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Nature Mar 2002It has been suggested that losses of twin conceptuses in very early pregnancy are high, and that for every liveborn twin pair there are a further 10-12 twin pregnancies...
It has been suggested that losses of twin conceptuses in very early pregnancy are high, and that for every liveborn twin pair there are a further 10-12 twin pregnancies that end up as a singleton birth. Here we show that in a group of women who had double-ovulated and conceived, the probability of the second egg also becoming fertilized and developing is 20-30% - which is comparable to the probability of conception and survival of a single conceptus. We conclude that the presence of one embryo does not affect the development of its twin.
Topics: Embryo Loss; Female; Humans; Models, Biological; Ovulation Detection; Pregnancy; Survival Rate; Twins, Dizygotic; Ultrasonography, Doppler
PubMed: 11894085
DOI: 10.1038/416142a -
Fertility and Sterility Feb 2011To consider the risk of intercourse without contraception during infertility treatment.
OBJECTIVE
To consider the risk of intercourse without contraception during infertility treatment.
DESIGN
Case report.
SETTING
Leiden University Medical Center.
PATIENT(S)
An infertile couple underwent IVF for tubal pathology.
INTERVENTION(S)
Transfer of one embryo during a natural cycle.
MAIN OUTCOME MEASURE(S)
Human leukocyte antigen typing, histochemical analysis of the fetal membranes, neonatal and maternal clinical outcomes.
RESULT(S)
A dizygotic twin pregnancy was confirmed after birth by human leukocyte antigen typing of both fetuses and mother and by histochemical analysis of the dividing fetal membranes. This suggests a pregnancy of concurrent IVF and spontaneous conception. Pregnancy was complicated by preeclampsia and intrauterine growth retardation of both fetuses.
CONCLUSION(S)
We state that couples should abstain from intercourse without contraception during infertility treatment to prevent multiple gestation and its related complications for mother and fetuses.
Topics: Adult; Female; Fertilization; Fertilization in Vitro; Humans; Pregnancy; Pregnancy, Multiple; Single Embryo Transfer; Twins, Dizygotic
PubMed: 20850717
DOI: 10.1016/j.fertnstert.2010.08.026 -
Nature Genetics Dec 1997Before one starts the hunt for quantitative trait loci (QTLs) for a complex trait, it is necessary to show that the trait is genetically influenced. This evidence is... (Review)
Review
Before one starts the hunt for quantitative trait loci (QTLs) for a complex trait, it is necessary to show that the trait is genetically influenced. This evidence is most likely to come from the classical twin study--the demonstration that monozygotic twins are more similar for the trait than dizygotic twins. The strengths and weaknesses of twin studies are discussed, and it is suggested that, far from becoming irrelevant with advances in molecular biology, they can improve the efficiency of QTL detection and play an important role in unravelling developmental genetic mechanisms.
Topics: Diseases in Twins; Genetic Linkage; Genetic Markers; Humans; Models, Genetic; Multivariate Analysis; Quantitative Trait, Heritable; Social Environment; Twins, Dizygotic; Twins, Monozygotic
PubMed: 9398838
DOI: 10.1038/ng1297-387 -
Human Reproduction (Oxford, England) May 2018Are there more same-sex (SS) than opposite-sex (OS) pairs among dizygotic twins?
STUDY QUESTION
Are there more same-sex (SS) than opposite-sex (OS) pairs among dizygotic twins?
SUMMARY ANSWER
In violation of Weinberg's Differential Rule, there are significantly more SS than OS pairs among dizygotic twins in nationally representative samples both in the UK and the USA.
WHAT IS KNOWN ALREADY
Since at least 1874, twin researchers have assumed that dizygotic twins were equally likely to be SS or OS (later formalized as Weinberg's Differential Rule). However, recent research on the sex-specific nature of breastmilk suggests that OS twins might be at a developmental disadvantage relative to SS twins. There may therefore be evolutionary selection for the tendency to have SS twins and against the tendency to have OS twins.
STUDY DESIGN, SIZE, DURATION
We analyze two population samples (not subject to Lykken's rule of two-thirds): the National Child Development Study in the UK (n = 17 419) from 1958 to present, and the National Longitudinal Study of Adolescent Health in the USA (n = 20 745) from 1994 to present.
PARTICIPANTS/MATERIALS, SETTING, METHODS
We performed a one-sample t-test of the proportion of SS dizygotic twins against the theoretical null value of 0.5022.
MAIN RESULTS AND THE ROLE OF CHANCE
The proportion of SS pairs among dizygotic twins was 0.6043 (t(325) = 3.838, P = 0.00015) in the UK and 0.5739 (t(520) = 3.398, P = 0.00073) in the USA.
LIMITATIONS, REASONS FOR CAUTION
Twin type (monozygotic versus dizygotic) was classified by the mother, not by DNA typing, although supplementary data suggest that misclassification was negligible and supplementary analysis shows that potential misclassifications do not change our main conclusions.
WIDER IMPLICATIONS OF THE FINDINGS
Weinberg's Differential Rule may be incorrect in its assumption of independence of sexes within dizygotic pairs, and there may be evolutionary selection for SS, and against OS, dizygotic pairs.
STUDY FUNDING/COMPETING INTERESTS
None.
Topics: Adolescent; Child; Female; Humans; Longitudinal Studies; Male; Sex Ratio; Twins, Dizygotic; Twins, Monozygotic
PubMed: 29534175
DOI: 10.1093/humrep/dey046 -
Frontiers in Cellular and Infection... 2021The objectives are to estimate the vertical transmission rate in twins relative to singleton pregnancies, to evaluate whether discordance within twin pairs is rare, and...
OBJECTIVE
The objectives are to estimate the vertical transmission rate in twins relative to singleton pregnancies, to evaluate whether discordance within twin pairs is rare, and to characterize concordance within monozygotic and dizygotic twin pairs in relation to hereditability.
METHODS
We first sought to estimate the vertical transmission rate of congenital CMV infection in twins by gathering cohort-based studies of congenital CMV in which vertical transmission in both singleton and twin pregnancies was reported. This also allowed us to compare singleton and twin infection rates. From the above studies and other large cohorts of congenitally infected infants, the percentage of discordantly infected twin pairs determined whether this is a rare phenomenon. Theorizing discordance is not rare, we then analyzed data from cases with twin outcomes for congenital CMV infection, according to whether the twins were monozygotic or dizygotic, and calculated their corresponding concordance rates to estimate the broad-sense heritability. Lastly, we described other factors that might affect vertical transmission.
RESULTS
From five articles following at-risk pregnancies, the rate of vertical transmission in twin pregnancies is 58.7% (95% CI 43.3-72.3%) whereas in singleton pregnancies it is 31.4% (95% CI: 29.0-34.0%) = 0.0002. Of ten studies of larger cohorts of infants with congenital CMV infection, 21 of 42 twin pairs with at least one twin infected were discordant for congenital CMV (50.0%, 95% CI: 34.4-65.6%) indicating discordance of congenital CMV infection in twin pairs is not rare. Of 28 studies covering 37 twin pairs where at least one twin had congenital CMV, and zygosity was known, eleven of thirteen monozygotic twin pairs (84.6%; 95% CI: 53.7-97.3%) were concordant for CMV infection, and nine of twenty-four dizygotic twin pairs (37.5%; 95% CI: 19.6-59.2%) were concordant for infection giving an estimated hereditability of 94.2%. Within these 37 twin pairs, factors such as primary or recurrent maternal infection, prematurity, growth discordance, and sex are described; however, in many of these cases these factors are unknown.
CONCLUSION
The rate of vertical transmission of congenital CMV is higher for twins than singletons. Discordance of congenital CMV in twins is not rare and suggests a possible genetic susceptibility to congenital CMV.
Topics: Cytomegalovirus; Diseases in Twins; Female; Humans; Pregnancy; Pregnancy, Twin; Twins, Dizygotic; Twins, Monozygotic
PubMed: 34350131
DOI: 10.3389/fcimb.2021.676988 -
Scientific Reports Jul 2022Individual differences in behaviour, traits and mental-health are partially heritable. Traditionally, studies have focused on quantifying the heritability of high-order...
Individual differences in behaviour, traits and mental-health are partially heritable. Traditionally, studies have focused on quantifying the heritability of high-order characteristics, such as happiness or education attainment. Here, we quantify the degree of heritability of lower-level mental processes that likely contribute to complex traits and behaviour. In particular, we quantify the degree of heritability of cognitive and affective factors that contribute to the generation of beliefs about risk, which drive behavior in domains ranging from finance to health. Monozygotic and dizygotic twin pairs completed a belief formation task. We first show that beliefs about risk are associated with vividness of imagination, affective evaluation and learning abilities. We then demonstrate that the genetic contribution to individual differences in these processes range between 13.5 and 39%, with affect evaluation showing a particular robust heritability component. These results provide clues to which mental factors may be driving the heritability component of beliefs formation, which in turn contribute to the heritability of complex traits.
Topics: Educational Status; Humans; Multifactorial Inheritance; Phenotype; Twins, Dizygotic
PubMed: 35821231
DOI: 10.1038/s41598-022-15492-0 -
Human Reproduction (Oxford, England) Jun 2009Common knowledge of over a century has it that monozygotic and dizygotic twinning events occur by unrelated mechanisms: monozygotic twinning 'splits' embryos, producing... (Review)
Review
Common knowledge of over a century has it that monozygotic and dizygotic twinning events occur by unrelated mechanisms: monozygotic twinning 'splits' embryos, producing anomalously re-arranged embryogenic asymmetries; dizygotic twinning begins with independent ovulations yielding undisturbed parallel embryogeneses with no expectation of departures from singleton outcomes. The anomalies statistically associated with twin births are due to the re-arranged embryos of the monozygotics. Common knowledge further requires that dizygotic pairs are dichorionic; monochorionicity is exclusive to monozygotic pairs. These are fundamental certainties in the literature of twin biology. Multiple observations contradict those common knowledge understandings. The double ovulation hypothesis of dizygotic twinning is untenable. Girl-boy twins differ subtly from all other humans of either sex, absolutely not representative of all dizygotics. Embryogenesis of dizygotic twins differs from singleton development at least as much as monozygotic embryogenesis does, and in the same ways, and the differences between singletons and twins of both zygosities represent a coherent system of re-arranged embryogenic asymmetries. Dizygotic twinning and monozygotic twinning have the same list of consequences of anomalous embryogenesis. Those include an unignorable fraction of dizygotic pairs that are in fact monochorionic, plus many more sharing co-twins' cells in tissues other than a common chorion. The idea that monozygotic and dizygotic twinning events arise from the same embryogenic mechanism is the only plausible hypothesis that might explain all of the observations.
Topics: Embryonic Development; Female; Humans; Male; Ovulation; Pregnancy; Twins, Dizygotic; Twins, Monozygotic
PubMed: 19252194
DOI: 10.1093/humrep/dep030 -
The Psychiatric Quarterly 2002Twin studies are frequently cited in support of the influence of genetic factors for a wide range of psychiatric conditions and psychological trait differences. The most... (Comparative Study)
Comparative Study Review
Twin studies are frequently cited in support of the influence of genetic factors for a wide range of psychiatric conditions and psychological trait differences. The most common method, known as the classical twin method, compares the concordance rates or correlations of reared-together identical (MZ) vs. reared-together same-sex fraternal (DZ) twins. However, drawing genetic inferences from MZ-DZ comparisons is problematic due to methodological problems and questionable assumptions. It is argued that the main theoretical assumption of the twin method--known as the "equal environment assumption"--is not tenable. The twin method is therefore of doubtful value as an indicator of genetic influences. Studies of reared-apart twins are discussed, and it is noted that these studies are also vulnerable to methodological problems and environmental confounds. It is concluded that there is little reason to believe that twin studies provide evidence in favor of genetic influences on psychiatric disorders and human behavioral differences.
Topics: Diseases in Twins; Humans; Mental Disorders; Research Design; Schizophrenia; Schizophrenic Psychology; Social Environment; Twins, Dizygotic; Twins, Monozygotic
PubMed: 11780600
DOI: 10.1023/a:1012896802713 -
American Journal of Medical Genetics.... Oct 2009Trichotillomania (TTM) is a disorder with putative genetic underpinnings. Family studies report higher than expected rates of TTM among relatives of affected...
Trichotillomania (TTM) is a disorder with putative genetic underpinnings. Family studies report higher than expected rates of TTM among relatives of affected individuals, but no twin concordance studies have been completed to estimate heritability rates. Same-sex twin pairs with hair pulling in at least one co-twin were included. Subjects were recruited following phone screens and questionnaire completion for zygosity and hair pulling variables. Three sets of criteria were used to define hair pulling and TTM. Two other sets of criteria were widened to include skin picking and bothersome hair manipulation. Fisher exact tests assessed pairwise concordance rates for monozygotic and dizygotic twin pairs and heritability estimates were calculated where significant differences existed. Among 34 identified twin pairs, 24 were monozygotic (MZ) and 10 were dizygotic (DZ). Respective concordance rates for MZ and DZ twin pairs were significantly different at 38.1% and 0% for DSM-IV TTM criteria, 39.1% and 0% using modified DSM criteria, and 58.3% and 20% for noticeable non-cosmetic hair pulling (heritability estimates 76.2%). MZ and DZ concordance rates were not significantly different when broadening hair pulling criteria to include skin picking or when including bothersome hair manipulation. Concordance rates from this study suggest that genetic factors play a significant role in the etiology of TTM. Given the reported discordance rates among the MZ twins, further research is required to fully understand contributory non-genetic factors.
Topics: Adult; Female; Humans; Inheritance Patterns; Male; Surveys and Questionnaires; Trichotillomania; Twins, Dizygotic; Twins, Monozygotic
PubMed: 19199280
DOI: 10.1002/ajmg.b.30922 -
Genes Feb 2019Studies with twins provide fundamental insights to lifespans of humans. We aim to clarify if monozygotic and dizygotic twin individuals differ in lifespan, that is, if...
Studies with twins provide fundamental insights to lifespans of humans. We aim to clarify if monozygotic and dizygotic twin individuals differ in lifespan, that is, if zygosity matters. We investigate whether a possible difference in mortality after infancy between zygosities is stable in different age cohorts, and whether the difference remains when twins with unknown zygosity are taken into account. Further, we compare the distribution of long-livers, that is, the upper-tail of the lifespan distribution, between monozygotic and same-sex dizygotic twin individuals. The Danish Twin Registry provides a nationwide cohort of 109,303 twins born during 1870 to 1990 with valid vital status. Standard survival analysis is used to compare mortality in monozygotic and dizygotic twin individuals and twin individuals with unknown zygosity. The mortality of monozygotic and dizygotic twin individuals differs slightly after taking into consideration effects of birth- and age-cohorts, gender differences, and that twins are paired. However, no substantial nor systematic differences remain when taking twins with unknown zygosity into account. Further, the distribution of long-livers is very similar by zygosity, suggesting the same mortality process. The population-based and oldest twin cohort ever studied suggests that monozygotic and dizygotic twins have similar lifespans.
Topics: Adult; Aged; Denmark; Female; Humans; Longevity; Male; Middle Aged; Mortality; Registries; Twins, Dizygotic; Twins, Monozygotic
PubMed: 30791679
DOI: 10.3390/genes10020166