Schizophrenia

About 1% of the world’s population suffers from schizophrenia,a severe mental disturbance characterized by psychotic episodes in which patients lose the ability to distinguish reality. The symptoms of schizophrenia typically include hallucinations and delusions, as well as blunted emotions, distractibility, lack of initiative and poverty of speech. Despite the commonly held belief,schizophrenics do not necessarily exhibit a split personality. There seems to be several different forms of schizophrenia,and it is unclear whether they represent different disorders or variations of the same underlying disease.

The cause of schizophrenia is unknown,although the disease has a strong genetic component. Studies of identical twins show that if one twin has Schizophrenia,there is a 50% chance that the other twin has it too. Since identical twins have identical genes,the fact that this likelihood is not 100% implies that Schizophrenia must have an equally strong environmental component,which is unidentified. Now that the human genome has been sequenced,there is a vigorous effort under way to find the mutant genes that predispose a person to the disease. This effort includes DNA sequencing of individuals in families with a high incidence of Schizophrenia. Multiple genes must be involved because the inheritance does not follow the Mendelian pattern expected for a single-gene mutation.

Treatments for Schizophrenia have focused mostly on brain pathways that use dopamine as a neurotransmitter. Two lines of evidence support this protocol. First amphetamine,which stimulates dopamine release,can produce symptoms indistinguishable from those of schizophrenia. Second, many of the drugs that alleviate the symptoms block dopamine receptors,especially a sub-form called D2 receptor. However, additional neurotransmitters may also be involved because other drugs successful in treating schizophrenia,called antipsychotics, block D2 receptors only very weakly but have strong effects on serotonin or norepinephrine receptors. Furthermore, there are indications that glutamate receptors may play a role in schizophrenia:the street drug ‘angel dust’ or PCP blocks the NMDA type glutamate receptor(but not dopamine receptors) and induces strong schizophrenia-like symptoms.

Identification of the genetic mutations responsible for schizophrenia may yield new insights about the causes of the diseases,which may in turn lead to new therapies.

References:

Davidson's Principles and Practise of Medicine,23rd edition

Lange clinical neurology and neuroanatomy, Aaron L Berkowitz