Schizophrenia is a complex and severe mental health disorder that is classified as a type of psychosis. It is characterized by significant alterations in thoughts, perception, mood, and behaviors. The causes are not well known; however, it was suggested that the causes may be associated with a cognitive decline due to alterations in brain development, particularly of the cerebral cortex .
It is estimated that 20 million people have schizophrenia worldwide with a predominance in individuals aged between 16 and 30 years .
Although schizophrenia is classified as a type of psychosis, this classification has been challenged due to the long and progressive cognitive decline before the onset of psychosis (Dementia praecox) and which suggests a more neurobiological basis.
This hypothesis is based on neuroimaging technologies, such as CT scan and MRI, that showed a reduced brain volume in patients with schizophrenia that may be due to abnormal neuronal connectivity . The reduction of brain volume has been associated with volume loss in the prefrontal lobes, thalamus, superior temporal cortex, and hippocampus.
What Are the Risk Factors of Schizophrenia?
1- Genetic Factors
Although the exact nature of genetic transmission, twin and adoption studies have shown that schizophrenia is mostly associated with genetic factors that contribute to about 70-80% . These genetic factors may be related to genomic rare copy variations such as deletions and duplications of genes  or to heritable traits associated with brain volume and intelligence .
2- Environmental Factors
Several factors are proposed to contribute to schizophrenia through mechanisms that involve chronic inflammation and abnormal prenatal development. These factors include:
- Childhood trauma
- Prenatal maternal stress and obesity
- social isolation
- Substance use
- Urban environment during childhood.
What Are the Symptoms of Schizophrenia?
Schizophrenia is characterized by significant alterations in thoughts, perception, mood, and behaviors. These alterations are related to the following symptoms:
1- Positive Symptoms
These symptoms are mainly associated with psychosis symptoms which include:
- Hallucinations (perception of things that do not exist outside the mind)
- Delusions (fixed belief)
- Thought and speech dysfunctions (disorganized thoughts and speech)
2- Negative Symptoms
- Asociality (preference for solitary activities)
- Alogia (briefness of spontaneous speech)
- Anhedonia (reduced motivation to experience pleasure)
- Blunted affect (reduction in emotional reactivity)
- Avolition (reduction in the capacity to start and persist in doing something)
3- Cognitive Symptoms
Cognitive deficits such a reduced verbal memory, working memory, attention, and executive functions are also major characteristics of schizophrenia.
What Are the Subtypes of Schizophrenia?
1- Paranoid schizophrenia
This subtype is predominantly characterized by positive symptoms of schizophrenia such as hallucinations and delusions. Individuals with the type of schizophrenia have a strong conviction that someone or something is planning to harm them .
2- Catatonic schizophrenia
This subtype of schizophrenia is characterized by extreme psychomotor dysfunctions resulting in physical immobility or excessive movement without purpose, extreme negativism, or mutism, sitting in odd postures for long periods of time, asociality, and social and emotional deficits .
3- Undifferentiated schizophrenia
This is a subtype of schizophrenia is characterized by positive symptoms of schizophrenia and the presence of catatonic behavior .
4- Hebephrenic (Disorganized) schizophrenia
This subtype of schizophrenia is characterized by disorganized behavior and speech that impair the individual capacity to carry out daily activities. It can also manifest some negative symptoms such as anhedonia and Avolition .
5- Residual schizophrenia
This subtype of schizophrenia is associated with patients who progressed from an early period of schizophrenia; however, still have some rare or very infrequent occurrences of positive symptoms such as delusions and hallucinations.
Treatment of schizophrenia involves the combination of antipsychotic medications and personalized cognitive behavioral therapy. This treatment is accompanied by social support that involves daily visits by a community mental health team.
However, antipsychotic medications such as dopamine antagonists are only used to reduce the symptoms of anxiety and are not meant to directly treat schizophrenia.
Although significant progress has been made in our understanding of the causes and illness course of schizophrenia, more efforts are needed in improving the outcome of this highly incapacitating illness.
 Fusar-Poli, P., Smieskova, R., Kempton, M.J., Ho, B.C., Andreasen, N.C. and Borgwardt, S., 2013. Progressive brain changes in schizophrenia related to antipsychotic treatment? A meta-analysis of longitudinal MRI studies. Neuroscience & Biobehavioral Reviews, 37(8), pp.1680-1691.
 Haijma, S.V., Van Haren, N., Cahn, W., Koolschijn, P.C.M., Hulshoff Pol, H.E. and Kahn, R.S., 2013. Brain volumes in schizophrenia: a meta-analysis in over 18 000 subjects. Schizophrenia bulletin, 39(5), pp.1129-1138.
 van Haren, N.E., Rijsdijk, F., Schnack, H.G., Picchioni, M.M., Toulopoulou, T., Weisbrod, M., Sauer, H., van Erp, T.G., Cannon, T.D., Huttunen, M.O. and Boomsma, D.I., 2012. The genetic and environmental determinants of the association between brain abnormalities and schizophrenia: the schizophrenia twins and relatives consortium. Biological psychiatry, 71(10), pp.915-921.
 Pfuhlmann, B. and Stöber, G., 2001. The different conceptions of catatonia: historical overview and critical discussion. European archives of psychiatry and clinical neuroscience, 251(1), pp.I4-I7.
 Takeda, T., Watanabe, Y. and Hasegawa, K., 2004. Behavior patterns of patients with hebephrenic schizophrenia when they attempt academic study. Psychiatry and clinical neurosciences, 58(2), pp.125-132.