Advancing paternal age is associated with deficits in social and exploratory behaviors in the offspring: a mouse model

The Role of Advanced Parental Age in Reproductive Genetics

The increase of parental reproductive age is a worldwide trend in modern society in recent decades. In general, older parents have a significant impact on reproductive genetics and the health of offspring. In particular, advanced parental age contributes to the increase in the risk of adverse neurodevelopmental outcomes in offspring. However, it is currently under debate how and to what extent the health of future generations was affected by the parental age. In this review, we aimed to (i) provide an overview of the effects of age on the fertility and biology of the reproductive organs of the parents, (ii) highlight the candidate biological mechanisms underlying reproductive genetic alterations, and (iii) discuss the relevance of the effect of parental age on offspring between animal experiment and clinical observation. In addition, we think that the impact of environmental factors on cognitive and emotional development of older offspring will be an interesting direction.

Parental Age and Childhood Risk for Cerebral Palsy in California

OBJECTIVE

To investigate the associations between maternal or paternal age at the time of delivery and offspring's risk for cerebral palsy (CP) in California.

STUDY DESIGN

We conducted a population-based, case-control study that included 8736 singleton CP cases and 90 250 singleton controls, matched by sex and birth year, selected from California birth certificate records from 1994 to 2010. We estimated OR and 95% CIs for CP diagnosis according to maternal and paternal age recorded on the birth certificates. Causal mediation analysis was performed to estimate direct and indirect effects of parental ages on CP with preterm delivery as a potential mediator.

RESULTS

Children born to younger mothers (≤19 years) or older mothers (35-39 years; ≥40 years) had a greater risk of CP compared with children of mothers aged 25-29 years (ORs ranging from 1.13 to 1.59). Compared with paternal age 25-29 years, older paternal age (40-44 years; ≥45 years) also was associated with an increased risk for CP independent of maternal age. When analyzing jointly using both parents of ages 20-34 years as the reference, the greatest risk was estimated for older parents (≥35 years). Preterm birth was estimated to mediate 19%-34% of the total effects between maternal or paternal age and offspring CP risk.

CONCLUSIONS

Young maternal age and an older age in either or both parents were associated with a greater risk of CP in their children. Although preterm birth was a mediator, additional factors related to parental age need further exploration to explain risk of CP.

Paternal age and 13 psychiatric disorders in the offspring: a population-based cohort study of 7 million children in Taiwan

Although paternal age has been linked to certain psychiatric disorders, the nature of any causal relationship remains elusive. Here, we aimed to comprehensively assess the magnitude of a wide range of offspring's psychiatric risk conferred by paternal age, leveraging a pedigree inferred from covered-insurance relationship (accuracy >98%) in Taiwan's single-payer compulsory insurance program. We also examined whether there is an independent role of paternal age and explored the potential effect of parental age difference. A total cohort of 7,264,788 individuals born between 1980 and 2018 were included; 5,572,232 with sibling(s) were selected for sibling-comparison analyses and 1,368,942 and 1,044,420 children with information of paternal-grandparents and maternal-grandparents, respectively, were selected for multi-generation analyses. Using inpatient/outpatient claims data (1997-2018), we identified schizophrenia, autism, bipolar disorder (BPD), attention deficit-hyperactivity disorder (ADHD), major depressive disorder (MDD), eating disorder (ED), substance use disorder (SUD), mental retardation (MR), tic disorder, obsessive-compulsive disorder (OCD), anxiety, and somatoform disorder. We identified suicides using death certificates. Logistic regression analysis was used to estimate the paternal/maternal/grand-paternal age association with psychiatric risk in the offspring. The total cohort and sibling-comparison cohort resulted in similar estimates. Paternal age had a U-shaped relationship with offspring's MDD, ED, SUD, and anxiety. A very young maternal age (<20 years) was associated with markedly higher risk in offspring's SUD, MR, and suicide. Older paternal age (>25 years) was linearly associated with offspring's schizophrenia, autism, BPD, ADHD, MDD, ED, SUD, MR, OCD, anxiety, and suicide. Older grand-paternal age was linearly associated with offspring's schizophrenia, autism, ADHD, and MR. Dissimilar parental age was positively associated with offspring's ADHD, MDD, SUD, MR, anxiety, and suicide, and negatively associated with offspring's OCD. This comprehensive assessment provides solid evidence for the independent role of paternal age in psychiatric risk in the offspring and clarifies the significance of both early parenthood and delayed paternity.

Animal models of male reproductive ageing to study testosterone production and spermatogenesis

Ageing is the time-dependent gradual decline of the functional characteristics in an organism. It has been shown that it results in the loss of reproductive health and fertility. The age-dependent decline of fertility is a potential issue as the parenthood age is increasing in Western countries, mostly due to socioeconomic factors. In comparison to women, for whom the consequences of ageing are well documented and general awareness of the population is extensively raised, the effects of ageing for male fertility and the consequences of advanced paternal age for the offspring have not been widely studied. Studies with humans are welcome but it is hard to implement relevant experimental approaches to unveil the molecular mechanisms by which ageing affects male reproductive potential. Animal models have thus been extensively used. These models are advantageous due to their reduced costs, general easy maintenance in laboratory facilities, rigorous manipulation tools, short lifespan, known genetic backgrounds, and reduced ethical constraints. Herein, we discuss animal models for the study of male reproductive ageing. The most well-known and studied reproductive ageing models are rodents and non-human primates. The data collected from these models, particularly studies on testicular ageing, steroidogenesis, and genetic and epigenetic changes in spermatogenesis are detailed. Notably, some species challenge the currently accepted ageing theories and the concept of senescence itself, which renders them interesting animal models for the study of male reproductive ageing.

Effect of advanced parental age on pregnancy outcome and offspring health

PURPOSE

Fertility at advanced age has become increasingly common, but the aging of parents may adversely affect the maturation of gametes and the development of embryos, and therefore the effects of aging are likely to be transmitted to the next generation. This article reviewed the studies in this field in recent years.

METHODS

We searched the relevant literature in recent years with the keywords of "advanced maternal/paternal age" combined with "adverse pregnancy outcome" or "birth defect" in the PubMed database and classified the effects of parental advanced age on pregnancy outcomes and birth defects. Related studies on the effect of advanced age on birth defects were classified as chromosomal abnormalities, neurological and psychiatric disorders, and other systemic diseases. The effect of assisted reproduction technology (ART) on fertility in advanced age was also discussed.

RESULTS

Differences in the definition of the range of advanced age and other confounding factors among studies were excluded, most studies believed that advanced parental age would affect pregnancy outcomes and birth defects in offspring.

CONCLUSION

To some extent, advanced parental age caused adverse pregnancy outcomes and birth defects. The occurrence of these results was related to the molecular genetic changes caused by aging, such as gene mutations, epigenetic variations, etc. Any etiology of adverse pregnancy outcomes and birth defects related to aging might be more than one. The detrimental effect of advanced age can be corrected to some extent by ART.

Interaction between social behavior and paternal age in offspring of the same paternal mice

AIM

Previous studies reported that advanced paternal age (APA) may increase the risk of autism spectrum disorder (ASD) in offspring. However, effects of APA on behaviors have not been investigated in offspring of the same paternal mice. The present study sought to identify behavioral differences in mouse offspring of the same fathers at different paternal ages.

METHODS

We assessed locomotor activity, anxiety-like behavior, and social behavior in male mouse offspring that were born from the same fathers at three different paternal ages (3, 12, and 15 months old).

RESULTS

No differences in locomotor activity or anxiety-like behavior were observed among any of the offspring groups. In the three-chamber test, although the control group (3-month-old paternal age) exhibited significantly higher approach behavior toward the novel mouse compared with the novel object, the APA groups (12- and 15-month-old paternal ages) did not exhibit significant approach toward the novel mouse.

CONCLUSION

Offspring of 3-month-old fathers but not 12- or 15-month-old APA fathers exhibited social preference behavior. Although the present study was only exploratory, it demonstrated an interaction between social behavior and paternal age in offspring of the same paternal mice.

Delayed parenthood and its influence on offspring health: What have we learned from the mouse model

Delayed parenthood is constantly increasing worldwide due to various socio-economic factors. In the last decade, a growing number of epidemiological studies have suggested a link between advanced parental age and an increased risk of diseases in the offspring. Also, poor reproductive outcome has been described in pregnancies conceived by aged parents. Similarly, animal studies showed that aging negatively affects gametes, early embryonic development, pregnancy progression and the postnatal phenotype of resulting offspring. However, how and to what extent parental age is a risk factor for the health of future generations is still subject to debate. Notwithstanding the limitation of an animal model, the mouse model represents a useful tool to understand not only the influence of parental age on offspring phenotype but also the biological mechanisms underlying the poor reproductive outcome and the occurrence of diseases in the descendants. The present review aims at i) providing an overview of the current knowledge from mouse model about the risks associated with conception at advanced age (e.g. neurodevelopmental and metabolic disorders), ii) highlighting the candidate biological mechanisms underlying this phenomenon, and iii) discussing on how murine-derived data can be relevant to humans.

Application of animal experimental models in the research of schizophrenia

Schizophrenia is a relatively common but serious mental illness that results in a heavy burden to patients, their families, and society. The disease can be triggered by multiple factors, while the specific pathogenesis remains unclear. The development of effective therapeutic drugs for schizophrenia relies on a comprehensive understanding of the basic biology and pathophysiology of the disease. Therefore, effective animal experimental models play a vital role in the study of schizophrenia. Based on different molecular mechanisms and modeling methods, the currently used experimental animal experimental models of schizophrenia can be divided into four categories that can better simulate the clinical symptoms and the interplay between susceptible genes and the environment: neurodevelopmental, drug-induced, genetic-engineering, and genetic-environmental interaction of animal experimental models. Each of these categories contains multiple subtypes, which has its own advantages and disadvantages and therefore requires careful selection in a research application. The emergence and utilization of these models are promising in the prediction of the risk of schizophrenia at the molecular level, which will shed light on effective and targeted treatment at the genetic level.

Parental age and risk of depression: A nationwide, population-based case-control study

BACKGROUND

The global prevalence of depression has increased in recent decades and so has the average age of parenthood. Younger and older parental age have been associated with several mental disorders in their offspring, but the associations for depression have been inconsistent.

METHODS

This study comprised 37,682 singleton births in Finland from 1987- 2007. The subjects were living in Finland at the end of 2012 and had a depressive disorder recorded in the Care Register for Health Care. We also randomly identified 148,795 controls from the Population Register. When missing obsevations excluded the sample was N_cases=18,708 and N_controls=77,243. The results were adjusted for the parents' psychiatric history, depression history, marital status and place of birth, the mothers' maternal socioeconomic status, smoking during pregnancy and previous births and the children's birth weight.

RESULTS

We found a U-shaped association between offspring depression and the age of both parents. The highest odds of depression occurred when the fathers were aged 50 plus years (adjusted Odds Ratio (ORa) 1.51, 95% CI 1.23-1.86) and the mothers were under 20 (ORa 1.44, 95% CI 1.29-1.60) compared to the reference category of parents aged 25-29 years.

LIMITATIONS

The study was limited to depression diagnosed by specialised health care services and had a relatively short follow-up period. Some data were missing and that could lead to risk estimation biases.

CONCLUSION

Diagnosed depression was higher among the offspring of younger and older parents. The results suggest that the age of the parent is etiologically associated with offspring depression.

Heterogenous effects of father and mother age on offspring development

Maternal age has long been described to influence a broad range of offspring life-history traits, including longevity. However, relatively few studies have tested experimentally for the effects of paternal age and even fewer the potential interactive effects of father and mother age on offspring life-history traits from conception to death. To tackle these questions, I performed a factorial experimental design where I manipulated the age of both male and female field crickets (Gryllus bimaculatus) and subsequently assessed their effects over the offspring’s entire lifetime. I found that, despite coming from larger eggs, the embryos of old females grew up at a slower rate, took more time to develop, and showed lower hatching success than those of young females. Offspring postnatal viability was unaffected by female age but, at adulthood, the offspring of old females were bigger and lived shorter than those of young females. Male age effects were mostly present during offspring postnatal development as nymphs sired by old males having increased early mortality. Moreover, father age strongly influenced the development of offspring adult personality as revealed by the shyer personality of crickets sired by an old male. My results indicate that father and mother age at reproduction have different effects that affect offspring traits at different stages of their development. The results further suggest that father and mother age effects could be mediated by independent mechanisms and may separately influence the evolution of aging.

Effects of age on sperm quality metrics in endangered Mississippi gopher frogs (Lithobates sevosus) from captive populations used for controlled propagation and reintroduction efforts

A decline in sperm quality with age is a common prediction of senescence-based hypotheses and empirical studies. While widely studied across taxa, there is little known on the effect of ageing on sperm quality in amphibians, especially in captive populations used for controlled propagation and reintroduction efforts. Here, we investigated variation in sperm quality metrics (i.e., motility, concentration, and morphology) in the endangered Mississippi gopher frog (Lithobates sevosus) among males of three age categories using individuals from captive breeding populations housed at three different zoological institutions. Different aged males across the species expectant lifespan (1-9, 1-2, 3-4, and 8-9-year-old subcategories) were chosen in an attempt to identify an optimal breeding age relevant for captive breeding programs. Moreover, we explored and statistically controlled for potential differences in sperm quality which may be attributed to the type of induction hormones and source populations that differed among institutions. Results indicated that males of different ages did not differ in sperm motility or concentration. However, we did find that older males (8-9 years old) had significantly longer sperm than other age categories and younger males (1-2 years old) had significantly more atypical sperm than other age categories. Furthermore, we found no significant differences in any sperm quality metrics between the different induction hormones or source populations used at the different institutions. Within a captive breeding program, this information is especially valuable as our results indicate that males that have only recently sexually matured may not be ready to breed, while older males maintain sperm quality metrics presumably related to fertilization success.

Paternal age affects offspring via an epigenetic mechanism involving REST/NRSF

Advanced paternal age can have deleterious effects on various traits in the next generation. Here, we establish a paternal‐aging model in mice to understand the molecular mechanisms of transgenerational epigenetics. Whole‐genome target DNA methylome analyses of sperm from aged mice reveal more hypo‐methylated genomic regions enriched in REST/NRSF binding motifs. Gene set enrichment analyses also reveal the upregulation of REST/NRSF target genes in the forebrain of embryos from aged fathers. Offspring derived from young mice administrated with a DNA de‐methylation drug phenocopy the abnormal vocal communication of pups derived from aged fathers. In conclusion, hypo‐methylation of sperm DNA can be a key molecular feature modulating neurodevelopmental programs in offspring by causing fluctuations in the expression of REST/NRSF target genes.

Mapping the past, present and future research landscape of paternal effects

BACKGROUND

Although in all sexually reproducing organisms an individual has a mother and a father, non-genetic inheritance has been predominantly studied in mothers. Paternal effects have been far less frequently studied, until recently. In the last 5 years, research on environmentally induced paternal effects has grown rapidly in the number of publications and diversity of topics. Here, we provide an overview of this field using synthesis of evidence (systematic map) and influence (bibliometric analyses).

RESULTS

We find that motivations for studies into paternal effects are diverse. For example, from the ecological and evolutionary perspective, paternal effects are of interest as facilitators of response to environmental change and mediators of extended heredity. Medical researchers track how paternal pre-fertilization exposures to factors, such as diet or trauma, influence offspring health. Toxicologists look at the effects of toxins. We compare how these three research guilds design experiments in relation to objects of their studies: fathers, mothers and offspring. We highlight examples of research gaps, which, in turn, lead to future avenues of research.

CONCLUSIONS

The literature on paternal effects is large and disparate. Our study helps in fostering connections between areas of knowledge that develop in parallel, but which could benefit from the lateral transfer of concepts and methods.

Advanced paternal age as a risk factor for neurodevelopmental disorders: a translational study

Advanced paternal age (APA) is a risk factor for several neurodevelopmental disorders, including autism and schizophrenia. The potential mechanisms conferring this risk are poorly understood. Here, we show that the personality traits schizotypy and neuroticism correlated with paternal age in healthy subjects (N = 677). Paternal age was further positively associated with gray matter volume (VBM, N = 342) in the right prefrontal and the right medial temporal cortex. The integrity of fiber tracts (DTI, N = 222) connecting these two areas correlated positively with paternal age. Genome-wide methylation analysis in humans showed differential methylation in APA individuals, linking APA to epigenetic mechanisms. A corresponding phenotype was obtained in our rat model. APA rats displayed social-communication deficits and emitted fewer pro-social ultrasonic vocalizations compared to controls. They further showed repetitive and stereotyped patterns of behavior, together with higher anxiety during early development. At the neurobiological level, microRNAs miR-132 and miR-134 were both differentially regulated in rats and humans depending on APA. This study demonstrates associations between APA and social behaviors across species. They might be driven by changes in the expression of microRNAs and/or epigenetic changes regulating neuronal plasticity, leading to brain morphological changes and fronto-hippocampal connectivity, a network which has been implicated in social interaction.

Parental age effects on neonatal white matter development

•

Advanced paternal age is associated with a range of later negative outcomes.

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It is not known if these negative outcomes are due to genetics or environment.

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We use neonatal diffusion MRI to demonstrate paternal age effect on white matter.

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The babies of older fathers had reduced fractional anisotropy in multiple areas.

•

These changes correlated with cognitive outcome at 18 months.

Objective

Advanced paternal age is associated with poor offspring developmental outcome. Though an increase in paternal age-related germline mutations may affect offspring white matter development, outcome differences could also be due to psychosocial factors. Here we investigate possible cerebral changes prior to strong environmental influences using brain MRI in a cohort of healthy term-born neonates.

Methods

We used structural and diffusion MRI images acquired soon after birth from a cohort (n = 275) of healthy term-born neonates. Images were analysed using a customised tract based spatial statistics (TBSS) processing pipeline. Neurodevelopmental assessment using the Bayley-III scales was offered to all participants at age 18 months. For statistical analysis neonates were compared in two groups, representing the upper quartile (paternal age ≥38 years) and lower three quartiles. The same method was used to assess associations with maternal age.

Results

In infants with older fathers (≥38 years), fractional anisotropy, a marker of white matter organisation, was significantly reduced in three early maturing anatomical locations (the corticospinal tract, the corpus callosum, and the optic radiation). Fractional anisotropy in these locations correlated positively with Bayley-III cognitive composite score at 18 months in the advanced paternal age group. A small but significant reduction in total brain volume was also observed in in the infants of older fathers. No significant associations were found between advanced maternal age and neonatal imaging.

Conclusions

The epidemiological association between advanced paternal age and offspring outcome is extremely robust. We have for the first time demonstrated a neuroimaging phenotype of advanced paternal age before sustained parental interaction that correlates with later outcome.

Age-associated sperm DNA methylation patterns do not directly persist trans-generationally

Background

The impact of aging on the sperm methylome is well understood. However, the direct, subsequent impact on offspring and the role of altered sperm DNA methylation alterations in this process remain poorly understood. The well-defined impact of aging on sperm DNA methylation represents an excellent opportunity to trace the direct, transgenerational transmission of these signals.

Results

We utilized the Illumina MethylationEPIC array to analyze the sperm of 16 patients with older (> 40 years of age) paternal grandfathers (‘old grand paternal age’ patients; OGPA) and 16 patients with younger (< 25 years of age) grandfathers (‘young grand paternal age’ patients; YGPA) identified through the Subfertility Health Assisted Reproduction and the Environment (SHARE) cohort to investigate differences in DNA methylation. No differentially methylated regions were identified between the OGPA and YGPA groups. Further, when assessing only the sites previously shown to be altered by age, no statistically significant differences between OGPA and YGPA were identified. This was true even despite the lower bar for significance after removing multiple comparison correction in a targeted approach. Interestingly though, in an analysis of the 140 loci known to have decreased methylation with age, the majority (~ 72%) had lower methylation in OGPA compared to YGPA though the differences were extremely small (~ 1.5%).

Conclusions

This study suggests that the robust and consistent age-associated methylation alterations seen in human sperm are ‘reset’ during large-scale epigenetic reprograming processes and are not directly inherited trans-generationally (over two generations). An extremely small trend was present between the YGPA and OGPA groups that resemble the aging pattern in older sperm. However, this trend was not significant and was so small that, if real, is almost certainly biologically inert.

The neural mechanisms and consequences of paternal caregiving

In recent decades, human sociocultural changes have increased the numbers of fathers that are involved in direct caregiving in Western societies. This trend has led to a resurgence of interest in understanding the mechanisms and effects of paternal care. Across the animal kingdom, paternal caregiving has been found to be a highly malleable phenomenon, presenting with great variability among and within species. The emergence of paternal behaviour in a male animal has been shown to be accompanied by substantial neural plasticity and to be shaped by previous and current caregiving experiences, maternal and infant stimuli and ecological conditions. Recent research has allowed us to gain a better understanding of the neural basis of mammalian paternal care, the genomic and circuit-level mechanisms underlying paternal behaviour and the ways in which the subcortical structures that support maternal caregiving have evolved into a global network of parental care. In addition, the behavioural, neural and molecular consequences of paternal caregiving for offspring are becoming increasingly apparent. Future cross-species research on the effects of absence of the father and the transmission of paternal influences across generations may allow research on the neuroscience of fatherhood to impact society at large in a number of important ways.

AutDB: a platform to decode the genetic architecture of autism

AutDB is a deeply annotated resource for exploring the impact of genetic variations associated with autism spectrum disorders (ASD). First released in 2007, AutDB has evolved into a multi-modular resource of diverse types of genetic and functional evidence related to ASD. Current modules include: Human Gene, which annotates all ASD-linked genes and their variants; Animal Model, which catalogs behavioral, anatomical and physiological data from rodent models of ASD; Protein Interaction (PIN), which builds interactomes from direct relationships of protein products of ASD genes; and Copy Number Variant (CNV), which catalogs deletions and duplications of chromosomal loci identified in ASD. A multilevel data-integration strategy is utilized to connect the ASD genes to the components of the other modules. All information in this resource is manually curated by expert scientists from primary scientific publications and is referenced to source articles. AutDB is actively maintained with a rigorous quarterly data release schedule. As of June 2017, AutDB contains detailed annotations for 910 genes, 2197 CNV loci, 1060 rodent models and 38 296 PINs. With its widespread use by the research community, AutDB serves as a reference resource for analysis of large datasets, accelerating ASD research and potentially leading to targeted drug treatments. AutDB is available at http://autism.mindspec.org/autdb/Welcome.do.

Social behavior and aging: A fly model

The field of behavioral genetics has recently begun to explore the effect of age on social behaviors. Such studies are particularly important, as certain neuropsychiatric disorders with abnormal social interactions, like autism and schizophrenia, have been linked to older parents. Appropriate social interaction can also have a positive impact on longevity, and is associated with successful aging in humans. Currently, there are few genetic models for understanding the effect of aging on social behavior and its potential transgenerational inheritance. The fly is emerging as a powerful model for identifying the basic molecular mechanisms underlying neurological and neuropsychiatric disorders. In this review, we discuss these recent advancements, with a focus on how studies in Drosophila melanogaster have provided insight into the effect of aging on aspects of social behavior, including across generations.

Parental Age and Differential Estimates of Risk for Neuropsychiatric Disorders: Findings From the Danish Birth Cohort

OBJECTIVE

Parental age at birth has been shown to affect the rates of a range of neurodevelopmental disorders, but the understanding of the mechanisms through which it mediates different outcomes is still lacking. A population-based cohort was used to assess differential effects of parental age on estimates of risk across pediatric-onset neuropsychiatric disorders: autism spectrum disorder (ASD), attention-deficit/hyperactivity disorder (ADHD), obsessive-compulsive disorder (OCD), and Tourette's disorder/chronic tic disorder (TD/CT).

METHOD

The study cohort included all singleton births in Denmark from 1980 through 2007 with full information on parental ages (N = 1,490,745) and was followed through December 31, 2013. Cases of ASD, ADHD, OCD, and TD/CT were identified in the Danish Psychiatric Central Register and the National Patient Register. Associations with parental age were modeled using a stratified Cox regression, allowing for changes in baseline diagnostic rates across time.

RESULTS

Younger parental age was significantly associated with increased estimates of risk for ADHD and TD/CT, whereas older parental age was associated with ASD and OCD. Except for OCD, no evidence for differential effects of parental ages on male versus female offspring was observed.

CONCLUSION

This study provides novel evidence for the association between age at parenthood and TD/CT and OCD and for the first time shows in a population-based sample that parental age confers differential risk rates for pediatric-onset psychiatric disorders. These results are consistent with a model of shared and unshared risk architecture for pediatric-onset neuropsychiatric conditions, highlighting unique contributions of maternal and paternal ages.

Paternal and maternal age as risk factors for schizophrenia: a case-control study

OBJECTIVE

Advanced parental age might constitute a generic risk factor for mental and somatic disorders. The current study tested whether this concerns also patients with schizophrenia.

METHODS

A total of 231 schizophrenic, 56 other severe mental disorders patients and 204 controls were diagnosed according to DSM-IV-TR. Data were tested with ANOVA models including relative risk and odds ratios.

RESULTS

Patients with schizophrenia manifested higher paternal (32.55 ± 6.35 vs. 29.42 ± 6.07, p < .001) and maternal age (27.66 ± 5.57 vs. 25.46 ± 4.52, p < .001). Patients with other mental disorders had higher paternal (33.29 ± 8.35; p = .001) but not maternal age (26.69 ± 5.89; p = .296) compared to controls. There was no difference between the two patient groups concerning either paternal or maternal age (p > .05). There seems to be a higher risk for the development of schizophrenia in offspring with paternal age above 25 years and maternal age above 22 years at delivery.

CONCLUSIONS

The current study provides further support for the suggestion that advanced paternal age constitutes a risk factor (in a non-dose dependent and gender-independent way) for the development of schizophrenia but also for other mental disorders. In contrast, advanced maternal age characterises schizophrenia specifically. The higher risk is evident after 25 years of paternal and 22 years of maternal age, respectively.

Sperm epigenetics and aging

Advanced paternal age has very real consequences in fertility, embryogenesis, and even offspring health. Specifically, advanced paternal age has been linked to delayed time to pregnancy and in some studies even appears to be linked to a decreased likelihood of achieving a pregnancy. Epidemiological and animal model evidence also suggests that the offspring of older fathers are at an elevated risk for neuropsychiatric disease. For these reasons it is essential that we have a comprehensive understanding of what actually occurs in the gametes of the aging male. Available data suggest that there are very clear patterns of aging in the sperm epigenome that can be directly detected in DNA methylation patterns. Importantly, these alterations are so consistent that a predictive model has been successfully generated to predict an individual's age based only on sperm DNA methylation signatures. Because this metric is the most direct way to detect aging in sperm, it is logical that these signatures may offer predictive value for the offspring abnormalities that are also correlated with advanced paternal age and as such may offer a unique opportunity to generate diagnostic tools that can identify personalized risks for each couple hoping to achieve a pregnancy. While a great deal of work still needs to be performed to understand the real diagnostic utility of sperm epigenetic marks, the potential is real and warrants further investigation particularly in the context of advanced paternal age.

Progeny of old parents have increased social space in Drosophila melanogaster

We report the effects of aging and parental age in Drosophila melanogaster on two types of responses to social cues: the choice of preferred social spacing in an undisturbed group and the response to the Drosophila stress odorant (dSO) emitted by stressed flies. The patterns of changes during aging were notably different for these two social responses. Flies were initially closer in space and then became further apart. However, the pattern of change in response to dSO followed a more typical decline in performance, similarly to changes in locomotion. Interestingly, the increased social space of old parents, as well as their reduced performance in avoiding dSO, was passed on to their progeny, such that young adults adopted the behavioural characteristic of their old parents. While the response to social cues was inherited, the changes in locomotion were not. We were able to scale the changes in the social space of parents and their progeny by accelerating or decelerating the physiological process of aging by increasing temperatures and exposure to oxidative stress, or via caloric restriction, respectively. Finally, when we aged only one parent, only the male progeny of old fathers and the progeny of very old mothers were more distant.

Paternal Age Alters Social Development in Offspring

OBJECTIVE

Advanced paternal age (APA) at conception has been linked with autism and schizophrenia in offspring, neurodevelopmental disorders that affect social functioning. The current study explored the effects of paternal age on social development in the general population.

METHOD

We used multilevel growth modeling to investigate APA effects on socioemotional development from early childhood until adolescence, as measured by the Strengths and Difficulties Questionnaire (SDQ) in the Twins Early Development Study (TEDS) sample. We also investigated genetic and environmental underpinnings of the paternal age effects on development, using the Additive genetics, Common environment, unique Environment (ACE) and gene-environment (GxE) models.

RESULTS

In the general population, both very young and advanced paternal ages were associated with altered trajectory of social development (intercept: p = .01; slope: p = .03). No other behavioral domain was affected by either young or advanced age at fatherhood, suggesting specificity of paternal age effects. Increased importance of genetic factors in social development was recorded in the offspring of older but not very young fathers, suggesting distinct underpinnings of the paternal age effects at these two extremes.

CONCLUSION

Our findings highlight that the APA-related deficits that lead to autism and schizophrenia are likely continuously distributed in the population.

Stress and the Emerging Roles of Chromatin Remodeling in Signal Integration and Stable Transmission of Reversible Phenotypes

The influence of early life experience and degree of parental-infant attachment on emotional development in children and adolescents has been comprehensively studied. Structural and mechanistic insight into the biological foundation and maintenance of mammalian defensive systems (metabolic, immune, nervous and behavioral) is slowly advancing through the emerging field of developmental molecular (epi)genetics. Initial evidence revealed that differential nurture early in life generates stable differences in offspring hypothalamic-pituitary-adrenal (HPA) regulation, in part, through chromatin remodeling and changes in DNA methylation of specific genes expressed in the brain, revealing physical, biochemical and molecular paths for the epidemiological concept of gene-environment interactions. Herein, a primary molecular mechanism underpinning the early developmental programming and lifelong maintenance of defensive (emotional) responses in the offspring is the alteration of chromatin domains of specific genomic regions from a condensed state (heterochromatin) to a transcriptionally accessible state (euchromatin). Conversely, DNA methylation promotes the formation of heterochromatin, which is essential for gene silencing, genomic integrity and chromosome segregation. Therefore, inter-individual differences in chromatin modifications and DNA methylation marks hold great potential for assessing the impact of both early life experience and effectiveness of intervention programs—from guided psychosocial strategies focused on changing behavior to pharmacological treatments that target chromatin remodeling and DNA methylation enzymes to dietary approaches that alter cellular pools of metabolic intermediates and methyl donors to affect nutrient bioavailability and metabolism. In this review article, we discuss the potential molecular mechanism(s) of gene regulation associated with chromatin modeling and programming of endocrine (e.g., HPA and metabolic or cardiovascular) and behavioral (e.g., fearfulness, vigilance) responses to stress, including alterations in DNA methylation and the role of DNA repair machinery. From parental history (e.g., drugs, housing, illness, nutrition, socialization) to maternal-offspring exchanges of nutrition, microbiota, antibodies and stimulation, the nature of nurture provides not only mechanistic insight into how experiences propagate from external to internal variables, but also identifies a composite therapeutic target, chromatin modeling, for gestational/prenatal stress, adolescent anxiety/depression and adult-onset neuropsychiatric disease.

Advanced paternal age effects in neurodevelopmental disorders-review of potential underlying mechanisms

Multiple epidemiological studies suggest a relationship between advanced paternal age (APA) at conception and adverse neurodevelopmental outcomes in offspring, particularly with regard to increased risk for autism and schizophrenia. Conclusive evidence about how age-related changes in paternal gametes, or age-independent behavioral traits affect neural development is still lacking. Recent evidence suggests that the origins of APA effects are likely to be multidimensional, involving both inherited predisposition and de novo events. Here we provide a review of the epidemiological and molecular findings to date. Focusing on the latter, we present the evidence for genetic and epigenetic mechanisms underpinning the association between late fatherhood and disorder in offspring. We also discuss the limitations of the APA literature. We propose that different hypotheses relating to the origins of the APA effects are not mutually exclusive. Instead, multiple mechanisms likely contribute, reflecting the etiological complexity of neurodevelopmental disorders.

Paternal Aging Affects Behavior in Pax6 Mutant Mice: A Gene/Environment Interaction in Understanding Neurodevelopmental Disorders

Neurodevelopmental disorders such as autism spectrum disorder (ASD) and attention deficit and hyperactivity disorder (ADHD) have increased over the last few decades. These neurodevelopmental disorders are characterized by a complex etiology, which involves multiple genes and gene-environmental interactions. Various genes that control specific properties of neural development exert pivotal roles in the occurrence and severity of phenotypes associated with neurodevelopmental disorders. Moreover, paternal aging has been reported as one of the factors that contribute to the risk of ASD and ADHD. Here we report, for the first time, that paternal aging has profound effects on the onset of behavioral abnormalities in mice carrying a mutation of Pax6, a gene with neurodevelopmental regulatory functions. We adopted an in vitro fertilization approach to restrict the influence of additional factors. Comprehensive behavioral analyses were performed in Sey/+ mice (i.e., Pax6 mutant heterozygotes) born from in vitro fertilization of sperm taken from young or aged Sey/+ fathers. No body weight changes were found in the four groups, i.e., Sey/+ and wild type (WT) mice born to young or aged father. However, we found important differences in maternal separation-induced ultrasonic vocalizations of Sey/+ mice born from young father and in the level of hyperactivity of Sey/+ mice born from aged fathers in the open-field test, respectively, compared to WT littermates. Phenotypes of anxiety were observed in both genotypes born from aged fathers compared with those born from young fathers. No significant difference was found in social behavior and sensorimotor gating among the four groups. These results indicate that mice with a single genetic risk factor can develop different phenotypes depending on the paternal age. Our study advocates for serious considerations on the role of paternal aging in breeding strategies for animal studies.

Paternal age effects on sperm FOXK1 and KCNA7 methylation and transmission into the next generation

Children of older fathers carry an increased risk for developing autism and other disorders. To elucidate the underlying mechanisms, we investigated the correlation of sperm DNA methylation with paternal age and its impact on the epigenome of the offspring. Methylation levels of nine candidate genes and LINE-1 repeats were quantified by bisulfite pyrosequencing in sperm DNA of 162 donors and 191 cord blood samples of resulting children (conceived by IVF/ICSI with the same sperm samples). Four genes showed a significant negative correlation between sperm methylation and paternal age. For FOXK1 and KCNA7, the age effect on the sperm epigenome was replicated in an independent cohort of 188 sperm samples. For FOXK1, paternal age also significantly correlated with foetal cord blood (FCB) methylation. Deep bisulfite sequencing and allele-specific pyrosequencing allowed us to distinguish between maternal and paternal alleles in FCB samples with an informative SNP. FCB methylation of the paternal FOXK1 allele was negatively correlated with paternal age, whereas maternal allele was unaffected by maternal age. Since FOXK1 duplication has been associated with autism, we studied blood FOXK1 methylation in 74 children with autism and 41 age-matched controls. The FOXK1 promoter showed a trend for accelerated demethylation in the autism group. Dual luciferase reporter assay revealed that FOXK1 methylation influences gene expression. Collectively, our study demonstrates that age-related DNA methylation changes in sperm can be transmitted to the next generation and may contribute to the increased disease risk in offspring of older fathers.

Effects of Paternal Predation Risk and Rearing Environment on Maternal Investment and Development of Defensive Responses in the Offspring

Detecting past experiences with predators of a potential mate informs a female about prevailing ecological threats, in addition to stress-induced phenotypes that may be disseminated to offspring. We examined whether prior exposure of a male rat to a predator (cat) odor influences the attraction of a female toward a male, subsequent mother-infant interactions and the development of defensive (emotional) responses in the offspring. Females displayed less interest in males that had experienced predator odor. Mothers that reared young in larger, seminaturalistic housing provided more licking and grooming and active arched back-nursing behavior toward their offspring compared with dams housed in standard housing, although some effects interacted with paternal experience. Paternal predation risk and maternal rearing environment revealed sex-dependent differences in offspring wean weight, juvenile social interactions, and anxiety-like behavior in adolescence. Additionally, paternal predator experience and maternal housing independently affected variations in crf gene promoter acetylation and crf gene expression in response to an acute stressor in offspring. Our results show for the first time in mammals that variation among males in their predator encounters may contribute to stable behavioral variation among females in preference for mates and maternal care, even when the females are not directly exposed to predator threat. Furthermore, when offspring were exposed to the same threat experienced by the father, hypothalamic crf gene regulation was influenced by paternal olfactory experience and early housing. These results, together with our previous findings, suggest that paternal stress exposure and maternal rearing conditions can influence maternal behavior and the development of defensive responses in offspring.

Influence of paternal preconception exposures on their offspring: through epigenetics to phenotype

Historically, research into congenital defects has focused on maternal impacts on the fetal genome during gestation and prenatal periods. However, recent findings have sparked interest in epigenetic alterations of paternal genomes and its effects on offspring. This emergent field focuses on how environmental influences can epigenetically alter gene expression and ultimately change the phenotype and behavior of progeny. There are three primary mechanisms implicated in these changes: DNA methylation, histone modification, and miRNA expression. This paper provides a summary and subsequent review of past research, which highlights the significant impact of environmental factors on paternal germ cells during the lifetime of an individual as well as those of future generations. These findings support the existence of transgenerational epigenetic inheritance of paternal experiences. Specifically, we explore epidemiological and laboratory studies that demonstrate possible links between birth defects and paternal age, environmental factors, and alcohol consumption. Ultimately, our review highlights the clinical importance of these factors as well as the necessity for future research in the field.

Effects of advanced paternal age on trajectories of social behavior in offspring

Our study is the first investigation of the effects of advanced paternal age (APA) on the developmental trajectory of social behavior in rodent offspring. Given the strong epidemiological association between APA and sexually dimorphic neurodevelopmental disorders that are characterized by abnormalities in social behavior (autism, schizophrenia), we assessed sociability in male and female inbred mice (C57BL/6J) across postnatal development (N = 104) in relation to paternal age. We found differences in early social behavior in both male and female offspring of older breeders, with differences in this social domain persisting into adulthood in males only. We showed that these social deficits were not present in the fathers of these offspring, confirming a de novo origin of an altered social trajectory in the offspring generation. Our results, highly novel in rodent research, support the epidemiological observations in humans and provide evidence for a causal link between APA, age-related changes in the paternal sperm DNA and neurodevelopmental disorders in their offspring.

Advancing parental age and autism: multifactorial pathways

Converging evidence from epidemiological, genetic, and animal studies supports the hypothesis that advancing parental age, both of the father and mother, increases the risk of autism spectrum disorders (ASD) in offspring. Paternal age has received considerable attention, with whole-genome sequencing studies linking older fathers to higher rates of de novo mutations and increased risk of ASD. The current evidence suggests that the increased risk of ASD in the offspring of older mothers may be related to mechanisms different from those operating in older fathers. Causal pathways probably involve the interaction of multiple risk factors. Although the etiology of ASD is still poorly understood, studies of parental age provide clues into the genetic and environ-mental mechanisms that mediate the risk of ASD.

The scent of stress: environmental challenge in the peripartum environment of mice affects emotional behaviours of the adult offspring in a sex-specific manner

Early adverse experiences are known to influence the risk of developing psychiatric disorders later. To shed further light on the development of laboratory mice, we systematically examined the influence of a prenatal or postnatal olfactory stressor, namely unfamiliar male mouse faeces, presented to pregnant or nursing mouse dams. Maternal and offspring behaviours were then examined. Maternal behaviours relative to controls revealed changes in nest building by the pregnant dams exposed to the unfamiliar faeces. There were no differences among groups on pup retrieval or exploration by the dams. Behavioural phenotyping of male and female offspring as adults included measures of exploration, anxiety, social and depressive-like behaviours. Additionally, serum corticosterone was assessed as a marker of physiological stress response. Group differences were dependent on the sex of the adult offspring. Males raised by dams that were stressed during pregnancy presented elevated emotionality as indicated by increased numbers of faecal boluses in the open field paradigm. Consistent with the effects of prenatal stress on the males only the prenatally stressed females had higher body weights than their respective controls. Indeed, males in both experimental groups had higher circulating corticosterone levels. By contrast, female offspring of dams exposed to the olfactory stressor after parturition were more anxious in the O-maze as indicated by increased latencies in entering the exposed areas of the maze. These findings emphasize the necessity for researchers to consider the pre- and postnatal environments, even of mice with almost identical genetic backgrounds, in designing experiments and interpreting their data.

Age-related sperm DNA methylation changes are transmitted to offspring and associated with abnormal behavior and dysregulated gene expression

Advanced paternal age (APA) has been shown to be a significant risk factor in the offspring for neurodevelopmental psychiatric disorders, such as schizophrenia and autism spectrum disorders. During aging, de novo mutations accumulate in the male germline and are frequently transmitted to the offspring with deleterious effects. In addition, DNA methylation during spermatogenesis is an active process, which is susceptible to errors that can be propagated to subsequent generations. Here we test the hypothesis that the integrity of germline DNA methylation is compromised during the aging process. A genome-wide DNA methylation screen comparing sperm from young and old mice revealed a significant loss of methylation in the older mice in regions associated with transcriptional regulation. The offspring of older fathers had reduced exploratory and startle behaviors and exhibited similar brain DNA methylation abnormalities as observed in the paternal sperm. Offspring from old fathers also had transcriptional dysregulation of developmental genes implicated in autism and schizophrenia. Our findings demonstrate that DNA methylation abnormalities arising in the sperm of old fathers are a plausible mechanism to explain some of the risks that APA poses to resulting offspring.

Paternal age and mental health of offspring

The influence of paternal age on the risk for sporadic forms of Mendelian disorders is well known, but a burgeoning recent literature demonstrates, in addition, a paternal age effect for complex neuropsychiatric conditions, including schizophrenia, autism, bipolar disorder, and even for learning potential, expressed as intelligence. Mental illness is costly to patients, their family, and the public health system, accounting for the largest portion of disability costs in our economy. The delayed onset of neuropsychiatric conditions and lack of physical manifestations at birth are common frequencies in the population that have obscured the recognition that a portion of the risks for mental conditions is associated with paternal age. Identification of these risk pathways may be leveraged for knowledge about mental function and for future screening tests. However, only a small minority of at-risk offspring are likely to have such a psychiatric or learning disorder attributable to paternal age, including the children of older fathers.

Grand-paternal age and the development of autism-like symptoms in mice progeny

Advanced paternal age (APA) contributes to the risk of autism spectrum disorders (ASDs) in children. In this study, we used a mouse model to investigate the effects of APA on behavioral features related to autistic syndromes (that is, social deficits, communication impairments and stereotypic/repetitive behaviors). We also examined whether such effects are transmitted across generations. To do this, males aged 15 months (APA) and 4 months (control) were bred with 4-month-old females, and the resulting offspring (F1) and their progeny (F2; conceived by 4-month-old parents) were tested for the presence and severity of ASD-like behaviors. Our results indicate that APA resulted in offspring that displayed distinctive symptoms of ASD. We found that both F1 conceived from old fathers and F2 derived from old grandfathers displayed increased ultrasound vocalization (USV) activity, decreased sociability, increased grooming activity and increased anxiety-like responses. Moreover, such abnormalities were partially transmitted to the second generation of mice, having APA grandfathers. In conclusion, our study suggests that the risk of ASD could develop over generations, consistent with heritable mutations and/or epigenetic alterations associated with APA.

Parental age and risk of bipolar disorder in offspring

We investigated prospectively documented parental age and bipolar disorder (BD) in a multi-ethnic birth cohort. The study was based on a nested case-control design from the Child Health and Development Study (CHDS) birth cohort from 1959 to 1966. Potential cases with BD were ascertained by database linkages between CHDS, Kaiser Permanente Medical Care Plan (KPNC), and Alameda County Behavioral Health Care Services, and mailed questionnaires. Consensus diagnoses with the SCID for DSM-IV-TR were made. The total number of BD cases was 94. Controls (N=746) were selected from the birth cohort and matched on date of birth, sex, and KPNC membership or residence in Alameda County. For every 10-year increment of paternal age, there was no significant association with BD, adjusting for maternal age. There was also no significant association between maternal age, modeled in 10-year increments, and risk of BD after adjustment for paternal age and maternal race, although there was a suggestion for a protective relationship between increasing maternal age and BD with psychotic features. These findings suggest that if advanced paternal age is a risk factor for BD, the strength of the relationship is small.

Paternal aging and associated intraindividual alterations of global sperm 5-methylcytosine and 5-hydroxymethylcytosine levels

OBJECTIVE

To evaluate the relative intraindividual changes in sperm 5-methylcytosine (5-mC) and 5-hydroxymethylcytosine (5-hmC) levels associated with age and to compare the levels of 5-hmC in mature human sperm to blood DNA.

DESIGN

Prospective research study.

SETTING

University-based andrology and in vitro fertilization (IVF) laboratory.

PATIENT(S)

Fifteen known fertile sperm donors, 22 other known fertile controls, and 41 male blood donors from a general population tissue bank.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Measurements of global 5-mC and 5-hmC levels via an enzyme-linked immunosorbent assay (ELISA)-based assay.

RESULT(S)

Global sperm 5-mC levels exhibit a statistically significant increase with age, and a similar trend was seen in 5-hmC levels. On average, in the age ranges we analyzed, 5-mC increased by 1.76% per year, and 5-hmC, though more variable, increased by approximately 5% per year. Additionally, we found that 5-hmC levels in sperm are 32.59% of that found in blood DNA.

CONCLUSION(S)

Global sperm DNA methylation patterns are stable over short periods of time but increase with age, which raises important questions regarding the risks of advanced paternal age. Additionally, as we would predict for a transcriptionally quiescent cell type, 5-hmC levels are statistically significantly lower in human sperm than in blood DNA.

"Selfish spermatogonial selection": a novel mechanism for the association between advanced paternal age and neurodevelopmental disorders

There is robust evidence from epidemiological studies that the offspring of older fathers have an increased risk of neurodevelopmental disorders, such as schizophrenia and autism. The authors present a novel mechanism that may contribute to this association. Because the male germ cell undergoes many more cell divisions across the reproductive age range, copy errors taking place in the paternal germline are associated with de novo mutations in the offspring of older men. Recently it has been recognized that somatic mutations in male germ cells that modify proliferation through dysregulation of the RAS protein pathway can lead to within-testis expansion of mutant clonal lines. First identified in association with rare disorders related to paternal age (e.g., Apert syndrome, achondroplasia), this process is known as "selfish spermatogonial selection." This mechanism favors propagation of germ cells carrying pathogenic mutations, increasingly skews the mutational profile of sperm as men age, and enriches de novo mutations in the offspring of older fathers that preferentially affect specific cellular signaling pathways. This mechanism not only offers a parsimonious explanation for the association between advanced paternal age and various neurodevelopmental disorders but also provides insights into the genetic architecture (role of de novo mutations), neurobiological correlates (altered cell cycle), and some epidemiological features of these disorders. The authors outline hypotheses to test this model. Given the secular changes for delayed parenthood in most societies, this hypothesis has important public health implications.

Advancing paternal age and offspring violent offending: a sibling-comparison study

Children born to older fathers are at higher risk to develop severe psychopathology (e.g., schizophrenia and bipolar disorder), possibly because of increased de novo mutations during spermatogenesis with older paternal age. Because severe psychopathology is correlated with antisocial behavior, we examined possible associations between advancing paternal age and offspring violent offending. Interlinked Swedish national registers provided information on fathers' age at childbirth and violent criminal convictions in all offspring born from 1958 to 1979 (N = 2,359,921). We used ever committing a violent crime and number of violent crimes as indices of violent offending. The data included information on multiple levels; we compared differentially exposed siblings in within-family analyses to rigorously test causal influences. In the entire population, advancing paternal age predicted offspring violent crime according to both indices. Congruent with a causal effect, this association remained for rates of violent crime in within-family analyses. However, in within-family analyses, we found no association with ever committing a violent crime, suggesting that factors shared by siblings (genes and environment) confounded this association. Life-course persistent criminality has been proposed to have a partly biological etiology; our results agree with a stronger biological effect (i.e., de novo mutations) on persistent violent offending.

The neurodevelopmental hypothesis of schizophrenia: convergent clues from epidemiology and neuropathology

The neurodevelopmental hypothesis of schizophrenia suggests that the disruption of early brain development increases the risk of later developing schizophrenia. This hypothesis focuses attention on critical periods of early brain development. From an epidemiologic perspective, various prenatal and perinatal risk factors have been linked to schizophrenia, including exposures related to infection, nutrition, and obstetric complications. From a genetic perspective, candidate genes have also been linked to altered brain development. In recent decades evidence from neuropathology has provided support for the neurodevelopmental hypothesis. Animal models involving early life exposures have been linked to changes in these same brain systems, providing convergent evidence for this long-standing hypothesis.

Pregnancy-related maternal risk factors of attention-deficit hyperactivity disorder: a case-control study

Background. The etiology of attention-deficit hyperactivity disorder (ADHD) is complex.This study was conducted to evaluate the pregnancy-related maternal risk factors of ADHD. Methods. 164 ADHD children attending to Child and Adolescent Psychiatric Clinics compared with 166 normal children selected in a random-cluster method from primary schools. ADHD rating scale and clinical interview based on Schedule for Affective disorders and Schizophrenia for School-Aged Children (K-SADS) were used to diagnose ADHD cases and to select the control group. Results. The mean maternal age at pregnancy, duration of pregnancy, and the mean paternal age were alike in two groups. The ADHD children's mothers compared with those of control group had higher frequencies of somatic diseases, psychiatric disorders, and alcohol and cigarette exposure during the pregnancies (P < 0.01). Also birth by cesarean section was more common among mothers of ADHD children (P < 0.001). These factors plus trauma to the abdomen during pregnancy were significantly predictors of ADHD in children. Conclusions. Some pregnancy-related maternal factors may be considered as environmental risk factors for ADHD. Each of these factors considered in our study as a risk factor needs to be tested and confirmed through next methodologically appropriate researches in this field.

Advanced paternal and grandpaternal age and schizophrenia: a three-generation perspective

BACKGROUND

Advanced paternal age has been linked with an increased risk of schizophrenia in the offspring. If age-related de novo mutations in the male germ line underlie this association, grandpaternal and paternal age would both be expected to influence the risk of schizophrenia. The aim of the current study was to explore the links between both paternal and grandpaternal age with respect to the risk of schizophrenia in a large, national register-based cohort.

METHOD

We linked the Swedish Multi-Generation and Hospital Discharge Registers and compared parents' ages at offspring birth for 20,582 schizophrenia-affected and 100,176 non-affected individuals. Grandparents' ages at the birth of the parent were compared between 2511 affected and 15,619 non-affected individuals. The risk of schizophrenia was examined with logistic regression when the predictor variable (parent or grandparent age) varied across age strata.

RESULTS

After adjusting for maternal age, birth year and proband sex, we confirmed that offspring of older fathers had an increased risk of schizophrenia. Compared to those with paternal age 20-24years, those with fathers >55years had a two-fold increased risk of schizophrenia. With respect to grandparent age, older maternal (but not paternal) grandfather age was associated with an increased risk of schizophrenia. Compared to maternal grandfather age 20-24years, those with maternal grandfathers >55years had a significantly increased risk of schizophrenia (adjusted odds ratio and 95% confidence intervals; 2.79, 1.71-4.56). The pattern of results was essentially unchanged when we examined male and female probands separately.

CONCLUSION

This is the first study to report an association between grandpaternal age and risk of schizophrenia. The selective effect of advanced maternal grandfather age suggests that the biological mechanisms involving the X-chromosome may differentially contribute to the association between paternal age and offspring risk of schizophrenia.