In the La Trobe Twin Study, data are collected on temperament and social development in 3-15 year old twins and singletons from four different sources: questionnaires to parents covering development from birth to the present plus the Bristol Social Adjustment Guide completed by the teacher, Sattler's Behavior and Attitude Checklist completed by the tester, and the Qualitative Score on the Porteus Maze Test. Particular stresses are identified which the parents perceive as distinguishing a multiple from a singleton birth. Whereas they perceive no differences between the first and second-born in birth complications, the second-born is judged less favourably particularly in MZ pairs. The distinction continues in the later assessments by the teacher and tester, where in addition the male twins are seen as being different from other children both in cognition and in temperament. It is proposed that social and cognitive development of twins are interrelated and have two unique components, one related to the greater problems accompanying a multiple birth and the other to comparisons between cotwins.

A total of 204 cases of twin pregnancy occurred between 1970 and 1972 have been compared with 102 cases occurred between 1976 and 1978. During the interval of time, specialised care was instituted for the early diagnosis and management of twins. The incidence of twin pregnancy in Singapore decreased from 1:131 to 1:141 pregnancies. With a background of improved socioeconomic conditions and obstetric care, there has been a dramatic decline in perinatal mortality from 76.4 to 29 per 1000. In undiagnosed cases, the perinatal mortality of the first vs the second twin in the earlier group was 64.4 vs 93.6 per 1000. No such difference was observed in the later period, with the average birthweights of twins being significantly higher. The principles of our antenatal supervision, antenatal tocography, and management are presented and the value of early diagnosis, bedrest, and tocolytic therapy discussed. The reduced perinatal mortality and mobidity gives evidence of an improvement in prematurity and augmented intrauterine growth.

High resolution tracings of atrial depolarization can be obtained by surface signal averaging technique. A study was conducted on 4 male and 4 female healthy MZ twin pairs aged 10.4 ± 1.3 yrs. Each subject underwent 3 or more recordings, at 10-days intervals. The essential reproducibility could be confirmed, with personal characteristics, as well as the reliability of the technique and the electrophysiological value of the spikes complex. In 3/8 pairs the cotwins showed a significant likeness of the atriogram, while in 5/8 pairs the tracings were not quite resembling between the twins and that is attributed to variations in the chronogenetic characteristics of MZ twins.

The value of single determinations of serum hCG, hPL, and αFP for the detection of multiple pregnancy was investigated in a consecutive series of 992 women between the 14th and 24th week of pregnancy. With the 90th percentile as referent value, all twin pregnancies (n = 10) were detected by the combined results of the three determinations. Considered separately, hPL proved to be the most useful indicator of multiple gestation; the sensitivity of hPL alone was 70% and the predictive value of hPL concentrations above the 90th percentile was 8.1.

A Cox proportional hazard regression analysis was carried out that evaluated age-specific death risk among 21,890 twins born in Sweden during 1886 through 1925 and followed during 1962 through 1980. Cotwin's survival was used as the primary covariable, and auxiliary covariables were smoking, marital status and, among men, police registration for alcohol abuse. In each age, sex and zygosity group, except the oldest DZ males, cotwin's mortality had a significant, independent, positive relationship to the mortality risk of the individual. The auxiliary covariables, except marital status among females, had significant, independent, positive relationships to mortality among the youngest twins of both zygosity groups and in the middle age group of MZ twins. In the oldest age group, the death of MZ cot wins was the only variable significantly related to the individual's mortality. Heritability estimates for the age-specific probability or death risk, developed by different methods for different analysis groups, range between 0.4 and 0.6. They have reasonable internal consistency, are not much affected by the covariates, and are in agreement with other studies that did not control covariates.

Central pockets were defined as small, loop-enclosed whorls whose quantitative values must not exceed the third part of the quantitative value of the loop or as small, whorl-like patterns in the core of a loop having at least one curved ridge with its convexity towards the opening of the loop. Applying this classification scheme, the frequency of central pockets was found to be 17.5% in 200 males and 17.0% in 200 females, but was significantly higher in a sample of 21 male and 22 female pairs of MZ twins (33.2% and 34.1%, respectively). Twin as well as family data (94 families with 269 children) pointed to a rather weak hereditary influence upon the formation of central pockets. Rudimentary central pockets occurred in 9.5% of males and 10.0% of females. Since no common genetic basis could be established for central pockets and rudimentary central pockets, the latter should not be scored as central pockets.

The authors have performed selective birth in two twin pregnancies in the same patient. The couple's first pregnancy resulted in the birth of a male with Tay Sachs disease: their Pergonal-induced second pregnancy was a twin gestation discordant for Tay Sachs disease. A fetal intracardiac puncture, exsanguination, and fetal intracardiac air embolization were then performed. The patient went into premature labor 9 days later and delivered a normal immature infant, who died, and the macerated cotwin. The third Pergonal-induced pregnancy was a singleton with Tay Sachs disease and the pregnancy was terminated. Their fourth Pergonal-induced pregnancy was a twin gestation discordant for Tay Sachs disease. At 20 weeks gestation, fetal intracardiac air embolization was performed with immediate demise of the affected fetus. The pregnancy was followed closely with ultrasonography and coagulation studies and proceeded to term without complication. A normal female and a fetus papyraceous were delivered by cesarean section.

In a Swedish longitudinal twin study, teacher ratings of school adjustment were collected in grades 3 and 6 for approximately 80 pairs of MZ twins, 100 pairs of DZ like-sex twins, and 70 pairs of opposite-sex twins. These same groups of twins then rated their own school adjustment in grades 4 and 6 as seen by the home, the school, their classmates, and themselves.

A comparison of within-pair similarity for the different types of self-ratings tends to show more consistency and a higher concordance for MZ compared to DZ in grade 6 than in grade 4.

The teacher ratings tend to show a larger and more consistent difference between MZ and DZ than the twins' own ratings.

The results reported have certain implications for heritability estimates based on different types of ratings. Ratings by others thus seem to give the highest intraclass correlations, probably due to a certain halo effect. Self ratings, on the other hand, tend to fluctuate more over time at least for children before and at puberty. Also the construction of items seems to influence the magnitude of the correlations.

Data from the young cohort of the Swedish Twin Registry are being used in an attempt to describe characteristics which distinguish among current, non- and ex- smokers prior to the development of a smoking habit versus those present after establishment of the habit (or lack of one). With twins as a sample of individuals, the psychosocial variables instability, extroversion, leisure activity, relative weight, alcohol, coffee and psycho-pharmaceutic drug use were examined jointly as predictors of current smoking status in multiple regression analyses. This phase was intended to replicate and expand upon earlier studies characterizing current, non- and ex-smokers. These analyses were then performed on MZ nonsmoking twin individuals who were classified on the basis of their cotwins' smoking status. Pattern of variation in the psychosocial variables across the groups of nonsmokers were similar to the pattern seen for current, ex- and nonsmokers. Characteristics in MZ nonsmokers which are predictive of their cotwins' smoking status may be interpreted as those present prior to development of a smoking habit. Selected results from these analyses will be presented.

Resemblances on five cognitive tests were compared in fifty quartets of school children. Each quartet consisted of a twin pair (MZ or DZ) and a matched singleton pair from the same kibbutz peer group. Similarities of MZs and DZs on test scores essentially replicate those reported previously in other studies. The median correlation for singleton control pairs is 0.29, as compared with that of 0.26 reported in the Texas Adoption Study for unrelated children raised in the same home. In the two spatial tests, control pairs were as similar as the DZ pairs. This suggests a more powerful influence on shared environment in aspects of perceptual performance. A new structural analysis (POSAC) of individual profiles of test scores is presented. Comparison of space diagrams of MZ, DZ, and singleton pair profiles shows systematic differences in structure among the three groups, in accordance with the predicted levels of genetic influences. Such structural differences transcend mere differences in size of correlation, and may give more stringent evidence for the respective roles of genetics and environment.

The diagnosis of multiple gestation at the time of genetic amniocentesis is a routine occurrence. In a combined series of 2765 patients referred for antenatal genetic studies from the Medical College of Virginia and the University of Iowa, 34 twin pregnancies were encountered (1.2%). Twenty-six of the patients with twins were referred for advanced maternal age. The other indications were previous neural tube defects (1), previous trisomy 21 (2), known carriers of Tay Sachs disease (2), previous Turner's syndrome (1), family history of trisomy 21 (1), and one pregnancy was referred because of an abnormal ultrasound. Amniocentesis procedures, outcome of the twin pregnancies, and genetic counseling issues, are discussed.

Evidence for and against the validity of the assumption of equal environments for MZ and DZ twins is reviewed, and the consequences of possible violations of the assumption are considered. Further methods of testing the validity of the assumption, as well as possible means of correcting in part for violations, are suggested.

Fifteen cases were reviewed over a five-year period at a perinatal centre with intrauterine demise of one member of a multiple gestation. Nine cases were monozygotic twin pairs, two were dizygotic, and two were triples. Gestational age ranged from 27 to 39 weeks. The management protocol consisted of delivery in all cases after confirmation of the diagnosis. In 4 cases delivery was immediate because of spontaneous labor. In the other cases elective delivery was performed if the gestational age was 37 weeks or greater or there was evidence of preeclampsia or if amniocentesis revealed a mature lecithinsphingomyelin (L/S) ratio. Steroids were given if the L/S was immature or the attempt at amniocentesis was unsuccessful and delivery was performed 48 hours after initiation of steroid therapy. Cesarean section was the mode of delivery in 14 of the 15 cases. All of the cotwins and cotriplets survived. One survivor of a monozygous twin pair has multicystic encephalomalacia possibly implicating perinatal arterial occlusion or in utero disseminated intravascular coagulation (DIC). The intrauterine deaths are categorized into possibly avoidable deaths (2/15), unavoidable due to congenital anomalies (3/15), and unknown or unavoidable deaths (8/15).

Data on alcohol use and smoking habits was available from the 1975 questionnaire of the entire cohort. Prior to pairwise analyses, the data of individuals was compared to that of age-sex matched groups of pairs reared together. The early separated twins had a higer alcohol consumption, while for smoking only slight differences were observed compared to twins reared together. Probandwise concordance rates were computed from smoking status (ever smoker/never smoker), alcohol use (user/nonuser) and “heavy” drinking (half-bottle of spirits on one occasion at least once a month). The following results were obtained in those pairs with the environmental dissimilarity score > 15:

A genetic analysis of alcohol consumption in 3810 pairs of adult twins is reported. When no correction was made for age, individual environmental variance, including non-repeatable errors of reporting, accounted for approximately 44% of variation in both sexes. In females, there was no evidence of shared environmental effects and 56% of the variance was genetic in origin. In males, only 36% of the variance was genetic and common environmental effects accounted for the remaining 20% of individual differences.

For females, the results for younger (30 years and under) and older (over 30) twins were similar. For males, however, the effect of age was striking. In younger male twins over 60% of the variance was genetic in origin, with the remaining variance due to environmental influences unique to the indiviudal. In older twins genetic differences do not appear to be important, with approximately 50% of the total variance due to individual environmental differences and the remaining 50% due to the effect of the common family environment. Our results suggest that both age and sex need to be considered when analysing the causes of variation in alcohol consumption.

In 1975 the Australian Council of Educational Research (ACER) conducted a nationwide survey of literacy and numeracy in 10- to 14-year olds. A total of 297 of the 12875 children involved were twins. By age 14, only 42% of the twin boys achieved adequate standards of literacy compared with 71% of single-born boys. The deficit in twin girls was much less and twins of both sexes were only moderately behind in numeracy. A survey of 9-13-year-old twin boys in the La Trobe Twin Study (LTS) produced similar results with 75% being below average in reading skills and 23% behind by 18 months or more, despite above average IQs. The ACER data are corroborated by teachers' reports obtained in the same survey, which indicate also how few of the twins with problems are receiving remediation and the high incidence of classroom problems in spelling and reading reversals. The pattern of mistakes twins make on specific items in the ACER survey can be explained as resulting either from specific cognitive deficits or from problems in concentration. The same factors influence performance on different tasks, so that literacy and numeracy are much more closely interrelated in twins than in singletons, and also correlate more with a measure of verbal intelligence. Implications for genetic analysis of scholastic achievement are examined, centering around the different factor structure of abilities in twins and common family environmental effects which are unique to twins.

An increased incidence of twinning has been reported among patients with Klinefelter's syndrome (XXY) and their relatives, but no data have been reported about the incidence of XXY among twins. Results from our institution's antenatal testing clinic provide data about twins and XXY. In 1842 pregnancies tested, 21 were noted to be twin gestations. Five fetuses with XXY were detected in all pregnancies, of which there was a pair of MZ twins concordant for XXY and a pair of DZ twins discordant for XXY. The incidence of XXY in twins was thus 7,1%. The fetal phenotype of XXY was examined in aborted MZ twins and found to be mild. Notably, the testicular histology was normal. These cases confirm the previously reported association of twinning and XXY. The association of twinning and XXY implies a commonality of causation; however, a maternal age effect cannot be excluded. Our data suggest that there is an increased risk of XXY among twins.