Identical twins doubly exchanged at birth: a case report of genetic and environmental influences on the adult epigenome

Twins Standing in for Co-Twins: Explanation and Speculation/Twin Research Reviews: Single v. Multiple Embryo Transfer; Neurimaging of Twins with Periventricular Nodular Heterotopia; Twin Dietary Study; New Hungarian Text on Twins/Human Interest: Valedictorian and Salutatorian Twins; Twin Mother at Age Seventy; Twins Reunited by Tiktok; New Film on Twins with Selective Mutism; Becoming Twin Doctors

An overview of circumstances in which twins take the place of their co-twin is presented. Various explanations and speculations are proposed for understanding twins' willingness to do so in certain situations. This section is followed by reviews of timely twin research, namely single versus multiple embryo transfer; neurimaging of twins with periventricular nodular heterotopia; a twin dietary comparison; and a new book of twin-related readings from Hungary. The final portion of this article concerns human interest stories that both inform and entertain. They involve valedictorian and salutatorian twins; a mother delivering twins at age seventy; twins reunited by TikTok; a new film about twins with selective mutism; and twins becoming doctors.

Handedness in twins reared apart: A review of the literature and new data

Reared-apart twin studies are a powerful means for identifying the relative contributions of heredity and environment to variation in human physical and behavioural traits. One such characteristic is handedness, for which it has long been noted that approximately 20% of twin pairs are comprised of one right-handed cotwin and one left-handed cotwin. Reared-together twin studies suggest a slightly greater concordance in monozygotic (MZT) than dizygotic (DZT) twins, implying that genetics influences hand preference. We report here two studies of handedness in reared-apart twins. Study 1 synthesizes the available data and estimates that at least N = 560 same-sex reared-apart twin pairs (for which zygosity is known with reasonable confidence) have been identified. Of these, handedness data are available for both members of n = 415 pairs. We observed similar levels of concordance/discordance for reared-apart monozygotic (MZA) and dizygotic (DZA) twins. However, although direction of handedness (right or left) has frequently been examined, strength of handedness (strong or weak) has not. Study 2 examined strength of hand preference and relative hand skill, as well as right- and left-hand speed, information available for participants in the Minnesota Study of Twins Reared Apart (MISTRA). We provide evidence of heritability for right-hand and left-hand speed. We also found hand preference strength was more alike than chance in DZA, but not MZA, twins. Findings are discussed in relation to genetic and environmental influences on human handedness.

Epigenetics as a Mechanism of Developmental Embodiment of Stress, Resilience, and Cardiometabolic Risk Across Generations of Latinx Immigrant Families

Psychosocial stressors can become embodied to alter biology throughout the life course in ways that may have lasting health consequences. Immigrants are particularly vulnerable to high burdens of stress, which have heightened in the current sociopolitical climate. This study is an investigation of how immigration-related stress (IRS) may impact the cardiometabolic risk and epigenetic markers of Latinx immigrant mothers and children in Nashville, TN. We compared stress and resilience factors reported by Latina immigrant mothers and their children (aged 5-13) from two time points spanning the 2016 U.S. presidential election (June 2015-June 2016 baseline, n = 81; March-September 2018 follow-up, n = 39) with cardiometabolic risk markers (BMI, waist circumference, and blood pressure). We also analyzed these factors in relation to DNA methylation in saliva of stress-related candidate genes (SLC6A4 and FKBP5), generated via bisulfite pyrosequencing (complete case n's range from 67-72 baseline and 29-31 follow-up) (n's range from 80 baseline to 36 follow-up). We found various associations with cardiometabolic risk, such as higher social support and greater acculturation were associated with lower BMI in mothers; discrimination and school stress associated with greater waist circumferences in children. Very few exposures associated with FKBP5, but various stressors associated with methylation at many sites in SLC6A4, including immigrant-related stress in both mothers and children, and fear of parent deportation in children. Additionally, in the mothers, total maternal stress, health stress, and subjective social status associated with methylation at multiple sites of SLC6A4. Acculturation associated with methylation in mothers in both genes, though directions of effect varied over time. We also find DNA methylation at SLC6A4 associates with measures of adiposity and blood pressure, suggesting that methylation may be on the pathway linking stress with cardiometabolic risk. More research is needed to determine the role of these epigenetic differences in contributing to embodiment of stress across generations.

Global DNA methylation in rats´ liver is not affected by hypercholesterolemic diet

Increased plasma cholesterol levels are listed between the major atherosclerosis risk factors. The final plasma cholesterol levels result from the interplay between the genetic and environmental (diet, physical activity) factors. Little is known, how dietary factor influence epigenetics. We have analyzed, if an over-generation feeding of rat with cholesterol influences total liver-DNA methylation, and if total liver-DNA methylation differ between the different rat strains (Prague hereditary hypercholesterolemic rats, Prague hereditary hypertriglyceridemic rats and Wistar Kyoto rats). The animals were feed with high fat (additional 5 % over normal capacity) high cholesterol (2 %) diet for 14 days. DNA methylation in the liver tissue in different generations was analyzed using the liquid chromatography coupled with tandem mass spectrometry. We have not observed any significant changes in total liver-DNA methylation over the 9 generations of animals feed by fat/cholesterol enriched diet. Additionally, there were no differences in DNA methylation between different rat strains. In animal model, the dietary changes (hypercholesterolemic diet) not significantly influence the total DNA methylation status within the liver.

DNA methylation changes in infants between 6 and 52 weeks

Infants undergo extensive developments during their first year of life. Although the biological mechanisms involved are not yet fully understood, changes in the DNA methylation in mammals are believed to play a key role. This study was designed to investigate changes in infant DNA methylation that occurs between 6 and 52 weeks. A total of 214 infant saliva samples from 6 or 52 weeks were assessed using principal component analyses and t-distributed stochastic neighbor-embedding algorithms. Between the two time points, there were clear differences in DNA methylation. To further investigate these findings, paired two-sided student’s t-tests were performed. Differently methylated regions were defined as at least two consecutive probes that showed significant differences, with a q-value < 0.01 and a mean difference > 0.2. After correcting for false discovery rates, changes in the DNA methylation levels were found in 42 genes. Of these, 36 genes showed increased and six decreased DNA methylation. The overall DNA methylation changes indicated decreased gene expression. This was surprising because infants undergo such profound developments during their first year of life. The results were evaluated by taking into consideration the extensive development that occurs during pregnancy. During the first year of life, infants have an overall three-fold increase in weight, while the fetus develops from a single cell into a viable infant in 9 months, with an 875-million-fold increase in weight. It is possible that the findings represent a biological slowing mechanism in response to extensive fetal development. In conclusion, our study provides evidence of DNA methylation changes during the first year of life, representing a possible biological slowing mechanism. We encourage future studies of DNA methylation changes in infants to replicate the findings by using a repeated measures model and less stringent criteria to see if the same genes can be found, as well as investigating whether other genes are involved in development during this period.

Eye Refraction in Doubly Exchanged Monozygotic Twins

This case study examined the hypothesis that longer outdoor time results in normal vision and refractive status, using unique genetically informative kinships. The participants were the members of 29-year-old doubly exchanged monozygotic male twin pairs from Bogotá, Colombia, in South America. Comprehensive ophthalmological examinations, including uncorrected and corrected visual acuity, refraction and keratometry, and visual life history interviews were undertaken; all examinations were conducted by two ophthalmologists blind to the hypothesis, relatedness, and rearing status of the four participants. Normal uncorrected vision and refractive status were present in the two rural-raised, unrelated brothers, relative to their urban-raised counterparts. Uncorrected visual acuities were 20/160 and 20/200 for the city-raised twins and 20/20 and 20/30 for the country-raised twins. Premature birth, low birth weight, computer use, and reading time could not explain these differences. It was concluded that time spent outdoors appears to be a significant factor in the development of myopia, reinforcing extant findings via a novel experimental approach.

Double Vision: Eye Findings in Twins Reared Apart/Twin Research: Perinatology and Conjoined Twins; Thoracopagus Twin Cattle; MZ Twins Discordant for Musical Training/In the News: College Benefits for Twin Parents; Octomom Revisited; Genetic Editing of Infant Twins; Quarternary Marriages; Unusual Twin Pregnancy

Findings related to visual functioning, drawn from early reared-apart twin studies, are summarized. These data are supplemented by more recent research from similar investigations. This section is followed by a survey of findings and conclusions from a special issue of the journal Seminars in Perinatology concerning the challenges and management of conjoined twins. An early case report on thoracopagus-conjoined twin cattle is also presented, as are neuroanatomical findings from a study of monozygotic twins discordant for musical training. Items noted in the news include college benefits for twin parents, an update on octomom, claims of gene editing of infant twins, the nature of quarternary marriages and an unusual planned twin pregnancy.

Twins Switched at Birth: Frequency, Life Histories, Twin Relationships, and Critical Issues/Twin Research Reviews: Classroom Placement; Mirror Syndrome; Unusual Twinning; Parenting Stress/Human Interest: Triplet Film; Educational Achievement; Prison Release; Co-Twin Impersonation; Facial Recognition Technology

Twins switched at birth are a rare subtype of twins who grow up apart. The frequency with which this event occurs, as well as selected life history events, twin relationships, and critical issues generated by the nine recorded cases are reviewed. This is followed by summaries of recent studies addressing classroom placement for twins, mirror syndrome in mothers, unusual twin types, and parenting stress. The article concludes with a review of human interest items from the general media, namely a triplet film, educational achievement, prison release, co-twin impersonation, and facial recognition technology.

A Possible Twin: The 1960s Twin Study Revisited/Twin Research: Twin-to-Twin Heart Transplantation; Distinguishing Monozygotic Twins; Twin Conceptions via Oocyte Donation; Factors Affecting Craniofacial Traits/In the Media: Triplet Delivery in the UK; Conjoined Twins and the Concept of Self; Colombian Twin Trainers; Skin Grafting to Save an Identical Co-Twin; Lack of Physical Flaws in Dolly the Cloned Sheep; Possible Conjoined Twins of Opposite-Sex; Passing of the Remaining Twin From the World's Longest Separated Pair

This article begins with the story of a 51-year-old Los Angeles, California man, Justin Goldberg, whose daughter caught a glimpse of his striking look-alike at a popular market. Many people have so-called doppelgängers, but this occurrence is especially intriguing - the individual in question, born in New York City in the mid-1960s to an unwed mother, was an adoptee placed by the Louise Wise Adoption Agency. This agency, under the guidance of a prominent psychiatrist, decided to place twins in separate homes. Some of these twin children were part of a controversial child development study that was hidden from them and their parents. Next, recent and current twin research on heart transplantation, distinguishing monozygotic co-twins, twin conceptions via oocyte donation and factors affecting craniofacial traits are summarized. The article concludes with highlights on twins in the media, specifically, a triplet delivery in the United Kingdom, self-concept and consciousness in conjoined twins, Colombian twin trainers, skin grafting to save an identical co-twin, lack of physical flaws in Dolly the cloned sheep, possible opposite-sex conjoined twins, and the passing of the remaining twin from the world's longest separated pair.