Mortality among twins after age 6: fetal origins hypothesis versus twin method.

OBJECTIVE--To test the validity of the fetal origins hypothesis and the classic twin method. DESIGN--Follow up study of pairs of same sex twins in which both twins survived to age 6. SETTING--Denmark. SUBJECTS--8495 twin individuals born 1870-1900, followed through to 31 December 1991. MAIN OUTCOME MEASURES--Mortality calculated on a cohort basis. RESULTS--Mortality among twins and the general population was not significantly different except among females aged 60-89, in whom mortality among twins was 1.14 times (SE 0.03) higher than in the general population. Mortality among female dizygotic twins was 1.77 times (0.18) higher than among monozygotic twins at age 30-59. Otherwise, mortality for monozygotic and dizygotic twins did not consistently differ after age 6. CONCLUSION--According to the fetal origins hypothesis the risk of adult morbidity and mortality is heightened by retardation in intrauterine growth. Twins, and in particular monozygotic twins, experience growth retardation in utero. The findings in the present study suggest that the fetal origins hypothesis is not true for the retardation in intrauterine growth experienced by twins. Furthermore, the data are inconsistent with the underlying assumption of a recent claim that the classic twin method is invalid for studies of adult diseases. The present study is, however, based on the one third of all pairs of twins in which both twins survived to age 6. The possible impact of this selection can be evaluated in future studies of cohorts of younger twins with lower perinatal and infant mortality.     

Cardiovascular mortality in twins and the fetal origins hypothesis.

The intrauterine growth patterns for twins are characterized by normal development during the first two trimesters and reduced growth during the third trimester. According to the fetal origins hypothesis this growth pattern is associated with risk factors for cardiovascular morbidity and mortality. We studied cause-specific mortality of 19,986 Danish twin individuals from the birth cohorts 1870-1930 followed from 1952 through 1993. Despite the large sample size and follow-up period we were not able to detect any difference between twins and the general population with regard to all-cause mortality or cardiovascular mortality. Hence, the intrauterine growth retardation experienced by twins does not result in any "fetal programming" of cardiovascular diseases. There is still an important role for twins (and other sibs) to play in the testing of the fetal origins hypothesis, namely in studies of intra-pair differences, which can assess the role of genetic confounding in the association between fetal growth and later health outcome.     

Potential bias regarding birth weight in historical and contemporary twin data bases.

In this study we examine the hypothesis that monozygotic (MZ) twins in historical databases are less discordant for birth weight due to negative selection of severely discordant MZ twins. Furthermore, we test the hypothesis that MZ twins are less discordant for birth weight when comparing a volunteer based twin registry with a population based twin registry, due to selective registration. Data were available on 3927 twin pairs from the volunteer Australian Twin Registry born before 1964, 3059 volunteer twin pairs from the Netherlands Twin Register born 1987-1989 and 454 Belgian twin pairs from The East Flanders Prospective Twin Survey born 1987-1989. Intrapair relative birth weight differences (RBWD) were computed for MZ and dizygotic (DZ) twins from each twin registry. Comparing birth weight differences between MZ and DZ twins provides support for the hypothesis that MZ twins are subject to a negative selection in historical databases. Furthermore, Australian MZ twins have a lower RBWD compared to Dutch MZ twins when corrected for the RBWD of Australian and Dutch DZ twins, indicating circumstances which only affect MZ twins. Our hypothesis that MZ twins are less discordant for birth weight in a volunteer based twin registry compared to a population based twin registry had to be rejected. We suggest that investigators using historical databases to test the fetal origins hypothesis should be aware of this increased likelihood of selective exclusion of individuals with extreme morphometric parameters at time of birth.     

A twin study of genetic and environmental influences on psychological traits of eating disorders in a Japanese female sample.

The purpose of the present study was to clarify genetic and environmental origins of psychological traits of eating disorders using a Japanese female twin sample. Participants were 162 pairs of female twins consisting of 116 pairs of monozygotic (MZ) twins and 46 pairs of dizygotic (DZ) twins in their adolescence. Psychological traits of eating disorders were assessed with five subscales of the Eating Disorder Inventory (EDI). As a result of using univariate twin analyses, among five subscales of EDI (maturity fears, ineffectiveness, interpersonal distrust, interoceptive awareness, and perfectionism), perfectionism showed significant additive genetic contributions and individual specific environmental effects. On the other hand, maturity fears, ineffectiveness, interoceptive awareness, and interpersonal distrust indicated significant shared environment contributions and individual specific environment effects. The results suggest the importance of both genetic and shared environmental influences on psychological traits of eating disorders in the present study.     

Universal growth modes of high-elevation conifers

In order to characterize the main growth modes of high-elevation conifers, such as typical variations inherent to annual tree growth records, we resolved eigen problems related to intra-record correlation coefficient matrices of several large sample sets for (A) very long-lived Chinese junipers and (B) shorter-lived European pines and larches. Such modes allow for the identification of tree growth variations of different origins, i.e., resulting from climate and/or microenvironments as well as origins that are purely biological in nature. We determined that these modes are universal, namely, that they are identical for both ring width (RW) and maximum latewood density (MXD) records. Certain specific shapes found in these main modes were indicative of anomalous tree growth. Cross-correlations between identical modes related to RW and MXD data were determined to be nonessential. This suggests that RW and MXD data likely represent different aspects of tree growth response to varying climatic and environmental conditions.     

Twins early development study (TEDS): a multivariate, longitudinal genetic investigation of language, cognition and behavior problems in childhood.

The Twins Early Development Study (TEDS) focuses on the early development of the three most common psychological problems in childhood: communication disorders, mild mental impairment and behavior problems. The TEDS twins were assessed longitudinally at 2, 3, 4 and 7 years of age in order to investigate genetic and environmental contributions to change and continuity in language and cognitive development; it is multivariate in order to examine the origins of comorbidity; and it uses a large sample in order to study abnormal development in the context of normal development. The twins were identified from birth records of twins born in the UK in 1994-96. More than 15,000 pairs of twins have been enrolled in TEDS and the participating families are representative of the UK. The measures at 2, 3 and 4 years are administered by parents. At 7 years, children are assessed for language and cognitive development using telephone testing, parents and children are interviewed about behavior problems, and teachers also assess behavior problems as well as academic achievement. One set of findings is that the same genes largely contribute to both language and cognitive problems and the same genes affect normal and abnormal development, a result that suggests that general impairment may be a better target for genetic research than specific language impairment independent of nonverbal cognitive problems. DNA has been obtained so far for more than 4000 pairs and is being used initially in molecular genetic studies of language problems and hyperactivity.     

Dating the evolutionary origins of wrasse lineages (Labridae) and the rise of trophic novelty on coral reefs

We estimated ages of divergence between major labrid tribes and the timing of the evolution of trophic novelty. Sequence data for 101 labrid taxa and 14 outgroups consisting of two mitochondrial gene regions (12s, 16s), and two nuclear protein-coding genes (RAG2, TMO4c4), a combined 2567 bp of sequence, were examined using novel maximum likelihood, maximum parsimony and mixed model Bayesian inference methods. These analyses yielded well supported trees consistent with published phylogenies. Bayesian inference using five fossil calibration points estimated the minimum ages of lineages. With origins in the late Cretaceous to early tertiary, the family diversified quickly with both major lineages (hypsigenyine and julidine) present at approximately 62.7 Ma, shortly after the K/T boundary. All lineages leading to major tribes were in place by the beginning of the Miocene (23 Ma) with most diversification in extant lineages occurring within the Miocene. Optimisation of trophic information onto the chronogram revealed multiple origins of novel feeding modes with two distinct periods of innovation. The Palaeocene/Eocene saw the origins of feeding modes that are well represented in other families: gastropod feeders, piscivores and browsing herbivores. A wave of innovation in the Oligocene/Miocene resulted in specialized feeding modes, rarely seen in other groups: coral feeding, foraminifera feeding and fish cleaning. There is little evidence of a general relationship between trophic specialization and species diversity. The current trophic diversity of the Labridae is a result of the accumulation of feeding modes dating back to the K/T boundary at 65 Ma, with all major feeding modes on present day reefs already in place 7.5 million years ago.     

Torsional vibrational modes of tryptophan studied by terahertz time-domain spectroscopy

The low-frequency torsional modes, index of refraction, and absorption of a tryptophan film and pressed powders from 0.2 to 2.0 THz (6.6-66 cm(-1)) were measured by terahertz time-domain spectroscopy at room temperature. It was found that there were two dominated torsional vibrational modes at around 1.435 and 1.842 THz. The associated relaxation lifetimes ( approximately 1 ps) for these modes of the tryptophan molecule were measured. Using a density-functional calculation, the origins of the observed torsional vibrations were assigned to the chain and ring of the tryptophan molecule.     

The evolutionary origins of diadromy inferred from a time-calibrated phylogeny for Clupeiformes (herring and allies)

One of the most remarkable types of migration found in animals is diadromy, a life-history behaviour in which individuals move between oceans and freshwater habitats for feeding and reproduction. Diadromous fishes include iconic species such as salmon, eels and shad, and have long fascinated biologists because they undergo extraordinary physiological and behavioural modifications to survive in very different habitats. However, the evolutionary origins of diadromy remain poorly understood. Here, we examine the widely accepted productivity hypothesis, which states that differences in productivity between marine and freshwater biomes determine the origins of the different modes of diadromy. Specifically, the productivity hypothesis predicts that anadromous lineages should evolve in temperate areas from freshwater ancestors and catadromous lineages should evolve in tropical areas from marine ancestors. To test this, we generated a time-calibrated phylogeny for Clupeiformes (herrings, anchovies, sardines and allies), an ecologically and economically important group that includes high diversity of diadromous species. Our results do not support the productivity hypothesis. Instead we find that the different modes of diadromy do not have predictable ancestry based on latitude, and that predation, competition and geological history may be at least as important as productivity in determining the origins of diadromy.     

The foetal origins of adult disease: interpreting the evidence from twin studies.

Twin studies have a contribution to make to the debate concerning the foetal origins of adult disease. Twins are growth retarded compared to singletons and experience post-natal catch-up growth. However, there is no evidence that twins are at increased risk of cardiovascular disease. Studying whether discordance in size at birth within monozygotic twin pairs is predictive of discordance in later life disease should help resolve whether the association between size at birth and later disease is due to common genetic factors. Results from studies of blood pressure in childhood and adult life looking at these within twin effects are far from conclusive. There are, however, methodological problems in the interpretation of these results, not least of which is the relatively small numbers of twin pairs studied. Studies exploring the effect of zygosity and chorion type on later disease provide may provide a useful extension of the research agenda. In summary, twin studies to date have raised more questions about the foetal origins hypothesis than they have resolved.     

Genetic aspects of hemifacial microsomia

Summary The majority of patients with hemifacial microsomia (HM) including Goldenhar syndrome are sporadic cases. The sporadic nature of this disorder is emphasized by the discordant occurrence of HM in one of female monozygotic twins reported here. Previous publications, however, also suggest autosomal dominant and autosomal recessive modes of inheritance. Possible formes frustes will also have to be considered when giving genetic counsel.     

Origins of the Hawaiian flora: Phylogenies and biogeography reveal patterns of long‐distance dispersal

Botanists have long considered the origins of the Hawaiian flora in terms of long‐distance dispersal from particular source areas. We extensively reviewed phylogenetic studies of the Hawaiian angiosperm flora to determine the most likely region of origin for each lineage from a defined set of source areas. We also evaluated dispersal modes of each lineage to assess whether certain dispersal modes are associated with a given source area. The largest source category was Widespread (involving related taxa that extend across more than one region), although many of these comprised native non‐endemic species, and accounted for little of the total species diversity (after accounting for in situ speciation). The next largest source regions were Indo‐Malayan and Neotropical. Comparatively few lineages originated from the East Asian region, although these include the single largest lineage. Lineages originating in the Indo‐Malayan region predominantly arrived via Pacific Islands, whereas dispersal from all other regions appears to have been mostly direct. Compared with previous analyses, we found a higher proportion of lineages originating in the Neotropics and temperate North America. Widespread origins were positively associated with dispersal via flotation on water, whereas other origins were associated with dispersal by birds, either through internal transport or external adhesion. We identified thirty‐one potential cases of dispersal out of Hawaii to other islands. Our assessment is complicated by lineages with ancient origins, with further complications likely stemming from hybridization events. Overall, numerous lineages including some distinctive endemic genera have not had sufficient phylogenetic study to determine an origin.     

Origins of diverse feeding ecologies within Conus, a genus of venomous marine gastropods

Specialized predators on polychaetes, fishes, hemichordates or other molluscs, members of the predominantly tropical gastropod genus Conus diversified rapidly during the Miocene to constitute the most species-rich modern marine genus. We used DNA sequence data from mitochondrial and nuclear loci of 76 Conus species to generate species-level phylogenetic hypotheses for this genus and then mapped known diets onto the phylogenies to elucidate the origins and evolutionary histories of different feeding specializations. The results indicate that dramatically new feeding modes arose only a few times, that the most derived feeding modes likely arose in the Miocene, and that much of the known diversity of Conus that was generated during Miocene radiations has survived to the present.     

Observed frequency of monozygotic twinning in Holstein dairy cattle

Bonnier's equation is used to mathematically estimate the frequency of monozygotic (MZ) twinning in epidemiologic studies of twinning in dairy cattle; however, no empirical determination of MZ twinning has been reported in the literature. Our objectives were to empirically determine the frequency of MZ twinning in lactating Holstein cows and to compare this result with published estimates predicted using Bonnier's equation. Ear biopsies were collected from 107 sets of Holstein twins from six Wisconsin dairies resulting in 40 opposite-sex twins, 29 same-sex male twins, and 38 same-sex female twins. To empirically determine the frequency of MZ twinning, DNA extracted from ear biopsies collected from the 67 same-sex twins was PCR amplified using primers for a minimum of 5 polymorphic microsatellite DNA markers. Opposite-sex twins were classified as dizygotic (DZ) as well as same-sex twins differing in at least one microsatellite DNA marker. Same-sex twins were classified as MZ when all genotypes for a minimum of five markers were identical. Of the 67 same-sex twins, 62 were classified as DZ and 5 MZ resulting in a MZ twinning frequency of 7.5% of same-sex twins and 4.7% of all twins. The estimated frequency of MZ twinning in this population of twin calves using Bonnier's equation was 39.5% of same-sex twins and 24.7% of all twins. We concluded that MZ twinning occurred infrequently in Holstein cattle and perhaps less frequently than that reported in studies using Bonnier's equation to estimate MZ twinning.     

Feasibility of using different approaches for recruiting younger twins to establish a population based twin register in Sri Lanka.

Identifying twins for a population-based register can be achieved through birth records or community surveys. We studied the feasibility and effectiveness of different methods of identifying and recruiting twins to establish a population based register. To trace twins a population survey was carried out using an interviewer administered questionnaire. We also inspected the birth registration certificates at a divisional secretariat reported from a specified hospital between the years of 1985-1997 and compared it to the birth register of this same hospital. To recruit twins a random sample of 75 twin pairs (150 twins) identified at the Divisional Secretariat were contacted through the post and 25 twin pairs (50 twins) were personally visited. The prevalence of twins was 6.5 twins per 1000 people in the area surveyed. The twinning rate at the hospital was 18.92 twins per 1000 births. A discrepancy of 38 multiples births between the hospital labour room records and those registered at the DS was noted. The response from the postal invitation for recruitment was 59% and the response from the personal invitation was 68%. (Difference 9.4% 95% CI; 7.06-11.73). Community survey and systematic inspection of birth records either at the hospital or the birth registration office was an effective method to trace twins. Once traced, personal contact was more effective than the postal invitation for recruitment of younger twins. A cost-effective approach would be to use a postal coverage followed by personal contact for non-responders. The alternative method, community coverage, would have financial implications.     

Assortative mating in monozygotic twins

Abstract

This study investigated assortative mating in a series of monozygotic twins in terms of anthropométrie variables. Initially the twins were analyzed independent of each other, and the results showed fairly clear homogamy among female MZ twins and their spouses, after correcting for age. Further, when stature was partialled out, several anthropometric measures remained significantly correlated. The results for male MZ twins and their spouses were not nearly so clear‐cut. A second analysis treated the co‐twins together, and once again, the female MZ sets tended to show assortative mate choice for stature while the male MZ twins/spouses were not significantly correlated. A follow‐up analysis investigated whether husbands of the female twins were correlated to each other, and negative results were found for all of the 46 anthropometric variables. An apparent contradiction was resolved in the case of stature by regressing spouse stature against that of the co‐twins. It was found that although each of the twins was assortatively mating, one member of the twin set consistently married a taller husband, but the difference was not constant. This had the effect of producing divergent regression lines.