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The rate of multiple births and the incidence of congenital anomalies in Tokyo Metropolitan Hospitals were studied during the period 1979-1990. The number of twins was 968 pairs (8.23 per 1,000 deliveries) and of triplets 18 sets (15.3 per 100,000 deliveries) among 117,672 deliveries including 1,587 stillbirths after 16 weeks gestation. Multiple birth rates increased yearly. Stillbirth rates in twins and triplets were 5.5% and 16.7% respectively, which were both significantly higher than that in singletons (1.3%). The number of congenital anomalies was 42 in 1,936 twins (2.17%), 2 in 54 triplets (3.7%) and 1721 in 116,686 singletons (1.47%). The most common defects in twins were those of the cardiovascular system (0.72% in twins vs 0.52% in singletons) and of the musculoskeletal system (0.72% in twins vs 0.50% in singletons), followed by upper respiratory tract and/or mouth conditions (0.67% in twins vs 0.35% in singletons), all of which had no significant difference in frequency between twins and singletons. Though some anomalies had a significantly higher frequency in twins than in singletons, the concordance rate in the like-sexed twins was very low.
Familial aggregation for disease is important; strong familial risk factors must exist even if the increased risk to a relative of an affected individual is modest. It is in practice difficult, however, to conduct studies in genetic epidemiology which conform to strict epidemiological principles. For twin studies there are two major questions: Are twins ‘no different’ from the population on which inference is to be made? Are study twins ‘no different’ to twins in the population? The importance of each question of bias depends on the scientific question, the trait(s) studied, and sampling issues. The strength of the twin design is its ability to refute the null hypothesis that genetic factors do not explain variation in a trait. Following the Popperian paradigm, alternate hypotheses should be considered in depth (both theoretically and empirically), with a design and sample size sufficient to exclude not just naive explanations. More sophisticated statistical techniques are now being applied, so the philosophy, assumptions, and limitations of statistical modelling must be appreciated. The concept of ‘heritability’ has, in the past, been misunderstood and misused. New advances in DNA technology promise to revolutionise epidemiological thinking, and so case-control-pedigree designs may well become standard tools. The strengths and limitations of studies based on related individuals as the sampling unit are discussed.
In a previous Swedish twin project (the SLU-project), approximately 300 MZ and DZ twin pairs and controls were followed through the Swedish compulsory school from grade 3 to grade 9. Results from this study indicated an increase of genetic influences on school achievement over time for children from a permissive home environment and a decrease for children from a restrictive home environment. These types of data have generated a more general model for studying heredity-environment interaction in educational settings. To test this model, a cross-cultural comparison over time of twins and controls in the Israeli kibbutz school and in the Swedish compulsory school has been made. Restrictions on the child were originally assumed to be more apparent in the kibbutz environment.
Reading and mathematics performance data from a sample of 264 reading-disabled twin pairs and 182 matched control twin pairs were subjected to multivariate behavior genetic analysis. The factor structure of reading and math performance measures was found to be highly similar for both groups. Consistent with previous findings obtained using alternative methods, a significant heritable component to individual differences in reading performance was found both within the reading-disabled (h2 = 0.78) and control (h2 = 0.74) twin samples. In addition, a substantial genetic influence on mathematics performance was found (h2 = 0.51 and 0.60 in the reading-disabled and control samples, respectively), although shared environmental influences common to both members of a twin pair also contribute significantly to the variance in math scores of both groups (c2 = 0.44 and 0.37). Moreover, genetic influences accounted for 98% of the observed correlation between reading and math performance within the sample of reading-disabled twin pairs, and for 55% of the observed correlation in the control sample. Thus, individual differences in both reading and mathematics perfomance are highly heritable and appear to be caused by many of the same genetic influences.
A nine-year-old girl with short stature was referred to the department of pediatrics at Kyushu University. The clinical diagnosis was Turner syndrome; karyotypic analysis performed on peripheral blood, using GTG techniques, demonstrated a 45,X/47,XYY (17:83) mosaicism. Her twin brother, a phenotypically normal male, had the same karyotype; 45,X/47,XYY (3:97) on peripheral blood. Their skin fibroblast karyotypes showed the same mosaicism, ie. 45,X/47,XYY (41:59 and 31:69 respectively). On eleven biochemical genetic markers the twin pair were concordant, thus the likelihood of monozygosity was 0.99527034. In addition, the analysis of variable number of tandem repeat (VNTR) markers revealed the likelihood of monozygosity to be 0.99944386. The most plausible explanation of the X/XYY mosaicism was nondisjunction of the Y in the first cleavage division of the 46,XY zygote. A disproportionate rate of cell populations with 45,X and 47.XYY in the twinning process of the X/XYY embryo, especially in the germ lines, would result in discordant sex in twin pairs.
In 1988, questionnaires were received from 1,400 twin pairs (17% MZM, 23% MZF, 17% DZM, 19% DZF, 24% DZO) aged 11 to 18, registered with the Australian NHMRC Twin Registry. Twins reported independently on themselves and on the perceived behaviour of their parents, siblings and friends. For smoking and for drinking in the previous month, the prevalence was modelled as a logistic function of age, sex, perceived smoking or drinking behaviour of family and friends, and the Junior Eysenck Personality Questionnaire (JEPQ) scales. Strenghts of association were: family behaviour, odds ratio (OR) ≤2; Extraversion and Psychoticism, interquartile OR ≈ 1.6; behaviour of friend, OR ≈ 3 to 6. Twin associations were represented by odds ratios. For smoking they were 16 in MZ and 7 in DZ same-sex pairs, and 3 in DZO pairs. Although the former is consistent with genetic factors determining adolescent smoking behaviour, the reduced association in DZO pairs and strong association with smoking by friends argue to the contrary. For drinking, twin odds ratios were 11 in MZM, MZF and DZF pairs, and 4 in DZM and DZO pairs, consistent with genetic factors determining alcohol use in male but not female, adolescents. Twin odds ratios were not influenced by adjustment for the JEPQ scales; this does not support the hypothesis that genetic factors which determine personality also determine smoking or drinking behaviour during adolescence.
The laterality effects in 10 symmetrical EEG derivations in twins (20 MZ and 20 DZ pairs with a mean age of 20.5 years) were examined. The quantitative and qualitative analyses gave the following results: (1) cotwins in the MZ and DZ pairs differed particularly in the intensity of asymmetry for EEG parameters — one was more asymmetrical than the other; (2) among the MZ twins there were no “mirror” pairs (opposite asymmetry of the EEG), even where opposite-handedness existed. For example, a right-handed twin had an asymmetrical EEG, while the other, a left-hander, had a symmetrical one; (3) the most asymmetrical EEG was in the temporal derivations showing a more active left hemisphere; and, (4) there was no evidence of genetic influence in the intensity of EEG asymmetry.
The present study compared two different types of English-language teaching approaches, the grammatical approach (GA) and the communicative approach (CA), by the cotwin control method. This study has two purposes: to study the effects of teaching approaches and to estimate genetic influences upon learning aptitudes. Seven pairs of identical twins (MZ) and 4 pairs of fraternal twins (DZ) participated in the experiment along with 68 other nontwin fifth graders. Each cotwin was assigned to the GA and CA respectively and received 20 hours of lessons over a 10-day period. The behavioral similarities between MZ cotwins were statistically and descriptively depicted. No major effect of either teaching approach was noted, but the genetic influence upon individual differences of learning achievement was obvious. Furthermore, an interesting interaction between the teaching approaches and intelligence was found, that is, that the GA capitalises on and CA compensates for intelligence. This interactional pattern could be interpreted as an example of genotype-environment interaction. The relationship between genetic factors and learning aptitudes is discussed.
Multiple pregnancy is NEVER planned. A few years ago one could categorically make such a statement. Perhaps nowadays one cannot be so sure. Although parents are still unlikely to be able to plan such an event, it does seem that current infertility treatments may allow or even encourage practitioners to use methods which predispose to a multiple pregnancy. The practice of returning several fertilised embryos to the uterus in the hope of achieving a successful result has meant that many parents who longed for a baby have had to adjust to the realisation of a multiple pregnancy with all the effects such an occurrence has on family physical, social and emotional resources.
The Study of Triplets and Higher Order Births by the Office of Population Censuses and Surveys  highlighted the striking increase in Multiple Births in recent years. This was particularly evident in the case of triplets and higher order births. (Fig. 1) Care of these high-risk infants is costly in resources and no increased funding has been given to the National Health Service or Social Services budgets to provide care and support for the families.
This study endeavours to ascertain the needs of such families preconceptually, antenatally, intra-partum, postnatally and in the early months following the birth. It also tries to assess how appropriate current practice is in meeting these needs.