De novo mutations in children born after medical assisted reproduction

Post-implantation analysis of genomic variations in the progeny from developing fetus to birth

The analysis of genomic variations in offspring after implantation has been infrequently studied. In this study, we aim to investigate the extent of de novo mutations in humans from developing fetus to birth. Using high-depth whole-genome sequencing, 443 parent-offspring trios were studied to compare the results of de novo mutations (DNMs) between different groups. The focus was on fetuses and newborns, with DNA samples obtained from the families' blood and the aspirated embryonic tissues subjected to deep sequencing. It was observed that the average number of total DNMs in the newborns group was 56.26 (54.17-58.35), which appeared to be lower than that the multifetal reduction group, which was 76.05 (69.70-82.40) (F = 2.42, P = 0.12). However, after adjusting for parental age and maternal pre-pregnancy body mass index (BMI), significant differences were found between the two groups. The analysis was further divided into single nucleotide variants (SNVs) and insertion/deletion of a small number of bases (indels), and it was discovered that the average number of de novo SNVs associated with the multifetal reduction group and the newborn group was 49.89 (45.59-54.20) and 51.09 (49.22-52.96), respectively. No significant differences were noted between the groups (F = 1.01, P = 0.32). However, a significant difference was observed for de novo indels, with a higher average number found in the multifetal reduction group compared to the newborn group (F = 194.17, P < 0.001). The average number of de novo indels among the multifetal reduction group and the newborn group was 26.26 (23.27-29.05) and 5.17 (4.82-5.52), respectively. To conclude, it has been observed that the quantity of de novo indels in the newborns experiences a significant decrease when compared to that in the aspirated embryonic tissues (7-9 weeks). This phenomenon is evident across all genomic regions, highlighting the adverse effects of de novo indels on the fetus and emphasizing the significance of embryonic implantation and intrauterine growth in human genetic selection mechanisms.

Frequency, morbidity and equity - the case for increased research on male fertility

Currently, most men with infertility cannot be given an aetiology, which reflects a lack of knowledge around gamete production and how it is affected by genetics and the environment. A failure to recognize the burden of male infertility and its potential as a biomarker for systemic illness exists. The absence of such knowledge results in patients generally being treated as a uniform group, for whom the strategy is to bypass the causality using medically assisted reproduction (MAR) techniques. In doing so, opportunities to prevent co-morbidity are missed and the burden of MAR is shifted to the woman. To advance understanding of men's reproductive health, longitudinal and multi-national centres for data and sample collection are essential. Such programmes must enable an integrated view of the consequences of genetics, epigenetics and environmental factors on fertility and offspring health. Definition and possible amelioration of the consequences of MAR for conceived children are needed. Inherent in this statement is the necessity to promote fertility restoration and/or use the least invasive MAR strategy available. To achieve this aim, protocols must be rigorously tested and the move towards personalized medicine encouraged. Equally, education of the public, governments and clinicians on the frequency and consequences of infertility is needed. Health options, including male contraceptives, must be expanded, and the opportunities encompassed in such investment understood. The pressing questions related to male reproductive health, spanning the spectrum of andrology are identified in the Expert Recommendation.

Intracytoplasmic sperm injection induces transgenerational abnormalities in mice

In vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) are 2 major assisted reproductive techniques (ARTs) used widely to treat infertility. Recently, spermatogonial transplantation emerged as a new ART to restore fertility to young patients with cancer after cancer therapy. To examine the influence of germ cell manipulation on behavior of offspring, we produced F1 offspring by a combination of two ARTs, spermatogonial transplantation and ICSI. When these animals were compared with F1 offspring produced by ICSI using fresh wild-type sperm, not only spermatogonial transplantation-ICSI mice but also ICSI-only control mice exhibited behavioral abnormalities, which persisted in the F2 generation. Furthermore, although these F1 offspring appeared normal, F2 offspring produced by IVF using F1 sperm and wild-type oocytes showed various types of congenital abnormalities, including anophthalmia, hydrocephalus, and missing limbs. Therefore, ARTs can induce morphological and functional defects in mice, some of which become evident only after germline transmission.

DNA damage in testicular germ cells and spermatozoa. When and how is it induced? How should we measure it? What does it mean?

This review surveys the causes and consequences of DNA damage in the male germ line from spermatogonial stem cells to fully differentiated spermatozoa. Within the stem cell population, DNA integrity is well maintained as a result of excellent DNA surveillance and repair; however, a progressive increase in background mutation rates does occur with paternal age possibly as a result of aberrant DNA repair as well as replication error. Once a germ cell has committed to spermatogenesis, it responds to genetic damage via a range of DNA repair pathways or, if this process fails, by the induction of apoptosis. When fully-differentiated spermatozoa are stressed, they also activate a truncated intrinsic apoptotic pathway which results in the activation of nucleases in the mitochondria and cytoplasm; however, the physical architecture of these cells prevents these enzymes from translocating to the nucleus to induce DNA fragmentation. Conversely, hydrogen peroxide released from the sperm midpiece during apoptosis is able to penetrate the nucleus and induce DNA damage. The base excision repair pathway responds to such damage by cleaving oxidized bases from the DNA, leaving abasic sites that are alkali-labile and readily detected with the comet assay. As levels of oxidative stress increase and these cells enter the perimortem, topoisomerase integrated into the sperm chromatin becomes activated by SUMOylation. Such activation may initially facilitate DNA repair by reannealing double strand breaks but ultimately prepares the DNA for destruction by nucleases released from the male reproductive tract. The abasic sites and oxidized base lesions found in live spermatozoa are mutagenic and may increase the mutational load carried by the offspring, particularly in the context of assisted conception. A variety of strategies are described for managing patients expressing high levels of DNA damage in their spermatozoa, to reduce the risks such lesions might pose to offspring health.

The rate of de novo structural variation is increased in in vitro-produced offspring and preferentially affects the paternal genome

Assisted reproductive technologies (ARTs), including in vitro maturation and fertilization (IVF), are increasingly used in human and animal reproduction. Whether these technologies directly affect the rate of de novo mutation (DNM), and to what extent, has been a matter of debate. Here we take advantage of domestic cattle, characterized by complex pedigrees that are ideally suited to detect DNMs and by the systematic use of ART, to study the rate of de novo structural variation (dnSV) in this species and how it is impacted by IVF. By exploiting features of associated de novo point mutations (dnPMs) and dnSVs in clustered DNMs, we provide strong evidence that (1) IVF increases the rate of dnSV approximately fivefold, and (2) the corresponding mutations occur during the very early stages of embryonic development (one- and two-cell stage), yet primarily affect the paternal genome.

The impact of paternal age on new mutations and disease in the next generation

Advanced paternal age is associated with an increased risk of fathering children with genetic disorders and other adverse reproductive consequences. However, the mechanisms underlying this phenomenon remain largely unexplored. In this review, we focus on the impact of paternal age on de novo mutations that are an important contributor to genetic disease and can be studied both indirectly through large-scale sequencing studies and directly in the tissue in which they predominantly arise-the aging testis. We discuss the recent data that have helped establish the origins and frequency of de novo mutations, and highlight experimental evidence about the close link between new mutations, parental age, and genetic disease. We then focus on a small group of rare genetic conditions, the so-called "paternal age effect" disorders that show a strong association between paternal age and disease prevalence, and discuss the underlying mechanism ("selfish selection") and implications of this process in more detail. More broadly, understanding the causes and consequences of paternal age on genetic risk has important implications both for individual couples and for public health advice given that the average age of fatherhood is steadily increasing in many developed nations.

Phasing of de novo mutations using a scaled-up multiple amplicon long-read sequencing approach

De novo mutations (DNMs) play an important role in severe genetic disorders that reduce fitness. To better understand their role in disease, it is important to determine the parent-of-origin and timing of mutational events that give rise to these mutations, especially in sex-specific developmental disorders such as male infertility. However, currently available short-read sequencing approaches are not ideally suited for phasing, as this requires long continuous DNA strands that span both the DNM and one or more informative single-nucleotide polymorphisms. To overcome these challenges, we optimized and implemented a multiplexed long-read sequencing approach using Oxford Nanopore technologies MinION platform. We focused on improving target amplification, integrating long-read sequenced data with high-quality short-read sequence data, and developing an anchored phasing computational method. This approach handled the inherent phasing challenges of long-range target amplification and the normal accumulation of sequencing error associated with long-read sequencing. In total, 77 of 109 DNMs (71%) were successfully phased and parent-of-origin identified. The majority of phased DNMs were prezygotic (90%), the accuracy of which is highlighted by an average mutant allele frequency of 49.6% and standard error of 0.84%. This study demonstrates the benefits of employing an integrated short-read and long-read sequencing approach for large-scale DNM phasing.

Age-associated epigenetic changes in mammalian sperm: implications for offspring health and development

BACKGROUND

Modern reproductive behavior in most developed countries is characterized by delayed parenthood. Older gametes are generally less fertile, accumulating and compounding the effects of varied environmental exposures that are modified by lifestyle factors. Clinicians are primarily concerned with advanced maternal age, while the influence of paternal age on fertility, early development and offspring health remains underappreciated. There is a growing trend to use assisted reproductive technologies for couples of advanced reproductive age. Thus, the number of children born from older gametes is increasing.

OBJECTIVE AND RATIONALE

We review studies reporting age-associated epigenetic changes in mammals and humans in sperm, including DNA methylation, histone modifications and non-coding RNAs. The interplay between environment, fertility, ART and age-related epigenetic signatures is explored. We focus on the association of sperm epigenetics on epigenetic and phenotype events in embryos and offspring.

SEARCH METHODS

Peer-reviewed original and review articles over the last two decades were selected using PubMed and the Web of Science for this narrative review. Searches were performed by adopting the two groups of main terms. The first group included 'advanced paternal age', 'paternal age', 'postponed fatherhood', 'late fatherhood', 'old fatherhood' and the second group included 'sperm epigenetics', 'sperm', 'semen', 'epigenetic', 'inheritance', 'DNA methylation', 'chromatin', 'non-coding RNA', 'assisted reproduction', 'epigenetic clock'.

OUTCOMES

Age is a powerful factor in humans and rodent models associated with increased de novo mutations and a modified sperm epigenome. Age affects all known epigenetic mechanisms, including DNA methylation, histone modifications and profiles of small non-coding (snc)RNA. While DNA methylation is the most investigated, there is a controversy about the direction of age-dependent changes in differentially hypo- or hypermethylated regions with advanced age. Successful development of the human sperm epigenetic clock based on cross-sectional data and four different methods for DNA methylation analysis indicates that at least some CpG exhibit a linear relationship between methylation levels and age. Rodent studies show a significant overlap between genes regulated through age-dependent differentially methylated regions and genes targeted by age-dependent sncRNA. Both age-dependent epigenetic mechanisms target gene networks enriched for embryo developmental, neurodevelopmental, growth and metabolic pathways. Thus, age-dependent changes in the sperm epigenome cannot be described as a stochastic accumulation of random epimutations and may be linked with autism spectrum disorders. Chemical and lifestyle exposures and ART techniques may affect the epigenetic aging of sperm. Although most epigenetic modifications are erased in the early mammalian embryo, there is growing evidence that an altered offspring epigenome and phenotype is linked with advanced paternal age due to the father's sperm accumulating epigenetic changes with time. It has been hypothesized that age-induced changes in the sperm epigenome are profound, physiological and dynamic over years, yet stable over days and months, and likely irreversible.

WIDER IMPLICATIONS

This review raises a concern about delayed fatherhood and age-associated changes in the sperm epigenome that may compromise reproductive health of fathers and transfer altered epigenetic information to subsequent generations. Prospective studies using healthy males that consider confounders are recommended. We suggest a broader discussion focused on regulation of the father's age in natural and ART conceptions is needed. The professional community should be informed and should raise awareness in the population and when counseling older men.

Comparing Clinical and Genetic Characteristics of De Novo and Inherited COL1A1/COL1A2 Variants in a Large Chinese Cohort of Osteogenesis Imperfecta

PURPOSE

Nearly 85%-90% of osteogenesis imperfecta (OI) cases are caused by autosome dominant mutations of COL1A1 and COL1A2 genes, of which de novo mutations cover a large proportion, whereas their characteristics remain to be elucidated. This study aims to compare the differences in clinical and genetic characteristics of de novo and inherited COL1A1/COL1A2 mutations of OI, assess the average paternal and maternal age at conception in de novo mutations, and research the rate of nonpenetrance in inherited mutations.

MATERIALS AND METHODS

A retrospective comparison between de novo and inherited mutations was performed among 135 OI probands with COL1A1/COL1A2 mutations. Mutational analyses of all probands and their family members were completed by Sanger sequencing. A new clinical scoring system was developed to assess the clinical severity of OI quantitatively.

RESULTS

A total of 51 probands (37.78%) with de novo mutations and 84 probands (62.22%) with inherited mutations were grouped by the results of the parental gene verification. The proportion of clinical type III (P<0.001) and clinical scores (P<0.001) were significantly higher in de novo mutations. Missense mutations covered a slightly higher proportion of de novo COL1A1 mutations (46.34%) compared with inherited COL1A1 mutations (33.33%), however, lacking a significant difference (P=0.1923). The mean BMD Z/T-score at the lumbar spine in de novo mutations was -2.3 ± 1.5, lower than inherited mutations (-1.7 ± 1.8), but lacking statistical significance (P=0.0742). There was no significant difference between the two groups in OI-related phenotypes (like fracture frequency, blue sclera, and hearing loss) and biochemical indexes. In de novo mutations, the average paternal and maternal age at conception was 29.2 (P<0.05) and 26.8 (P<0.0001), respectively, which were significantly younger than the average gestational age of the population. Additionally, 98.04% of pedigrees (50/51) with de novo mutations were spontaneous conception. The rate of nonpenetrance of parents with pathogenic variants in the inherited mutation group was 25.64% (20/78).

CONCLUSIONS

Our data revealed that the proportion of clinical type III and clinical scores were significantly higher in de novo mutations than in inherited mutations, demonstrating that de novo mutations are more damaging because they have not undergone purifying selection.