Schizophrenia today: heredity and environment

The origin of schizophrenia
Researchers have many different opinions on the origin of schizophrenia. Almost all researchers agree that both heredity and environmental factors are important for the development of the disease. However, opinions differ on the relative importance of heredity versus environment. New knowledge on the plasticity of the brain and its continuous development during life will most likely turn many "obvious facts" upside down. Researchers will now have to reassess their findings and their attitude toward different theories on the origin of schizophrenia.

The importance of hereditary factors
McNeil finds researchers´ narrow-minded fascination with hereditary factors somewhat strange. Family-, twin- and adoption studies clearly illustrate the importance of heredity for schizophrenia; however the concordance for schizophrenia is relatively low (30-40%) in modern investigations of identical twins. Less than 50% of the children to two schizophrenic parents develop the disease, and genetic factors do not explain everything. Estimations show that 30-50% of the development of the disease may be caused by environmental factors. In spite of massive research in the area, no specific genetic factors have yet been associated to schizophrenia. Researchers do not even know the number of genes relevant for schizophrenia, or the mechanism of the presumptive genetic factor. Even if the researchers succeed in identifying genes related to schizophrenia in the future, there is still much to investigate. The question at issue is not answered until scientists succeed in understanding the mechanism of the genes, how they interact with the environment (genes always act in an environment) and how the new knowledge can be applied in prevention and treatment.

Many environmental factors are associated with schizophrenia
In contrast to the fuzzy picture of the genetics of schizophrenia, at least 50 different investigations have been able to identify a relationship between schizophrenia and early "environmental factors". Examples are obstetric complications, early infections (especially influenza), maternal stress during pregnancy, maternal starvation during pregnancy, birth and childhood in urban areas, birth during winter and early spring etc. Since the environmental factors may show a greater frequency than single "schizophrenic genes" in the population it is possible that environmental factors cause more cases of schizophrenia than do genes. (A recent Danish study supports this theory). The correlation between schizophrenia and environmental factors is especially important to the development of theories on the importance of brain damage to the development of schizophrenia. In contrast to the diffuse knowledge regarding the genetic factors, knowledge exists on the effects of oxygen deficiency and early infections on brain development. Scientists can also identify individuals who have been exposed to these environmental factors.