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Genetics and metabolic disorders
Published in Jagdish M. Gupta, John Beveridge, MCQs in Paediatrics, 2020
Jagdish M. Gupta, John Beveridge
The vascular anastomosis in monozygotic twins may be artery to artery, vein to vein, or artery to vein. Monozygotic twins show a higher incidence of congenital malformations than dizygotic twins. It is not possible to establish monozygosity with 100% certainty by examination of the placenta and membranes. However, the diagnosis of dizygosity can be made with more certainty if the presence of two chorions is shown or, more reliably, the twins are of opposite sex. DNA 'fingerprinting' is now the method of choice if zygosity needs to be determined with certainty. The incidence of monozygotic twins is less than that of dizygotic twins. Monozygous twins are rarely familial but there is a familial tendency for dizygous twinning.
Misconceptions, Experimental Design, and Behavioral Genetics
Published in Gail S. Anderson, Biological Influences on Criminal Behavior, 2019
Therefore, one zygote, which came from only one sperm and one egg, becomes two zygotes and, therefore, two people. The difference between monozygotic twins and dizygotic twins is that monozygotic twins are genetically identical; they have the same genetic makeup exactly, so they are natural clones. They will grow into two identical people with exactly the same versions (or alleles) of every gene. They still share 50% of that 1% of their genes with each parent, but they share 100% between each other. These are MZ twins. Unlike DZ twins, who share 50% of that 1% of their genes with each other, they share everything.
Special issues in genetic counselling
Published in Angus Clarke, Alex Murray, Julian Sampson, Harper's Practical Genetic Counselling, 2019
Monozygotic twins are rarely familial and have a rather constant incidence of around 4 in 1,000 pregnancies. Dizygotic twinning, by contrast, shows marked geographical variation and is frequently around 6 in 1,000 in European and white American populations, but it occurs in about 1% of pregnancies in American blacks, and up to 4% of pregnancies in parts of Nigeria. The recurrence risk for dizygotic twins is about 1.7% for Europeans.
WAGR, Sex Reversal, Bilateral Gonadoblastomas, and Intralobar Nephrogenic Rests: Uncertainties of Pre-Biopsy Chemotherapy in a High Risk Syndrome for Nephroblastoma.
Published in Fetal and Pediatric Pathology, 2023
Randall Craver, Matthew Stark, Stephanie Moss, Sarah Long, Pinki Prasad, Christopher C. Roth
This child was a diamniotic dichorionic twin, which may not eliminate the possibility of an identical twin, the twinning occurring early in embryonal development, before the blastocyst cavity forms [12]. Sexually discordant monozygotic twins have been described, and usually are the result of non-disjunction involving the sex chromosomes [13, 14]. Recently, segmental aneuploidy in human oocytes and preimplantation embryos have been shown to not be unusual events. If this segmental aneuploidy affected one of the male sex determining genes in only one of the monozygotic male twins, then this conceivably could result in discordant monozygotic twins with the female of the pair possibly manifesting multiple abnormalities. If the twins in our report were monozygotic, the twinning would have had to occur early in that they were dichorionic and that there was no evidence of mosaicism. Search of the literature revealed no reports of discordant monozygotic twins due to a syndromic sexual reversal, so this remains only a theoretical concern.
Physical health status in first-degree relatives of patients with bipolar disorder, a systematic review
Published in Nordic Journal of Psychiatry, 2022
Louise Holm Madsen, Kimie Stefanie Ormstrup Sletved, Lars Vedel Kessing, Maj Vinberg
What remains unclear in our analysis is whether genetics, epigenetics, or environmental factors or all three of them contributes to this underlying vulnerability of physical diseases in first-degree relatives to patients with bipolar disorder. Studies in monozygotic twins can assess the role of genetics vs environmental factors and establish potential risk factors, as twins have a high familial risk of getting the same disease as their genes are identical. A twin-study from 2019 [41] included a sample of monozygotic twins, either affected with unipolar or bipolar disorder or at a high-risk unaffected co-twin group (to the affected) and a low-risk healthy twin group. The high-risk group had a significantly higher prevalence of metabolic syndrome compared to the low-risk group (15% vs 2.5%, p = .0006) also when adjusted for age, sex, smoking and alcohol consumption and excluding participants receiving potential weight gaining psychotropic medication [41]. The study did not assess lifestyle habits none of the twin pairs (except for one) lived together and may not have shared nutritional habits [41]. However, even though the twin pairs didn’t live together, they might still have inherited the same dietary habits as their upbringing was the same. However, a classical twin study including dizygotic twins could better elucidate whether genetics are a shared risk factor for physical diseases in unaffected first-degree relatives to bipolar probands.
Genetic and shared environmental risk factors do not lead to eosinophil activation in healthy twins of IBD patients
Published in Scandinavian Journal of Gastroenterology, 2020
Jonas Halfvarson, Maria Ling Lundström, Maria Lampinen, Ida Schoultz, Lennart Bodin, Marie Carlson
Intriguingly, the onset of clinical manifest IBD seems to be preceded by a pre-clinical phase, characterized by immunological changes [9]. Experiences from other chronic immune-mediated diseases indicate that exposure to genetic and environmental risk factors represents the initial key drivers that lead to the initiation and propagation of a dysregulated immune response and ultimately clinical manifest IBD. Studies of healthy first-degree relatives of patients with IBD have reported that a subset of these relatives express increased levels of various markers of innate and adaptive immunity. More specifically, we previously demonstrated that healthy twin siblings in twin pairs discordant for IBD display a dysfunctional intestinal barrier [10], with a subclinical mucosal inflammation and increased neutrophil activity, as reflected by elevated mucosal levels of nuclear factor kappaB (NFκB) and myeloperoxidase (MPO) as well as faecal levels of calprotectin [11]. Whether the eosinophil granulocytes are activated as part of this early subclinical immune response, or if these cells become activated as a consequence of disease is unknown. Similarly, the relative contribution of genetic and environmental risk factors to activation of eosinophils in IBD is yet to be explored. Twin studies could be of value in this respect. Monozygotic twins are genetically identical and share environmental factors during childhood and adolescence while dizygotic twins share environment but only half of the genes are common.