Inheritance patterns of digital ridge counts have been analyzed using multivariate statistical methods and data from the offspring of half-sib twin kinships. Prior studies found the univariate measure total ridge count to be highly heritable and the counts on individual fingers to be somewhat less heritable, and exploratory factor analytic studies indicated that at least two, and possibly three, independent genetic influences are responsible for this ten variable multivariate trait.

Two statistical methods have been employed to elucidate the factors controlling ridge count development on all ten fingers. An exploratory method developed by Bock and Vandenberg [4] has been applied to the among and between mean square matrices from a multivariate nested analysis of variance on thirty balanced male twin kinships. A principal component analysis on the resulting matrix of pure genetic effects has revealed two substantial genetic factors. One strongly influences the counts on all ten fingers, with the largest loadings on the three central fingers of each hand, while the other has an impact on the thumbs and fifth fingers. For both factors the loadings on homologous fingers are nearly equal. This exploratory procedure is wasteful of the data that is available in half-sib twin kinships, however.

Confirmatory factor analyses, employing the LISREL IV program, have been conducted on all available ridge count data from the offspring of forty-eight unbalanced male twin kinships and fiftynine unbalanced female twin kinships. Nested analyses of variance performed on sex-adjusted data yielded five 10 × 10 variance-covariance matrices containing 275 unique statistics for the estimation of genetic and environmental parameters and the testing of hypotheses.

A series of ten genetic and environmental hypothetical models for ridge count development, each more complex than the previous one, have been tested. They include a simple environmental model, an additive genetic and environmental model proposed by Holt [16], a full additive genetic model including five separate finger factors, two laterality factors and a general genetic factor, and seven models augmenting this full additive genetic model with factors for maternal epistatic and general environmental effects. The most complete model, which includes eight additive (one general, two laterality, and five finger) as well as maternal, epistatic, and general environmental factors cannot be rejected at a .05 level of significance. This model accounts for 99% of the variance that cannot be accounted for by a simple environmental model, and 95% of the variance unaccounted for by Holt's model. It suggests that while a strong genetic factor influences the ridge counts on all ten fingers, there are other factors affecting the counts on the homologous fingers separately as well as different factors affecting the counts on the left and right hands. In addition to these additive effects, influences due to the maternal environment common to all pregnancies of the mother, and those due to the unique environment of each pregnancy of the mother, and those due to the interaction of genes at separate loci have also been detected.

Results of the Bock and Vandenberg analysis are concordant with those obtained by the LISREL program. While the former only requires the availability of standard statistical packages, it is wasteful of data from the half-sib families. The latter, on the other hand, while it requires the use of a specific program, LISREL or its equivalent, uses all half-sibship data and allows one to test genetic and environmental hypotheses as well as conduct exploratory factor analyses.

Behavioral development during childhood is examined in relation to recent concepts and data from evolutionary theory and developmental genetics. The epigenetic framework of Waddington is proposed as a powerful tool for analyzing the progressions in behavior, particularly for recognizing that development involves coordinated pathways of change over time. Many of these pathways appear to depend upon the activity of timed gene-action systems that switch off and on according to a predetermined plan. Behavioral development thus gives expression to the dynamics of preprogrammed change; and in this perspective, behavioral discontinuities may be as strongly rooted in the epigenetic ground plan as the continuities are. The present paper aims to pull together some common themes from different areas that bear on the central issues of behavioral development—the neural foundations, the time course followed, the interplay of maturation and experience, the extent of preorganization furnished by the genetic program, and the adaptive significance of such behaviors in an evolutionary perspective. The final section touches on some hypotheses drawn from developmental neurobiology and developmental genetics that may enrich the analyses of human behavioral development.

This study describes a 5-year survey of activity in a single institution, and the effects of a change of policy for prevention of preterm birth in twin pregnancies.

The results show the advantages and drawbacks from the financial and medical viewpoints.

A new approach is proposed in twin research based on the study of twins who, though reared together, have subsequently lived apart for a period of at least five years. With respect to the more powerful study of twins reared apart, the twins living apart test has the advantages of being more realistic and affording easier access to sufficiently large samples. In this pilot study, the test has been applied to a sample of 92 monozygotic pairs now aged 35–45; 15 pairs were still living together and 77 had lived apart for over five years. As a first approach, comparisons have been made, in the cotwins of the two subsamples, with respect to the following traits: height, weight, presbyopia, presbyacusia, alcohol consumption, tobacco consumption, blood pressure (systolic and diastolic), dental caries, and hours of sleep.

Scores from a behavioral assessment of 160 stable preterm newborn twins were compared with those obtained from 120 full-term newborn twins. The twins were examined during various activities to obtain representative samples of behavior in the following behavioral categories: irritability, resistance to soothing, reactivity, reinforcement value, and activity level. Within-pair correlations were found in all of the behavioral categories, suggesting a constitutional influence on behavioral patterns during the neonatal period. The preterm infants demonstrated internal consistency of behavior similar to that of the full-term group in the first three categories. However, group differences were found when comparing the preterm with the full-term infants on actual ratings of the items. Behavioral differences between these full-term and preterm twins were comparable to those published for samples of singleton infants.

The genetic and environmental effects on the levels of 17 serum biochemical quantitative traits (calcium, phosphorus, glucose, urea nitrogen, uric acid, total protein, albumin, total bilirubin, alkaline phosphatase, lactate dehydrogenase (LDH), glutamic-oxaloacetic transaminase (SGOT), total lipid, cholesterol, triglyceride, α-lipoprotein, pre-β-lipoprotein and β-lipoprotein) were estimated in 105 pairs of healthy twins of both sexes (57 MZ and 48 DZ) by path analysis. The genotype effect was significant for all traits (P < 0.001) and its value extended from 0.52 (α-lipoprotein) to 0.81 (alkaline phosphatase), whereas environmental effect was significant (P < 0.05) in only 10 traits of the 17 analyzed, with the maximum value of 0.13 (cholesterol). Correlations between genotypes of paired traits were estimated and, of 136 values, 47 were significant at the 5% levels, thus indicating partial and common genetic mechanisms.

This study analyzes costs for neonatal care and costs for care of handicapped children related to twin pregnancies and births. These costs are highly related to the unfavorable birthweight distribution for twins. Each twin pregnancy may cost 10 times more than a single pregnancy. This economic analysis favors all kinds of preventive policies and a calculation is proposed for measuring the probable effect in costs of even a slight decrease in the proportion of very low and low birthweight for twins.

The birth of twins was believed by the earlier Yoruba communities to be an omen. Drastic measures were adopted in the form of infanticide, or, sometimes, banishment of the twins with their mothers. The ritual killings were gradually replaced by acceptance and reverence of the twins, and thus evolved the kinship cult of twins in which the orisa ibeji, a tutelary deity of twins, became part of the Yoruba pantheon. Twins could be identified in the community by their fixed names of Taiwo and Kehinde. The community prescribes occupations to the mothers, which is learned through consultation with the oracle. The usual forms of occupation, which reflect the nature of the twins, are trading in oil, beans, or clothing, or requesting alms. The orisa ibeji and, by association, the twins were attributed powers of fertility, prosperity, avenger, detector of thieves, and rainmaker. Propitiation and supplication with offerings and sacrifices are an integral part of the cult of twins.

Previous results regarding a seasonality of twin births have been conflicting. Since the biology of monozygotic (MZ) twinning differs from that of dizygotic (DZ) twinning, it is possible that the seasonality of birth for these two twin types might differ. However, all previous studies examining the seasonality of birth by zygosity has estimated zygosity by Weinberg's method. In this report, the month of birth of all MZ and DZ veteran twins from the United States National Academy of Sciences-National Research Council (NAS-NRC) Twin Registry are compared with that found for an unselected group of veterans. Zygosity in the registry has been individually assigned to all twin pairs by a well-validated method. Compared to unselected veterans, the distribution of births by months did not differ significantly for all the veteran twin pairs or for the MZ and DZ twin pairs considered separately. The distribution of month of birth of the MZ and DZ twin pairs did not differ significantly from one another. These results are not consistent with a significant seasonality of MZ, DZ, or all twin births in the United States.

Data with regard to the proportion of congenital malformations found at birth are presented from a survey of 657 pairs of twins of known zygosity and placentation delivered in Aberdeen and Northeast Scotland between 1968 and 1979. There was an excess of malformed individuals from monozygotic (MZ) pairs, but this did not reach statistical significance. The possible effect of monochorionic placentation in the causation of malformations in MZ twins in general is discussed. It seems that this type of placentation may be of less causative importance than has been previously suggested.

Seventeen head and face measurements of 205 twin pairs, aged 18 to 25 years, are analyzed. In both sexes a significant genetic variance component is found for head length, head breadth, and frontal breadth, for seven breadth measurements of the face, for physio-face height, and nose height. A significant genetic variance component is found for nasion-gnathion, nasion-stomion, and lips height in males and for the two ear measurements in females. We suggest that the sex difference for heritability may be due to random factors and to continued growth from 18 to 25 years in males.

A study of cigarette smoking was undertaken in a pair of craniopagus twins to determine how a transfer of products of smoking is occurring between the twins. Alternately and independently, one twin smoked a nicotine-free cigarette, then the second twin smoked a nicotine-containing cigarette. The procedure enabled the investigators to study the migration of nicotine and carbon monoxide from one twin to the other. Salivary determination provided a noninvasive method of measuring cross circulation in conjoined twins. Measurements of salivary nicotine, however, indicated that, although the nicotine levels rose following smoking, there was relatively little transfer from one twin to the other through the circulation.

Variation in plasma uric acid levels in 206 pairs of male and female twins, aged from 18 to 34 years, was consistent with a simple model including only individual environmental and additive genetic effects and a heritability of h2 = 0.73. Individual environmental variation was estimated to be approximately the same as variation of individuals measured on two occasions. Correlations of DZ pairs were also consistent with sex-linked genetic effects. In men there was a significant genetic correlation with weekly alcohol consumption and as much as 18% of the variation in uric acid levels could be accounted for by genetic variation in alcohol consumption.

In their general model of twin concordance Allen and Hrubec recently introduced the concept of secondary ascertainment rate to consider partial ascertainment of secondary cases. This concept is found to be of limited interest because only pairs where valid information can be obtained from both twins should be included in genetic analyses. It is furthermore shown that the validity of the proband method and the Allen/Hrubec model depends on the equivalence of ascertainment in twins from concordant and discordant pairs. However, if this condition is fulfilled, it has been shown how the ascertainment probability in cotwins of probands is related to the overall ascertainment probability in the total twin population.

A flexible method based on maximum likelihood theory is introduced for the analysis of binary response data in twins. The method allows for explanatory variables such as age and sex, is free of the untestable distributional assumption of bivariate normality of liability, and makes more efficient use of the data available. The method is illustrated with preliminary data on drinking status in adult twins. Although there is some bias in the ascertainment of male dizygous twins, the results suggest that monozygous twins are more concordant than dizygous twins for drinking status.

A case report is given of a pair of monozygotic twin girls with neurofibromatosis caused by a new mutation. The symptomatology was dominated by a neurofibrosarcoma on the leg of one twin and by a large plexiform neurofibroma on the neck of the other twin. Otherwise, the disease showed similar, although not identical or mirror-image distribution of subcutaneous neurofibromas and café-au-lait spots. The twins had identical HLA and blood group antigens and the same chromosome aberration. These case reports indicate that nonhereditary factors may influence the manifestations of neurofibromatosis. A review of the literature on monozygotic twins with neurofibromatosis is given.

A survey of triplet pregnancies in Linköping, Sweden, 1973-1981, showed a low perinatal mortality (4%) and low morbidity possibly due to prophylactic bed rest and tocolytic treatment. All children were followed at child health clinics. In one child, a persistent growth retardation was recorded at 4 years of age. No psychomotor deviations were found in the group. An interview concerning social and economic factors after delivery was carried out. The answers revealed considerable strain in daily life for all families.