Monochorionic twins may differ from dichorionic monozygotic (MZ) twins because of the transfusion syndrome and the timing of the cleavage of the zygote. Intrapair birthweight differences may be an indicator of these intrauterine variables. Previous evidence concerning weight differences and intellectual ability in MZ twins is reviewed with recommendations that future research also incorporates full placental data. Poorer scores on a nonverbal test are found for the lighter male twin of pairs with large intrapair differences in birthweight. Co-twin concordance rates for test scores are also highest for this group indicating that they vary consistently from other groups. Some evidence is presented from the present and earlier studies implicating anomalies of asymmetry or the transfusion syndrome as possible causes of these differences in brain functioning. The study adds further doubts as to the validity of any assumption of developmental equivalence between MZ twins and the general population.

The purpose of this study has been a comparison of a group of twins (145 pairs) and a whole cohort of singletons (114,828 individuals) born 1953 and living in the Stockholm metropolitan area in 1963. The twins and singletons have been followed from birth onwards. A pertinent question is whether twins are at greater risk at birth and whether they are predisposed to below-average mental and physical growth. The results show that twins are more susceptible to lower birth weight, shorter gestation period and birth complications. These factors also seem to have a lasting effect on later physical and mental development. Monozygotic twins, twin girls, and male twins with low birth weight, seem to be particularly at risk for below-average mental and physical growth. An interaction between social background and birth weight can also be seen for the male twin group.

A total of 22 monozygotic (MZ) and 41 dizygotic (DZ) twin pairs were given 72 trials on a stabilometer balance task over six days to study the extent of the genetic contribution to learning and performance of a gross motor skill. The expectations that interindividual differences would be less for the MZ than for the DZ twins and that intraindividual variability would not be different between the two groups were supported. Intraclass correlations were used to provide estimates for the proportions of total phenotypic variance accounted for by heritability (h2), systematic environmental variance (E2), and nonsystematic environmental effects (e2). Heritability was found to be low during the early stages of learning, before it increased to stabilize at approximately 65% for the remaining practice. E2 was highest during these early stages (24%), then declined quickly to stabilize at half that level. Error variance (e2) constituted the remaining variance. Learning profiles of the twin pairs were also analyzed, with a greater intrapair resemblance being found for the MZ twins. The present findings indicate that, for gross motor skills, there is considerable potential for influencing both the levels of performance (and learning) and the differences between individuals by judicious use of systematic environmental effects.

During the last 33 years, the perinatal mortality of twins has decreased regularly in our department. When examined by duration of pregnancy, mortality was lowest at 37–38 weeks. Below 38 weeks, fetal loss was paradoxically higher in twins born from multiparae. When delivery occurred beyond 38 weeks, mortality rates were increased, but only differences for primiparous group showed statistical significance. Near-term fetal loss was predominantly due to antepartal intrauterine deaths. Analysis of individual cases indicated that early termination of pregnancy might help prevent near-term stillbirths in twins delivered by primiparae. Efforts should be directed at specific detection of twins threatened by antepartum death.

Shortened fifth middle phalanges, defined as being less than half the length of the fourth middle phalanx, were found in 12 of 96 Philadelphia Chinese and none of 200 Philadelphia Negro children. At least nine of these can be characterized as having stunted cratered diaphyses, with precocious cone epiphyses, which underwent very early epiphyseal union.

The possible extension of a current vascular hypothesis for cone epiphyses, to include inherited osseous variation in this region of the little finger, is discussed.

A classification of metacarpal brachydactyly is presented, with the intention of investigating the syndrome of pseudopseudohypoparathyroidism. Reports of cases which have been held to negate the theory that Albright's hereditary osteodystrophy is sex linked were found to have the pattern of phalangeal shortening exhibited by one of the forms of metacarpal brachydactyly. This finding lends support to the contention of others that these reported cases are not pseudo-pseudohypoparathyroidism.

The determination of twin zygosity by bloodtyping is reconsidered, and the model for the individual case is reformulated. The crucial diagnostic question may be phrased as follows: Given the particular array of bloodgroup phenotypes that the twins display and are concordant for, how might this array have been obtained by a pair of dizygotic twins, and how might the array have been obtained by a monozygotic pair? The solution yields a differential probability value that is uniquely tailored to the actual phenotype array shown. The procedure offers a coherent and more direct method for arriving at the needed probability figures, and it is recommended to supersede previous methods. Some similarities and differences between the methods are discussed.

Vor vierzehn Jahren konnte ich (1) in dieser Zeitschrift zusammenfassend über «Erbbiologische Untersuchungen über die Entstehung der Homosexualität» berichten. Wenn ich nunmehr nochmals auf diese Untersuchungen, die in der Zwischenzeit durch die Berechnung von möglichen Valenzen der geschlechtsbestimmenden Faktoren bei Homosexuellen und deren Eltern ergänzt wurden zurückkomme, so liegt die letzte unmittelbare Veranlassung darin, dass neuere cytologische Untersuchungen prinzipiell die Prämissen, von denen ich bei meinen Untersuchungen ausgegangen bin, bestätigten. Beim derzeitigen Ueberwiegen der psychologischen Literatur auf dem Gebiet der Homosexualitätsforschung schien es dazu schon an und für sich angezeigt, das Problem der Triebumkehr mit Fragen und Ergebnissen der Genetik und Erbbiologie darzustellen.

Die Untersuchungen, die von mir, nachdem sie schon einige Jahre geplant waren, im Jahre 1934 begonnen wurden, nahmen ihren Ausgang von folgenden Ueberle-gungen. Die Homosexualität ist eine ubiquitäre, bei allen Völkern, zu allen Zeiten und in allen Kulturkreisen auftretende Erscheinung, weshalb auch die meisten führenden Psychiater und Sexualforscheres sei nur an E. Kraepelin, A. Forel, E. Bleuler und R. von Krafft-Ebing erinnert stets neben den exogen bedingten Formen von Homosexualität eine Kerngruppe von genuiner, anlagebedingter Triebumkehr annahmen. Wir können also ihre Erklärung mindestens mit derselben Wahrscheinlichkeit wie in psychischen Faktoren in den ebenfalls ubiquitären physiologischen oder pathophysiologischen Vorgängen, die die Anziehung oder Abstossung der Geschlechter bedingen, suchen.

A review of the literature on twin studies in craniofacial genetics is presented. The following areas are particularly dealt with: tooth form and size, tooth formation and eruption, dental arch and occlusion, facial form and size, and cleft lip and palate.

A generalization of the F test is proposed to see how many independent components are statistically significant when the co-variances between DZ twin differences on several psychological tests are compared with similar co-variances for MZ twins. When applied to the 6 scores of Thurstone's Primary Mental Abilities test battery, at least 4 separate components were found to be significant independently. Then 4 components are tentatively identified as similar to, although not identical with, the Number, Verbal, Space and Word fluency scores. While the procedure bears some resemblance to factor analysis, it may lead to quite different results since it is based on the comparison of two co-variance matrices of twin differences.

In conclusion, it should be kept in mind that these results are based on small samples of MZ and DZ twins, so that a repetition of the study seems indicated. This replication is now in progress.

Taste threshold for phenylthiocarbamide (PTC) was measured in 393 offspring from the families of 85 monozygotic (MZ) twin pairs. PTC scores were bimodally distributed with modes at one and eight and the antimode at five. Because of the non-normality of the distribution, a jackknife procedure was used to obtain 95% confidence intervals for the estimates of genetic, maternal, and environmental parameters. Analyses which assumed no epistasis and which included additive genetic effects revealed that 37.9% of the observed variation in PTC threshold was due to additive genetic effects, 16.6% was due to dominance effects, 14.2% was due to maternal effects, 13.7% was due to a common sibship environment, and 17.6% was due to random environmental effects, yielding a broad sense heritability of 0.55 for the threshold ability to taste PTC. Analyses which did not include additive genetic effects revealed 26.6% of the observed variance was due to dominance effects, 23.6% to maternal effects, and 49.8% to environmental effects at the 0.67 confidence levels, but that environmental factors accounted for 72.4% and dominance effects for 23.6% of the observed variation at the 95% level.

Twinning is regarded as a very important phenomenon among the Yorubas in Western Nigeria. In this population, special ceremonies are performed to mark twin deliveries, and twin babies and their parents are given special names. Twins are therefore more readily identified, and data relating to twinning in families are likely to be fairly accurate.

Furthermore, the practice of polygamy in Western Nigeria provides a good opportunity for studying both maternal and paternal factors in the inheritance of twinning. The high incidence of twinning in the population (45‰: Nylander, 1969) is also an additional advantage, since it allows a large number of twin maternities to be studied in a short space of time.

Among 18 737 deliveries in the three major hospitals in Ibadan, Western Nigeria, between October 1967 and June 1969, there were 977 twin maternities. Every mother was interrogated immediately after delivery to find out whether she or her husband was a twin or had twins previously (including those delivered by the husband's other wives), and whether she or her husband had twin siblings. Obstetric data, including maternal age and parity, were collected for each patient, and zygosity of the newborn twins was determined by sex, placentation, blood groups, placental enzymes, haemoglobin types, and G6PD electro-phoretic studies, as will be described in a subsequent paper.

In a 3¾ year old boy with mental and physical retardation, a chromosome analysis from lymphocyte cultures revealed a partial deletion of chromosome 1q following a pericentric inversion. The chromosomes of the parents were normal. The clinical picture of the patient included the following characteristics: prominent occiput, small chin, deep-seated and dysplastic ears, abnormal vortices of the hair, divided tip of the tongue, high palate, small finger and toe nails, inguinal hernia both sides, undescended but normal sized testes, hypotonic musculature and overextensible joints, retardation of ossification in the left hand by 6-12 months, slight osteoporosis, EQ~0.5.

This follow-up study of twins includes 35 families from the Stockholm area. One section concerns the physical and mental development of the twins. The other sections compare the development of the children with their parents' expectations of them and the parents' feelings about the delivery. Seven twin pairs (20%) in the total group were born before 37 complete gestational weeks. Thirty-seven of the twins weighed less than 2,500g at birth; of these, 23 (9 boys and 14 girls) weighed less than 2,500g, although they were born after 37 gestational weeks. At four years of age, 22 of the 68 twins still showed some impairment of locomotor, language/speech and emotional development, as assessed by the Griffiths Mental Development Scales. All the prematurely born and small-for-date infants were in this group. There also seems to be a relationship between developmental problems and the mother's negative or ambivalent expectations concerning the twin pregnancy.

The decrease trend of multiple births temporarily broke off in Hungary in 1970, with an increase from 18.18‰ (1968) to 20.94‰ (1970), i.e., about 400 cases of excess.

The male preponderance in twin births is lower than in single births, and triplets actually show a female excess.

There are more boys than girls among the first-born of multiple births.

According to the 1959 and 1968 figures, both DZ and MZ twin births were significantly more frequent in mothers aged 16 or less than in mothers aged 17-19 years.

The monthly distribution of DZ twins is characteristic, while the monochorial MZ twins did not show seasonal variations.

When the univariate twin design is extended by including parents of twins, it is possible to assess additive genetic effects in the presence of assortative mating and genotype-environment correlation, the effects of parental influence, as well as the extent of residual shared environmental influences. The analysis of data obtained in such an extended twin design can be carried out by means of constrained maximum likelihood confirmatory factor analysis. Specifically, the structural model underlying this design can be represented as a LISREL model with nonlinear constraints. This representation offers the possibility to consider extended multivariate twin designs involving common genetic and environmental factors. The proposed method will be illustrated with applications to simulated and real data.

Whereas modern assisted conception with such techniques as in vitro fertilisation now helps many subfertile couples to fulfil their ambition to have a child, it has not been without a price. The increased incidence of multiple pregnancies, with their attendant maternal and perinatal sequelae following assisted conception is well known, but perinatologists may be less familiar with the Ovarian Hyperstimulation Syndrome (OHSS) which is the other major complication when controlled ovarian hyperstimulation is used during assisted conception treatment. Mild forms of OHSS are common and require no more than symptomatic treatment. Severe forms of OHSS are uncommon occurring in 0.6% to 14% of IVF cycles [15, 5], but are nonetheless very important to identify as they may lead to thrombo-embolic disease, cardiorespiratory dysfunction, renal failure and even death [6]. This review considers whether OHSS may be related to multiple pregnancy by reviewing the available literature and local experience.

This three-year study was based on individual interviews of over 200 bereaved MZ and DZ adult twins. Its purpose was to record the Ione twins' response to the loss of their twin and to investigate factors that correlated with either the severity or amelioration of the loss.

Over 80,000 multiple birth babies are born each year in the U.S. Their families must cope with a constellation of complex physical and psychosocial challenges, which jeopardizes their health and functioning. The demands of twin pregnancy and the parenting of twins, triplets, quadruplets, quintuplets or more puts these families at disproportionately high risk for infant mortality, birth defects, child abuse, substance abuse, financial problems and marital problems. Health and social service resources must be developed to alleviate the stresses associated with multiple birth and to empower parents to cope well. Guidelines for policies, parent education, professional training and service delivery developed for the California Department of Health Service, Maternal and Child Health Branch, are here offered for the consideration of policy makers and public health planners.

In Hungary the frequency of multiple births has been decreasing. In 1920 the rate of multiple births was 23-5‰; by 1968 this rate decreased to 18.2‰, i.e., only 77% of the 1920 data. The male preponderance in twin births is lower than in single births, and in triplets actually a female excess can be observed. Furthermore, it can be observed that there are more boys than girls among the first-born of multiple births. The average birth weight of liveborn and stillborn twins, and of liveborn triplets is 2101 g, 1458 g, and 1723 g respectively. The ratio of MZ to DZ twins is about 30:70 in 1968. The frequency of DZ twin births increases with maternal age (the peak is now over 40 years) and birth order. According to the 1959, i960, and 1968 figures, both DZ and MZ twin births were significantly more frequent in mothers aged 16 or less than in mothers aged 17-19 years.

This demographic survey belonged to preparatory works connected with the setting up of the Budapest Twin Register which came into force on January 1st, 1970.

The course and outcome of 23 monoamniotic (MA) twin pregnancies, delivered in Tampere University Central Hospital during the years 1964-1984, were studied retrospectively and compared to 1056 diamniotic (DA) twin pregnancies. The frequency of MA twins was 2.1% of twin pregnancies. Polyhydramnion complicated the pregnancy in 26% of MA vs 6% of DA pregnancies. Two cases were defined as acute polyhydramnion. Preterm labour was stated in 70% of MA pregnancies and deliveries before the 34th week were 4 times more common in MA than DA pregnancies. The cesarean section rate was more than double in MA pregnancies (39%). Entanglement of the umbilical cords was noted four times, and prolapse of the cord in three vaginally delivered cases. Perinatal mortality was 28% in MA vs 5% in DA twins. The most common causes of death were respiratory distress syndrome, congenital malformation and feto-fetal transfusion.