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Twin Research and Human Genetics : the... Apr 2017Traditionally, it is understood that dizygotic (DZ) twins always have a dichorionic placenta. However, with 8% blood chimerism in DZ twins, placental sharing is probably... (Review)
Review
Traditionally, it is understood that dizygotic (DZ) twins always have a dichorionic placenta. However, with 8% blood chimerism in DZ twins, placental sharing is probably more common than previously has been recognized. In this article, we will review all available cases of monochorionic dizygotic (MCDZ) twins. A total of 31 twins have been described in literature. A monochorionic diamniotic placenta is reported in all cases. Assisted reproductive technology is responsible for the origin of the pregnancy in 82.1% of the cases. In 15.4% of the sex-discordant twins, a genital anomaly was reported in one of the twins. Chimerism is demonstrable in 90.3% of the twins, leading to various diagnostic difficulties. As this review shows that most MCDZ twins are discovered by accident, it can be argued that it is far more common than has been assumed until now. However, the prevalence is still unclear. Awareness of MCDZ twinning is important, with subsequently correct medical strategies. Similarly, the resulting (blood) chimerism is essential to consider in diagnostic procedures, pre- and postnatally. More research on the effect of placental transfusion between sex-discordant twins is required.
Topics: Chimerism; Chorion; Female; Humans; Male; Placenta; Pregnancy; Pregnancy, Twin; Reproductive Techniques, Assisted; Twins, Dizygotic; Ultrasonography, Prenatal
PubMed: 28236812
DOI: 10.1017/thg.2017.4 -
European Journal of Endocrinology May 2009Brain volume of boys is larger than that of girls by approximately 10%. Prenatal exposure to testosterone has been suggested in the masculinization of the brain. For... (Comparative Study)
Comparative Study
OBJECTIVE
Brain volume of boys is larger than that of girls by approximately 10%. Prenatal exposure to testosterone has been suggested in the masculinization of the brain. For example, in litter-bearing mammals intrauterine position increases prenatal testosterone exposure through adjacent male fetuses, resulting in masculinization of brain morphology.
DESIGN
The influence of intrauterine presence of a male co-twin on masculinization of human brain volume was studied in 9-year old twins.
METHODS
Magnetic resonance imaging brain scans, current testosterone, and estradiol levels were acquired from four groups of dizygotic (DZ) twins: boys from same-sex twin-pairs (SSM), boys from opposite-sex twin-pairs (OSM), girls from opposite-sex twin-pairs (OSF), and girls from same-sex twin-pairs (SSF; n=119 individuals). Data on total brain, cerebellum, gray and white matter volumes were examined.
RESULTS
Irrespective of their own sex, children with a male co-twin as compared to children with a female co-twin had larger total brain (+2.5%) and cerebellum (+5.5%) volumes. SSM, purportedly exposed to the highest prenatal testosterone levels, were found to have the largest volumes, followed by OSM, OSF and SSF children. Birth weight partly explained the effect on brain volumes. Current testosterone and estradiol levels did not account for the volumetric brain differences. However, the effects observed in children did not replicate in adult twins.
CONCLUSIONS
Our study indicates that sharing the uterus with a DZ twin brother increases total brain volume in 9-year olds. The effect may be transient and limited to a critical period in childhood.
Topics: Brain; Child; Cohort Studies; Female; Humans; Magnetic Resonance Imaging; Male; Organ Size; Radiography; Sex Factors; Siblings; Testosterone; Twins, Dizygotic
PubMed: 19218283
DOI: 10.1530/EJE-08-0915 -
Annals of Human Genetics Jan 2017Genome-wide association studies with moderate sample sizes are underpowered, especially when testing SNP alleles with low allele counts, a situation that may lead to...
Genome-wide association studies with moderate sample sizes are underpowered, especially when testing SNP alleles with low allele counts, a situation that may lead to high frequency of false-positive results and lack of replication in independent studies. Related individuals, such as twin pairs concordant for a disease, should confer increased power in genetic association analysis because of their genetic relatedness. We conducted a computer simulation study to explore the power advantage of the disease-concordant twin design, which uses singletons from disease-concordant twin pairs as cases and ordinary healthy samples as controls. We examined the power gain of the twin-based design for various scenarios (i.e., cases from monozygotic and dizygotic twin pairs concordant for a disease) and compared the power with the ordinary case-control design with cases collected from the unrelated patient population. Simulation was done by assigning various allele frequencies and allelic relative risks for different mode of genetic inheritance. In general, for achieving a power estimate of 80%, the sample sizes needed for dizygotic and monozygotic twin cases were one half and one fourth of the sample size of an ordinary case-control design, with variations depending on genetic mode. Importantly, the enriched power for dizygotic twins also applies to disease-concordant sibling pairs, which largely extends the application of the concordant twin design. Overall, our simulation revealed a high value of disease-concordant twins in genetic association studies and encourages the use of genetically related individuals for highly efficiently identifying both common and rare genetic variants underlying human complex diseases without increasing laboratory cost.
Topics: Computer Simulation; Diseases in Twins; Gene Frequency; Genetic Predisposition to Disease; Genome-Wide Association Study; Humans; Models, Genetic; Risk; Twins, Dizygotic; Twins, Monozygotic
PubMed: 28009044
DOI: 10.1111/ahg.12181 -
Molecular Psychiatry Aug 2021Depression and cardiovascular disease (ischemic heart disease and stroke) are associated in a bidirectional manner. Their relatively high heritability has led to the...
Depression and cardiovascular disease (ischemic heart disease and stroke) are associated in a bidirectional manner. Their relatively high heritability has led to the hypothesis that this co-occurrence is related to shared familial and genetic factors; this study aims to test this hypothesis. We included 23,498 monozygotic and 39,540 same-sex dizygotic twins from the Danish Twin Registry followed from January 1977 until December 2011 in nationwide Danish registries. We used survival analyses accounting for censoring and competing risk of death to estimate cumulative incidence, casewise concordance, relative recurrence risk, and heritability of the co-occurrence of depression and cardiovascular disease by age using monozygotic and same-sex dizygotic twin pairs. The casewise concordance of ischemic heart disease or stroke in twins whose co-twin was diagnosed with depression was at all ages similar for the monozygotic and dizygotic twin pairs and to the cumulative incidence of ischemic heart disease or stroke, respectively, in the entire twin population. A similar pattern was seen in analyses of depression risk given the co-twin being diagnosed with ischemic heart disease or stroke. Relative recurrence risk and heritability estimates were also of modest size and with confidence intervals including unity. Results were similar after stratification by gender as well as when redefining depression to include the use of antidepressant medication from 1995. Our findings do not support that co-occurrence between depression and cardiovascular disease is explainable by shared genetic factors, nor did we find strong evidence of a familial effect.
Topics: Cardiovascular Diseases; Cohort Studies; Denmark; Depression; Diseases in Twins; Genetic Predisposition to Disease; Humans; Registries; Twins, Dizygotic; Twins, Monozygotic
PubMed: 33219357
DOI: 10.1038/s41380-020-00954-6 -
Statistics in Medicine Jun 2022It is challenging to evaluate the genetic impacts on a biologic feature and separate them from environmental impacts. This is usually achieved through twin studies by...
It is challenging to evaluate the genetic impacts on a biologic feature and separate them from environmental impacts. This is usually achieved through twin studies by assessing the collective genetic impact defined by the differential correlation in monozygotic twins vs dizygotic twins. Since the underlying order in a twin, determined by latent genetic factors, is unknown, the observed twin data are unordered. Conventional methods for correlation are not appropriate. To handle the missing order, we model twin data by a mixture bivariate distribution and estimate under two likelihood functions: the likelihood over the monozygotic and dizygotic twins separately, and the likelihood over the two twin types combined. Both likelihood estimators are consistent. More importantly, the combined likelihood overcomes the drawback of mixture distribution estimation, namely, the slow convergence. It yields correlation coefficient estimator of root-n consistency and allows effective statistical inference on the collective genetic impact. The method is demonstrated by a twin study on immune traits.
Topics: Humans; Likelihood Functions; Phenotype; Twin Studies as Topic; Twins, Dizygotic; Twins, Monozygotic
PubMed: 35253253
DOI: 10.1002/sim.9367 -
The Journal of Clinical Pediatric... Nov 2021The aim of this study is to investigate the relative contributions of genetic and environmental factors to variations in dental dimensions in a sample of Turkish twins,...
BACKGROUND
The aim of this study is to investigate the relative contributions of genetic and environmental factors to variations in dental dimensions in a sample of Turkish twins, and to estimate heritability using dental casts.
STUDY DESIGN
The study samples were selected from the twin children between 3-15 years old who referred for their first dental examination. Fifty nine monozygotic and one hundred and forty three dizygotic twin pairs were examined in the study. The alginate impression material used to create the plaster model of maxilla and mandible. Anterior arch width, posterior arch width, arch length and arch circumference were measured on models prepared from measurements taken for both maxilla and mandible with digital caliper. The similarities and differences of the measurements were compared between pairs of twins and zygocytes. Morever, the effects of bad oral habits, bruxism, a result of psychosocial factors on measurements were examined. Statistical analysis was performed using Paired T Test, Wilcoxon Test and Mann Whitney U test.
RESULTS
A total of 404 dental models of 118 (29.2%) monozygotic and 286 (70.8%) dizygotic twins were evaluated. There was no statistical difference between sibling pairs in both monozygotic and dizygotic twins. The measurement similarity between twin siblings differed according to zygosity in all measurements (p<0.05). It has been observed that the finger sucking and mouth breathing affect the dental arch measurements (p<0.05).
CONCLUSION
These results indicate that the differences in dental arch dimensions between monozygotic twin pairs are less than the difference between dizygotic twin pairs.
Topics: Adolescent; Child; Child, Preschool; Dental Arch; Humans; Mandible; Maxilla; Twins, Dizygotic; Twins, Monozygotic
PubMed: 34740261
DOI: 10.17796/1053-4625-45.5.12 -
BMC Pregnancy and Childbirth Jul 2022Monochorionic dizygotic twins are a rare condition, mostly related to assisted reproductive technology. This type of twinning is burdened by the same risk of pregnancy...
BACKGROUND
Monochorionic dizygotic twins are a rare condition, mostly related to assisted reproductive technology. This type of twinning is burdened by the same risk of pregnancy complications found in monochorionic monozygotic pregnancies.
CASE PRESENTATION
We report a case of spontaneous monochorionic dizygotic twins sharing situs inversus abdominalis and isolated levocardia, with only one twin affected by biliary atresia with splenic malformation syndrome. We also conducted a literature review of the 14 available documented monochorionic dizygotic twin gestations spontaneously conceived.
CONCLUSIONS
It is still unclear how this unusual type of twinning can occur in spontaneous conception. The evidence so far suggest the importance to timely diagnose the chorionicity, in order to adequately manage the typical complications associated with monochorionicity.
Topics: Chorion; Female; Humans; Pregnancy; Pregnancy Complications; Pregnancy, Twin; Reproductive Techniques, Assisted; Twins, Dizygotic; Twins, Monozygotic
PubMed: 35836143
DOI: 10.1186/s12884-022-04866-x -
Ophthalmic Epidemiology Dec 2003To evaluate the genetic contribution in age-related macular degeneration (ARMD) by a disease-ascertained twin study. (Comparative Study)
Comparative Study
PURPOSE
To evaluate the genetic contribution in age-related macular degeneration (ARMD) by a disease-ascertained twin study.
METHODS
Concordance rates for ARMD in 25 twins were obtained by using four masked graders to confirm the diagnosis of ARMD and place subjects in one of three categories; concordant, intermediate, or discordant. Demographic features and known risk factors for ARMD were compared between monozygotic and dizygotic twin pairs.
RESULTS
Of the 25 twin pairs, 15 were monzygotic and 10 were dizygotic. All 15 monozygotic twins were concordant or intermediate for ARMD. Of the dizygotic twin pairs, only one was concordant and five were discordant. In the demographic and risk factor analysis no unusual contributing or confounding variables were detected.
CONCLUSIONS
The association between zygosity and concordance for ARMD suggests a major importance for genetics in the etiology of ARMD. Our data further support a multi-factorial, primarily polygenic etiology for the condition.
Topics: Aged; Aged, 80 and over; Diseases in Twins; Female; Humans; Macular Degeneration; Male; Middle Aged; Prospective Studies; Risk Factors; Twins, Dizygotic; Twins, Monozygotic; United States
PubMed: 14566632
DOI: 10.1076/opep.10.5.315.17317 -
Twin Research and Human Genetics : the... Apr 2020In the course of twin studies whose main focus was elucidation of genetic and environmental factors on behavioral traits, many twin researchers became aware of the...
In the course of twin studies whose main focus was elucidation of genetic and environmental factors on behavioral traits, many twin researchers became aware of the strong tendency for dizygotic (DZ) twinning to run in families. Over four decades, Nick Martin and others initiated hormone and ultrasound studies, performed segregation and pedigree analyses, tested candidate genes, carried out linkage projects in sister pairs and formed large collaborations to illuminate the genetics of DZ twinning by genome-wide association studies and meta-analysis. This article summarizes the early work on hormone and genetic studies and describes the meta-analyses that have at last met with success in finding the first genes that predispose to DZ twinning, which also appear to influence many other female reproductive traits.
Topics: Genome-Wide Association Study; Genotype; History, 20th Century; History, 21st Century; Humans; Pedigree; Twin Studies as Topic; Twinning, Dizygotic; Twins, Dizygotic; Twins, Monozygotic
PubMed: 32383427
DOI: 10.1017/thg.2020.15 -
Twin Research and Human Genetics : the... Feb 2009This study presents a general model of two binary variables and applies it to twin sex pairing data from 21 twin data sources to estimate the frequency of dizygotic... (Comparative Study)
Comparative Study
This study presents a general model of two binary variables and applies it to twin sex pairing data from 21 twin data sources to estimate the frequency of dizygotic twins. The purpose of this study is to clarify the relationship between maximum likelihood and Weinberg's differential rule zygosity estimation methods. We explore the accuracy of these zygosity estimation measures in relation to twin ascertainment methods and the probability of a male. Twin sex pairing data from 21 twin data sources representing 15 countries was collected for use in this study. Maximum likelihood estimation of the probability of dizygotic twins is applied to describe the variation in the frequency of dizygotic twin births. The differences between maximum likelihood and Weinberg's differential rule zygosity estimation methods are presented as a function of twin data ascertainment method and the probability of a male. Maximum likelihood estimation of the probability of dizygotic twins ranges from 0.083 (95% approximate CI: 0.082, 0.085) to 0.750 (95% approximate CI: 0.749, 0.752) for voluntary ascertainment data sources and from 0.374 (95% approximate CI: 0.373, 0.375) to 0.987 (95% approximate CI: 0.959, 1.016) for active ascertainment data sources. In 17 of the 21 twin data sources differences of 0.01 or less occur between maximum likelihood and Weinberg zygosity estimation methods. The Weinberg and maximum likelihood estimates are negligibly different in most applications. Using the above general maximum likelihood estimate, the probability of a dizygotic twin is subject to substantial variation that is largely a function of twin data ascertainment method.
Topics: Databases, Factual; Female; Humans; Male; Models, Genetic; Probability; Twins, Dizygotic
PubMed: 19210182
DOI: 10.1375/twin.12.1.79