizophrenia).

The researchers analyzed blood samples collected from 909 individuals diagnosed with schizophrenia and 917 controls living in South Africa. Their study revealed that participants with schizophrenia are significantly more likely to carry rare, damaging genetic mutations compared to participants without schizophrenia.

These rare mutations were also more likely to affect the brain and synaptic function. Synapses coordinate the communication between brain nerve cells called neurons; the organization and firing of neuronal synapses are ultimately responsible for learning, memory, and brain function.

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