Grand-maternal smoking in pregnancy and grandchild's autistic traits and diagnosed autism

Dopamine Dysregulation in Reward and Autism Spectrum Disorder

Autism spectrum disorder (ASD) is primarily characterized by core deficits in social skills, communication, and cognition and by repetitive stereotyped behaviors. These manifestations are variable between individuals, and ASD pathogenesis is complex, with over a thousand implicated genes, many epigenetic factors, and multiple environmental influences. The mesolimbic dopamine (DA) mediated brain reward system is held to play a key role, but the rapidly expanding literature reveals intricate, nuanced signaling involving a wide array of mesolimbic loci, neurotransmitters and receptor subtypes, and neuronal variants. How altered DA signaling may constitute a downstream convergence of the manifold causal origins of ASD is not well understood. A clear working framework of ASD pathogenesis may help delineate common stages and potential diagnostic and interventional opportunities. Hence, we summarize the known natural history of ASD in the context of emerging data and perspectives to update ASD reward signaling. Then, against this backdrop, we proffer a provisional framework that organizes ASD pathogenesis into successive levels, including (1) genetic and epigenetic changes, (2) disrupted mesolimbic reward signaling pathways, (3) dysregulated neurotransmitter/DA signaling, and finally, (4) altered neurocognitive and social behavior and possible antagonist/agonist based ASD interventions. This subdivision of ASD into a logical progression of potentially addressable parts may help facilitate the rational formulation of diagnostics and targeted treatments.

Childhood trauma as a mediator between autistic traits and depression: evidence from the ALSPAC birth cohort

Background

Autism and autistic traits have been associated with greater risk of childhood trauma and adulthood psychopathology. However, the role that childhood trauma plays in the association between autism, autistic traits and depression in adulthood is poorly understood.

Methods

We used a UK-based birth cohort with phenotype and genotype data on autism, autistic traits, childhood trauma and depression in up to 9,659 individuals prospectively followed up from birth until age 28 years. Using mixed-effects growth-curve models, we assessed trajectories of depression symptoms over time according to the presence or absence of autism/ autistic traits and explored whether these differed by trauma exposure. We further investigated the association between autism/ autistic traits and depression in adulthood using confounder-adjusted logistic regression models and undertook mediation analyses to investigate the relationship with childhood trauma.

Results

All autism variables demonstrated increased depressive symptom trajectories between ages 10-28 years. Social communication difficulties (SCDs) were the most strongly associated with a depression diagnosis in adulthood (age 24 OR= 2.15; 95%CIs: 1.22-3.76). Trauma and autistic traits combined to further increase depression symptom scores. Mediation analyses provided evidence for direct pathways between autistic traits and increased risk of depression alongside indirect pathways through increased risk of trauma.

Conclusions

Autism/ autistic traits increase the odds of experiencing childhood trauma and of being diagnosed with depression at age 18 and 24. Depressive symptom trajectories emergent in childhood persist into adulthood. The combined effect of SCDs and childhood trauma is greater than the individual exposures, suggesting worse depression symptomatology following trauma in individuals with SCDs.

Lay abstract

Autism and autistic traits are linked to higher chances of experiencing traumatic events in childhood and having mental health problems as an adult. However, we don't understand how childhood trauma influences the link between autistic traits and depression in adulthood.Using data from a large birth cohort study in the UK, we tracked up to 9,659 people from birth until age 28 years. We looked at the links between autism, autistic traits, childhood trauma, and depression.We found that all features related to autism were associated with more symptoms of depression between the ages of 10 and 28. Among these, difficulties in social communication were the most strongly connected to depression when they reached adulthood, more than doubling the risk.We discovered that when childhood difficulties and autistic traits came together, the risk of experiencing depression symptoms increased even more. We showed that autistic traits raised the chances of depression both directly and indirectly, by increasing the chance of experiencing childhood trauma.Taken together, our research shows that autism and autistic traits increase the likelihood of experiencing childhood trauma and being diagnosed with depression at ages 18 and 24. Signs of depression that appear in childhood tend to persist into adulthood. The combination of social communication difficulties and childhood trauma has a stronger impact on depression symptoms, indicating that people with these traits may experience more severe depression after facing traumatic events.

Preclinical Models of Attention Deficit Hyperactivity Disorder: Neurobiology, Drug Discovery, and Beyond

OBJECTIVE

We offer an overview of ADHD research using mouse models of nicotine exposure.

METHOD

Nicotine exposure of C57BL/6 or Swiss Webster mice occurred during prenatal period only or during the prenatal and the pre-weaning periods. Behavioral, neuroanatomical and neurotransmitter assays were used to investigate neurobiological mechanisms of ADHD and discover candidate ADHD medications.

RESULTS

Our studies show that norbinaltorphimine, a selective kappa opioid receptor antagonist is a candidate novel non-stimulant ADHD treatment and that a combination of methylphenidate and naltrexone has abuse deterrent potential with therapeutic benefits for ADHD. Other studies showed transgenerational transmission of ADHD-associated behavioral traits and demonstrated that interactions between untreated ADHD and repeated mild traumatic brain injury produced behavioral traits not associated with either condition alone.

CONCLUSION

Preclinical models contribute to novel insights into ADHD neurobiology and are valuable tools for drug discovery and translation to benefit humans with ADHD.

A scoping review of multigenerational impacts of grandparental exposures on mental health in grandchildren

PURPOSE OF REVIEW

The multigenerational effects of grandparental exposures on their grandchildren's mental health and neurodevelopment are gaining research attention. We conducted a scoping review to summarize the current epidemiological studies investigating pregnancy-related and environmental factors that affected grandparental pregnancies and mental health outcomes in their grandchildren. We also identified methodological challenges that affect these multigenerational health studies and discuss opportunities for future research.

RECENT FINDINGS

We performed a literature search using PubMed and Embase and included 18 articles for this review. The most investigated grandparental pregnancy-related factors were the grandparental age of pregnancy (N = 6), smoking during pregnancy (N = 4), and medication intake (N = 3). The most frequently examined grandchild outcomes were autism spectrum disorder (N = 6) and attention-deficit/hyperactivity disorder (N = 4). Among these studies, grandparental smoking and the use of diethylstilbestrol were more consistently reported to be associated with neurodevelopmental disorders, while the findings for grandparental age vary across the maternal or paternal line. Grandmaternal weight, adverse delivery outcomes, and other spatial-temporal markers of physical and social environmental stressors require further scrutiny. The current body of literature has suggested that mental and neurodevelopmental disorders may be outcomes of unfavorable exposures originating from the grandparental generation during their pregnancies. To advance the field, we recommend research efforts into setting up multigenerational studies with prospectively collected data that span through at least three generations, incorporating spatial, environmental, and biological markers for exposure assessment, expanding the outcome phenotypes evaluated, and developing a causal analytical framework including mediation analyses specific for multigenerational research.

Learning and memory deficits produced by aspartame are heritable via the paternal lineage

Environmental exposures produce heritable traits that can linger in the population for one or two generations. Millions of individuals consume substances such as artificial sweeteners daily that are declared safe by regulatory agencies without evaluation of their potential heritable effects. We show that consumption of aspartame, an FDA-approved artificial sweetener, daily for up to 16-weeks at doses equivalent to only 7-15% of the FDA recommended maximum daily intake value (equivalent to 2-4 small, 8 oz diet soda drinks per day) produces significant spatial learning and memory deficits in mice. Moreover, the cognitive deficits are transmitted to male and female descendants along the paternal lineage suggesting that aspartame's adverse cognitive effects are heritable, and that they are more pervasive than current estimates, which consider effects in the directly exposed individuals only. Traditionally, deleterious environmental exposures of pregnant and nursing women are viewed as risk factors for the health of future generations. Environmental exposures of men are not considered to pose similar risks. Our findings suggest that environmental exposures of men can produce adverse impact on cognitive function in future generations and demonstrate the need for considering heritable effects via the paternal lineage as part of the regulatory evaluations of artificial sweeteners.

Inter and transgenerational impact of H3K4 methylation in neuronal homeostasis

Epigenetic marks and associated traits can be transmitted for one or more generations, phenomena known respectively as inter- or transgenerational epigenetic inheritance. It remains unknown if genetically and conditionally induced aberrant epigenetic states can influence the development of the nervous system across generations. Here, we show, using Caenorhabditis elegans as a model system, that alteration of H3K4me3 levels in the parental generation, caused by genetic manipulation or changes in parental conditions, has, respectively, trans- and intergenerational effects on H3K4 methylome, transcriptome, and nervous system development. Thus, our study reveals the relevance of H3K4me3 transmission and maintenance in preventing long-lasting deleterious effects in nervous system homeostasis.

Autism, autistic traits and multiple risk behaviours in adolescence: a longitudinal birth cohort study

BACKGROUND

Multiple risk behaviours (MRBs), typically beginning in adolescence, are associated with increased risk of adverse health and social outcomes. The association between autism and MRBs is little understood.

METHODS

Data were from the Avon Longitudinal Study of Parents and Children, an UK-based longitudinal, birth cohort study. Exposures were diagnosed autism and four autistic traits: social communication difficulties, pragmatic language, repetitive behaviours and reduced sociability. Outcomes were participation in up to 14 risk behaviours, including alcohol consumption, smoking, risky sexual behaviours and physical inactivity. Outcome data were collected at ages approximately 12, 14, 16 and 18.

RESULTS

Up to 4300 participants were included in latent basis growth curve analyses with adjustment for confounders. Social communication difficulties were associated with an above average level of MRBs engagement at ~12 years (mean difference β 0.26; 95% CI 0.13-0.40), and above average rate of engagement from ages ~12-18 (β 0.08; 95% CI 0.02-0.13). Repetitive behaviours were associated with above average levels of engagement in MRBs at ~12 years (β 0.24; 95% CI 0.09-0.38). Contrastingly, reduced sociability was associated with a reduced rate of engagement in MRBs from ages ~12-18 (β -0.06; 95% CI -0.11 to -0.02). In sex-specific analyses, persisting differences in MRB engagement patterns from ages ~12-18 were observed in males with social communication difficulties and females with reduced sociability temperament.

CONCLUSIONS

Having elevated levels of some autistic traits appear to have differentiated effects on MRB engagement patterns. These findings could reflect difficulties fitting in and/or coping mechanisms relating to difficulties with fitting in.

Associations between maternal exposure to surgery or pregnancy exposure to fluorinated anesthetics and children's cognitive development and educational outcomes

A transgenerational, epigenetic effect of anesthesia, particularly fluorinated agents, has been examined in rat models, but translation to humans is unclear. This study examined associations of maternal lifetime exposure to anesthesia and pregnancy exposure to fluorinated anesthetics with child cognitive and educational outcomes. Women in the US Collaborative Perinatal Project (1959-1963) reported lifetime history of surgeries, and the obstetric record captured pregnancy exposure to anesthetics. Children were followed to age 7 for global cognitive ability and educational outcomes (n=47,977). Logistic and linear regressions were adjusted for maternal and child birth years, race and ethnicity, smoking, education, parity, study site. Many outcomes were not associated with exposure to maternal surgery that occurred at various life stages. However, maternal surgery in early childhood was associated both with being in a special school or not in school (adj OR=1.42; 95% CI 1.02, 1.98) and with slightly better cognitive ability across childhood (e.g., WISC IQ (adj β=0.59; CI 0.13, 1.04) (especially among boys)). Maternal surgery in puberty was associated with slightly lower IQ (adj β = -0.42; CI -0.79, -0.05) and poorer spelling at age 7. Children's prenatal exposure to fluorinated anesthetics was associated with slightly better spelling ability (adj β = 1.20; CI 0.02, 2.38) but lower performance IQ at age 7 (only among boys, adj β = -1.97; CI -3.88, -0.06). This study shows inconsistent evidence of effects of maternal exposure to surgery or prenatal exposure to fluorinated agents on child developmental and educational outcomes Residual confounding by indication and socioeconomic status may explain observed associations.

Nicotine on the developing brain

Developmental periods such as gestation and adolescence have enhanced plasticity leaving the brain vulnerable to harmful effects from nicotine use. Proper brain maturation and circuit organization is critical for normal physiological and behavioral outcomes. Although cigarette smoking has declined in popularity, noncombustible nicotine products are readily used. The misperceived safety of these alternatives lead to widespread use among vulnerable populations such as pregnant women and adolescents. Nicotine exposure during these sensitive developmental windows is detrimental to cardiorespiratory function, learning and memory, executive function, and reward related circuitry. In this review, we will discuss clinical and preclinical evidence of the adverse alterations in the brain and behavior following nicotine exposure. Time-dependent nicotine-induced changes in reward related brain regions and drug reward behaviors will be discussed and highlight unique sensitivities within a developmental period. We will also review long lasting effects of developmental exposure persisting into adulthood, along with permanent epigenetic changes in the genome which can be passed to future generations. Taken together, it is critical to evaluate the consequences of nicotine exposure during these vulnerable developmental windows due to its direct impact on cognition, potential trajectories for other substance use, and implicated mechanisms for the neurobiology of substance use disorders.

Possible transgenerational associations between grandparents’ childhood exposures and religious belief in their granddaughters: a longitudinal cohort study

Background: Research in non-genetic inheritance indicates that grandparents’ smoking habits and their childhood experiences of trauma can influence the physical and psychological attributes of their grandchildren. This was particularly apparent for outcomes such as autism and obesity where the population prevalence changed over time. Other factors which have changed temporally include religious and spiritual beliefs (RSBs) which have been declining in Western populations. Methods: We used data from the Avon Longitudinal Study of Parents and Children (ALSPAC) to explore whether grandparental exposures were associated with the religious and/or spiritual beliefs of their grandchildren as measured with a positive response to the question “Do you believe in God or some divine power?” . In line with other inter/trans-generational human studies we hypothesised that: (H1) grandparents’ childhood exposures to cigarette smoking (whether in utero or by active smoking) and/or exposure to traumatic events during childhood will be associated with their grandchild’s RSB; (H2) associations will differ between maternal and paternal lines of inheritance; (H3) relationships will vary with age at grandparental exposure, and (H4) associations will differ between grandsons and granddaughters. Results: We found significant associations between the grandchild’s RSB and both the grandparents’ smoking and their childhood trauma histories (H1 supported). These associations were mainly found down the maternal line (H2 possibly supported) and results varied with age of exposure of the grandparents; being strongest for in utero exposure of cigarette smoke and for pre-puberty exposure of traumatic events (H3 supported), and that granddaughters were more affected than grandsons (H4 supported). Conclusions: We hope that these results will motivate collection of similar data to further evaluate these questions in other populations, including a possible role for biological mechanisms.

Cohort-guided insights into gene-environment interactions in autism spectrum disorders

Prospective birth cohorts offer unprecedented opportunities to investigate the pathogenesis of complex disorders such as autism, in which gene-environment interactions must be appreciated in a temporal context. This Perspective article considers the history of autism research, including missteps that reflected an incomplete understanding of the epidemiology of autistic spectrum disorders, the effects of advocacy and philanthropy on the trajectory of scientific inquiry, and the current and future roles of prospective birth cohort research in illuminating the pathology of these and other complex disorders wherein exposures during gestation might not manifest until later in life.

Paternal transmission of behavioural and metabolic traits induced by postnatal stress to the 5th generation in mice

Life experiences and environmental conditions in childhood can change the physiology and behaviour of exposed individuals and, in some cases, of their offspring. In rodent models, stress/trauma, poor diet, and endocrine disruptors in a parent have been shown to cause phenotypes in the direct progeny, suggesting intergenerational inheritance. A few models also examined transmission to further offspring and suggested transgenerational inheritance, but such multigenerational inheritance is not well characterized. Our previous work on a mouse model of early postnatal stress showed that behaviour and metabolism are altered in the offspring of exposed males up to the 4th generation in the patriline and up to the 2nd generation in the matriline. The present study examined if symptoms can be transmitted beyond the 4th generation in the patriline. Analyses of the 5th and 6th generations of mice revealed that altered risk-taking and glucose regulation caused by postnatal stress are still manifested in the 5th generation but are attenuated in the 6th generation. Some of the symptoms are expressed in both males and females, but some are sex-dependent and sometimes opposite. These results indicate that postnatal trauma can affect behaviour and metabolism over many generations, suggesting epigenetic mechanisms of transmission.

Maternal vitamin D during pregnancy and offspring autism and autism-associated traits: a prospective cohort study

BACKGROUND

There has been a growing interest in the association between maternal levels of vitamin D during pregnancy and offspring autism. However, whether any associations reflect causal effects is still inconclusive.

METHODS

We used data from a UK-based pregnancy cohort study (Avon Longitudinal Study of Parents and Children) comprising 7689 births between 1991 and 1992 with maternal blood vitamin D levels recorded during pregnancy and at least one recorded outcome measure, including autism diagnosis and autism-associated traits. The association between each outcome with seasonal and gestational age-adjusted maternal serum 25-hydroxyvitamin D during pregnancy was estimated using confounder-adjusted regression models. Multiple imputation was used to account for missing data, and restricted cubic splines were used to investigate nonlinear associations. Mendelian randomization was used to strengthen causal inference.

RESULTS

No strong evidence of an association between maternal serum 25-hydroxyvitamin D during pregnancy and any offspring autism-associated outcome was found using multivariable regression analysis (autism diagnosis: adjusted OR = 0.98, 95% CI = 0.90-1.06), including with multiple imputation (autism diagnosis: adjusted OR = 0.99, 95% CI = 0.93-1.06), and no evidence of a causal effect was suggested by Mendelian randomization (autism diagnosis: causal OR = 1.08, 95% CI = 0.46-2.55). Some evidence of increased odds of autism-associated traits at lower levels of maternal serum 25-hydroxyvitamin D was found using spline analysis.

LIMITATIONS

Our study was potentially limited by low power, particularly for diagnosed autism cases as an outcome. The cohort may not have captured the extreme lows of the distribution of serum 25-hydroxyvitamin D, and our analyses may have been biased by residual confounding and missing data.

CONCLUSIONS

The present study found no strong evidence of a causal link between maternal vitamin D levels in pregnancy and offspring diagnosis or traits of autism.

Thyroid hormone elicits intergenerational epigenetic effects on adult social behavior and fetal brain expression of autism susceptibility genes

Genetic mutations identified in genome-wide association studies can only explain a small percentage of the cases of complex, highly heritable human conditions, including neurological and neurodevelopmental disorders. This suggests that intergenerational epigenetic effects, possibly triggered by environmental circumstances, may contribute to their etiology. We previously described altered DNA methylation signatures in the sperm of mice that experienced developmental overexposure to thyroid hormones as a result of a genetic defect in hormone clearance (DIO3 deficiency). Here we studied fetal brain gene expression and adult social behavior in genetically normal F2 generation descendants of overexposed mice. The brain of F2 generation E13.5 fetuses exhibited abnormal expression of genes associated with autism in humans, including Auts2, Disc1, Ldlr, Per2, Shank3, Oxtr, Igf1, Foxg1, Cd38, Grid2, Nrxn3, and Reln. These abnormal gene expression profiles differed depending on the sex of the exposed ancestor. In the three-chamber social box test, adult F2 generation males manifested significantly decreased interest in social interaction and social novelty, as revealed by decrease total time, distance traveled and time immobile in the area of interaction with novel strangers. F1 generation mice, compared to appropriate controls also exhibited altered profiles in fetal brain gene expression, although these profiles were substantially different to those in the F2 generation. Likewise adult F1 generation mice showed some abnormalities in social behavior that were sexually dimorphic and milder than those in F2 generation mice. Our results indicate that developmental overexposure to thyroid hormone causes intergenerational epigenetic effects impacting social behavior and the expression of autism-related genes during early brain development. Our results open the possibility that altered thyroid hormone states, by eliciting changes in the epigenetic information of the germ line, contribute to the susceptibility and the missing-but heriTables-etiology of complex neurodevelopmental conditions characterized by social deficits, including autism and schizophrenia.

Effects of glyphosate and glyphosate-based herbicides like Roundup™ on the mammalian nervous system: A review

Glyphosate is the active ingredient in glyphosate-based herbicides (GBHs), such as Roundup™, the most widely used herbicides in the world. Glyphosate targets an essential enzyme in plants that is not found in animals. However, both glyphosate and GBHs are rated as Group 2A, probable human carcinogens, and also have documented effects on reproduction, acting as endocrine disruptive chemicals. We have reviewed reports of the effects of glyphosate and GBHs on mammalian nervous system function. As with several other herbicides, GBHs exposure has been associated with an increased risk of Parkinson's Disease and death of neurons in the substantia nigra. There is also some evidence implicating Roundup™ in elevated risk of autism. Other studies have shown the effects of GBHs on synaptic transmission in animal and cellular studies. The major mechanism of action appears to be oxidative stress, accompanied by mitochondrial dysfunction. In addition, some gut bacteria utilize the enzyme used by plants, and glyphosate and GBHs use has been shown to alter the gut microbiome. There is a large and growing body of evidence that the gut microbiome alters susceptibility to great number of human diseases, including nervous system function. The weight of the evidence indicates that in addition to cancer and reproductive effects, glyphosate and GBHs have significant adverse effects on the brain and behavior and increase the risk of at least some serious neurological diseases.

Beyond Genes: Germline Disruption in the Etiology of Autism Spectrum Disorders

Investigations into the etiology of autism spectrum disorders have been largely confined to two realms: variations in DNA sequence and somatic developmental exposures. Here we suggest a third route-disruption of the germline epigenome induced by exogenous toxicants during a parent's gamete development. Similar to cases of germline mutation, these molecular perturbations may produce dysregulated transcription of brain-related genes during fetal and early development, resulting in abnormal neurobehavioral phenotypes in offspring. Many types of exposures may have these impacts, and here we discuss examples of anesthetic gases, tobacco components, synthetic steroids, and valproic acid. Alterations in parental germline could help explain some unsolved phenomena of autism, including increased prevalence, missing heritability, skewed sex ratio, and heterogeneity of neurobiology and behavior.

Possible transgenerational associations between grandparents’ childhood exposures and religious belief in their granddaughters: a longitudinal cohort study

Background: Research in non-genetic inheritance indicates that grandparents’ smoking habits and their childhood experiences of trauma can influence the physical and psychological attributes of their grandchildren. This was particularly apparent for outcomes such as autism and obesity where the population prevalence changed over time. Other factors which have changed temporally include religious and spiritual beliefs (RSBs) which have been declining in Western populations. Methods: We used data from the Avon Longitudinal Study of Parents and Children (ALSPAC) to explore whether grandparental exposures were associated with the religious and/or spiritual beliefs of their grandchildren. In line with other inter/trans-generational human studies we predicted that: (P1) grandparents’ childhood exposures to cigarette smoking (whether in utero or by active smoking) and/or exposure to traumatic events during childhood will be associated with their grandchild’s RSB; (P2) associations will differ between maternal and paternal lines of inheritance; (P3) relationships will vary with age at grandparental exposure, and (P4) associations will differ between grandsons and granddaughters. Results: We found significant associations between the grandchild’s RSB and both the grandparents’ smoking and their childhood trauma histories (P1 supported). These associations were mainly found down the maternal line (P2 possibly supported) and results varied with age of exposure of the grandparents; being strongest for in utero exposure of cigarette smoke and for pre-puberty exposure of traumatic events (P3 supported), and that granddaughters were more affected than grandsons (P4 supported). Conclusions: We hope that these results will motivate collection of similar data to further evaluate these questions in other populations, including a possible role for biological mechanisms.

Smoking During Pregnancy and Risk of Attention-deficit/Hyperactivity Disorder in the Third Generation

BACKGROUND

Animal experiments indicate that environmental factors, such as cigarette smoke, can have multigenerational effects through the germline. However, there are little data on multigenerational effects of smoking in humans. We examined the associations between grandmothers' smoking while pregnant and risk of attention-deficit/hyperactivity disorder (ADHD) in her grandchildren.

METHODS

Our study population included 53,653 Nurses' Health Study II (NHS-II) participants (generation 1 [G1]), their mothers (generation 0 [G0]), and their 120,467 live-born children (generation 2 [G2]). In secondary analyses, we used data from 23,844 mothers of the nurses who were participants in the Nurses' Mothers' Cohort Study (NMCS), a substudy of NHS-II.

RESULTS

The prevalence of G0 smoking during the pregnancy with the G1 nurse was 25%. ADHD was diagnosed in 9,049 (7.5%) of the grandchildren (G2). Grand-maternal smoking during pregnancy was associated with increased odds of ADHD among the grandchildren (adjusted odds ratio [aOR] = 1.2; 95% confidence interval [CI] = 1.1, 1.2), independent of G1 smoking during pregnancy. In the Nurses' Mothers' Cohort Study, odds of ADHD increased with increasing cigarettes smoked per day by the grandmother (1-14 cigarettes: aOR = 1.1; 95% CI = 1.0, 1.2; 15+: aOR = 1.2; 95% CI = 1.0, 1.3), compared with nonsmoking grandmothers.

CONCLUSIONS

Grandmother smoking during pregnancy is associated with an increased risk of ADHD among the grandchildren.

Paternal grandmother's smoking in pregnancy is associated with extreme aversion to bitter taste in their grandchildren

Although there are many examples in the experimental literature of an environmental exposure in one generation impacting the phenotypes of subsequent generations, there are few studies that can assess whether such associations occur in humans. The Avon Longitudinal Study of Parents and Children (ALSPAC) has, however, been able to determine whether there are associations between grandparental exposures and their grandchildren's development. Several of our studies, including sensitivity to loud noise, have shown associations between a grandmother smoking in pregnancy and the phenotype of the grandchild. These results were mostly specific to the sex of the grandchild and to whether the prenatal (i.e. during pregnancy) smoking occurred in the maternal or paternal grandmother. Here, we have used ancestral data on prenatal smoking among the grandmothers of the ALSPAC index children to examine possible effects on the grandchild's ability to detect the bitter taste of PROP (6 n-propylthiouracil), distinguishing between the 10% deemed 'extreme tasters', and the rest of the population (total N = 4656 children). We showed that grandchildren whose paternal (but not maternal) grandmothers had smoked in pregnancy were more likely than those of non-smoking grandmothers to be extreme tasters [odds ratio (OR) 1.28; 95% confidence interval (CI) 1.03, 1.59] and that this was more likely in granddaughters (OR 1.42; 95% CI 1.03, 1.95) than grandsons (OR 1.18; 95% CI 0.88, 1.60). This pattern of association between paternal foetal exposure and the granddaughter's development has been found with several other outcomes, suggesting that investigations should be undertaken to investigate possible mechanisms.

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.

Genetic liability to rheumatoid arthritis on autism and autistic traits: polygenic risk score and Mendelian randomization analyses

Higher prevalence of autism in offspring born to mothers with rheumatoid arthritis has been reported in observational studies. We investigated (a) the associations between maternal and offspring's own genetic liability for rheumatoid arthritis and autism-related outcomes in the offspring using polygenic risk scores (PRS) and (b) whether the effects were causal using Mendelian randomization (MR). Using the latest genome-wide association (GWAS) summary data on rheumatoid arthritis and individual-level data from the Avon Longitudinal Study of Parents and Children, United Kingdom, we constructed PRSs for maternal and offspring genetic liability for rheumatoid arthritis (single-nucleotide polymorphism [SNP] p-value threshold 0.05). We investigated associations with autism, and autistic traits: social and communication difficulties, coherence, repetitive behaviours and sociability. We used modified Poisson regression with robust standard errors. In two-sample MR analyses, we used 40 genome-wide significant SNPs for rheumatoid arthritis and investigated the causal effects on risk for autism, in 18,381 cases and 27,969 controls of the Psychiatric Genetics Consortium and iPSYCH. Sample size ranged from 4992 to 7849 in PRS analyses. We found little evidence of associations between rheumatoid arthritis PRSs and autism-related phenotypes in the offspring (maternal PRS on autism: RR 0.89, 95%CI 0.73-1.07, p = 0.21; offspring's own PRS on autism: RR 1.11, 95%CI 0.88-1.39, p = 0.39). MR results provided little evidence for a causal effect (IVW OR 1.01, 95%CI 0.98-1.04, p = 0.56). There was little evidence for associations between genetic liability for rheumatoid arthritis on autism-related outcomes in offspring. Lifetime risk for rheumatoid arthritis has no causal effects on autism.

DNA methylome perturbations: an epigenetic basis for the emergingly heritable neurodevelopmental abnormalities associated with maternal smoking and maternal nicotine exposure†

Maternal smoking during pregnancy is associated with an ensemble of neurodevelopmental consequences in children and therefore constitutes a pressing public health concern. Adding to this burden, contemporary epidemiological and especially animal model research suggests that grandmaternal smoking is similarly associated with neurodevelopmental abnormalities in grandchildren, indicative of intergenerational transmission of the neurodevelopmental impacts of maternal smoking. Probing the mechanistic bases of neurodevelopmental anomalies in the children of maternal smokers and the intergenerational transmission thereof, emerging research intimates that epigenetic changes, namely DNA methylome perturbations, are key factors. Altogether, these findings warrant future research to fully elucidate the etiology of neurodevelopmental impairments in the children and grandchildren of maternal smokers and underscore the clear potential thereof to benefit public health by informing the development and implementation of preventative measures, prophylactics, and treatments. To this end, the present review aims to encapsulate the burgeoning evidence linking maternal smoking to intergenerational epigenetic inheritance of neurodevelopmental abnormalities, to identify the strengths and weaknesses thereof, and to highlight areas of emphasis for future human and animal model research therein.

Heritable consequences of paternal nicotine exposure: from phenomena to mechanisms†

Our understanding of the interactions between genetic and environmental factors in shaping behavioral phenotypes has expanded to include environment-induced epigenetic modifications and the intriguing possibility of their association with heritable behavioral phenotypes. The molecular basis of heritability of phenotypes arising from environment-induced epigenetic modifications is not well defined yet. However, phenomenological evidence in favor of it is accumulating rapidly. The resurgence of interest has led to focus on epigenetic modification of germ cells as a plausible mechanism of heritability. Perhaps partly because of practical reasons such as ease of access to male germ cells compared to female germ cells, attention has turned toward heritable effects of environmental influences on male founders. Public health implications of heritable effects of paternal exposures to addictive substances or to psycho-social factors may be enormous. Considering nicotine alone, over a billion people worldwide use nicotine-containing products, and the majority are men. Historically, the adverse effects of nicotine use by pregnant women received much attention by scientists and public policy experts alike. The implications of nicotine use by men for the physical and mental well-being of their children were not at the forefront of research until recently. Here, we review progress in the emerging field of heritable effects of paternal nicotine exposure and its implications for behavioral health of individuals in multiple generations.

Ancestral smoking and developmental outcomes: a review of publications from a population birth cohort†

The adverse effects on the child of maternal smoking in pregnancy is well-recognized, but little research has been carried out on the possible non-genetic effects of ancestral smoking prior to the pregnancy including parental initiation of cigarette smoking in their own childhoods or a grandmother smoking during pregnancy. Here, we summarize the studies that have been published mainly using data from the Avon Longitudinal Study of Parents and Children. We demonstrate evidence that ancestral smoking prior to or during pregnancy can often be beneficial for offspring health and both ancestor- and sex-specific. More specifically, we report evidence of (i) adverse effects of the father starting to smoke pre-puberty on his son's development; (ii) beneficial effects on the grandson if his maternal grandmother had smoked in pregnancy; and (iii) mainly adverse effects on the granddaughter when the paternal grandmother had smoked in pregnancy. The ancestor- and sex-specificity of these results are consistent with earlier studies reporting associations of health and mortality with ancestral food supply in their parents' and grandparents' pre-pubertal childhoods.

Associations of parental birth characteristics with autism spectrum disorder (ASD) risk in their offspring: a population-based multigenerational cohort study in Denmark

BACKGROUND

Fetal exposure risk factors are associated with increased autism spectrum disorder (ASD) risk. New hypotheses regarding multigenerational risk for ASD have been proposed, but epidemiological evidence is largely lacking. We evaluated whether parental birth characteristics, including preterm birth and low birthweight, were associated with ASD risk in offspring.

METHODS

We conducted a nationwide register-based cohort study that included 230 174 mother-child and 157 926 father-child pairs in Denmark. Logistic regression models were used to estimate odds ratios (OR) and 95% confidence intervals (CI) for offspring ASD according to parental preterm (<37 weeks) and low birthweight (<2500 g) status, with or without adjustment for certain grandmaternal sociodemographic factors. Mediation analyses were performed for selected parental and offspring health-related factors.

RESULTS

Offspring of mothers or fathers with adverse birth characteristics had about 31-43% higher risk for ASD (maternal preterm birth, OR = 1.31, 95% CI= 1.12, 1.55; maternal low birthweight, OR = 1.35, 95% CI: 1.17,1.57; paternal preterm birth, OR = 1.43, 95% CI = 1.18, 1.73; paternal low birthweight, OR = 1.38, 95% CI= 1.13, 1.70). Parents born very preterm (<32 weeks) marked a nearly 2-fold increase in ASD risk in their children. These associations were slightly attenuated upon adjustment for grandmaternal sociodemographic factors. Mediation analyses suggested that parental social-mental and offspring perinatal factors might explain a small magnitude of the total effect observed, especially for maternal birth characteristic associations.

CONCLUSIONS

Offspring of parents born with adverse characteristics had an elevated risk for ASD. Transmission of ASD risk through maternal and paternal factors should be considered in future research on ASD aetiology.

Association Between Periconceptional Weight of Maternal Grandmothers and Attention-Deficit/Hyperactivity Disorder in Grandchildren

IMPORTANCE

Neurodevelopmental disorders have been proposed to involve alterations to epigenetic regulation, and epigenetic effects may extend to germline cells to affect later generations. Weight status may affect DNA methylation, and maternal weight before and during pregnancy has been associated with offspring DNA methylation as well as attention-deficit/hyperactivity disorder (ADHD).

OBJECTIVE

To assess whether a woman's weight before and during pregnancy is associated with ADHD in her grandchild.

DESIGN, SETTING, AND PARTICIPANTS

This cohort study analyzed data from 19 835 grandmother-mother dyads and 44 720 grandchildren in the Nurses' Health Study II (NHS-II) cohort (2001-2013), a population-based prospective cohort study. Cluster-weighted generalized estimating equations were modeled to estimate the association of grandmother's prepregnancy body mass index (BMI) and gestational weight gain with grandchild risk of ADHD. Data analyses were conducted from May 2018 to April 2021. Grandmothers reported their height and weight before, and weight gain during, their pregnancy with the NHS-II participants. Mothers self-reported height and weight prior to pregnancy. From those data, grandmother BMI and mother BMI were calculated as weight in kilograms divided by height in meters squared and categorized as underweight (<18.5), healthy/normal (18.5-24.9), overweight (25.0-29.9), or obese (≥30).

MAIN OUTCOMES AND MEASURES

Cases of ADHD identified by maternal report of having a child with a diagnosis of ADHD.

RESULTS

In total, 19 835 grandmothers (97.6% White race/ethnicity; 2113 [10.7%] prepregnancy underweight and 1391 [7.0%] prepregnancy overweight or obese) were included in this cohort study. Of 44 720 grandchildren, 3593 (8%) received a diagnosis of ADHD. Higher odds of ADHD among grandchildren were found for those whose grandmother was underweight compared with healthy weight prior to pregnancy with the NHS-II participant (adjusted odds ratio, 1.25; 95% CI, 1.10-1.42). By contrast, grandmother gestational weight gain was not significantly associated with risk of grandchild ADHD (adjusted odds ratio for <20 lbs [9.1 kg], 1.06; 95% CI, 0.96-1.16; adjusted odds ratio for >29 lbs [13.2 kg], 1.01; 95% CI, 0.91-1.13). Mother prepregnancy BMI showed an association with ADHD among offspring, with a stronger association detected for obese status (adjusted odds ratio, 1.27; 95% CI, 1.07-1.49) than for overweight status (adjusted odds ratio, 1.13; 95% CI, 1.02-1.26) compared with normal weight as a reference group. The positive association between grandmother prepregnancy underweight and ADHD risk among the grandchildren remained unchanged after further adjustment for potential mediators, including maternal prepregnancy BMI.

CONCLUSIONS AND RELEVANCE

The results of this cohort study indicate that grandmother underweight prior to pregnancy is associated with an increased risk of ADHD among grandchildren, independent of grandmother gestational weight gain and independent of maternal prepregnancy weight status.

The Intergenerational Transmission of Developmental Nicotine Exposure-Induced Neurodevelopmental Disorder-Like Phenotypes is Modulated by the Chrna5 D397N Polymorphism in Adolescent Mice

Maternal tobacco smoking during pregnancy constitutes developmental nicotine exposure (DNE) and is associated with nicotine dependence and neurodevelopmental disorders in both children and grandchildren as well as animal models thereof. Genetic variants such as the CHRNA5 single nucleotide polymorphism (SNP) rs16969968, which leads to an aspartic acid to asparagine substitution at amino acid position 398 (D398N) in the alpha-5 nicotinic acetylcholine receptor subunit, can also confer risk for nicotine dependence and neurodevelopmental disorders in the absence of DNE. However, the degrees to which, the consequences of maternal smoking on offspring outcomes are influenced by genetic variants and interactions therewith are not well understood. Addressing this void in the literature, the present study utilizes a DNE mouse model engineered to possess the equivalent of the human D398N SNP in CHRNA5 (D397N SNP in mice) to assess how the N397 risk allele impacts the induction and intergenerational transmission of a range of neurodevelopmental disorder-related behavioral phenotypes in first- and second-generation DNE offspring. Results reveal that offspring possessing the N397 variant in the absence of DNE as well as DNE offspring and grand offspring possessing theD397 variant exhibit analogous neurodevelopmental disorder-like phenotypes including hyperactivity, risk-taking behaviors, aberrant rhythmicity of activity, and enhanced nicotine consumption. DNE amplified these behavioral anomalies in first-generation N397 progeny, but the severity of DNE-evoked behavioral perturbations did not significantly differ between first-generation D397 and N397 DNE mice for any measure. Remarkably, the behavioral profiles of second-generation N397 DNE progeny closely resembled DNE-naive D397 mice, suggesting that the N397 variant may protect against the intergenerational transmission of DNE-induced neurodevelopmental disorder-like behaviors.

Exploring the evidence for epigenetic regulation of environmental influences on child health across generations

Environmental exposures, psychosocial stressors and nutrition are all potentially important influences that may impact health outcomes directly or via interactions with the genome or epigenome over generations. While there have been clear successes in large-scale human genetic studies in recent decades, there is still a substantial amount of missing heritability to be elucidated for complex childhood disorders. Mounting evidence, primarily in animals, suggests environmental exposures may generate or perpetuate altered health outcomes across one or more generations. One putative mechanism for these environmental health effects is via altered epigenetic regulation. This review highlights the current epidemiologic literature and supporting animal studies that describe intergenerational and transgenerational health effects of environmental exposures. Both maternal and paternal exposures and transmission patterns are considered, with attention paid to the attendant ethical, legal and social implications.

Maternal Nicotine Exposure Alters Hippocampal Microglia Polarization and Promotes Anti-inflammatory Signaling in Juvenile Offspring in Mice

Accumulating evidence reveal that maternal smoking or perinatal nicotine replacement therapy impairs hippocampal neurogenesis, neural development, and cognitive behaviors in the offspring. Microglia is a source of non-neural regulation of neuronal development and postnatal neurogenesis. In this study, we explored the impact of nicotine on the microglia during the development of hippocampus. Developmental nicotine exposure in a mouse model was conducted by supplementing nicotine in the drinking water to mother mice during gestation and lactation period. We found that juvenile offspring with maternal nicotine exposure presented physical and neurobehavioral development delay and an increase in anxiety-like behavior in the open field test on postnatal day (PND) 20. To further detect possible developmental neurotoxic effects of nicotine in offspring and underlying mechanism, whole genome microarray analysis of the expression profile of the hippocampus was performed on postnatal day 20. Significant alterations in the expression of genes related to inflammatory, neurotransmitter, and synapsis were observed in the hippocampus after maternal nicotine exposure, as compared to the vehicle control. Concurrently, an increase in microglial markers and the presence of M2 polarity state in the hippocampus of the nicotine offspring were observed by histological analysis and confocal z-stacking scanning. The M2 microglial polarization state was further confirmed with in vitro primary microglia culture by cytokine array, and double-positive expression of BDNF/Iba1 in microglia by immunohistochemical staining in the juvenile offspring hippocampus was visualized. We also found that nicotine offspring showed an increase of neurite length in the molecular layer and CA1 by Tuj1 staining, as well as an increase in the expression of synapse associated protein, PSD95, but the expression of NeuroD1 in CA1 and CA3 reduced. In summary, maternal nicotine exposure dysregulates immune-related genes expression by skewing the polarity of M2 microglia in the hippocampus, which may cause abnormal cognitive and behavioral performance in the offspring.

Effect of Grandmaternal Smoking on Body Size and Proportions at Birth

Many long-term adverse effects of smoking during pregnancy are known. Increasingly, adverse effects in the grandchild after grandmaternal smoking during pregnancy are reported. We explored this in a birth cohort of 24,000 grandmother–mother–child triads identified from the Finnish Medical Birth Register in 1991–2016. Multiple logistic regression was used to analyze the association between any smoking during pregnancy by both grandmother and mother, or only grandmother or mother on adverse birth outcomes. No smoking by neither grandmother nor mother was used as the reference. As endpoints, preterm birth, low birth weight, small for gestational age (birth weight, birth length, head circumference), and body proportionality (low ponderal index, high brain-to-body ratio, high head-to-length ratio) were included. Smoking by both grandmother and mother was consistently associated with higher risks than smoking only by the mother. Birth length and weight were especially sensitive to (grand)maternal smoking. In conclusion, the combined effect of grandmaternal and maternal smoking is associated with higher risks than only maternal smoking.

How Family Histories Can Inform Research About Germ Cell Exposures: The Example of Autism

Throughout the scientific literature, heritable traits are routinely presumed to be genetic in origin. However, as emerging evidence from the realms of genetic toxicology and epigenomics demonstrate, heritability may be better understood as encompassing not only DNA sequence passed down through generations, but also disruptions to the parental germ cells causing de novo mutations or epigenetic alterations, with subsequent shifts in gene expression and functions in offspring. The Beyond Genes conference highlighted advances in understanding these aspects at molecular, experimental and epidemiological levels. In this commentary I suggest that future research on this topic could be inspired by collecting parents' germ cell exposure histories, with particular attention to cases of families with multiple children suffering idiopathic disorders. In so doing I focus on the endpoint of autism spectrum disorders (ASD). Rates of this serious neurodevelopment disability have climbed around the world, a growing crisis that cannot be explained by diagnostic shifts. ASD's strong heritability has prompted a research program largely focused on DNA sequencing to locate rare and common variants, but decades of this gene-focused research have revealed surprisingly little about the molecular origins of the disorder. Based on my experience as the mother of two children with idiopathic autism, and as a research philanthropist and autism advocate, I suggest ways researchers might probe parental germ cell exposure histories to develop new hypotheses that may ultimately reveal sources of non-genetic heritability in a subset of idiopathic heritable pathologies.

Grandchild's IQ is associated with grandparental environments prior to the birth of the parents

Background. Despite convincing animal experiments demonstrating the potential for environmental exposures in one generation to have demonstrable effects generations later, there have been few relevant human studies. Those that have been undertaken have demonstrated associations, for example, between exposures such as nutrition and cigarette smoking in the grandparental generation and outcomes in grandchildren. We hypothesised that such transgenerational associations might be associated with the IQ of the grandchild, and that it would be likely that there would be differences in results between the sexes of the grandparents, parents, and children. Method. We used three-generational data from the Avon Longitudinal Study of Parents and Children (ALSPAC).  We incorporated environmental factors concerning grandparents (F0) and focussed on three exposures that we hypothesised may have independent transgenerational associations with the IQ of the grandchildren (F2): (i) UK Gross Domestic Product (GDP) at grandparental birth year; (ii) whether grandfather smoked; and (iii) whether the grandmother smoked in the relevant pregnancy. Potential confounders were ages of grandparents when the relevant parent was born, ethnic background, education level and social class of each grandparent. Results. After adjustment, all three target exposures had specific associations with measures of IQ in the grandchild. Paternal grandfather smoking was associated with reduced total IQ at 15 years; maternal grandfather smoking with reduced performance IQ at 8 years and reduced total IQ at 15.  Paternal grandmother smoking in pregnancy was associated with reduced performance IQ at 8, especially in grandsons. GDP at grandparents' birth produced independent associations of reduced IQ with higher GDP; this was particularly true of paternal grandmothers. Conclusions. These results are complex and need to be tested in other datasets. They highlight the need to consider possible transgenerational associations in studying developmental variation in populations.

Heritable hazards of smoking: Applying the "clean sheet" framework to further science and policy

All the cells in our bodies are derived from the germ cells of our parents, just as our own germ cells become the bodies of our children. The integrity of the genetic information inherited from these germ cells is of paramount importance in establishing the health of each generation and perpetuating our species into the future. There is a large and growing body of evidence strongly suggesting the existence of substances that may threaten this integrity by acting as human germ cell mutagens. However, there generally are no absolute regulatory requirements to test agents for germ cell effects. In addition, the current regulatory testing paradigms do not evaluate the impacts of epigenetically mediated intergenerational effects, and there is no regulatory framework to apply new and emerging tests in regulatory decision making. At the 50th annual meeting of the Environmental Mutagenesis and Genomics Society held in Washington, DC, in September 2019, a workshop took place that examined the heritable effects of hazardous exposures to germ cells, using tobacco smoke as the example hazard. This synopsis provides a summary of areas of concern regarding heritable hazards from tobacco smoke exposures identified at the workshop and the value of the Clean Sheet framework in organizing information to address knowledge and testing gaps.

Exposure to drugs of abuse induce effects that persist across generations

Substance use disorders are highly prevalent and continue to be one of the leading causes of disability in the world. Notably, not all people who use addictive drugs develop a substance use disorder. Although substance use disorders are highly heritable, patterns of inheritance cannot be explained purely by Mendelian genetic mechanisms. Vulnerability to developing drug addiction depends on the interplay between genetics and environment. Additionally, evidence from the past decade has pointed to the role of epigenetic inheritance in drug addiction. This emerging field focuses on how environmental perturbations, including exposure to addictive drugs, induce epigenetic modifications that are transmitted to the embryo at fertilization and modify developmental gene expression programs to ultimately impact subsequent generations. This chapter highlights intergenerational and transgenerational phenotypes in offspring following a history of parental drug exposure. Special attention is paid to parental preconception exposure studies of five drugs of abuse (alcohol, cocaine, nicotine, cannabinoids, and opiates) and associated behavioral and physiological outcomes in offspring. The highlighted studies demonstrate that parental exposure to drugs of abuse has enduring effects that persist into subsequent generations. Understanding the contribution of epigenetic inheritance in drug addiction may provide clues for better treatments and therapies for substance use disorders.

Sperm DNA methylation altered by THC and nicotine: Vulnerability of neurodevelopmental genes with bivalent chromatin

Men consume the most nicotine and cannabis products but impacts on sperm epigenetics are poorly characterized. Evidence suggests that preconception exposure to these drugs alters offspring neurodevelopment. Epigenetics may in part facilitate heritability. We therefore compared effects of exposure to tetrahydrocannabinol (THC) and nicotine on DNA methylation in rat sperm at genes involved in neurodevelopment. Reduced representation bisulfite sequencing data from sperm of rats exposed to THC via oral gavage showed that seven neurodevelopmentally active genes were significantly differentially methylated versus controls. Pyrosequencing data revealed majority overlap in differential methylation in sperm from rats exposed to THC via injection as well as those exposed to nicotine. Neurodevelopmental genes including autism candidates are vulnerable to environmental exposures and common features may mediate this vulnerability. We discovered that autism candidate genes are significantly enriched for bivalent chromatin structure, suggesting this configuration may increase vulnerability of genes in sperm to disrupted methylation.

Evidence for germline non-genetic inheritance of human phenotypes and diseases

It is becoming increasingly apparent that certain phenotypes are inherited across generations independent of the information contained in the DNA sequence, by factors in germ cells that remain largely uncharacterized. As evidence for germline non-genetic inheritance of phenotypes and diseases continues to grow in model organisms, there are fewer reports of this phenomenon in humans, due to a variety of complications in evaluating this mechanism of inheritance in humans. This review summarizes the evidence for germline-based non-genetic inheritance in humans, as well as the significant challenges and important caveats that must be considered when evaluating this process in human populations. Most reports of this process evaluate the association of a lifetime exposure in ancestors with changes in DNA methylation or small RNA expression in germ cells, as well as the association between ancestral experiences and the inheritance of a phenotype in descendants, down to great-grandchildren in some cases. Collectively, these studies provide evidence that phenotypes can be inherited in a DNA-independent manner; the extent to which this process contributes to disease development, as well as the cellular and molecular regulation of this process, remain largely undefined.

Grandchild's IQ is associated with grandparental environments prior to the birth of the parents

Background: In spite of convincing animal experiments demonstrating the potential for environmental exposures in one generation to have demonstrable effects generations later, there have been few relevant human studies. Those that have been undertaken have demonstrated associations, for example, between exposures such as nutrition and cigarette smoking in the grandparental generation and outcomes in grandchildren. We hypothesised that such transgenerational associations might be associated with the IQ of the grandchild, and that it would be likely that there would be differences in results between the sexes of the grandparents, parents and children. Methods: We used three-generational data from the Avon Longitudinal Study of Parents and Children (ALSPAC).  We incorporated environmental factors concerning grandparents (F0) and focussed on three exposures that we hypothesised may have independent transgenerational associations with the IQ of the grandchildren (F2): (i) UK Gross Domestic Product (GDP) at grandparental birth year; (ii) whether the grandfather smoked; and (iii) whether the grandmother smoked in the relevant pregnancy. Potential confounders were ages of grandparents when the relevant parent was born, ethnic background, education level and social class of each grandparent. Results: After adjustment, all three target exposures had specific associations with measures of IQ in the grandchild. Paternal grandfather smoking was associated with reduced total IQ at 15 years; maternal grandfather smoking with reduced performance IQ at 8 years and reduced total IQ at 15.  Paternal grandmother smoking in pregnancy was associated with reduced performance IQ at 8, especially in grandsons. GDP at grandparents' birth produced independent associations of reduced IQ with higher GDP; this was particularly true of paternal grandmothers. Conclusions: These results are complex and need to be tested in other datasets. They highlight the need to consider possible transgenerational associations in studying developmental variation in populations.

Parental locus of control and the failure to obtain a child diagnosis: a longitudinal cohort study

Background: Data from the Avon Longitudinal Study of Parents and Children (ALSPAC) were analysed to investigate associations between parents’ locus of control (LOC) and their use of their children’s symptoms to pursue a diagnosis of autism.  Methods: Comparison of parental LOC obtained prenatally with various aspects of the child’s (<12 years) development, used the prevalence of four autistic traits, to ascertain the likelihood that they qualified for an autism diagnosis. Results: Parents with an external LOC had children who were more likely to demonstrate extreme levels of each of the four autistic traits (e.g. for social communication 8.9% of offspring of internal LOC versus 12.3% of external LOC mothers; P<0.0001). However, the rate of autism diagnosis was considerably greater if the mother was internal compared to external (13.3 v 9.6 per 1000). To determine whether the difference was autism specific, we compared parental LOC with children diagnosed with dyslexia and those with reading impairments. Although externals’ children had more reading impairment indicators than internals, this was not reflected by them being more likely to be diagnosed as dyslexic. Conclusions: We conclude that children of parents with an externally oriented LOC may be less likely to be diagnosed appropriately than children of internally oriented parents. Interventions to increase parental internality may improve the likelihood of appropriate diagnoses and hence an improvement in child well-being.

An Inventory of European Birth Cohorts

Many birth cohorts have been carried out. We performed a review of European birth cohorts to see the countries involved, provide a panorama of the current research topics and design, and, more generally, provide input for those creating collaborations and laying out guidelines aimed at unifying cohort methodologies to enable data merging and maximize knowledge acquisition. We searched PubMed and Embase for articles referring to longitudinal, prospective European birth cohorts and searched online cohort inventories. We found references to 111 birth cohorts, 45 of which began enrolment at birth. These cohorts began between 1921 and 2015 and represented 19 countries, with varying sample sizes (236 to 21,000 children). As of 5 January 2020, were still recruiting. The main areas addressed were allergic diseases (14 cohorts) and environmental exposure (f12 cohorts) and most cohorts were publicly funded. Given the large costs of running cohorts and the importance of long follow-up periods in identifying the risk factors for disorders thought to have a perinatal/early life etiology, current cohorts must be designed to answer research questions considering several aspects, from genetic ones to psychological, social, and environmental ones. Furthermore, universally recognized methodological aspects are needed to permit the comparison and merging of cohort data.

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.

Developmental nicotine exposure engenders intergenerational downregulation and aberrant posttranslational modification of cardinal epigenetic factors in the frontal cortices, striata, and hippocampi of adolescent mice

BACKGROUND

Maternal smoking of traditional or electronic cigarettes during pregnancy, which constitutes developmental nicotine exposure (DNE), heightens the risk of neurodevelopmental disorders including ADHD, autism, and schizophrenia in children. Modeling the intergenerationally transmissible impacts of smoking during pregnancy, we previously demonstrated that both the first- and second-generation adolescent offspring of nicotine-exposed female mice exhibit enhanced nicotine preference, hyperactivity and risk-taking behaviors, aberrant rhythmicity of home cage activity, nicotinic acetylcholine receptor and dopamine transporter dysfunction, impaired furin-mediated proBDNF proteolysis, hypocorticosteronemia-related glucocorticoid receptor hypoactivity, and global DNA hypomethylation in the frontal cortices and striata. This ensemble of multigenerational DNE-induced behavioral, neuropharmacological, neurotrophic, neuroendocrine, and DNA methylomic anomalies recapitulates the pathosymptomatology of neurodevelopmental disorders such as ADHD, autism, and schizophrenia. Further probing the epigenetic bases of DNE-induced multigenerational phenotypic aberrations, the present study examined the expression and phosphorylation of key epigenetic factors via an array of immunoblot experiments.

RESULTS

Data indicate that DNE confers intergenerational deficits in corticostriatal DNA methyltransferase 3A (DNMT3A) expression accompanied by downregulation of methyl-CpG-binding protein 2 (MeCP2) and histone deacetylase 2 (HDAC2) in the frontal cortices and hippocampi, while the expression of ten-eleven translocase methylcytosine dioxygenase 2 (TET2) is unaltered. Moreover, DNE evokes multigenerational abnormalities in HDAC2 (Ser394) but not MeCP2 (Ser421) phosphorylation in the frontal cortices, striata, and hippocampi.

CONCLUSIONS

In light of the extensive gene regulatory roles of DNMT3A, MeCP2, and HDAC2, the findings of this study that DNE elicits downregulation and aberrant posttranslational modification of these factors in both first- and second-generation DNE mice suggest that epigenetic perturbations may constitute a mechanistic hub for the intergenerational transmission of DNE-induced neurodevelopmental disorder-like phenotypes.

Intolerance of loud sounds in childhood: Is there an intergenerational association with grandmaternal smoking in pregnancy?

Recent research using the Avon Longitudinal Study of Parents and Children (ALSPAC) demonstrated an association between maternal grandmother smoking in pregnancy and the autistic traits of impaired social communication and repetitive behaviour in granddaughters but not grandsons, but of paternal grandmother smoking and early development of myopia in the grandchild. Here we investigate whether grandmaternal smoking in pregnancy is associated with intolerance to loud sounds. ALSPAC collected information during the index pregnancy from the study parents on the smoking habits, social and other features of their own parents. Maternal report when the child was aged 6 and 13 included hating loud sounds; at age 11 the child was tested for volume preference for listening to music through headphones. Statistical analysis compared results for grandchildren in relation to whether a parent had been exposed in utero to maternal smoking, adjusted for their grandparents' social and demographic attributes. We hypothesised that there would be sex differences in the effects of grandmaternal prenatal smoking, based on previous intergenerational studies. For 6-year-old children maternal report of intolerance to loud noise was more likely in grandsons if the maternal grandmother had smoked [adjusted odds ratio (AOR) 1.27; 95% confidence interval (CI) 1.03,1.56; P = 0.025], but less likely in girls [AOR 0.82; 95%CI 0.63,1.07] Pinteraction <0.05. If the paternal grandmother had smoked the grandchildren were less likely to be intolerant, especially girls. The objective measure of choice of volume for music through headphones showed that grandsons of both maternal and paternal smoking grandmothers were less likely to choose high volumes compared with granddaughters (P<0.05). In line with our prior hypothesis of sex differences, we showed that grandsons were more intolerant of loud sounds than granddaughters particularly at age 6, and this was confirmed by objective measures at age 11.

General anesthesia, germ cells and the missing heritability of autism: an urgent need for research

Agents of general anesthesia (GA) are commonly employed in surgical, dental and diagnostic procedures to effectuate global suppression of the nervous system, but in addition to somatic targets, the subject's germ cells-from the embryonic primordial stage to the mature gametes-may likewise be exposed. Although GA is generally considered safe for most patients, evidence has accumulated that various compounds, in particular the synthetic volatile anesthetic gases (SVAGs) such as sevoflurane, can exert neurotoxic, genotoxic and epigenotoxic effects, with adverse consequences for cellular and genomic function in both somatic and germline cells. The purpose of this paper is to review the evidence demonstrating that GA, and in particular, SVAGs, may in some circumstances adversely impact the molecular program of germ cells, resulting in brain and behavioral pathology in the progeny born of the exposed cells. Further, we exhort the medical and scientific communities to undertake comprehensive experimental and epidemiological research programs to address this critical gap in risk assessment.

The role of environmental exposures and the epigenome in health and disease

The genetic material of every organism exists within the context of regulatory networks that govern gene expression, collectively called the epigenome. Epigenetics has taken center stage in the study of diseases such as cancer and diabetes, but its integration into the field of environmental health is still emerging. As the Environmental Mutagenesis and Genomics Society (EMGS) celebrates its 50th Anniversary this year, we have come together to review and summarize the seminal advances in the field of environmental epigenomics. Specifically, we focus on the role epigenetics may play in multigenerational and transgenerational transmission of environmentally induced health effects. We also summarize state of the art techniques for evaluating the epigenome, environmental epigenetic analysis, and the emerging field of epigenome editing. Finally, we evaluate transposon epigenetics as they relate to environmental exposures and explore the role of noncoding RNA as biomarkers of environmental exposures. Although the field has advanced over the past several decades, including being recognized by EMGS with its own Special Interest Group, recently renamed Epigenomics, we are excited about the opportunities for environmental epigenetic science in the next 50 years. Environ. Mol. Mutagen. 61:176-192, 2020. © 2019 Wiley Periodicals, Inc.

Grandmothers' smoking in pregnancy is associated with a reduced prevalence of early-onset myopia

Myopia (near sightedness) is the most common vision disorder resulting in visual impairment worldwide. We tested the hypothesis that intergenerational, non-genetic heritable effects influence refractive development, using grandparental prenatal smoking as a candidate exposure. Using data from the Avon Longitudinal Study of Parents and Children (ALSPAC), we found that the prevalence of myopia at age 7 was lower if the paternal grandmother had smoked in pregnancy, an association primarily found among grandsons compared to granddaughters. There was a weaker, non-sex-specific, reduction in the prevalence of myopia at age 7 if the maternal grandmother had smoked in pregnancy. For children who became myopic later (between 7 and 15 years of age) there were no associations with either grandmother smoking. Differences between early and late-onset myopia were confirmed with DNA methylation patterns: there were very distinct and strong associations with methylation for early-onset but not later-onset myopia.

Familial confounding of the association between maternal smoking in pregnancy and autism spectrum disorder in offspring

Evidence supports no link between maternal smoking in pregnancy and autism spectrum disorder (autism) overall. To address remaining questions about the unexplained heterogeneity between study results and the possibility of risk for specific autism sub-phenotypes, we conducted a whole-population cohort study in Denmark. We followed births 1991-2011 (1,294,906 persons, including 993,301 siblings in 728,271 families), from 1 year of age until an autism diagnosis (13,547), death, emigration, or December 31, 2012. Autism, with and without attention deficit hyperactivity disorder (ADHD) and with and without intellectual disability (ID) were based on ICD-8 and ICD-10 codes from Danish national health registers, including 3,319 autism + ADHD, 10,228 autism - no ADHD, 2,205 autism + ID, and 11,342 autism - no ID. We estimated hazard ratios (HRs) and 95% confidence intervals (95% CIs) between any maternal smoking (from birth records) and autism (or sub-phenotypes) using survival models with robust standard errors, stratifying by birth year and adjusting for child sex, parity, and parental age, education, income, and psychiatric history. To additionally address confounding using family designs, we constructed a maternal cluster model (adjusting for the smoking proportion within the family), and a stratified sibling model. Associations with maternal smoking and autism were elevated in conventional adjusted analyses (HR of 1.17 [1.13-1.22]) but attenuated in the maternal cluster (0.98 [0.88-1.09]) and sibling (0.86 [0.64-1.15]) models. Similarly, risks of autism sub-phenotypes with maternal smoking were attenuated in the family-based models. Together these results support that smoking in pregnancy is not linked with autism or select autism comorbid sub-phenotypes after accounting for familial confounding. Autism Res 2020, 13: 134-144. © 2019 International Society for Autism Research, Wiley Periodicals, Inc. LAY SUMMARY: Smoking during pregnancy has many harmful impacts, which may include harming the baby's developing brain. However, in a study of thousands of families in Denmark, it does not appear that smoking in pregnancy leads to autism or autism in combination with intellectual problems or attention deficits, once you account for the way smoking patterns and developmental disabilities run in families.

Developmental nicotine exposure elicits multigenerational disequilibria in proBDNF proteolysis and glucocorticoid signaling in the frontal cortices, striata, and hippocampi of adolescent mice

Maternal smoking of conventional or vapor cigarettes during pregnancy, a form of developmental nicotine exposure (DNE), enhances the risk of neurodevelopmental disorders such as ADHD, autism, and schizophrenia in children. Modeling the multigenerational effects of smoking during pregnancy and nursing in the first- (F1) and second- (F2) generation adolescent offspring of oral nicotine-treated female C57BL/6J mice, we have previously reported that DNE precipitates intergenerational transmission of nicotine preference, hyperactivity and impulsivity-like behaviors, altered rhythmicity of home cage activity, corticostriatal nicotinic acetylcholine receptor and dopamine transporter dysfunction, and corticostriatal global DNA methylome deficits. In aggregate, these DNE-evoked behavioral, neuropharmacological, and epigenomic anomalies mirror fundamental etiological aspects of neurodevelopmental disorders including ADHD, autism, and schizophrenia. Expanding this line of research, the current study profiled the multigenerational neurotrophic and neuroendocrine consequences of DNE. Results reveal impaired proBDNF proteolysis as indicated by proBDNF-BDNF imbalance, downregulation of the proBDNF processing enzyme furin, atypical glucocorticoid receptor (GR) activity as implied by decreased relative nuclear GR localization, and deficient basal plasma corticosterone (CORT) levels in adolescent DNE offspring and grandoffspring. Collectively, these data recapitulate the BDNF deficits and HPA axis dysregulation characteristic of neurodevelopmental disorders such as ADHD, autism, and schizophrenia as well as the children of maternal smokers. Notably, as BDNF is a quintessential mediator of neurodevelopment, our prior findings of multigenerational DNE-induced behavioral and neuropharmacological abnormalities may stem from neurodevelopmental insults conferred by the proBDNF-BDNF imbalance detected in DNE mice. Similarly, our findings of multigenerational GR hypoactivity may contribute to the increased risk-taking behaviors and aberrant circadian rhythmicity of home cage activity that we previously documented in first- and second-generation DNE mice.

Pregnancy drugs, fetal germline epigenome, and risks for next-generation pathology: A call to action

Drugs taken during pregnancy can affect three generations at once: the gestating woman (F0), her exposed fetus (F1), and the fetal germ cells that confer heritable information for the grandchildren (F2). Unfortunately, despite growing evidence for connections between F0 drug exposures and F2 pathology, current approaches to risk assessment overlook this important dimension of risk. In this commentary, we argue that the unique molecular vulnerabilities of the fetal germline, particularly with regard to global epigenomic reprogramming, combined with empirical evidence for F2 effects of F1 in utero drug and other exposures, should change the way we consider potential long-term consequences of pregnancy drugs and alter toxicology's standard somatic paradigm. Specifically, we (1) suggest that pregnancy drugs common in the postwar decades should be investigated as potential contributors to the "missing heritability" of many pathologies now surging in prevalence; (2) call for inclusion of fetal germline risks in pregnancy drug safety assessment; and (3) highlight the need for intensified research to ascertain generational impacts of diethylstilbestrol, a vanguard question of human germline toxicity. Only by fully addressing this important dimension of transplacental exposure can we responsibly evaluate safety of drug exposures during pregnancy and convey the full scope of risks, while also retrospectively comprehending the generational legacy of recent history's unprecedented glut of evolutionarily novel intrauterine exposures. Environ. Mol. Mutagen. 60:445-454, 2019. © 2019 Wiley Periodicals, Inc.