Like-sexed Twins Research Articles

First-trimester Genetic Diagnosis in Multiple Pregnancy

BRAMBATI, BRUNO; TULUI, LUCIA; LANZANI, ALESSANDRO; SIMONI, GIUSEPPE; TRAVI, MAURIZIO Author Information

Birth sex ratios in sheep over six lambing seasons

The birth sex ratio of a commercial flock of Suffolk × sheep, Ovis aries, were studied over six consecutive lambing seasons. In all, data from 1820 lambs were recorded and analysed. The overall birth sex ratio was 49.56% male lambs. Significantly more males (56.23%) were born to ewes with single lambs than to ewes with like-sex twins (47.73%). Significantly more female lambs were born to ewes with triplet births (41.79% male). A significant difference in the birth sex ratio was observed between the first and second half of the lambing season, among like-sex pairs of twin lambs. More males were born in the first half (51.43%) and significantly more females (43.59% male) in the second half of the lambing season. The results are discussed with reference to the theory of Trivers and Willard (1973).

Measuring the Similarities between the Lifetimes of Adult Danish Twins Born between 1881–1930

Abstract The survival of like-sex twins born between 1881 and 1930 in Denmark, of which both were alive by the age of 15, is studied by means of models for bivariate survival data, with special reference to the degree of dependence. The 8,985 pairs were followed until 1980. The dependence is assumed to be generated by a common unobserved risk level. Several families of distributions for this level, including positive stable and gamma, are compared. General aspects of such data are discussed, including how to measure the degree of dependence. A simple choice is Kendall's coefficient of concordance, which for monozygotic males and females is about .17 and .15 and for dizygotic .09 and .10. Adjusting for cohort effects by a covariate describing year of birth reduces the dependence measure only slightly. The dependence is so small that a prediction for one twin is only slightly improved if the survival status of the other is known.

A Twin Study of Genetic Variation in Proportional Radiographic Alveolar Bone Height

The purpose of this study was to estimate the genetic variance for alveolar bone height by means of the classic twin method and the study of monozygous twins reared apart. Panoramic radiographs were obtained from 120 pairs of adult twins (mean age = 40.4 years, S.D. = 10.4 years), for comparison of 62 pairs of monozygous twins reared together (MZT), 25 pairs of like-sexed dizygous twins reared together (DZT), and 33 pairs of monozygous twins reared apart (MZA). Mesial and distal bone heights were determined as a proportion of tooth length. A full-mouth bone score was computed for each twin by averaging these proportions from all measurable teeth. Between-pair (B) and within-pair (W) variances were computed for each twin group. The population variances (B + W) of the MZT and DZT twin groups were similar, which validated a basic assumption of the twin model. Intraclass correlations and heritability estimates were also computed for the reared-together and reared-apart twin groups. Boot-strap sampling was used to provide estimates and confidence limits for these values. The intraclass correlations for the twin groups were: MZT = 0.70, DZT = 0.52, and MZA = 0.55. The results of this study suggest that there is significant genetic variance in the population for proportional alveolar bone height.

Birth Defects in Twins: Study in a Spanish Population

The risk for specific defects among twins compared to singletons was studied using data collected by the Spanish Collaborative Study of Congenital Malformations (ECEMC). A total of 136 twins had a major and/or minor congenital defect. The overall rate of congenital defects in twins (2.37%) did not deviate significantly from the rate in singletons (2.21%). Like-sex (LS) and male-male (MM) twin pairs had a slightly higher rate of birth defects than unlike-sex (US) and female-female (FF) pairs, respectively. Defects of the central nervous system, cardiovascular system and genitourinary system were significantly more frequent in LS twins than in singletons, with relative risks of 2.8, 2.5 and 1.6, respectively. No significantly increased risk was found among US twins. Among defects of the central nervous system, the rates of anencephaly, encephalocele and hydrocephaly were significantly higher in total and LS twins; however, no significantly increased risk for spina bifida was observed when compared to singletons. MM twins were also 1.9 times more likely to have hypospadias, but the risk among males of male-female (FM) pairs was decreased.

First‐trimester genetic diagnosis in multiple pregnancy: Principles and potential pitfalls

Both the principles of first-trimester genetic diagnosis in multiple pregnancy and the special considerations required to avoid potential diagnostic pitfalls are presented. The experience consisted of 65 cases of twins and one case of quadruplets. Dichorionic twins were recognized by sonography in 54 cases. Transabdominal aspiration was generally preferred to transcervical for obtaining chorionic tissue, although in two cases both approaches were used. Diagnostic error following erroneous sampling was reported in 3 out of 54 sets of dichorionic twins (5.5 per cent). When like-sex dichorionic twins cannot be differentiated by cytogenetic or DNA polymorphism studies, amniocentesis should be recommended to confirm the reliability of the result on chorionic tissue.

Impact of Heredity in Myopia

A series of 109 like-sexed twin pairs in the age group 30-31 years (54 monozygotic and 55 dizygotic) with one or both members of the twins with myopia was found in the Finnish Twin Cohort. The series was based on a random sample of 1,200 twins in one age stratum of the cohort. The twins received a questionnaire on their health status with special reference to eye diseases and symptoms. The refractive status of the twin pairs was ascertained by asking the twins to send their latest prescription for glasses to the authors or the refraction was obtained from the ophthalmologists or opticians of the twins. The mean difference in refraction between the monozygotic twins was 1.19 dptr in the right eyes and 1.15 dptr in the left eyes. The difference between dizygotic pairs was 2.34 dptr in the right eyes and 2.47 dptr in the left eyes. Analysis of variance showed that the difference in refraction between the two eyes of a twin pair was not significant. The mean difference in refraction between the monozygotic twins was significantly lower than that between dizygotic twins (p less than or equal to 0.001). The intrapair variances were doubled among dizygotic twin pairs compared to monozygotic twin pairs in the male group. The intrapair variance in the female group was 4-fold among dizygotic twin pairs as compared to monozygotic twin pairs. Heritability of myopia was 0.58 (0.74 for males and 0.61 for females) when myopia was considered a dichotomous variable. This result suggests that inheritance has a substantial effect on the etiology of myopia.

Variability in expression of common fragile sites: in search of a new criterion

Fragile sites are nonrandom, heritable sites on chromosomes that can be induced to form gaps, breaks, and rearrangements under specific conditions. There is currently no established criterion to define a common fragile site. We applied seven published criteria to our data from three groups of subjects: (1) three pairs of like-sexed twins, (2) four unaffected von Hippel-Lindau (VHL) family members, and (3) six patients affected with VHL disease. Substantial differences were present in the numbers of sites considered positive by these criteria. While some of this variability can be attributed to technical factors, our data illustrate the problems in comparing results from different studies to assess the significance of fragile sites. A recently published criterion is based upon the Poisson distribution. We found this criterion to be flawed in its presentation, and furthermore, the Poisson distribution did not provide an adequate approximation to our data. We propose here an alternative approach based upon the negative binomial distribution.

The Effects of Maternal Age, Parity, and Sex of the Twins on Twin Perinatal Mortality. A Population Based Study

The aim of this study on all twin births in Sweden between 1973 and 1985 was to evaluate the effect of maternal age, parity, and sex on twin perinatal mortality (PNM), by using national data held at the Medical Birth Registry, National Board of Health and Welfare, Stockholm. Zygosity in this study was estimated by the Hardy-Weinberg formula. In all, 22,374 twins were born; 972 (4.3%) of these died perinatally. The relative risk for perinatal death (after standardization for maternal age, parity, and like sex) decreased significantly during the study period, and reached its lowest value (0.3) in 1983. Maternal age was not associated with PNM, while women having their first delivery had a significantly higher PNM than the rest of the parturients. The MZ twinning rate increased from 0.36% during 1973-76, to 0.40% during 1977-81 and 0.44% during 1982-85 (trend analysis: chi 2 = 40.1, p less than 0.001). After stratification for year of delivery and birthweight, like-sexed twins had a significantly higher PNM than unlike-sexed twins (odds ratio, OR = 1.25, 95% confidence interval, CI = 1.02-1.54). Males had a significantly higher PNM than females in like-sexed pairs (OR = 1.39, 95% CI = 1.16-1.66), and in unlike-sexed pairs (OR = 1.46, 95% CI = 1.01-2.10). MZ twins had a significantly higher estimated PNM than DZ ones (OR = 1.31, 95% CI = 1.02-1.67).

Twinning causative origin investigated by Sartwell's biometrical method.

Sartwell's biometrical model is useful to test potential causal factors at the origin of biological phenomena of unknown etiology. It postulates a lognormal distribution of the incubation time. The method has been applied in the past to infectious and neoplastic diseases and, only lately, to genetic diseases. We report here an application to unlike-sex and like-sex twins in an attempt to infer causal origin from a family of potentially related factors. Two hypotheses are tested: the maternal prenatal origin of unlike-sex twins, and the menopausal basis of like-sex twins. The hypotheses are respectively grounded in the presumed genetic origin of DZ twinning, and in the ovarian-dysfunction origin of MZ twinning. The study is population-based; it proceeds from a matched control group and considers various time windows (induction periods) of possible etiologic significance-namely, age at onset of twins, the time window from the first birth to the twin birth, and the time window from the twin birth to the last birth. The study of lognormality has been carried out with the Box-Cox transformations, Fisher's cumulants method, and the normal probability plots. Results show clearly that unlike-sex (presumably DZ) twins have their causal origin in the maternal prenatal period as age of onset is definitely lognormal. Median induction time is 31 ± 6 years. This is interpreted as a multiplicative age-related causal process involving hypophyseal hormones. The menopausal origin of like-sex twins, a mixture of MZ and DZ, is less clear-cut, as the fit of the distribution of the time window until last birth to a lognormal model is less than perfect. In spite of the heterogeneity of the like-sex twin group, there is evidence that some cases of MZ twins may be menopause-related. But this complex question needs more study.

Heritability of blood pressure in 7‐ to 12‐year‐old Chinese twins, with special reference to body size effects

Systolic and diastolic blood pressures and body-size indices such as body height, body weight, sitting height, chest circumference, skinfold thickness, and body mass index (BMI) were assessed in 110 pairs of like-sex Chinese twins (75 monozygotic and 35 dizygotic) aged 7-12 years. Significant correlations of blood pressure with body-size indices were found. Prior to adjusting for body-size effects, three twin methods yielded low heritability estimates for both systolic (0.32-0.41) and diastolic (0.32-0.51) pressures. Adjusting systolic pressure for body height and BMI via multiple regression nearly halved heritability estimates, but adjusting diastolic pressure for body height and skinfold thickness only changed the estimates slightly.

Antenatal Diagnosis of Bilateral Renal Agenesis in One of a Twin Pair

DOI: http://dx.doi.org/10.5915/22-1-13543 Bilateral renal agenesis (BRA) was diagnosed antenatally in one of like-sexed (probably monozygotic) twins. This is the first report of such a diagnosis. The difficulties of certain sonographic diagnosis of BRA are outlined and are possibly compounded in twin pregnancy in the presence of growth retardation/oligohydramnios of one of the twins. Recent evidence suggests that BRA is inherited in an autosomal dominant pattern with reduced penetrance and variable expressivity. The discordance for BRA in twins, even mono.zygotic twins, has been relatively frequent suggesting a possible role of environmental influences in the expression of the anomaly. Genetic counseling should include renal evaluation of asymptomatic parents and siblings and early detailed ultrasound evaluation of fetal kidneys in all subsequent pregnancies.

Population-Based Twin Registries: Illustrative Applications in Genetic Epidemiology and Behavioral Genetics from the Finnish Twin Cohort Study

The population-based twin registries of Denmark, Finland, Norway and Sweden represent an extraordinary resource for scientific research. Although each register has its own history and composition, they share certain common qualities. All the Nordic countries have a long tradition of population registration, a high standard of living and health-related registers of high quality. The large size of the registers means that they are uniquely placed for representative studies of rare occurrences. Examples of studies that these registers make possible are illustrated with data from the Finnish Twin Cohort, which in its first phase consisted of over 17,000 like-sexed twin pairs born before 1958. It has been recently expanded to include multiple births between 1958 and 1986 (nearly 23,000 sets) and their first-degree relatives. During this period the DZ/MZ ratio decreased, while an increase in MZ twinning rates was observed between 1974 and 1986.

Cigarette Smoking As a Cause of Lung Cancer and Coronary Heart Disease. A Study of Smoking-Discordant Twin Pairs

Despite increasing scientific evidence for a causal role of tobacco smoking in lung cancer and coronary heart disease, an alternative hypothesis was put forward several decades ago. The constitutional hypothesis has stated that there are genetic or other common factors, which predispose both to smoking and disease. A critical test of this hypothesis was considered the pattern of occurrence of disease in monozygotic (MZ) twin pairs in which one is a smoker and the other never has been a smoker. Initial twin studies found only small differences in the mortality of smoking and nonsmoking twins of discordant pairs. In the Finnish Twin Cohort, a population-based panel of adult like-sexed twin pairs, a questionnaire study carried out in 1975 permitted identification of 2488 twin pairs discordant for cigarette smoking. Analyses of total mortality and mortality due to coronary heart disease and lung cancer indicate that the smoking members of discordant MZ pairs are at higher risk than their nonsmoking cotwins; increased mortality of smoking cotwins was also found on 21-year follow-up of smoking-discordant pairs in Sweden. Incidence data and noninvasive studies of atherosclerosis in the Finnish sample provide confirmatory evidence for the causal role of smoking in the etiology of coronary heart disease and lung cancer.

Dental arch morphology in South Australian twins

Fourth-order polynomials were used to represent dental arch morphology in 29 monozygous and 19 dizygous like-sexed twin pairs, and in 45 unrelated individuals. The polynomial coefficients provided an accurate description of dental arch morphology with the quadratic ( x 2) and quartic ( x 4) terms reflecting arch shape and the linear ( x) and cubic ( x 3) terms summarizing asymmetry. There were no significant differences between the groups in either the quadratic or quartic terms. Values of correlations between polynomial terms indicated that there was no consistent relationship between maxillary and mandibular arch shape or asymmetry. Intraclass correlations between twins suggested that genetic factors contributed to variation in maxillary arch shape and to a lesser extent to variation in mandibular arch shape but not to arch asymmetry.

Concordance and discordance of congenital hydrocephalus in 107 twin pairs in Japan.

During the period from 1969 to 1985, 107 pairs of twins, of which at least one in each pair had congenital hydrocephalus, were ascertained in Japan. The rate of concordance for hydrocephalus among these twins was 15%, with a slightly higher rate in like-sex male twins (28%) than in like-sex female twins (14%). The rates were 21% in like-sex and 0% in unlike-sex pairs. Two twin pairs had one anencephalic twin and one hydrocephalic twin.

Twins, smoking and mortality: A 12-year prospective study of smoking-discordant twin pairs

Despite the increasing scientific evidence for a causal role of tobacco smoking in lung cancer and coronary heart disease, critics, several decades ago, put forward an alternative hypothesis. The constitutional hypothesis has stated that there are genetic or other common factors, which predispose both to smoking and disease, but that the two are not causally related. A critical test of this hypothesis is the study of disease in monozygotic (MZ) twin pairs in which one smokes and the other never has. Earlier twin studies found only small differences in the mortality of smoking and nonsmoking twins of discordant pairs. In the Finnish Twin Cohort, a population-based panel of adult like-sexed twin pairs, a questionnaire study carried in 1975 permitted identification of twin pairs discordant for cigarette smoking. The nonsmoking cotwins had never been regular smokers. The smoking twins were divided into 1278 current smokers [CS; 143 MZ and 598 dizygotic (DZ) males and 171 MZ and 585 DZ females] and 1210 former smokers (FS; 129 MZ and 408 DZ males and 113 MZ and 341 DZ females). Exposure to tobacco was much higher among males; over 25% of men smoked 20 or more cigarettes daily compared to less than 10% of women. Follow-up of mortality yielded data on time and cause of death. Analyzing on first deaths from concordant pairs, there were 13 deaths in the smokers of male CS MZ pairs and 1 death in the nonsmoking cotwins (relative risk = 13.0, P < 0.01). Excess mortality was also found for male CS DZ smokers (RR = 2.43, P <0.01). An effect of dose was seen: moderate and heavy smokers had higher relative risks than light smokers (1–9 cigarettes daily). Significant excess mortality from coronary heart disease was found among current smokers. All lung cancer cases ( n = 8) occured in smokers.

Twin study: relationship between birth weight, zygosity, placentation, and pathologic placental changes.

We examined the placentas of 182 like-sexed live-born twins: 73 placentas (40.1%) were monochorionic and 109 (59.9%) were dichorionic. All twin pairs with monochorionic placentas were monozygotic (MZ), but 28.9% of pairs with dichorionic placentas were MZ. Analysis of birth weights demonstrated that dichorionic and dizygotic (DZ) twins were heaviest, and suggested that the chorion status is a more important determinant of birth weight than zygosity. Vascular anastomoses were identified only in monochorionic placentas and occurred in 79.5% of cases. All placentas with deep anastomoses had superficial anastomoses. A higher proportion of velamentous and marginal insertions of the umbilical cord in monochorionic placentas (27.4%) compared to dichorionic placentas (13.8%) supports the belief that lateral placental growth is greatest in twin gestations in which the embryos are initially most closely apposed--The theory of trophotropism.

The validity of Weinberg's rule in the East Flanders Prospective Twin Survey (EFPTS).

Most population studies of twins estimate the number of monozygotic (MZ) and dizygotic (DZ) pairs by Weinberg's differential rule. This rule assumes that within the DZ twins the numbers of unlike-sexed (U) and like-sexed (L) twins are equal. The literature on the validity of Weinberg's rule is still controversial. In this prospective population-based study (EFPTS) of 2,589 twin pairs, of whom 2,577 were of known zygosity and placentation, the estimates of Weinberg's rule agree well with the results of direct zygosity determination.

Incidence of twinning in London from 1581 to 1760.

Baptism records of parishes in London and its vicinities from 1581 to 1760 (168,238 maternities) were investigated to estimate the twinning rate and its secular and seasonal variations. Total, estimated dizygotic (DZ), and estimated monozygotic (MZ) twinning rates were 1.1%, 0.8% and 0.3%, respectively. MZ twinning rate varied during the 18 decades, with a significantly low rate (0.11%) in the early 17th century (1621-1640). Significant seasonal variations of the twinning rate according to the month of baptism was observed in both DZ and MZ twins. DZ twins were born more frequently in spring and fall in general. Parish records obtained from four parishes near Manchester in England showed an inversed seasonal variation with peaks in winter and summer. An interpretation of this difference was discussed in a context of environmental factors. In the low MZ period, 1621-1640, MZ or like-sexed twins were apparently less frequent in summer (April to October). This result could be explained by a decrease of MZ twins and/or a greater loss of like-sexed DZ twins.