Schizophrenia risk factors

In 2005, a review pointed out that exposure to infection or nutritional deprivation during early fetal development may elevate the risk of later onset of schizophrenia.14 Lead exposure has also been established as a risk factor for schizophrenia, the lead correlations suggesting environmental chemicals as a new class of schizophrenia risk factors that are still inadequately investigated.15... 

Zammit S, Allebeck P, Andreasson S, Lundberg I and Lewis G (2002). Self reported cannabis use as a risk factor for schizophrenia in Swedish conscripts of 1969 Historical cohort study. British Medical Journal, 325, 1199-1201. 

These results suggest that the taxon is overinclusive It includes 28% of low-risk participants—instead of the 10% predicted by Meehl s theory—and misses some cases that later become symptomatic. This might mean that the identified taxon is not isomorphic with specific genetic liability for schizophrenia and reflects a construct that is overlapping, but not identical to, the genetic risk factor. Another explanation is that the DSM criteria for schizophrenia and spectrum conditions may be too broad. Tyrka et al. (1995) proposed this hypothesis and estimated that at least two-thirds of the misses (symptomatic cases not assigned to the taxon) can be accounted for by errors in the taxon classification scheme, but the remaining misses are due to... 

Demographic risk factors have also been studied. They reveal first that gender is not a risk factor. There is no difference in the rates between men and women. However, the illness tends to appear earlier in men (early 20s) than women (late 20s). Race is also not a risk factor. It was once believed that schizophrenia was more common in poor families. We now know this not to be true. It appears that poverty is a result of schizophrenia not a risk factor for it. 

Research into the risk factors for Cluster A personality disorders has focused on genetic factors. In particular, many researchers have looked for a shared genetic linkage between these disorders and schizophrenia. Only schizotypal personality appears to be genetically linked to schizophrenia. It may be that STPD exists on a biological continuum with schizophrenia. In other words, STPD could theoretically be a far milder variant of Axis I schizophrenia. There is less evidence linking PPD or SPD to schizophrenia nevertheless, certain characteristic symptoms of these other disorders also overlap with schizophrenia. 

TABLE 15.3 Risk Factors for Schizophrenia in Patients with Childhood Onset of the Disorder... 

Jones, P., Rodgers, B., Murray, R., and Marmot, M. (1994) Child development risk factors for schizophrenia in the British 1946 birth cohort. Lancet 344 1398-1402. 

Nicoison, R., Lenane, M., Singaracharlu, S., Malaspina, D., Giedd, J.N., Hamburger, S.D., Gochman, P., Bedwell, J., Thaker, G.K., Fernandez, T, Wudarsky, M., Hommer, D.W., and Rapoport, J.L. (2000c) Premorbid speech and language impairments in childhood-onset schizophrenia association with risk factors. Am J Psychiatry 157 794-800. 

Middle-aged or older individuals who complete suicide tend to suffer from a depressive disorder. Younger individuals who complete suicide usually suffer from schizophrenia or a bipolar disorder. The risk factors for suicide attempts versus completions are the following ... 

Insulin resistance is a major but not necessary risk factor for type 2 diabetes. Glucose metabolism in 36 out-patients with schizophrenia aged 18-65 years taking clozapine (n — 12), olanzapine (n — 12), or risperidone (n = 12) has been examined in a cross-sectional study... 

O Keane V, Meaney AM. A new risk factor for osteoporosis in young women with schizophrenia J Clin Psychopharmacol 2005 25 26-31. 

The exact cause of schizophrenia has been the subject of extensive research. It appears that genetic factors (i.e., chromosomal abnormalities that cause deviations in brain structure and function) are the primary risk factors in the majority of people with schizophrenia (70% to 80%).15,23 Environmental factors (social stresses, prenatal or childhood brain injury, and so forth) seem to be the underlying cause in the remaining 20% to 30% of people with schizophrenia.23 The precise role of these factors, and the interplay between genetic and environmental factors, continues to be elucidated.28,50 61... 

The dictum in the traditional folklore of medicine has been the treatment and alleviation of acute symptoms of disease. Aforementioned advances in our understanding of the risk factors and molecular basis of human diseases are now paving the way to develop medicines that can prevent or slow the progression of disease phenomena. Schizophrenia and some of the neurodegenerative diseases such as Alzheimer s or Parkinson s disease... 

Environmental factors that contribute to the development of schizophrenia also converge on NMDA receptors. For example, it has been hypothesized that perinatal hypoxia, an important risk factor for schizophrenia, leads to the neurotoxic degeneration of NMDA-bearing cells, an effect that may only produce behavioral symptoms later in development (Olney et al., 1999). 

Schumacher J, Jamra RA, Freudenberg J, Becker T, Ohlraun S, et al. 2004. Examination of G72 and D-amino-acid oxidase as genetic risk factors for schizophrenia and bipolar affective disorder. Mol Psychiatry 9 203-207. 

Glutamatergic abnormalities are also a major feature of schizophrenia. They may actually cause the dopaminergic abnormalities in that disorder and then be exacerbated by them (Laruelle et al., 2005). The glutamate hypothesis simply states that NMDAR hypofunction contributes to the pathophysiology of schizophrenia (Coyle, 2006 Lindsley et al., 2006). A variant of this is the NMDA synaptic deficit hypothesis of MacDonald and Chafee (2006), which posits that each risk factor for schizophrenia impacts the NMDA glutamate synapse such that the cumulative effect drives NMDA synaptic function below a threshold for normal function. Supporting either form of the glutamate hypothesis is evidence that... 

In conclusion, these genetic and functional results support the concept that a dysregulation of GSH metabolism, and in particular GSH synthesis, is one of the vulnerability factors that could contribute to the development of schizophrenia. These markers may contribute to obtain a complete picture of genetic risk factors of schizophrenia and may help to identify critical period and specific brain locations during development, where GSH deficits are important to the emergence of the disease. 

Rosso IM, Cannon TD, Huttunen T, Huttunen MO, Lonnqvist J, et al. 2000. Obstetric risk factors for early-onset schizophrenia in a Finnish birth cohort. Am J Psychiatry 157 801-807. 

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