The condition of low birth weight is compared in twins and in singletons in terms of birth weight distributions and with respect to factors such as the incidence of sillbirths, length of gestation, maternal age, parity, and legitimacy. In the light of demographic, biological, and developmental considerations, it is concluded that low birth weight in twins is a different condition from low birth weight in singletons and should be dealt with independently, especially in view of the different implications for child growth and survival.

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.

Within the Finnish Twin Cohort of like-sexed adult twin pairs, a subgroup of pairs separated at an early age has been identified. In 165 pairs, both cotwins responded to questionnaires in 1975 and 1979. An environmental dissimilarity score was formed which consists of items on whether the twins had lived after separation in the same community, attended the same school, were on the same grade at school, how often the cotwins met, how often they met common friends and relatives and whether they attended the same clubs etc, or not. To validate the zygosity diagnosis obtained by questionnaire in 1975, those pairs whose zygosity was unknown as well as those with the least contact after separation were contacted for blood sampling (11 bloodgroups). Of 15 pairs with no zygosity diagnosis, 10 responded (1 no address,2 abroad,2 refused). Six pairs were classified MZ and 4 DZ. In 12 MZ and 8 DZ pairs undergoing bloodgroup determination, the classification of only one pair changed from DZ to MZ. The following intraclass correlations for height and weight were found:

A review of the case histories of 471 diabetic children admitted to a children's hospital during the decade 1960 to 1970 showed that the proportion of diabetics among hospitalized Negro children was significantly lower than that among white children (3.8 Negro vs. 10.7 white per 1000 admissions same ethnic group, P < 0.005). However, the proportion of mild diabetes, characterized by absence of ketosis and no insulin requirement, was higher among Negro (18%) than among white diabetic children (0.5%). These differences could not be explained by differences in environmental factors considered. It is suggested that genetic factors may account for a substantial part of this Negro-white difference.

To search for an association of twin zygosity with tooth size, 56 dental variables measured from 65 pairs of twins (43 MZ, 22 DZ) were studied. Results of the t′ test for equality of the means showed no association of zygosity with any of the variables in males or in females. Results of the F′ test for homogeneity of total variances between zygosities showed evidence for unequal total variances in 15 variables in males and 13 in females. Sex influence was further noted on the association of zygosity with the variance of tooth size. Where total variances were unequal, genetic variance estimates differed when only the within-pair mean squares were used and when combined estimates designed to be unbiased by differences in environmental variances were used.

Among 93 cases of thalidomide embryopathy ascertained in Brazil, one pair of female dizygotic twins was found. One of them presented complete paraxial hemimelia in the right arm while the other showed a triphalangeal thumb at the left hand and had duodenal stenosis. Of the eight dizygotic twin pairs exposed to thalidomide in utero described thus far, only four were concordant for the type of malformation.

Twinning rates were studied in Swedes, Åland Islanders, Finns, Germans, and Dutch during years of starvation when death rates were two to three times higher than average. In contrast to the situation among some animals, this study suggests that nutrition above a certain threshold is unimportant for human reproduction, including twinning. The twinning rates for these different populations display marked temporal differences, but low values in the twinning rate are not consistently associated with periods of epidemics, famine, or similar nutritional stress. After years of privation and/or separation of spouses, a rapid “catch-up effect” can often be seen in the twinning rates, as well as marriage and birth rates. Psychoendocrine factors and interparental immunological conditions that may be involved in this phenomenon are discussed.

A case of monozygotic male twins discordant for skeletal and cardiac defect is reported. One twin had the hemifacial microsomia type of the oculo-auriculo-vertebral dysplasia. The cotwin had no asymmetry of the face and normal ears, but preaxial polydactyly and ventricular and auricular septal defects. The cotwins were concordant for craniostenosis with a ridge metopic suture. Karyotypes were normal.

The retardation of fetal growth in twin as compared to singleton gestations may be due to maternal and/or placental factors. The separate birthweights and related placental weights of 487 dichorial twin pairs were recorded, and the heavier placental weights of firstborns in comparison with second-borns were found to be related to the heavier birthweights of firstborns compared to second-borns. The lighter placental weights of firstborns compared to second-borns were found to be related to the lighter birthweights of firstborns compared to second-borns. Obviously, the placenta itself may may very well be the cause of the retardation of fetal growth in twin gestations.

Other than a specific case of concordant Vitiligo in MZ twins, the development of which has been followed for more than 11 years up to now, MZ twins suffering from Vitiligo have been described only three times. In all the four cases, three were concordant, one discordant; this last was accompanied by a discordant disorder of basal metabolism, by hyperhydrosis and exophtalmus. The greater degree of concordance found up to the present day, notably contrasts with the relative extreme rarity of familiar Vitiligo.

During the 10-year period, 1975-1984, 105 triplet pregnancies were delivered at Harare Maternity Hospital, Zimbabwe, among 286,338 pregnancies in the Greater Harare Unit, giving an incidence of triplets of 1:2,727. The mean gestational age at delivery was 32.5 wk with 81 women (77.1%) delivering before 37 wk. Primigravidas delivered at a significantly earlier mean gestational age (P < 0.05) and had a higher perinatal mortality (P < 0.001) compared with grand multigravidas. Of the 315 babies, 277 (87.9%) weighed < 2500 g. The overall perinatal mortality rate was 327‰, with a pernital mortality rate of 146‰ for infants weighing ≥ 1000 g. Women hospitalised for bed rest during the antenatal period had fewer perinatal deaths compared with those diagnosed during the antenatal period, but not hospitalised for bed rest (P < 0.02). No difference was found in the mean gestational age at delivery or the mean birth weights between these two groups. Among infants ≥ 28 wk gestation there were fewer perinatal deaths in triplets delivered by cesarean section compared with triplets delivered vaginally (P < 0.0004). This suggests that cesarean section may offer the optimal mode of delivery in triplet pregnancy.

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.

Sixteen pairs of term discordant twins (weight discrepancy of more than 20% when the, lighter twin was compared to the heavier) were evaluated at birth. Weight, length, head circumference, anterior fontanel area, and combined ossification of the knee epiphyses were measured, and ponderal index (weight/length ratio) calculated. The most severely growth retarded infants had markedly decreased ossification and larger anterior fontanels.

Eleven pairs had physical measurements at one year of age. With individual exceptions, the lighter twins at birth remained smaller in all dimensions. Despite these persistent differences between twin pairs, the values for length at one year of age were within normal limits for both the heavier and lighter twins. Infants without ossification at birth had a greater incremental linear growth by one year than those infants with ossification.

A study of 111 mothers of twins in Nottinghamshire, England, in 1981-82 showed that at least 12 had used ovulation stimulants, compared to 2 of 102 mothers of singletons. Thus, the use of ovulation stimulants increased the twinning rate of this population by about 10 percent; this may explain the recently noted levelling off in the secular decline in twinning rates. In contrast to a recent study in France, no association between twinning and prior use of oral contraceptives was seen.

The NHLBI Twin Study is a longitudinal study of cardiovascular disease risk factors in 514 pairs of white, middle aged, male, veteran twins. The initial examination took place between 1969-1973. Ten years later, 81% of the living cohort returned for a second examination. Data collected up to 30 years prior to recruitment for the initial examination were used to characterize participants and nonparticipants; data from the initial examination were used to characterize returnees and nonreturnees to the second examination. Participants had significantly lower diastolic blood pressure and higher socioeconomic status than nonparticipants as measured thirty years earlier. Between the first and second examinations, the mortality of participants was less than 50% of the mortality of nonparticipants. Returnees to the second examination had a better health profile at the initial examination than nonreturnees, with significantly lower levels of cigarette smoking, glucose intolerance, hypertension, and diabetes and higher levels of pulmonary function. However, returnees were more obese than nonreturnees. Thus, this study of cardiovascular disease risk factors in twins appears to be affected by response bias in a way similar to studies of individuals. Additional analyses of biases that may affect the genetic component of the study indicated that factors related to classical twin analyses were relatively unaffected by selection.

1. Investigations carried out on twins and the families have revealed that within the major group of brain gliomatosis and glioblastomatosis there is a minor group (up to day) of accumulated familiar clinical cases.

Topographically, they are tumours localized in the region of the ventricular germinative centres, that is to say, in the background of the brain (they are not cortical gliomas!). They depend on the disturbances and inhibition of the matricial cellules on the ventricular wall towards the cerebral cortex. Histologically they are considered as dysplasias with a blastomatosis character, that is to say, neoplastological productions on an heredogenetic basis the cause of which lies in histological disorders, disontoge-netic, and therefore, congenital.

2. A work hypothesis is settled and established according to wich 2 factors at least are necessary for the formation of a tumour: a local one, hereditary: the neuroglial dyplasia in the region of the ventricular germinal centres with a tendency to tumours degeneration; and another or several general factors dependent on endogenous and exogenous influences, which on account of a disturbance of the general constitution (for example, hormone mechanisms of puberty, of the premenopause and of the beginning of the involution) which would allow the tumour to develop starting with the tumours genetic disposition.

3. At the present time it is not known whether the genesis causing this neuroglial dyplasia and the concomitant malformations of other organs, sonsists in the mutation of a gen, since so far the gen is ignored as well the pleotropic effet of the action developed by the gen.

4. The fact, that within the major group, in the majority of cases evidently not hereditary of gliomatosis and glioblastomatosis, there should appear a minor group, hereditary, must be considered, within the general investigation of the neoplasias, as a further proof that the essential thing of the hereditary predisposition to the development of tumours, must be considered as a specific local factor.

5. The attention is called to the possible existence, within the astrocytomes of a small hereditary group of familial cases.

6. The casuistry so far known has been enlarged with 20 cases (discordant) of twins and 6 observation in families which were compiled at the Neurological Clinic of Miinster Westfalen University.

37 DZ and 12 MZ twin pairs underwent a clinical and ECG heart examination. As to their zygosity, it is suggested that a concurrent similar clinical finding, very similar ECG and a mean intrapair difference of corresponding unipolar chest lead waves d ≤ 1.5 definitely support monozygosity.

Paired analysis of the ECG curves shows that the difference between MZ and DZ twins is best characterized by Tv1-6 and, to a certain extent, by Rv1-6. The same applies — in partial agreement with Mathers et al. — for PQ and QTc intervals.

Considering the intrapair differences in both MZ and DZ twins, it was found that they tend to increase in the course of one cardiac cycle, thus indicating a gradual prevalence of peristatic factors.

A high frequency of twin births has been observed in Linha São Pedro, a small settlement which belongs to the city of Cândido Godói, located 524 km Northwest from Porto Alegre, Rio Grande do Sul, Brazil, in an ethnically homogeneous population of German descent restricted to a small geographic region. From 1990 to 1994, the proportion of twin births in Linha São Pedro was 10%, significantly higher than the 1.8% rate for the state of Rio Grande do Sul as a whole. Genealogical analysis showed a high recurrence of multiple births within families, as well as a high level of inbreeding in the community. Zygosity data indicated that 9 of the 17 pairs of twins studied (53%) were dizygotic. No external environmental factors were detected that could be influencing the appearance of this characteristic. This preliminary investigation confirmed the presumed existence of a high twinning rate in the community. The high familial recurrence and the high inbreeding rate suggests the presence of genetic twinning factors. Complementary studies of twins that have yet to be evaluated and the search for additional risk factors, as well as linkage studies, should contribute to a further understanding of the biological factors related to twin births in the human species.

Eleven reports of osteopetrosis due to dominant genes (table 1) establish in a firm basis the existence of such a genetic variant. By personal interview with all radiologists and orthopedists of Pòrto Alegre and larger Rio Grande do Sul cities, an estimate of 1: 100,000 was obtained for the frequency of osteopetrosis in this Brazilian State.