Monozygotic Twins Research Articles

The doctrine of ancillary restrictions as a delimitation tool and an absorption principle: twin notions but not identical twins

Abstract Contrary to the general view, ‘ancillary restrictions’ designate two separate conceptions, which should be treated as separate doctrines. As a ‘delimitation tool’, ancillarity separates ‘naked’ and ‘ancillary’ restrictions based on ‘reasonable necessity’. As an ‘absorption principle’, ancillarity is a rule of thumb that screens out certain lawful agreements based on the idea that a lawful main transaction (or the legality of the main transaction) absorbs all objectively necessary (indispensable) restrictions.

Novel multitarget directed ligands inspired by riluzole: A serendipitous synthesis of substituted benzo[b][1,4]thiazepines potentially useful as neuroprotective agents

Riluzole, the first clinically approved treatment for amyotrophic lateral sclerosis (ALS), represents a successful example of a drug endowed with a multimodal mechanism of action. In recent years, different series of riluzole-based compounds have been reported, including several agents acting as Multi-Target-Directed Ligands (MTLDs) endowed with neuroprotective effects. Aiming at identical twin structures inspired by riluzole (2a-c), a synthetic procedure was planned, but the reactivity of the system took a different path, leading to the serendipitous isolation of benzo[b][1,4]thiazepines 3a-c and expanded intermediates N-cyano-benzo[b][1,4]thiazepines 4a-c, which were fully characterized. The newly obtained structures 3a-c, bearing riluzole key elements, were initially tested in an in vitro ischemia/reperfusion injury protocol, simulating the cerebral stroke. Results identified compound 3b as the most effective in reverting the injury caused by an ischemia-like condition, and its activity was comparable, or even higher than that of riluzole, exhibiting a concentration-dependent neuroprotective effect. Moreover, derivative 3b completely reverted the release of Lactate Dehydrogenase (LDH), lowering the values to those of the control slices. Based on its very promising pharmacological properties, compound 3b was then selected to assess its effects on voltage-dependent Na+ and K+ currents. The results indicated that derivative 3b induced a multifaceted inhibitory effect on voltage-gated currents in SH-SY5Y differentiated neurons, suggesting its possible applications in epilepsy and stroke management, other than ALS. Accordingly, brain penetration was also measured for 3b, as it represents an elegant example of a MTDL and opens the way to further ex-vivo and/or in-vivo characterization.

Blink-induced changes in pupil dynamics are consistent and heritable.

Pupil size and blink rates are heritable but the extent to which they interact with one another has not been properly investigated. Though changes in pupil size due to eye blinks have been reported, they are considered a pupillary artifact. In this study we used the HCP 7T fMRI dataset with resting state eye-tracking data obtained in monozygous and dizygous twins to assess their heritability and their interactions. For this purpose, we characterized the pupil dilation (positive peak) and constriction (negative peak) that followed blink events, which we describe as blink-induced pupillary response (BIPR). We show that the BIPR is highly consistent with a positive dilatory peak (D-peak) around 500ms and a negative constricting peak (C-peak) around 1s. These patterns were reproducible within- and between- subjects across two time points and differed by vigilance state (vigilant versus drowsy). By comparing BIPR between monozygous and dizygous twins we show that BIPR have a heritable component with significant additive genetic (A) and environmental (E) factors dominating the structural equation models, particularly in the time-domain for both D- and C-peaks and amplitude domain for the C-peak. (a2 between 42-49%). Blink duration, pupil size and blink rate were also found to be highly heritable (a2 up to 62% for pupil size). Our study documents an association between BIPR and wakefulness and indicates that BIPR should not be treated as a coincidental artefact, but part of a larger oculomotor system that we label here as Oculomotor Adaptive System, OAS, that is genetically determined.

Association between adolescent alcohol use and cognitive function in young adulthood: A co-twin comparison study.

Studies on adolescent alcohol use and cognition are often unable to separate the potential causal effects of alcohol use on cognition from shared etiological influences, including genetic influences or other substance use comorbidities also known to be associated with cognition, such as nicotine use. The present study aimed to fill this gap and clarify the relationship between adolescent alcohol use and young adult cognition by accounting for both measured and unmeasured confounders. A random effects model accounting for nesting in families was used to control for measured confounders. Next, co-twin comparisons were conducted within the full sample and in monozygotic twin pairs (MZ) to control for unmeasured genetic and environmental confounders shared by co-twins. Participants were 812 individuals (58.6% female, 361 complete pairs, 146 MZ pairs) from the longitudinal FinnTwin12 study in Finland. Adolescent alcohol use was indexed with measures of frequency of use and intoxication averaged across ages 14 and 17. Cognitive outcomes were measured at average age 22 and included Trail Making Test, California Stroop test, Wechsler Adult Intelligence subtests (Vocabulary, Block Design, Digit Symbol), Digit Span subtest of Wechsler Memory Scale, Mental Rotation Test and Object Location Memory test. Covariates included sex, parental education, general cognitive ability, current alcohol use and nicotine use. Greater frequency of alcohol use and frequency of intoxication across adolescence was associated with decreased vocabulary scores in the co-twin control [freq: stnd beta = -0.12, 95% confidence interval (CI) = -0.234, -0.013] and MZ only co-twin control models (freq: stnd beta = -0.305, 95% CI = -0.523, -0.087; intox: stnd beta = -0.301, 95% CI = -0.528, -0.074). In Finland, there appears to be little evidence that adolescent alcohol use causes cognitive deficits in young adulthood, except modest evidence for association of higher adolescent alcohol use with lower young adult vocabulary scores.

Does Catch-Up Growth Come with a Cognitive Cost? Cognitive Outcome and Growth Patterns in Growth Discordant Identical Twins

To determine whether it is the magnitude of early postnatal catch-up growth (CUG) in response to fetal growth restriction (FGR) or the FGR itself that negatively impacts cognitive outcome in a model of monochorionic twins discordant for fetal growth. This analysis is part of the LEMON study, a cohort study including all monochorionic twins with selective FGR aged 3 through 17years. Growth measurements as documented by our primary care system were collected retrospectively. An age-appropriate neurodevelopmental test was performed generating a full-scale IQ (FSIQ). CUG at 2years was calculated as (weight [kg] at 2years-birth weight [kg]). We used a multivariable regression model investigating the association between FSIQ (outcome) and birth weight zscore, gestational age at birth and CUG at 2years (predictors). Generalized estimating equations accounted for the fact that observations between cotwins are not independent. Median age at follow-up of the 46 included twin pairs was 11 (IQR 8-13) years. Birth weight z score and gestational age at birth were significantly associated with FSIQ, with β-coefficients of 5.897 (95% CI 3.382-8.411), and 2.589 (95% CI 1.227-3.951), respectively (P<.0001). Adjusted for birth weight z score and gestational age, CUG in the first 2years after birth was not significantly associated with FSIQ (β-coefficient 0.108 [95% CI -1.373 to 1.590], P=.886). Our results, combining detailed growth measurements and neurodevelopmental follow-up in a discordant identical twin model, demonstrate that FGR itself rather than early postnatal CUG has negative consequences for cognitive development.

First successful ovarian cortex allotransplant to a Turner syndrome patient requiring immunosuppression: wide implications

ObjectiveTo determine whether we can safely and successfully transplant an ovary tissue allograft from a non-identical donor to her Turner syndrome sister. DesignTransplantation of cryopreserved ovary tissue, as well as fresh transplantation of ovarian tissue between identical twins, is now well established with numerous reported successful cases. However there have not yet been any ovary transplants between non-identical women requiring immunosuppression (ovary allotransplant). This could be a much more common indication for ovary tissue transplantation if safe and reliable immunosuppression were available. SubjectsA 20 year old amenorrheic woman with non-mosaic 45-XO Turner syndrome requested ovary tissue transplantation from her fertile 22 year old 46-XX sister. They were an HLA match but were ABO incompatible, a well known contra-indication to solid tissue or organ transplantation. The Turner syndrome sister strongly preferred to be able to become pregnant naturally without donor egg IVF, and to avoid HRT (hormone replacement therapy). In her religious group, that would also be important for finding a marital match. Despite the poor prognosis associated with ABO incompatibility, an ovary from her 22 year old non-identical fertile sister was transplanted to her employing the immunosuppression protocol now used for kidney transplant patients in our centers at Washington University and Johns Hopkins. Main Outcome MeasuresPost-operatively at 5 months she developed normal monthly menstrual ovarian function, and she became spontaneously pregnant with a normal baby girl. The relation between her post-op FSH and AMH levels continues to support the theory that tissue pressure controls primordial follicle recruitment. The fact that ABO incompatibility did not prevent success suggests that diffusion and not revascularization may be all that is required for successful long term ovarian cortex transplant survival with spontaneous pregnancy. ResultsOvary allotransplantation with safe immunosuppression allows natural conception, and also normal hormone function obviates the need for HRT. Orthotopic placement of the graft and surgical technique is critical for natural conception and a higher pregnancy rate. ConclusionAllotransplantation requiring safe immunosuppression, if successful, may be a much more commonly used indication for ovary transplantation in the future than frozen ovary grafts or grafts between identical twins.

Monozygotic Twins with Dissociation in CAP-RAST Results for Dust Mites

Monozygotic Twins with Dissociation in CAP-RAST Results for Dust Mites

Insights into clinical phenotypes and treatment responses in a Small cohort of Taiwanese patients with SCN1A variants: A Preliminary study

BackgroundSCN1A channelopathy is the most well-known cause for epileptic encephalopathies and contributes to a wide phenotypic spectrum. The variable expressivity is troublesome for the interpretation of clinical significance and prognoses. To investigate the clinical manifestations, medications and outcomes of patients with SCN1A channelopathies, we conducted this observation retrospective study in Taiwan. MethodsA cohort consisting of 16 patients (5 males and 11 females) from multiple centers with identified SCN1A variants was investigated and phenotypically relevant factors were recorded. The variants were identified using NGS and confirmed by Sanger sequencing. A panel of 90 epileptic-related genes was used to identify SCN1A variants and to evaluate some of the potential SCN1A modifier genes. ResultsThe mean age of seizure onset was 10.4 months. Twelve of the sixteen patients (75%) had different degrees of neurocognitive sequela and psychobehavioral comorbidity in our cohort. Cognitive impairment was noted in all ten patients with Dravet syndrome (DS) and in two of the patients with non-DS phenotypes. A lower response rate to medications was also noted in patients with DS. Notably, a medication-specific tendency towards valproic acid (VPA), clobazam (CLB), and levetiracetam (LEV) was observed, revealing the effective pharmacotherapies for SCN1A-related seizures. An asymptomatic carrier with a reported pathogenic SCN1A variant was reviewed along with her monozygotic twin sister with DS. Nine novel SCN1A mutations are herein reported, eight of which being classified as pathogenic. ConclusionOur study revealed unfavorable outcomes for patients with SCN1A variants. Some patients with SCN1A channelopathy showed specific responsiveness to the pharmacotherapies previously either recommended or contraindicated for these patients. Our study also expands the genotype and provides valuable prognostic insights in patients with SCN1A channelopathy.

Whole genome sequencing study of identical twins discordant for psychosis

Monozygotic (MZ) twins are often thought to have identical genomes, but recent work has shown that early post-zygotic events can result in a spectrum of DNA variants that are different between MZ twins. Such variants may explain phenotypic discordance and contribute to disease etiology. Here we performed whole genome sequencing in 17 pairs of MZ twins discordant for a psychotic disorder (schizophrenia, schizoaffective disorder or bipolar disorder). We examined various classes of rare variants that are discordant within a twin pair. We identified four genes harboring rare, predicted deleterious missense variants that were private to an affected individual in the cohort. Variants in FOXN1 and FLOT2 would have been categorized as damaging from recent schizophrenia and bipolar exome sequencing studies. Additionally, we identified four rare genic copy number variants (CNVs) private to an affected sample, two of which overlapped genes that have shown evidence for association with schizophrenia or bipolar disorder. One such CNV was a 3q29 duplication previously implicated in autism and developmental delay. We have performed the largest MZ twin study for discordant psychotic phenotypes to date. These findings warrant further investigation using other analytical approaches.

Monozygotic twins discordant for depression: An extended network comparison of depressive symptoms, cognitive functions and daily activities

Monozygotic twins share the same genotype; however, they can be phenotypically discordant on various traits. Studying discordant monozygotic twins allows the investigation of differences in associations between symptoms and psychopathological risk factors, controlled for shared genetic liability. The network approach to psychopathology suggests that depressive symptoms, along with risk and protective factors (e.g., cognition, daily activities), form a complex system of mutually interacting components. We compared monozygotic twins discordant for lifetime depression on their respective extended networks of depressive symptoms, cognitive functions and daily activities (intellectual, physical, social), and evaluated if these networks differ in their associations between variables and in the role of each variable within the network. Regularized partial correlations investigated the networks' composition in 147 monozygotic twin pairs discordant for depression from the Danish Twin Registry. Affected twins had stronger overall associations within their network of depressive symptoms, cognitive functions and daily activities than their unaffected co-twins, while the importance of the network components’ associations did not differ between the co-twins. In affected twins, decreased frequency in experiencing happiness had the strongest association with remaining variables (i.e., the most influence in activating other network elements). Also, variables from different groups were significantly associated (e.g., loneliness with delayed memory, pessimism with low social activities, verbal learning with intellectual activities). In unaffected twins, both mood symptoms and cognitive functions were important, but between-groups associations were quasi-absent. These results suggest that external events affecting the ability to feel happiness likely trigger the psychopathological process (depression network activation), independently from the genetic predisposition to depression.

Forging one’s identity as a twin: Balancing sibling cohesion and deidentification

Little is known about how twins influence one another’s development during emerging adulthood. Although the exact mechanisms that underlie sibling influence have not been firmly established, they likely encompass processes that highlight either sibling identification (e.g., seeking similarities and imitation in the service of building cohesion) or deidentification (e.g., seeking differences that distinguish themselves to reduce competition, rivalry, and jealousy). Because past research inferred these processes rather than directly assess them, we conducted a mixed methods study in which 20 sets of monozygotic (MZ, n = 11 dyads) and dizygotic (DZ, n = 9 dyads) twins, aged 19.70 years (SD = 1.11), were interviewed individually regarding their personal identity development and sibling relationship. A grounded theory approach guided the qualitative analysis, which included coordinating twins’ interview responses at the dyadic level. Each twin also completed the Adult Sibling Relationship Questionnaire which provided a complementary quantitative assessment. 75% of the dyads prioritized differentiation and felt that college was the optimal time to pursue unique identities and goals. Those who prioritized seeking similarity were MZ twins who sought emotional closeness and support and attended the same college. Rather than pitting social learning and deidentification as opposing processes, the results suggest that deidentification is a developmental process in which twins increasingly take steps towards independence while seeking to retain the closeness, trust, and reliance they have long enjoyed in their relationship. Practical implications for helping twins balance their needs for autonomy and distinctiveness, while maintaining emotional closeness, are discussed.

Genetic Foundations of Neurophysiological and Behavioural Variability Across the Lifespan.

Neurophysiological brain activity underpins cognitive functions and behavioural traits. Here, we sought to establish to what extent individual neurophysiological traits spontaneously expressed in ongoing brain activity are primarily driven by genetic variation. We also investigated whether changes in such neurophysiological features observed across the lifespan are supported by longitudinal changes in cortical gene expression. We studied the heritability of neurophysiological traits from task-free brain activity of monozygotic and dizygotic twins as well as non-related individuals recorded with magnetoencephalography. We found that these traits were more similar between monozygotic twins compared to dizygotic twins, and that these heritable core dynamical properties of brain activity are predominantly influenced by genes involved in neurotransmission processes. These genes are expressed in the cortex along a topographical gradient aligned with the distribution of major cognitive functions and psychological processes. Our data also show that the impact of these genetic determinants on cognitive and psychological traits increases with age. These findings collectively highlight the persistent genetic influence across the lifespan on neurophysiological brain activity that supports individual cognitive and behavioural traits.

A study of the effect of congenital heart disease on somatic growth by comparing identical twins anthropometric profiles

Abstract Purpose This study seeks to evaluate the impact of congenital heart disease (CHD) on somatic growth while controlling for the influence of other growth-related factors. Method A retrospective cohort study was conducted on identical twins, with one twin having CHD (CHD group) and the other without CHD (non-CHD group). Anthropometric measures, including weight-for-age (WAZ), height-for-age (HAZ), weight-for-height (WHZ), and head-circumference (HCZ) z-scores based on WHO growth standards, were employed, and growth failure was defined by z-scores below -2. Predictive factors of growth failure included gestational age, cyanosis, pulmonary arterial hypertension (PAH), heart failure, and ventricular physiology. Results Anthropometric indices from 41 pairs of twins were analyzed. The CHD group exhibited a significant decline in all growth parameters from the age of 1 year (p &amp;lt; .001). Although the growth disparity between twins lessened over time, the CHD group continued to lag behind the non-CHD group at follow-up (p &amp;lt; .05). Moreover, a higher proportion of the CHD group experienced malnutrition (46.3%) compared to the non-CHD group (7.5%, RR 1.724, 95% CI 1.280 to 2.232, p &amp;lt; .001, at the age of 1). Among disease characteristics, children with cyanosis, PAH, and heart failure displayed a significant decrease in growth z-scores compared to their unaffected twin siblings. However, statistical significance was observed only between weight-for-height z-scores and cyanosis (cyanosis 1.8±1.7 vs acyanosis -0.8±1.4, p = .032). Conclusion Children with CHD exhibited compromised growth compared to their non-affected twin siblings, with no complete catch-up growth observed during the observation period. The heightened prevalence of growth failure in the CHD group emphasizes the increased risk of malnutrition in children with CHD.

NFIX gene mutation causes Marshall-Smith syndrome in a pair of identical twins and literature review

This article reports on the clinical and genetic characteristics of monozygotic twins with Marshall-Smith syndrome (MRSHSS) due to a mutation in the NFIX gene, along with a review of related literature. Both patients presented with global developmental delays, a prominent forehead, shallow eye sockets, and pectus excavatum. Genetic testing revealed a heterozygous splicing site mutation c.697+1G>A in both children, with parents showing wild-type at this locus. According to the guidelines of the American College of Medical Genetics and Genomics, this mutation is considered likely pathogenic and has not been previously reported in the literature. A review of the literature identified 32 MRSHSS patients with splicing/frameshift mutations. Accelerated bone maturation and moderate to severe global developmental delay/intellectual disability are the primary clinical manifestations of patients with MRSHSS. Genetic testing results are crucial for the diagnosis of this condition.

Unlocking Security: The Significant Role of Machine Learning and Deep Learning Techniques in Fingerprint Recognition Systems

One of the more widely utilized biometrics for in-person identification is a fingerprint. It has been discovered that no two people have the same fingerprints and that each one is distinct. A person's fingerprint traits remain constant as they age. Compared to DNA, fingerprints are more distinctive. Identical twins cannot have the same fingerprints even though they have the same DNA. Artificial Intelligence encompasses the broader goal of creating intelligent systems, while Machine Learning focuses on developing algorithms that enable machines to learn from data. Deep Learning, as a subset of Machine Learning, leverages neural networks with multiple layers to learn complex representations of data. While Deep Learning has become increasingly prominent and successful in recent years, it is just one of the many approaches within the broader field of AI and Machine Learning. Fingerprint recognition stands as one of the oldest and most widely used biometric authentication methods, finding applications across diverse domains such as law enforcement, access control, and mobile device security. With the advent of machine learning and deep learning techniques, significant strides have been made in enhancing the accuracy, efficiency, and scalability of fingerprint recognition systems. This comprehensive review aims to provide a thorough examination of the pivotal role played by machine learning and deep learning methodologies in advancing fingerprint recognition technology. The paper commences with an introduction to the importance and ubiquity of fingerprint recognition, elucidating its significance in various real-world applications. Subsequently, it delves into the foundational concepts of machine learning and deep learning, elucidating their relevance to fingerprint recognition tasks. Key machine learning algorithms such as Support Vector Machines (SVM), k-Nearest Neighbors (k-NN), Random Forests, and neural network-based approaches are discussed, highlighting their strengths and limitations in the context of fingerprint recognition.

Heritability of functional gradients in the human subcortico-cortical connectivity

The human subcortex plays a pivotal role in cognition and is widely implicated in the pathophysiology of many psychiatric disorders. However, the heritability of functional gradients based on subcortico-cortical functional connectivity remains elusive. Here, leveraging twin functional MRI (fMRI) data from both the Human Connectome Project (n = 1023) and the Adolescent Brain Cognitive Development study (n = 936) datasets, we construct large-scale subcortical functional gradients and delineate an increased principal functional gradient pattern from unimodal sensory/motor networks to transmodal association networks. We observed that this principal functional gradient is heritable, and the strength of heritability exhibits a heterogeneous pattern along a hierarchical unimodal-transmodal axis in subcortex for both young adults and children. Furthermore, employing a machine learning framework, we show that this heterogeneous pattern of the principal functional gradient in subcortex can accurately discern the relationship between monozygotic twin pairs and dizygotic twin pairs with an accuracy of 76.2% (P < 0.001). The heritability of functional gradients is associated with the anatomical myelin proxied by MRI-derived T1-weighted/T2-weighted (T1w/T2w) ratio mapping in subcortex. This study provides new insights into the biological basis of subcortical functional hierarchy by revealing the structural and genetic properties of the subcortical functional gradients.

Cellular mechanisms of monozygotic twinning: clues from assisted reproduction.

Monozygotic (MZ) twins are believed to arise from the fission of a single fertilized embryo at different stages. Monochorionic MZ twins, who share one chorion, originate from the splitting of the inner cell mass (ICM) within a single blastocyst. In the classic model for dichorionic MZ twins, the embryo splits before compaction, developing into two blastocysts. However, there are a growing number of ART cases where a single blastocyst transfer results in dichorionic MZ twins, indicating that embryo splitting may occur even after blastocyst formation. For monochorionic MZ twins, we conducted a comprehensive analysis of the cellular mechanisms involved in ICM splitting, drawing from both ART cases and animal experiments. In addition, we critically re-examine the classic early splitting model for dichorionic MZ twins. We explore cellular mechanisms leading to two separated blastocysts in ART, potentially causing dichorionic MZ twins. Relevant studies including research articles, reviews, and conference papers were searched in the PubMed database. Cases of MZ twins from IVF clinics were found by using combinations of terms including 'monozygotic twins' with 'IVF case report', 'ART', 'single embryo transfer', or 'dichorionic'. The papers retrieved were categorized based on the implicated mechanisms or as those with unexplained mechanisms. Animal experiments relating to MZ twins were found using 'mouse embryo monozygotic twins', 'mouse 8-shaped hatching', 'zebrafish janus mutant', and 'nine-banded armadillo embryo', along with literature collected through day-to-day reading. The search was limited to articles in English, with no restrictions on publication date or species. For monochorionic MZ twins, ART cases and mouse experiments demonstrate evidence that a looser ICM in blastocysts has an increased chance of ICM separation. Physical forces facilitated by blastocoel formation or 8-shaped hatching are exerted on the ICM, resulting in monochorionic MZ twins. For dichorionic MZ twins, the classic model resembles artificial cloning of mouse embryos in vitro, requiring strictly controlled splitting forces, re-joining prevention, and proper aggregation, which allows the formation of two separate human blastocysts under physiological circumstances. In contrast, ART procedures involving the transfer of a single blastocysts after atypical hatching or vitrified-warmed cycles might lead to blastocyst separation. Differences in morphology, molecular mechanisms, and timing across various animal model systems for MZ twinning can impede this research field. As discussed in future directions, recent developments of innovative in vitro models of human embryos may offer promising avenues for providing fundamental novel insights into the cellular mechanisms of MZ twinning during human embryogenesis. Twin pregnancies pose high risks to both the fetuses and the mother. While single embryo transfer is commonly employed to prevent dizygotic twin pregnancies in ART, it cannot prevent the occurrence of MZ twins. Drawing from our understanding of the cellular mechanisms underlying monochorionic and dichorionic MZ twinning, along with insights into the genetic mechanisms, could enable improved prediction, prevention, and even intervention strategies during ART procedures. N/A.

A study on the association between insulin resistance and genome-wide DNA methylation based on Shanghai monozygotic twins

Objective: To explore the association between insulin resistance (IR) and genome-wide DNA methylation based on Shanghai twin study. Methods: Monozygotic twins (MZ) from Shanghai were recruited during 2012-2013, 2017-2018, and 2022-2023. Data were collected by questionnaire survey, physical examination and laboratory tests. Genome-wide DNA methylation was quantified. Generalized linear mixed effect model was applied to analyze the association between methylation level at each site and homeostatic model assessment 2-insulin resistance (HOMA2-IR). Non-paired and paired designs were used to assess the association between DNA methylation and phenotype of IR. Cluster analysis was conducted to identify the clusters of top significant sites. Generalized linear regression was performed to examine the differential methylation patterns from clusters. Results: A total of 100 MZ pairs were included in this study. Hypermethylated cg10535199-2q23.1 (β=0.74%, P=1.51×10-7, OR=1.06, 95%CI: 1.03-1.09) and ch.17.49619327-SPOP (β=0.23%, P=7.54×10-7, OR=1.17, 95%CI: 1.08-1.28) were identified with suggestive significance. After correcting for multiple testing, no sites reached genome-wide significance. There was no statistical significance in the paired analysis. Two clusters with hypomethylated (β=-0.39%, P<0.001) and hypermethylated (β=0.47%, P<0.001) patterns were observed for HOMA2-IR. Conclusions: IR was significantly associated with DNA methylation, and genetic factors might contribute to the association.

O-210 DNA methylation signature of monozygotic twinning: investigating the relationship with medically assisted reproduction, higher-order gestations, and common genetic variants

Abstract Study question To study a DNA methylation signature of monozygotic twins in relation to medically assisted reproduction (MAR), higher-order gestations, and genome-wide common genetic variants. Summary answer Monozygotic twinning and MAR show largely distinct DNA methylation signatures. Monozygotic triplets, like monozygotic twins, carry a comparable but stronger DNA methylation signature. What is known already Monozygotic twins arise when a zygote or embryo splits during pre-implantation stages of development. Higher-order monozygotic multiples including triplets have been hypothesized to arise from multiple consecutive splitting events. The underlying mechanisms are unknown. Some studies have reported a higher rate of monozygotic twins born after the use of medically-assisted reproductive technologies. We recently identified a DNA methylation signature in blood samples from adult monozygotic twins, which showed strong replication across cohorts and in buccal samples from children. This signature consists of 834 differentially methylated locations, enriched for loci with a role in embryonic processes, cell adhesion, and metastable epi-alleles. Study design, size, duration We compared buccal DNA methylation profiles of 934 naturally conceived monozygotic twins to 43 monozygotic twins conceived after IVF/ICSI (mean age=9). We generated monozygotic twinning DNA methylation scores in an independent buccal dataset (59 triplets, 198 twins, and 119 siblings of twins, mean age=15). A genome-wide association study (GWAS) on the DNA methylation score was performed in two datasets from the Netherlands Twin Register (NTR) (1: Blood, N = 2841, mean age=37, 2: Buccal, N = 1150, mean age=10). Participants/materials, setting, methods DNA methylation was assessed with Illumina arrays (450k/EPIC). To study the relationship between DNA methylation and MAR, we performed an epigenome-wide association study (EWAS) of MAR in monozygotic twins. We applied our previously developed DNA-methylation based predictor (trained on blood methylation data from twins using elastic net regression) to novel buccal methylation data from multiples including triplets. GWAS analysis was performed in gcta using --fastGWA-mlm correcting for 10 genetic ancestry PCs and genotype platform. Main results and the role of chance Through EWAS, we identified 29 differentially methylated CpGs in buccal cells from monozygotic twins conceived after MAR compared to naturally conceived monozygotic twins (after Bonferroni correction), of which 8 were previously identified in an EWAS meta-analysis of IVF on cord blood from singletons at birth. None of the 834 CpGs detected in our previous EWAS meta-analysis of monozygotic twinning were associated with MAR, suggesting that they are connected to natural monozygotic twinning. The monozygotic twinning epigenetic signature showed similar performance in buccal DNA methylation data from monozygotic twins as previously observed (81% of monozygotic twins correctly classified). Sensitivity was highest for monozygotic triplets (90% correctly classified), but specificity remains moderate (66% of DZ twins correctly predicted, 53% of non-twins correctly predicted). GWAS analysis of blood 450k array data identified three genome-wide significant loci. The top SNP (rs76157694, MAF=0.25) maps to TBX4; an embryonic transcription factor primarily known for its role in hindlimb development. This finding is consistent with our previous results of MZ-differentially methylated positions being enriched within TBX4 binding motifs. GWAS analysis of the buccal EPIC array data identified no genome-wide significant loci. We are planning a GWAS meta-analysis together with the Genetics of DNA methylation consortium. Limitations, reasons for caution Our research provides compelling hints towards an epigenomic event in monozygotic multiples, but whether the signature represents a cause, effect, or a byproduct of monozygotic twinning remains to be established. In ongoing research, we study the signature in pre- and perinatal tissues from twins (Dutch Fetal biobank and PANDA biobank). Wider implications of the findings The methylation signature may serve as a biomarker to retrospectively diagnose if a person was conceived as monozygotic twin, providing novel opportunities to examine links between vanishing monozygotic twin syndrome and certain congenital disorders. Examples include Beckwith-Wiedemann Syndrome and Amyoplasia (∼10-fold higher frequency of monozygotic twins among patients). Trial registration number not applicable

P-408 Monozygotic twins from in vitro fertilization: can bring the rate closer to that of natural conception?

Abstract Study question Whether the occurrence of monozygotic twins in human in vitro fertilization is associated with zona manipulations, and can we explore approaches to reduce its rates? Summary answer Monozygotic twinning is partially caused by zona manipulation, and it can be lowered by creating a larger opening in the zona before embryo transfer. What is known already While the rate of monozygotic twins in spontaneous conception is 0.5% of live births, the frequency of monozygotic twins after in vitro fertilization-embryo transfer can be a few times higher. Various factors have been suggested to contribute to this phenomenon, including ovarian stimulation, intracytoplasmic sperm injection, embryo cryopreservation, extended culture, embryo quality, maternal age, genetic factors, and micromanipulation of the zona pellucida, such as assisted hatching and biopsy. Due to the fact that the overall rate is low, it is difficult to pinpoint the main reason(s) contributing to it, and there are no effective approach(es) to lower this rate. Study design, size, duration We studied monozygotic twins in 8,063 clinical pregnancies resulting from single blastocyst transfers from 2016 to 2023. Blastocysts, whether fresh or frozen, were transferred with or without biopsy for preimplantation genetic testing and/or blastocyst collapse. Clinical pregnancy, embryo implantation, including twin implantation, and clinical outcomes such as live birth, ongoing pregnancy, and birth weight were further evaluated. Monozygotic twin rates were compared between partial zona removal (larger hole) and no zona removal (small hole) Participants/materials, setting, methods Monozygotic twins were initially evaluated in blastocysts with or without biopsy in 732 clinical pregnancies after fresh or frozen embryo transfer. Subsequently, monozygotic twins were further evaluated in 7331 clinical pregnancies after an approach to open a larger hole in the zona before blastocyst transfer. Additionally, 56 monozygotic twins were evaluated for live birth and birth weight outcomes. Main results and the role of chance In the context of fresh blastocyst transfer, the monozygotic twin rate following biopsy was significantly higher than that for blastocysts that did not undergo zona manipulation (3.4% vs. 0.29%; p = 0.025). After blastocysts underwent biopsy and cryopreservation/warming, the monozygotic twin rate was 2.79%, a similar rate as observed in fresh blastocyst transfer after biopsy. However, when frozen blastocysts (either biopsied and/or collapsed) underwent partial zona removal before transfer, the rate of monozygotic twins significantly decreased to 0.6% (p = 0.00001). When we further examined whether the biopsy procedure increased the monozygotic twin rate (28/4947) under the conditions that partial zona removal was performed by comparing those with blastocysts without biopsy (16/2384), we did not find a significant difference (0.57% vs. 0.67%, p = 0.587) between the two treatments. In this study, there were 34 twin live births (60.7%) including 5 ongoing twin pregnancies, and 9 (16.1%) singleton live births, contributing to an overall live birth rate of 76.8%. Ten cases (17.8%) experienced pregnancy loss with heartbeat cessation during the first trimester. Furthermore, 3 cases (5.4%) had abnormal pregnancies. When the birth weights were evaluated among the monozygotic twins, it was found that lower birth weight (&amp;lt; 1500g) was only observed in twin live birth. Limitations, reasons for caution This study only included data from one large clinic in the US under the conditions and protocols (embryo culture, embryo biopsy, and cryopreservation) used in this clinic. Different patients and protocols would affect the rate differently. Wider implications of the findings Zona manipulations are associated with an increased monozygotic twin rate in both fresh and frozen embryo transfers. This effect can be mitigated by creating a larger opening in the zona before embryo transfer, and this approach can bring the monozygotic twin rate closer to that of natural conception. Trial registration number NA