Usually beginning between 15 and 25 years, schizophrenia associates in variable proportion delirium, hallucinations (the person usually hears voices), a disorganization of the behavior and the thought, and a withdrawal in oneself.
It is accompanied by psychological suffering, sometimes intense, in the patient but also in his entourage, and a real handicap – the psychological handicap – characterized by difficulties in daily life and social and professional integration.
Like everything related to mental illness, this question is sensitive, especially since it concerns an illness whose occurrence in a family always raises an anguished and painful questioning of its origin.
Fortunately, the days when parents were blamed for being “bad” parents, and thus responsible for their child’s illness, are over. But the question of the hereditary nature of schizophrenia can give rise to another form of guilt, that of having bequeathed to one’s child “bad” genes, which would be the cause of the disease.
This guilt is no more justified than the previous one. If the existence in some patients of a genetic component is now demonstrated. Numerous studies on the family history of patients, as well as studies of twins and adopted subjects. That allows the respective weight of genetic factors to be assessed.
Family and environment, testify to a much more complex and nuanced reality. So, while in the general population about one in 100 people suffer from schizophrenia, in adults with a sick parent, 7 in 100 are at risk.
In the population of people with both parents who have schizophrenia, 27 out of 100 people are likely to be affected. While in brothers, sisters, and fraternal twins of schizophrenic patients who have only half of their genes in common, the risk is 10%, it reaches 50% in identical twins, who have an almost identical genome.
There is therefore a genetic component of the disease. But the fact that the risk of becoming schizophrenic in identical twins is 50% and not 100%.
Also, shows that schizophrenia is not a hereditary disease in the common sense of the term: being a carrier of this genetic component does not mean that one will necessarily become schizophrenic.
This means that we have an increased risk of developing schizophrenia, that we have a particular susceptibility or vulnerability to this disease because of so-called vulnerability genes, far from the notion of Bad genes.
Factors other than genetic must be present for the disease to occur. While many vulnerability genes have been suspected, only a small number of them have been confirmed by several independent scientific studies internationally.
They have in common that they are involved in the development and functioning of the brain. Finally, very recent studies suggest that the genetic vulnerability of schizophrenia is partly shared with a particular form of mood disorder, bipolar disorder.
Factors to Schizophrenia cause
The combinations of genes predisposing to schizophrenia are complex. One of these genes has recently been studied: mutated, it causes, in some patients, the accumulation of a substance toxic to neurons.
In more than a thousand diseases, an isolated defect in one gene is both necessary and sufficient to cause the pathology. Such diseases are transmitted within families according to precise patterns that follow the laws of genetics set out a century ago.
Yet in many diseases, such as schizophrenia, genetic risk factors are involved. Here we will discuss the myriad of genetic factors predisposing to schizophrenia, and we will examine the role of one of these genes.
Schizophrenia affects about one in 150 people. It is concentrated in certain families: a first-degree relative of a sick person has a 5 to 10 percent risk of developing the disease. Is this the psychological influence of the family environment or a genetic predisposition?
In a pair of monozygotic twins, of strictly identical genetics, when one becomes schizophrenic, the other has an approximately 50 percent risk of being too. Children of schizophrenic parents, adopted by families without pathology, have an increased risk of becoming schizophrenic. The genes are therefore partly involved in the family concentration of schizophrenia.