Is There a Causal Link Between Childhood Gender Nonconformity and Adult Homosexuality?
Robin M. Mathy, Jack Drescher in Childhood Gender Nonconformity and the Development of Adult Homosexuality, 2020
The path analysis presented here is based on the fact that monozygotic twins will be more similar than dizygotic twins on any trait with non-zero heritability. This is equivalent to saying that zygosity is itself correlated with trait similarity across pairs of twins: the higher the heritability of the trait, the higher the correlation. Accordingly, the unit of analysis here is the twin pair, and each variable is a measure of the pair’s similarity on the three variables at issue (the variables are actually all coded in the direction of dissimilarity). Genetic similarity (zygosity) is coded as 0 for monozygotic twin pairs and as 1 for dizygotic pairs. The similarity of a pair’s childhood gender nonconformity is the absolute value of the difference between their scores on a multi-item scale of childhood gender nonconformity; and, the similarity of their sexual orientations is the absolute value of the difference between their scores on the 7-point Kinsey scale of sexual orientation, which ranges from 0 = exclusively heterosexual to 6 = exclusively homosexual. A full description of the twin sample, the methodology of the study, and a more thorough analysis of the data can be found in Bailey et al. (2000).1
Amniocentesis
Hung N. Winn, Frank A. Chervenak, Roberto Romero in Clinical Maternal-Fetal Medicine Online, 2021
As far as zygosity represents the genetic makeup of the developing entity, accurate determination of this parameter is considered a prerequisite in multiple pregnancy prenatal screening for aneuploidies. In the clinical setting, zygosity is usually inferred from the ultrasound diagnosis of chorioni-city (44), the latter best achieved in the first trimester. In diamniotic (DA) pregnancies with fused placentas, measurements of the thickness of the dividing membrane using a cutoff value of 2 mm can differentiate MC from dichorionic (DC) twinning, though a high inter- and intra-observer variability has been reported. Sonographic detection of the “lambda” or “twin peak” sign is reported as a more reliable indicator of DC placentation with an accuracy of 100% in 10 to 14 weeks of gestation (45). Delayed sonographic evaluation in the second trimester is associated with a 10% to 12% chorionicity misinterpretation rate (46,47), while after 20 weeks of gestation, the determination may turn out impossible. Therefore, in the absence of the “lambda” or “twin peak” sign in a DA twin pregnancy, single placentation and monozygosity is concluded, when the rare cases of MC-DZ (dizygotic) gestations following ART reported are not taken into consideration. However, when a single amniotic sac is detected, monochorionicity is indisputable. Given that the great proportion (80–90%) of DC twins are DZ (48,49), chorionicity may roughly correspond to zygosity (50).
Multiple pregnancy and infertility
Janetta Bensouilah in Pregnancy Loss, 2021
Multiplets have a more complicated life in utero than singletons and, as previously mentioned, monozygotic twins are at higher risk than dizygotic twins, but it is chorionicity and amnionicity rather than zygosity that determines the degree of risk. The particular challenges of a monochorionic (MC) pregnancy arise from the unique structure of the shared placenta, with vascular structures connecting the umbilical circulations of both twins. This leads to unpredictable and significant blood volume shifts between the fetuses causing problems such as twin–twin transfusion and acute fetal transfusion following the intrauterine death of one twin. Furthermore, the shared placenta is often unequally divided, which explains the increased incidence of discordant fetal growth. Perinatal mortality is two to three times higher in MC twins than in DC twins, and morbidity rates are similarly raised.1
Facial asymmetry and chewing sides in twins
Published in Acta Odontologica Scandinavica, 2022
Elina V. Heikkinen, Ville Vuollo, Virpi Harila, Antanas Sidlauskas, Tuomo Heikkinen
This study included 106 Lithuanian twin pairs of the same sex where 59 pairs were MZ and the rest were DZ twins. The twins were selected to the study on the basis of their willingness to participate in the research conducted by the Lithuanian University of Health Sciences Twin Centre. The exclusion criteria were facial trauma, permanent dental extraction, congenital disorders as well as pregnancy. The mean age of the twins was 20.2 years, ranging from 8.6 to 45.7. The number of male and female pairs was 46 and 60, respectively. For each twin pair, a blinded DNA test (AmpFlSTR® Identifiler® PCR) was done to determine true zygosity. The test compared genetic profiles, which ensures quick and authentic determination of zygosity by utilizing specific DNA markers (D8S1179, D21S11, D7S820, CSF1PO, D3S1358, TH01, D13S317, D16S539, D2S1338, D19S433, vWA, TROX, D18S51, D5S818, FGA) and Amel fragment STRs (short tandem repeats). In the asymmetry analyses, one male pair was excluded because of facial hair which caused erroneous roughness on the 3D surface. Furthermore, one female pair was excluded because chewing side preference had not been registered. Thus, the number of twin pairs with both 3D asymmetry analysis and PCS is 104.
Monocyte secretory profiling in a clinical and MEFV genotype-characterized cohort of Danish familial Mediterranean fever patients: diagnostic potential of CCL1 and CXCL1.
Published in Scandinavian Journal of Rheumatology, 2023
SB Mortensen, AE Hansen, K-E Byg, L Diederichsen, C Schade Larsen, MI Goldschmidt, MA Jakobsen, K Assing, KL Lambertsen, DC Andersen, IS Johansen
MEFV genotypes were assessed by sequencing of the entire coding MEFV region and zygosity was resolved in all except five patients (see Supplemental Table S6 for a full list of MEFV genotypes). MEFV genotypes with no detected variants or variants classified as VUS were present in 23 patients (5.8% and 20.1%, respectively), and these were grouped in MEFV group 1, whereas MEFV groups 2 and 3 constituted 17 patients (19.8%) and 46 patients (53.5%) with monoallelic and biallelic presence of variants classified as pathogenic or likely pathogenic, respectively. Five patients with inconclusive variant zygosity were excluded from the genotype groups. In five patients, where MEFV screening was negative, targeted sequencing of 16 autoinflammatory-related genes identified one patient, with a yet undescribed intron variant [NG_007507.1(NM_014646.2):c.590 + 8 T > G] in the gene responsible for the Majeed syndrome, LPIN2 (43).
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
The twins included were identified from a previously described national population-based cohort of twins with IBD in Sweden. In short, the unique personal identification number, issued to all Swedish residents [12], was used to link records from the Twin Registry [13] and the National Patient Register. All twins who had been admitted to hospital with a diagnosis of IBD and their siblings were identified. Both twins in each pair were asked to respond to a questionnaire regarding general gastrointestinal symptoms. The medical notes were scrutinized, after written consent from each twin, for verification of diagnosis of IBD and for determination of disease phenotype, according to the Montreal Classification [14]. Zygosity was determined through questionnaire data about intra-pair similarities in childhood, being of opposite sex, or DNA analyses by the Twin Registry. The questionnaire has been validated previously and has an estimated accuracy of >98% when compared with DNA analyses [15].
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