Paternal age and psychiatric disorders: A review

Intergenerational epigenetic inheritance of cancer susceptibility in mammals

Susceptibility to cancer is heritable, but much of this heritability remains unexplained. Some 'missing' heritability may be mediated by epigenetic changes in the parental germ line that do not involve transmission of genetic variants from parent to offspring. We report that deletion of the chromatin regulator Kdm6a (Utx) in the paternal germ line results in elevated tumor incidence in genetically wild type mice. This effect increases following passage through two successive generations of Kdm6a male germline deletion, but is lost following passage through a wild type germ line. The H3K27me3 mark is redistributed in sperm of Kdm6a mutants, and we define approximately 200 H3K27me3-marked regions that exhibit increased DNA methylation, both in sperm of Kdm6a mutants and in somatic tissue of progeny. Hypermethylated regions in enhancers may alter regulation of genes involved in cancer initiation or progression. Epigenetic changes in male gametes may therefore impact cancer susceptibility in adult offspring.

Identifying psychiatric disorder-associated gut microbiota using microbiota-related gene set enrichment analysis

Psychiatric disorders are a group of complex psychological syndromes with high prevalence. It has been reported that gut microbiota has a dominant influence on the risks of psychiatric disorders through gut microbiota–brain axis. We extended the classic gene set enrichment analysis (GSEA) approach to detect the association between gut microbiota and complex diseases using published genome-wide association study (GWAS) and GWAS of gut microbiota summary data. We applied our approach to real GWAS data sets of five psychiatric disorders, including attention deficiency/hyperactive disorder (ADHD), autism spectrum disorder (AUT), bipolar disorder (BD), schizophrenia (SCZ) and major depressive disorder (MDD). To evaluate the performance of our approach, we also tested the genetic correlations of obesity and type 2 diabetes with gut microbiota. We identified several significant associations between psychiatric disorders and gut microbiota, such as ADHD and genus Desulfovibrio (P = 0.031), order Clostridiales (P = 0.034). For AUT, association signals were observed for genera Bacteroides (P = 0.012) and Desulfovibrio (P = 0.033). Genus Desulfovibrio (P = 0.005) appeared to be associated with BD. For MDD, association signals were observed for genus Desulfovibrio (P = 0.003), order Clostridiales (P = 0.004), family Lachnospiraceae (P = 0.007) and genus Bacteroides (P = 0.007). Genus Desulfovibrio (P = 0.012) and genus Bacteroides (P = 0.038) appeared to be associated with SCZ. Our study results provide novel clues for revealing the roles of gut microbiota in psychiatric disorders. This study also illustrated the good performance of GSEA approach for exploring the relationships between gut microbiota and complex diseases.

Schizotypal traits, neurocognition, and paternal age in unaffected first degree relatives of patients with familial or sporadic schizophrenia

Studies comparing cognitive processes between familial and sporadic schizophrenia have yielded inconsistent findings. In this study we examined differences in neurocognition and schizotypal traits in unaffected relatives of schizophrenia-spectrum patients with either the familial (multiplex) or the sporadic (simplex) subtype of the disorder, taking paternal age at birth into consideration. Simplex (n = 65; SR), multiplex (n = 35; MR) relatives and controls (n = 114) were compared on several cognitive functions and schizotypal traits; between-group differences were evaluated with and without including paternal age in the analyses. SR and MR had higher negative and paranoid traits compared with controls, but paternal age abolished the differences between the SR and control groups. When taking into account schizotypal traits and participants' age, controls outperformed MR in strategy formation and set-shifting and SR in psychomotor speed, set-shifting and executive working memory. After including paternal age in the analyses, controls outperformed MR in strategy formation, working memory and executive working memory and both groups in psychomotor speed and set-shifting. These findings suggest that multiplex relatives present with a "riskier" personality and cognitive profile when considering the effects of paternal age. Nevertheless, simplex relatives are impaired in fundamental cognitive processes, thus highlighting the detrimental effects of paternal age on neurocognition.

iMEGES: integrated mental-disorder GEnome score by deep neural network for prioritizing the susceptibility genes for mental disorders in personal genomes

BACKGROUND

A range of rare and common genetic variants have been discovered to be potentially associated with mental diseases, but many more have not been uncovered. Powerful integrative methods are needed to systematically prioritize both variants and genes that confer susceptibility to mental diseases in personal genomes of individual patients and to facilitate the development of personalized treatment or therapeutic approaches.

METHODS

Leveraging deep neural network on the TensorFlow framework, we developed a computational tool, integrated Mental-disorder GEnome Score (iMEGES), for analyzing whole genome/exome sequencing data on personal genomes. iMEGES takes as input genetic mutations and phenotypic information from a patient with mental disorders, and outputs the rank of whole genome susceptibility variants and the prioritized disease-specific genes for mental disorders by integrating contributions from coding and non-coding variants, structural variants (SVs), known brain expression quantitative trait loci (eQTLs), and epigenetic information from PsychENCODE.

RESULTS

iMEGES was evaluated on multiple datasets of mental disorders, and it achieved improved performance than competing approaches when large training dataset is available.

CONCLUSION

iMEGES can be used in population studies to help the prioritization of novel genes or variants that might be associated with the susceptibility to mental disorders, and also on individual patients to help the identification of genes or variants related to mental diseases.

De novo Mutations (DNMs) in Autism Spectrum Disorder (ASD): Pathway and Network Analysis

Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder (NDD) defined by impairments in social communication and social interactions, accompanied by repetitive behavior and restricted interests. ASD is characterized by its clinical and etiological heterogeneity, which makes it difficult to elucidate the neurobiological mechanisms underlying its pathogenesis. Recently, de novo mutations (DNMs) have been recognized as strong source of genetic causality. Here, we review different aspects of the DNMs associated with ASD, including their functional annotation and classification. In addition, we also focus on the most recent advances in this area, such as the detection of PZMs (post-zygotic mutations), and we outline the main bioinformatics tools commonly employed to study these. Some of these approaches available allow DNMs to be analyzed in the context of gene networks and pathways, helping to shed light on the biological processes underlying ASD. To end this review, a brief insight into the future perspectives for genetic studies into ASD will be provided.

Age at first birth in women is genetically associated with increased risk of schizophrenia

Previous studies have shown an increased risk for mental health problems in children born to both younger and older parents compared to children of average-aged parents. We previously used a novel design to reveal a latent mechanism of genetic association between schizophrenia and age at first birth in women (AFB). Here, we use independent data from the UK Biobank (N = 38,892) to replicate the finding of an association between predicted genetic risk of schizophrenia and AFB in women, and to estimate the genetic correlation between schizophrenia and AFB in women stratified into younger and older groups. We find evidence for an association between predicted genetic risk of schizophrenia and AFB in women (P-value = 1.12E-05), and we show genetic heterogeneity between younger and older AFB groups (P-value = 3.45E-03). The genetic correlation between schizophrenia and AFB in the younger AFB group is -0.16 (SE = 0.04) while that between schizophrenia and AFB in the older AFB group is 0.14 (SE = 0.08). Our results suggest that early, and perhaps also late, age at first birth in women is associated with increased genetic risk for schizophrenia in the UK Biobank sample. These findings contribute new insights into factors contributing to the complex bio-social risk architecture underpinning the association between parental age and offspring mental health.

Parental age and risk of epilepsy: A nationwide register-based study

OBJECTIVE

This study aims to examine the association between maternal age, paternal age, and parental age difference at the time of birth and the risk of epilepsy in the offspring.

METHODS

We carried out a prospective population-based register study of all singletons born in Denmark between 1981 and 2012. Cox regression was used to estimate hazard ratios (HRs) of epilepsy and their corresponding 95% confidence intervals (CIs), adjusted for relevant confounders.

RESULTS

We followed 1 587 897 individuals for a total of ~25 million person-years and identified 21 797 persons with epilepsy during the study period. An excess risk of epilepsy was found in individuals born to mothers younger than 20 years (HR = 1.17, 95% CI = 1.07-1.29) and born to parental couples where paternal age exceeded maternal age by at least 5 years. The risk of epilepsy increased with increasing parental age gap and was highest when the father was ≥15 years older than the mother (adjusted HR = 1.28, 95% CI = 1.16-1.41). In contrast to maternal age, we found that paternal age did not independently contribute to offspring epilepsy risk, once we accounted for the parental age difference (P = .1418). The observed associations with maternal age and parental age gap were invariant to epilepsy subtypes, but were modified by age of epilepsy onset, with the effect being most pronounced in the first 10 years of the child's life.

SIGNIFICANCE

Maternal age and parental age gap, but not paternal age, were associated with the offspring's risk of epilepsy. Our results do not support the hypothesis that de novo mutations associated with advanced paternal age increase the risk of epilepsy in the offspring.

Reproductive genetics and the aging male

PURPOSE

To examine current evidence of the known effects of advanced paternal age on sperm genetic and epigenetic changes and associated birth defects and diseases in offspring.

METHODS

Review of published PubMed literature.

RESULTS

Advanced paternal age (> 40 years) is associated with accumulated damage to sperm DNA and mitotic and meiotic quality control mechanisms (mismatch repair) during spermatogenesis. This in turn causes well-delineated abnormalities in sperm chromosomes, both numerical and structural, and increased sperm DNA fragmentation (3%/year of age) and single gene mutations (relative risk, RR 10). An increase in related abnormalities in offspring has also been described, including miscarriage (RR 2) and fetal loss (RR 2). There is also a significant increase in rare, single gene disorders (RR 1.3 to 12) and congenital anomalies (RR 1.2) in offspring. Current research also suggests that autism, schizophrenia, and other forms of "psychiatric morbidity" are more likely in offspring (RR 1.5 to 5.7) with advanced paternal age. Genetic defects related to faulty sperm quality control leading to single gene mutations and epigenetic alterations in several genetic pathways have been implicated as root causes.

CONCLUSIONS

Advanced paternal age is associated with increased genetic and epigenetic risk to offspring. However, the precise age at which risk develops and the magnitude of the risk are poorly understood or may have gradual effects. Currently, there are no clinical screenings or diagnostic panels that target disorders associated with advanced paternal age. Concerned couples and care providers should pursue or recommend genetic counseling and prenatal testing regarding specific disorders.

Widespread covariation of early environmental exposures and trait-associated polygenic variation

Although gene-environment correlation is recognized and investigated by family studies and recently by SNP-heritability studies, the possibility that genetic effects on traits capture environmental risk factors or protective factors has been neglected by polygenic prediction models. We investigated covariation between trait-associated polygenic variation identified by genome-wide association studies (GWASs) and specific environmental exposures, controlling for overall genetic relatedness using a genomic relatedness matrix restricted maximum-likelihood model. In a UK-representative sample (n = 6,710), we find widespread covariation between offspring trait-associated polygenic variation and parental behavior and characteristics relevant to children's developmental outcomes-independently of population stratification. For instance, offspring genetic risk for schizophrenia was associated with paternal age (R² = 0.002; P = 1e-04), and offspring education-associated variation was associated with variance in breastfeeding (R² = 0.021; P = 7e-30), maternal smoking during pregnancy (R² = 0.008; P = 5e-13), parental smacking (R² = 0.01; P = 4e-15), household income (R² = 0.032; P = 1e-22), watching television (R² = 0.034; P = 5e-47), and maternal education (R² = 0.065; P = 3e-96). Education-associated polygenic variation also captured covariation between environmental exposures and children's inattention/hyperactivity, conduct problems, and educational achievement. The finding that genetic variation identified by trait GWASs partially captures environmental risk factors or protective factors has direct implications for risk prediction models and the interpretation of GWAS findings.

Risk of impaired cognition after prenatal exposure to psychotropic drugs

OBJECTIVE

Prenatal exposure to psychotropic drugs may affect the trajectories of brain development. In a register study, we investigated whether such exposure is associated with long-term impaired cognitive abilities.

METHOD

Individuals born in Denmark in 1995-2008 were included. As proxies for cognitive impairment, requiring special needs education, attending special needs school, diagnoses of neurological/mental disorder, missed final examinations, and low school grade average were used. We accounted for maternal confounders.

RESULTS

We identified 868 159 individuals of whom 13 983 (1.6%) were prenatally exposed. The adjusted odds ratio (OR) was 0.97[0.92-1.02] for requiring special needs education, 1.28[1.14-1.43] for attending special needs school, 1.32[1.20-1.46] for a neurological/mental disorder diagnosis, 1.37[1.22-1.54] for missing the final examinations, and 1.13[0.82-1.55] for obtaining a low school grade average. Exposure to psycholeptics (primarily antipsychotics and sedatives) was correlated with significantly increased risk for four outcomes. The highest was the risk of missing the primary school examinations (OR: 1.51[1.29-1.76]). The overall highest risk concerned the presence of a neurological/mental disorder after prenatal exposure to psychoanaleptics (primarily antidepressants) (OR: 1.86[1.24-2.78).

CONCLUSION

Prenatal exposure to psychotropic drugs affects proxy outcomes of cognitive disabilities at school age. Exposure to psycholeptics carries the largest risk. The role of psychoanaleptics is currently unclear.