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

Reproductive Ageing: Current insights and a potential role of NAD in the reproductive health of aging fathers and their children

In brief

In light of the increasing age of first-time fathers, this article summarizes the current scientific knowledge base on reproductive aging in the male, including sperm quality and health impacts for the offspring. The emerging role of NAD decline in reproductive aging is highlighted.

Abstract

Over the past decades, the age of first-time fathers has been steadily increasing due to socio-economic pressures. While general mechanisms of aging are subject to intensive research, male reproductive aging has remained an understudied area, and the effects of increased age on the male reproductive system are still only poorly understood, despite new insights into the potential dire consequences of advanced paternal age for the health of their progeny. There is also growing evidence that reproductive aging is linked to overall health in men, but this review mainly focuses on pathophysiological consequences of old age in men, such as low sperm count and diminished sperm genetic integrity, with an emphasis on mechanisms underlying reproductive aging. The steady decline of NAD levels observed in aging men represents one of the emerging concepts in that regard. Because it offers some mechanistic rationale explaining the effects of old age on the male reproductive system, some of the NAD-dependent functions in male reproduction are briefly outlined in this review. The overview also provides many questions that remain open about the basic science of male reproductive aging.

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.

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.

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.

The Promise of DNA Methylation in Understanding Multigenerational Factors in Autism Spectrum Disorders

Autism spectrum disorder (ASD) is a group of neurodevelopmental disorders characterized by impairments in social reciprocity and communication, restrictive interests, and repetitive behaviors. Most cases of ASD arise from a confluence of genetic susceptibility and environmental risk factors, whose interactions can be studied through epigenetic mechanisms such as DNA methylation. While various parental factors are known to increase risk for ASD, several studies have indicated that grandparental and great-grandparental factors may also contribute. In animal studies, gestational exposure to certain environmental factors, such as insecticides, medications, and social stress, increases risk for altered behavioral phenotypes in multiple subsequent generations. Changes in DNA methylation, gene expression, and chromatin accessibility often accompany these altered behavioral phenotypes, with changes often appearing in genes that are important for neurodevelopment or have been previously implicated in ASD. One hypothesized mechanism for these phenotypic and methylation changes includes the transmission of DNA methylation marks at individual chromosomal loci from parent to offspring and beyond, called multigenerational epigenetic inheritance. Alternatively, intermediate metabolic phenotypes in the parental generation may confer risk from the original grandparental exposure to risk for ASD in grandchildren, mediated by DNA methylation. While hypothesized mechanisms require further research, the potential for multigenerational epigenetics assessments of ASD risk has implications for precision medicine as the field attempts to address the variable etiology and clinical signs of ASD by incorporating genetic, environmental, and lifestyle factors. In this review, we discuss the promise of multigenerational DNA methylation investigations in understanding the complex etiology of ASD.

Influence of Prenatal Drug Exposure, Maternal Inflammation, and Parental Aging on the Development of Autism Spectrum Disorder

Autism spectrum disorder (ASD) affects reciprocal social interaction and produces abnormal repetitive, restrictive behaviors and interests. The diverse causes of ASD are divided into genetic alterations and environmental risks. The prevalence of ASD has been rising for several decades, which might be related to environmental risks as it is difficult to consider that the prevalence of genetic disorders related to ASD would increase suddenly. The latter includes (1) exposure to medications, such as valproic acid (VPA) and selective serotonin reuptake inhibitors (SSRIs) (2), maternal complications during pregnancy, including infection and hypertensive disorders of pregnancy, and (3) high parental age. Epidemiological studies have indicated a pathogenetic role of prenatal exposure to VPA and maternal inflammation in the development of ASD. VPA is considered to exert its deleterious effects on the fetal brain through several distinct mechanisms, such as alterations of γ-aminobutyric acid signaling, the inhibition of histone deacetylase, the disruption of folic acid metabolism, and the activation of mammalian target of rapamycin. Maternal inflammation that is caused by different stimuli converges on a higher load of proinflammatory cytokines in the fetal brain. Rodent models of maternal exposure to SSRIs generate ASD-like behavior in offspring, but clinical correlations with these preclinical findings are inconclusive. Hypertensive disorders of pregnancy and advanced parental age increase the risk of ASD in humans, but the mechanisms have been poorly investigated in animal models. Evidence of the mechanisms by which environmental factors are related to ASD is discussed, which may contribute to the development of preventive and therapeutic interventions for ASD.

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.

Altered sperm tsRNAs in aged male contribute to anxiety-like behavior in offspring

Parental age at first pregnancy is increasing worldwide. The offspring of aged father has been associated with higher risk of several neuropsychiatric disorders, such as schizophrenia and autism, but the underlying mechanism remains elusive. Here we report that advanced paternal age in mice alters the profile of transfer RNA‐derived small RNAs (tsRNAs). Injection of sperm tsRNAs from aged male mice into zygotes induced anxiety‐like behaviors in F1 males. RNA sequencing of the cerebral cortex and hippocampus of those F1 male mice altered the gene expression of dopaminergic synapse and neurotrophin. tsRNAs from aged male mice injection also altered the neuropsychiatry‐related gene expression in two‐cell and blastocyst stage embryos. More importantly, the sperm tsRNA profile changes significantly during aging in human. The up‐regulated sperm tsRNA target genes were involved in neurogenesis and nervous system development. These results suggest that aging‐related changes of sperm tsRNA may contribute to the intergenerational transmission of behavioral traits.

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.

An Overview of the Main Genetic, Epigenetic and Environmental Factors Involved in Autism Spectrum Disorder Focusing on Synaptic Activity

Autism spectrum disorder (ASD) is a neurodevelopmental disorder that affects social interaction and communication, with restricted interests, activity and behaviors. ASD is highly familial, indicating that genetic background strongly contributes to the development of this condition. However, only a fraction of the total number of genes thought to be associated with the condition have been discovered. Moreover, other factors may play an important role in ASD onset. In fact, it has been shown that parental conditions and in utero and perinatal factors may contribute to ASD etiology. More recently, epigenetic changes, including DNA methylation and micro RNA alterations, have been associated with ASD and proposed as potential biomarkers. This review aims to provide a summary of the literature regarding ASD candidate genes, mainly focusing on synapse formation and functionality and relevant epigenetic and environmental aspects acting in concert to determine ASD onset.

Autism-like behaviors and abnormality of glucose metabolism in offspring derived from aging males with epigenetically modified sperm

Accumulating evidence from epidemiological studies of humans and genetic models in rodents has shown that offspring from males of advanced paternal age (APA) are susceptible to metabolic and neurological disorders. However, knowledge of molecular mechanism(s) underlying these metabolic and behavioral changes at the intergeneration and trans-generation levels from APA is limited. Here, we characterized changes on glucose and cholesterol metabolism, and also autism spectrum disorders (ASD)-like behaviors in 1^st and 2^nd generations from 12- and 18-month-old male mice, respectively. Whole Genome Bisulfite Sequencing (WGBS) of sperm from APA mice identified differentially methylated regions (DMRs) within the whole genome, and DMRs within promoter regions, suggesting that specific genes and relevant pathways might be associated with autism and aberrant glucose metabolism in the offspring from APA males. These results strongly suggest that epigenetic reprogramming induced by aging in male sperm may lead to high risks of aberrant glucose metabolism and the development of ASD behaviors in intergenerational and transgenerational offspring.

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.

Association of Grandparental and Parental Age at Childbirth With Autism Spectrum Disorder in Children

IMPORTANCE

Advanced parental age has been associated with autism spectrum disorders (ASDs) in children. However, little is known about the association between grandparental age at the time of birth of the parent and the risk of ASD in the grandchildren.

OBJECTIVE

To estimate the associations between parental and grandparental age and ASD risk in children.

DESIGN, SETTING, AND PARTICIPANTS

This population-based, multigenerational cohort study used data from Danish national health registries. A parental age cohort was constructed to evaluate the association between parental age and ASD in 1 476 783 singleton children born from 1990 to 2013, and a multigenerational cohort was also constructed including 362 438 fathers and 458 234 mothers born from 1973 to 1990 for whom information on grandparental age was available. Data analyses were conducted from November 1, 2018, through February 7, 2020.

EXPOSURES

Parental age at childbirth and grandparental age at the time of the birth of the parent.

MAIN OUTCOMES AND MEASURES

Diagnoses of ASD in children were obtained from the Danish Psychiatric Central Register (1994-2017). Logistic regression analysis was used to estimate the associations between parental or grandparental age and ASD in children.

RESULTS

Of the 1 476 783 children born from 1990 to 2013, 758 066 (51.3%) were male, and 27 616 (1.9%) had ASD (20 467 [74.1%] were male). Advanced paternal or maternal age over 30 years was monotonically associated with increased ASD risk, with odds ratios (ORs) of 1.56 (95% CI, 1.45-1.68) for maternal age 40 years and older and 1.57 (95% CI, 1.39-1.78) for paternal age 50 years and older, compared with parents aged 25 to 29 years. In the multigenerational cohort, 9364 grandchildren (1.7%) had ASD. This study found U-shaped associations, in that ASD risk was higher among grandchildren of younger (≤19 years) maternal grandmothers (OR, 1.68; 95% CI, 1.52-1.85), younger maternal grandfathers (OR, 1.50; 95% CI, 1.26-1.78), and younger paternal grandmothers (OR, 1.18; 95% CI, 1.04-1.34), and older (≥40 years) paternal grandmothers (OR, 1.40; 95% CI, 1.03-1.90) compared with the grandchildren of grandparents who were aged 25 to 29 years at the time of giving birth to the parents.

CONCLUSIONS AND RELEVANCE

These findings corroborate previous studies suggesting that advanced parental age is independently associated with increased ASD risk in children. This study also found that children with young maternal grandparents and children with young and old paternal grandparents had elevated ASD risk. Possible transmission of ASD risk across generations should be considered in etiological research on ASD.

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.

Transgenerational epigenetic influences of paternal environmental exposures on brain function and predisposition to psychiatric disorders

In recent years, striking new evidence has demonstrated non-genetic inheritance of acquired traits associated with parental environmental exposures. In particular, this transgenerational modulation of phenotypic traits is of direct relevance to psychiatric disorders, including depression, post-traumatic stress disorder, and other anxiety disorders. Here we review the recent progress in this field, with an emphasis on acquired traits of psychiatric illnesses transmitted epigenetically via the male lineage. We discuss the transgenerational effects of paternal exposure to stress vs. positive stimuli, such as exercise, and discuss their impact on the behavioral, affective and cognitive characteristics of their progeny. Furthermore, we review the recent evidence suggesting that these transgenerational effects are mediated by epigenetic mechanisms, including changes in DNA methylation and small non-coding RNAs in the sperm. We discuss the urgent need for more research exploring transgenerational epigenetic effects in animal models and human populations. These future studies may identify epigenetic mechanisms as potential contributors to the 'missing heritability' observed in genome-wide association studies of psychiatric illnesses and other human disorders. This exciting new field of transgenerational epigenomics will facilitate the development of novel strategies to predict, prevent and treat negative epigenetic consequences on offspring health, and psychiatric disorders in particular.

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.

Risk of Neurodevelopmental Disease by Paternal Aging: A Possible Influence of Epigenetic Alteration in Sperm

Sincethe theory of DOHaD has been thrown in the spotlight, most attention has focused on environmental effects of the uterus on developing embryos/fetuses. However, the ontogenesis traces back to gametogenesis. Compared to oogenesis, spermatogenesis goes through far more cell divisions and is therefore more prone to genetic variation and epigenetic alterations. This article will mainly discuss recent findings about the effects of the advanced paternal age on the next generation, in relation to the onset of psychiatric disorders such as autism spectrum disorder. We would like to advocate for further exploration on the DOHaD theory in a wider view.

Pregnancy at Advanced Maternal Age Affects Behavior and Hippocampal Gene Expression in Mouse Offspring

There is growing evidence that advanced maternal age is a risk factor for neurological and neuropsychiatric disorders in offspring. However, it remains unclear whether the altered brain programming induced by advanced maternal age is mediated by pre- or postnatal factors. Here, a mouse model was used to investigate whether pregnancy at advanced age may provoke behavioral and brain gene expression changes in offspring. Swiss Albino mice conceived by 3-month-old males and either 15-18-month-old (n = 11) or 3-month-old control females (n = 5), were delivered by cesarean section, fostered after birth by 3-month-old dams and subjected to a battery of behavioral tests. Furthermore, genome-wide mRNA expression was analyzed in the hippocampi of 4-month-old males offspring using microarrays. Offspring conceived by old mothers exhibited increased ultrasound vocalization activity during separation from the foster mother, increased anxiety-like behaviors in adult life, and altered patterns of hippocampal gene expression, compared to controls. These effects were not reversed by the postnatal maternal care provided by the young foster mothers, suggesting that the altered brain programming is already established at birth, consistent with prenatal effects related to maternal aging.

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.

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.

Transgenerational latent early-life associated regulation unites environment and genetics across generations

The origin of idiopathic diseases is still poorly understood. The latent early-life associated regulation (LEARn) model unites environmental exposures and gene expression while providing a mechanistic underpinning for later-occurring disorders. We propose that this process can occur across generations via transgenerational LEARn (tLEARn). In tLEARn, each person is a 'unit' accumulating preclinical or subclinical 'hits' as in the original LEARn model. These changes can then be epigenomically passed along to offspring. Transgenerational accumulation of 'hits' determines a sporadic disease state. Few significant transgenerational hits would accompany conception or gestation of most people, but these may suffice to 'prime' someone to respond to later-life hits. Hits need not produce symptoms or microphenotypes to have a transgenerational effect. Testing tLEARn requires longitudinal approaches. A recently proposed longitudinal epigenome/envirome-wide association study would unite genetic sequence, epigenomic markers, environmental exposures, patient personal history taken at multiple time points and family history.

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.

Mice age - Does the age of the mother predict offspring behaviour?

Increasing paternal age is known to be associated with a great variety of psychiatric disorders such as schizophrenia or autism. Hence the factor "age" may be taken as strategic tool to analyse specific scientific hypotheses. Additionally, this finding also needs to be addressed in rather pragmatically performed breeding protocols of model organisms, since otherwise artefacts may challenge the validity of the results. Our study was performed to investigate influences of advanced age of mouse dams (30 vs. 16weeks) on maternal- and offspring behaviour. Adult offspring of both sexes was analysed in a test battery comprising paradigms for exploration, anxiety and depressive-like behaviours. Final blood sampling was conducted for stressphysiological analysis. Interestingly, advanced age of the mothers was associated with increased nest-building quality while maternal activity was unaffected. Moreover "maternal (mice) age" (MA) affected emotionality in the offspring, which became apparent in the dark-light box and the social recognition paradigm. These findings not only emphasize MA to model a potent risk factor with regard to emotional stability, but also underscore the vast necessity to include information about breeding protocols into the methods section of any animal study.

Effects of increased paternal age on sperm quality, reproductive outcome and associated epigenetic risks to offspring

Over the last decade, there has been a significant increase in average paternal age when the first child is conceived, either due to increased life expectancy, widespread use of contraception, late marriages and other factors. While the effect of maternal ageing on fertilization and reproduction is well known and several studies have shown that women over 35 years have a higher risk of infertility, pregnancy complications, spontaneous abortion, congenital anomalies, and perinatal complications. The effect of paternal age on semen quality and reproductive function is controversial for several reasons. First, there is no universal definition for advanced paternal ageing. Secondly, the literature is full of studies with conflicting results, especially for the most common parameters tested. Advancing paternal age also has been associated with increased risk of genetic disease. Our exhaustive literature review has demonstrated negative effects on sperm quality and testicular functions with increasing paternal age. Epigenetics changes, DNA mutations along with chromosomal aneuploidies have been associated with increasing paternal age. In addition to increased risk of male infertility, paternal age has also been demonstrated to impact reproductive and fertility outcomes including a decrease in IVF/ICSI success rate and increasing rate of preterm birth. Increasing paternal age has shown to increase the incidence of different types of disorders like autism, schizophrenia, bipolar disorders, and childhood leukemia in the progeny. It is thereby essential to educate the infertile couples on the disturbing links between increased paternal age and rising disorders in their offspring, to better counsel them during their reproductive years.