WHY DOESN'T THE PUBLIC KNOW THAT UP TO AND BY NOW MAYBE MORE THAN 1/3 OF ALL SCHIZOPHRENIA IS CAUSED BY PATERNAL AGE AT CONCEPTION?

Someone recently wrote:


Saying autism is not a mental illness
is functionally incorrect. When the
mental illness schizophrenia is now
determined to be developmental - it
appears in late adolescence as the brain and body mature, while autism manifests itself in childhood - when
autism was once termed “childhood
schizophrenia”, when both illnesses
originate in the brain, when both
conditions share many symptoms, when in
any case it is NOT a disgrace to be called “mentally ill”, you are making
a distinction that is not a distinction.

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: Eur Psychiatry. 2007 Jan;22(1):22-6. Epub 2006 Dec 4.Click here to read Links
Paternal ages below or above 35 years old are associated with a different risk of schizophrenia in the offspring.

* Wohl M,
* Gorwood P.

INSERM U675, 16 rue Henri Huchard 75018 Paris, France.






BACKGROUND: A link between older age of fatherhood and an increased risk of schizophrenia was detected in 1958. Since then, 10 studies attempted to replicate this result with different methods, on samples with different origins, using different age classes.

Defining a cut-off at which the risk is significantly increased in the offspring could have an important impact on public health. METHODS: A meta-analysis (Meta Win) was performed, assessing the mean effect size for each age class, taking into account the difference in age class references, and the study design. RESULTS: An increased risk is detected when paternal age is below 20 (compared to 20-24), over 35 (compared to below 35), 39 (compared to less than 30), and 54 years old (compared to less than 25). Interestingly, 35 years appears nevertheless to be the lowest cut-off where the OR is always above 1, whatever the age class reference, and the smallest value where offspring of fathers below or above this age have a significantly different risk of schizophrenia. CONCLUSION: No threshold can be precisely defined, but convergent elements indicate ages below or above 35 years. Using homogeneous age ranges in future studies could help to clarify a precise threshold.

PMID: 17142012 [PubMed - indexed for MEDLINE]


Schizophrenia Risk and the Paternal Germ Line
By 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.