There is no known single cause of schizophrenia. Many diseases, such as heart disease, result from interplay of genetic, behavioral, and other factors; and this may be the case for schizophrenia as well.
Is Schizophrenia Inherited?
It has long been known that schizophrenia runs in families. People who have a close relative with schizophrenia are more likely to develop the disorder than are people who have no relatives with the illness. For example, an identical twin of a person with schizophrenia a has the highest risk – 40 to 50 percent – of developing the illness. A child whose parent has schizophrenia has about a 10 percent chance. By comparison, the risk of schizophrenia in the general population is about 1 percent.
Scientists are studying genetic factors in schizophrenia. It appears likely that multiple genes are involved in creating a predisposition to develop the disorder. In addition, factors such as prenatal difficulties like intrauterine starvation or viral infections, perinatal complications, and various nonspecific stressors, seem to influence the development of schizophrenia. However, it is not yet understood how the genetic predisposition is transmitted, and it cannot yet be accurately predicted whether a given person will or will not develop the disorder.
Several regions of the human genome are being investigated to identify genes that may confer susceptibility for schizophrenia. The strongest evidence to date leads to chromosomes 13 and 6 but remains unconfirmed. Identification of specific genes involved in the development of schizophrenia will provide important clues into what goes wrong in the brain to produce and sustain the illness and will guide the development of new and better treatments. To learn more about the genetic basis for schizophrenia, the National Institute of Mental Health (NIMH) has established a Schizophrenia Genetics Initiative that is gathering data from a large number of families of people with the illness.
Is Schizophrenia Associated With A Chemical Defect In The Brain?
Basic knowledge about brain chemistry and its link to schizophrenia is expanding rapidly. Neurotransmitters, substances that allow communication between nerve cells, have long been thought to be involved in the development of schizophrenia. It is likely, although not yet certain, that the disorder is associated with some imbalance of the complex, interrelated chemical systems of the brain, perhaps involving the neurotransmitters dopamine and glutamate. This area of research is promising.
Is Schizophrenia Caused By A Physical Abnormality In The Brain?
There have been dramatic advances in neuroimaging technology that permit scientists to study brain structure and function in living individuals. Many studies of people with schizophrenia have found abnormalities in brain structure (for example, enlargement of the fluid-filled cavities, called the ventricles, in the interior of the brain, and decreased size of certain brain regions) or function (for example, decreased metabolic activity in certain brain regions). It should be emphasized that these abnormalities are quite subtle and are not characteristic of all people with schizophrenia, nor do they occur only in individuals with this illness. Microscopic studies of brain tissue after death have also shown small changes in distribution or number of brain cells in people with schizophrenia. It appears that many (but probably not all) of these changes are present before an individual becomes ill, and schizophrenia may be, in part, a disorder in development of the brain.
Developmental neurobiologists funded by the NIMH have found that schizophrenia may be a developmental disorder resulting when neurons form inappropriate connections during fetal development. These errors may lie dormant until puberty, when changes in the brain that occur normally during this critical stage of maturation interact adversely with the faulty connections. This research has spurred efforts to identify prenatal factors that may have some bearing on the apparent developmental abnormality.
In other studies, investigators using brain-imaging techniques have found evidence of early biochemical changes that may precede the onset of disease symptoms, prompting examination of the neural circuits that are most likely to be involved in producing those symptoms. Meanwhile, scientists working at the molecular level are exploring the genetic basis for abnormalities in brain development and in the neurotransmitter systems regulating brain function.
Source: National Institutes of Mental Health articles and brochures on Schizophrenia
2 comments:
Sciences are ignoring connection schizophrenia with gluten intolerance. It is hormone zonulin, which should be look at.
I have son who was hospitalized for 4 years. His condition improved considerably on gluten free diet. He had no relapse for last 6 years. Many sciences have same opinion; except psychiatrists.
It is strange and cruel world out there.
Kevin Nadherny
One of the major causes of non-familial schizophrenia is older paternal age. Sperm stem cells mutate as the man ages. Schizophrenia Risk and the Paternal Germ Line
By Dolores Malaspina
Dolores Malaspina
Paternal age at conception is a robust risk factor for schizophrenia. Possible mechanisms include de novo point mutations or defective epigenetic regulation of paternal genes. The predisposing genetic events appear to occur probabilistically (stochastically) in proportion to advancing paternal age, but might also be induced by toxic exposures, nutritional deficiencies, suboptimal DNA repair enzymes, or other factors that influence the
fidelity of genetic information in the constantly replicating male germ line. We propose that de novo genetic alterations in the paternal germ line cause an independent and common variant of schizophrenia.
Seminal findings
We initially examined the relationship between paternal age and the risk for schizophrenia because it is well established that paternal age is the major source of de novo mutations in the human population, and most schizophrenia cases have no family history of psychosis. In 2001, we demonstrated a monotonic increase in the risk of schizophrenia as paternal age advanced in the rich database of the Jerusalem Perinatal Cohort. Compared with the offspring of fathers aged 20-24 years, in well-controlled analyses, each decade of paternal age multiplied the risk for schizophrenia by 1.4 (95 percent confidence interval: 1.2-1.7), so that the relative risk (RR) for offspring of fathers aged 45+ was 3.0 (1.6-5.5), with 1/46 of these offspring developing schizophrenia. There were no comparable maternal age effects (Malaspina et al., 2001).
Epidemiological evidence
This finding has now been replicated in numerous cohorts from diverse populations (Sipos et al., 2004; El-Saadi et al., 2004; Zammit et al., 2003; Byrne et al., 2003; Dalman and Allenbeck, 2002; Brown et al., 2002; Tsuchiya et al., 2005). By and large, each study shows a tripling of the risk for schizophrenia for the offspring of the oldest group of fathers, in comparison to the risk in a reference group of younger fathers. There is also a "dosage effect" of increasing paternal age; risk is roughly doubled for the offspring of men in their forties and is tripled for paternal age >50 years. These studies are methodologically sound, and most of them have employed prospective exposure data and validated psychiatric diagnoses. Together they demonstrate that the paternal age effect is not explained by other factors, including family history, maternal age, parental education and social ability, family social integration, social class, birth order, birth weight, and birth complications. Furthermore, the paternal age effect is specific for schizophrenia versus other adult onset psychiatric disorders. This is not the case for any other known schizophrenia risk factor, including many of the putative susceptibility genes (Craddock et al., 2006).
There have been no failures to replicate the paternal age effect, nor its approximate magnitude, in any adequately powered study. The data support the hypothesis that paternal age increases schizophrenia risk through a de novo genetic mechanism. The remarkable uniformity of the results across different cultures lends further coherence to the conclusion that this robust relationship is likely to reflect an innate human biological phenomenon that progresses over aging in the male germ line, which is independent of regional environmental, infectious, or other routes.
Indeed, the consistency of these data is unparalleled in schizophrenia research, with the exception of the increase in risk to the relatives of schizophrenia probands (i.e., 10 percent for a sibling). Yet, while having an affected first-degree relative confers a relatively higher risk for illness than having a father >50 years (~10 percent versus ~2 percent), paternal age explains a far greater portion of the population attributable risk for schizophrenia. This is because a family history is infrequent among schizophrenia cases, whereas paternal age explained 26.6 percent of the schizophrenia cases in our Jerusalem cohort. If we had only considered the risk in the cases with paternal age >30 years, our risk would be equivalent to that reported by Sipos et al. (2004) in the Swedish study (15.5 percent). When paternal ages >25 years are considered, the calculated risk is much higher. Although the increment in risk for fathers age 26 through 30 years is small (~14 percent), this group is very large, which accounts for the magnitude of their contribution to the overall risk. The actual percentage of cases with paternal germ line-derived schizophrenia in a given population will depend on the demographics of paternal childbearing age, among other factors. With an upswing in paternal age, these cases would be expected to become more prevalent.
Biological plausibility
We used several approaches to examine the biological plausibility of paternal age as a risk factor for schizophrenia. First, we established a translational animal model using inbred mice. Previously it had been reported that the offspring of aged male rodents had less spontaneous activity and worse learning capacity than those of mature rodents, despite having no noticeable physical anomalies (Auroux et al., 1983). Our model carefully compared behavioral performance between the progeny of 18-24-month-old sires with that of 4-month-old sires. We replicated Auroux's findings, demonstrating significantly decreased learning in an active avoidance test, less exploration in the open field, and a number of other behavioral decrements in the offspring of older sires (Bradley-Moore et al., 2002).
Next, we examined if parental age was related to intelligence in healthy adolescents. We reasoned that if de novo genetic changes can cause schizophrenia, there might be effects of later paternal age on cognitive function, since cognitive problems are intertwined with core aspects of schizophrenia. For this study, we cross-linked data from the Jerusalem birth cohort with the neuropsychological data from the Israeli draft board (Malaspina et al., 2005a). We found that maternal and paternal age had independent effects on IQ scores, each accounting for ~2 percent of the total variance. Older paternal age was exclusively associated with a decrement in nonverbal (performance) intelligence IQ, without effects on verbal ability, suggestive of a specific effect on cognitive processing. In controlled analyses, maternal age showed an inverted U-shaped association with both verbal and performance IQ, suggestive of a generalized effect.
Finally, we examined if paternal age was related to the risk for autism in our cohort. We found very strong effects of advancing paternal age on the risk for autism and related pervasive developmental disorders (Reichenberg et al., in press). Compared to the offspring of fathers aged 30 years or younger, the risk was tripled for offspring of fathers in their forties and was increased fivefold when paternal age was >50 years. Together, these studies provide strong and convergent support for the hypothesis that later paternal age can influence neural functioning. The translational animal model offers the opportunity to identify candidate genes and epigenetic mechanisms that may explain the association of cognitive functioning with advancing paternal age.
A variant of schizophrenia
A persistent question is whether the association of paternal age and schizophrenia could be explained by psychiatric problems in the parents that could both hinder their childbearing and be inherited by their offspring. If this were so, then cases with affected parents would have older paternal ages. This has not been demonstrated. To the contrary, we found that paternal age was 4.7 years older for sporadic than familial cases from our research unit at New York State Psychiatric Institute (Malaspina et al., 2002). In addition, epidemiological studies show that advancing paternal age is unrelated to the risk for familial schizophrenia (Byrne et al., 2003; Sipos et al., 2004). For example, Sipos found that each subsequent decade of paternal age increased the RR for sporadic schizophrenia by 1.60 (1.32 to 1.92), with no significant effect for familial cases (RR = 0.91, 0.44 to 1.89). The effect of late paternal age in sporadic cases was impressive. The offspring of the oldest fathers had a 5.85-fold risk for sporadic schizophrenia (Sipos et al., 2004); relative risks over 5.0 are very likely to reflect a true causal relationship (Breslow and Day, 1980).
http://www.schizophreniaforum.org/for/curr/Malaspina/default.asp
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