The prevalence of twinning and higher order multiple births is high and is increasing in many countries, due at least in part to fertility-enhancing medical therapies. About 1 in 40-45 births is a twin; it is thus important to investigate whether the twinning status confers a higher risk for morbidity and mortality, particularly early in life. Birth defects are a major cause of morbidity and mortality in the pediatric age-group. The purpose of this review is to consider the evidence for an increased risk of some birth defects associated with twinning, using data from the literature and the Italian Multicentre Birth Defects Registry (IPIMC), to illustrate some of the challenging aspects of the study of birth defects in twins, and to suggest some guidelines for future investigations.

Twins are a heterogeneous group. They may differ in origin and genetic similarity, as for monozygotic (MZ) and dizygotic (DZ) twins; and in placentation (monochorial monoamniotic, monochorial diamniotic, dichorial with separate or fused placentae). Likewise, birth defects are known to be heterogeneous in presentation, pathogenesis, and etiology. Thus, the question raised here is not whether or not birth defects ‘in general’ are more common in twins, but rather whether or not there are any specific types of defects that are more frequent among specific types of twins. To maintain the generality of the discussion, this review will focus on those structural defects which are not unique to twins; conjoined twins and arcadia, defects which are unique to the twinning process, will not be discussed.

The conclusions they arrive at, is that from the standpoint of the Rotest, the twins (mono-or-dizygotic) present themselves as distinct and original personalities. The predominant rôle played by the peristasis over the constitution is thus emphasized.

Thirty couples of twins (23 mono-and 7 dizygotic) were studied with the Rorschach-test.

Detailed analysis is given especially for the larger groupe of monozygotic twins; the identical responses and the quantitatively identical Ro-factors, being particularly discussed with the help of synoptic tables. In spite of their findings, the authors underline the scarcity and little significance of the identical factors.

Alder's anomaly of the leucocytes, which had been considered as a manifestation of the gene-carrier of Fuchs' atrophia gyrata chorioideae et retinae, has not been found in other cases of the latter disease.

Twin data on bipolar and unipolar affective disorders are analyzed by multiple threshold models of inheritance. The two illness types are represented in the models on a continuum of genetic–environmental liability in which bipolar illness has a higher liability threshold than unipolar disorder. Autosomal single major locus model provides an acceptable fit to observed concordance rates in monozygotic twins. The multifactorial-polygenic model is rejected.

The present paper deals with an analysis of the statistics concerning twin births in a sample of the Belgian population in 1960 and 1961. The frequency of twin births is of 0.01198 (± 0.00043), the frequency of a DZ birth among twins is 0.65081. Mothers of twins generally are older than mothers with children resulting from single gestation, the age difference concerning, as could be demonstrated, the distribution of DZ twins with the exclusion of MZ twins: whereas the frequencies of the total amount of twin births and of the total amount of DZ births increase with the mother's age, being highest in the 35-39 age class, the frequency of MZ births seems to be independent of the mother's age. The frequency of twin births also increases with the order of birth or gestation. Given that the mother's age and the order of birth are correlated, the influence of one of the two factors involved upon the frequency of twin births could be determined by keeping the other factor constant; the data from Mac Arthur (1953) were used to that effect.

Finally, a bibliographic survey revealed that whereas the frequency of DZ births is very variable, that of MZ births is more constant.

The dependency of probabilities of phenotypic concordance of gene frequencies in three-allele genetic systems is presented. A graphical display enables the rapid comparison of the relative effectiveness of different systems, taking into account dominance relationships within each genetic system. Four or more allele systems can also be approximated, while two-allele systems are considered to be special cases of three-allele ones.

From the genealogico-statistic inquiry made on a group of 252 leukemics hospitalised in Lombardy during the years 1945-1950, and from the comparison made on an adequate material of control; the Authors have come to the conclusion that for the realisation of the leukemia the idiotypic composition has less value than that of the surroundings. They have over more noticed a greater incidence of neoplasiae in the familiars of the acute leukemics and cronic myeloids in regard to the controls.

In an investigation in 1967 of about 100 male twin pairs collected from the Swedish Twin Register, discordance with respect to the presence of CHD was found in 37 pairs of which 19 were MZ. The investigation included physical examination, cholesterol measurements, and an interview regarding, among other things, smoking habits. In a follow-up study in 1974 — seven years after the original investigation — all but one of the 37 twins regarded in 1967 as free from overt CHD could be traced. Ten of the 36 twins had developed symptoms of overt CHD (angina pectoris or infarction); 18 twins were still healthy, 2 had died from other causes, and 6 had questionable complaints of breast pains. In a comparison of the two groups of twins with and without symptoms of overt CHD, no differences were found with respect to blood pressure, serum cholesterol, or smoking habits, as presented at the 1967 investigation. It is concluded that none of these factors seemed to influence the future development of CHD in twins apparently tainted with a heredity for this disease.

The present study deals with the relationship between blood uric acid level and human behavior. Subjects were 37 MZ and 7 DZ twins aged from 18 to 45 years. In males, blood uric acid level increased with age, while it decreased with age in females. Blood uric acid level was corrected and standardized using regression lines separately for males and females. The distribution of standardized uric acid level corresponded well with the theoretical curve of normal distribution. The intraclass correlation coefficient for standardized uric acid level was r = 0.370 (P < 0.05) for the 37 MZ twins, but not significant for the 7 DZ twins. These findings suggest that blood uric acid level is genetically controlled. By the analysis of 12 personality traits in YG (Yatabe-Guilford) character test, it was revealed that “General activity” was more controlled by genetically than environmentally. In the evaluation of the correlation between standardized uric acid level and the YG 12 personality traits, significant correlation was observed in “Lack of agreeableness” and “Rhathymia”. Since these two personality traits include the factor of “activity”, it is concluded that the plasma uric acid level and activity in a broader sense are under genetic control. This conclusion is consistent with the generally accepted view that persons with high uric acid level are more active and energetic than those with low level.

Data of 601 families with triplets and higher multiples have been collected. Since about nine years the number of higher-order births has been increasing enormously. The average pregnancy duration and the average birthweight of these mostly premature children have been declining from year to year. Despite the progress in neonatology, the death rate and the rate of handicapped children is very high. To prevent such disastrous outcomes, treatments for infertility should be performed only by physicians in centers with strong controls. Selective abortions are no regular solution to the problem of higher multiple gestation.

The switching of genes from the silent to the operating condition following a rigorous temporal sequence may be called “chronology of the gene”. The succession of times and its biocybernetic mechanism are peculiar to each species, but the duration of information exhibits wide intraspecific variations between populations, families, and individuals. The highly isochronic behavior of MZ twins is proof of the existence of an individual temporal constitution.

Our previous studies have proved that the duration of each information is a property of the corresponding genotype, depending on its potential time of activity (chronon), which depends in its turn on the same genotype's energy of stability (ergon).

In terms of molecular genetics, the stability against mutation of each gene, governing its Ergon/Chronon (E/G) system, is a function of three factors:

(1) Code degeneracy, i.e., the different stability of synonyms coding for the same information through different ratios of GC and AT bases, the former being the more stable.

In a girl affected by mental deficiency and slight malformations, a 46,XX, 18r chromosome set was found. Metaphases with irregularly sized or absent rings amounted to 14% in peripheral blood cultures. Tritiated thymidine incorporation pattern in the ring chromosome was similar to that of the normal 18 chromosome.

During the years 1964 to 1971 a group of twins and a control group of singletons in the same classes, were followed from grade 3 at 10 years of age to grade 9 at 16 years of age in the Swedish compulsory school. The study was called the SLU-project (Skolöverstyrelsens och Lärarhögskolans Utvecklingsprojekt) and the main purpose was to study physical and mental growth during puberty as well as heredity and environment influences on these growth processes. Originally 323 twin pairs, MZ and DZ, and 1193 controls were included in the sample. Among the DZ twin pairs there were both same-sex and opposite-sex pairs. They were a nationally representative sample. Several kinds of information were collected, such as, a) Physical measurements (height and weight measurements, menarche, ratings of secondary sex characteristics); b) Ability and achievement measures (intelligence tests, standardized achievement tests); c) Self ratings; d) Ratings by teachers and classmates; e) Socioeconomic background data (fathers occupation and income). For the boys, supplementary data on physical growth and mental ability was collected on enrollment to military service at the age of 18. In this pilotstudy, we have made a follow-up of the original SLU-sample after 20 years. They are now in their mid-thirties. The main purpose has been to investigate if they are willing to participate in a new study on health and well-being at mid-life.

A film has been made of 8 pairs of monozygotic and 4 pairs of dizygotic twins regarding their expression and behaviour, and we tried to examine their behaviour on genetical characters.

We do not agree, that all telencephalitic action is under control of the individuals' arbitribum; instead we stress that genetical characters are also important components.

A « plastic » adaptation to the given circumstances of the surroundings is provided by the qualitative and quantitative manyfoldednes of the telencephalon. The actions of man appear to be much more of free will than they really are.

Fifty MZ and 51 same-sex DZ twins were studied for ABH salivary secretions and the amount of these substances measured in those with the same A1A2BO blood groups. Using the classical, manual inhibition test we verified: (a) Levels for the H antigen in A2 and B persons similar to, but in O and A1 lower than those obtained in other places; (b) Low averages for the A and B substances; (c) Mean intrapair differences for A and H, which were the double in DZ as in MZ twins, the estimated degree of genetic determination being 0.86 and 0.69 respectively; in both cases the F-ratio was significant at the 0.01 level; (d) If one discrepant family is disregarded the correlation coefficient between O parents and DZ children for the H antigen (0.48) is of the order of magnitude expected under a simple additive model of polygenic inheritance.

Tests were also made using a fully automated method. The intraclass correlation coefficients thus obtained in MZ and DZ were similar to those reached using the data obtained with the classical technique. The degree of concordance arrived at by the two methods was only fair, but this may have been due to extraneous factors related to the way the samples were handled.

The Author reports on the striking frequency of marked hereditary pathologic anomalies in the family of a proposita suffering from Biemond's Syndrome (diencephalic obesity, debility, neurologic and mental disorders, endocrine troubles, syndactyly of the feet and bilateral coloboma of the iris).

In the 173 membres of the family (non including the proposita) the Author found 17 cases of unilateral or bilateral coloboma (6 of whom died blind), 4 cases of iris malformation with atrophy of the stroma, 4 cases of females with serious unilateral or bilateral malformation of the hip-joint, 1 uncertain case of a male with Perthes disease, 4 cases of epilepsy (included a concordant MZ twin-pair), 1 case of a male suffering at the same time from imbecility and underdevelopment, 1 case of a female affected by coloboma, arachnoidal cyst and epileptic convulsions, and, further, some cases of myopia, single cases of strabismus, hyphoscoliosis, lipomatosis, hemolytic icterus and 1 case of a still-born child with atresia recti and hypoplasia of one arm. Besides a case of suicide, some members of the family are supposed to have been somehow « queer ».

It is probable that a degree of linkage exists between the genes for coloboma and epilepsy. All other findings, for the moment, may only be recorded. In order to reach some final conclusions other family studies will have to be added to the present one.

Vital records of Saybrook and Plymouth in New England from the 17th century were investigated. Among 8,562 maternities 81 twin maternities were found, the twinning rate being 0.95%. Twinning rate was low at the lst and 2nd births as compared with the 3rd or later births, and was highest at the 7th and 8th births (1.6%). Twin maternity seemed to be a strong risk factor to terminate reproduction, particularly after 6 or more children had been delivered. The rate of mothers who had any other child (“fertile” mothers) at the 7th or later birth order was significantly lower for twin (13%) than for singleton maternities (63%). Twinning rate also varied by the size of offspring of a mother, and those mothers who had 5 or 6 children showed the highest twinning rate (1.3%). Those fertile mothers who had 7 or more children showed the lowest twinning rate (0.74%), although an exceptionally higher twinning rate was seen at their last births. Elongation of the last birth interval was observed for each group of every family size, and higher twinning rates were generally observed at their last births. Reduction in fecundity and rise in twinning rate seem to have occurred simultaneously at the last stage of the reproductive period of mothers, regardless of their family size.

Parents of multiples suffer unique stresses which can severely impair family health and welfare. Access to information, counseling, and community resources increase parents' abilities to cope, and reduce the risk of child and spousal abuse. Twinline, a social service agency in Califormia, provides a variety of free and low-cost nonmedical perinatal services to meet the needs of a heterogeneous population of over 1,000 multiple birth families and parents expecting multiples in the urban and rural counties of the San Francisco Bay Area.

A case of a patient carrying a 9p trisomy due to a maternal t(9;18) (p 13;p11) translocation is reported. In addition to the principal findings which characterize the 9p trisomy syndrome, this case presents some dysmorphic features due to the partial deletion of chromosome 18.

Genetics deals with ordered and directed biological change in time; psychiatry with the development or the breakdown over the human life span of thought, feeling, and social adaptation. With the growing acknowl-edgement of the contribution of the genotype to mental and emotional uniqueness, it is appropriate to con-sider chronological parameters of mental disease in a genetic framework. These parameters include age of onset of illness (in turn affecting clinical characteristics), sequence of morbid signs and symptoms, length of illness, periodicity of illness, and temporal relation of clinical episodes to other biological events. Data are reviewed from twin and family studies, retrospective and ongoing, that relate such time phenomena to genetic factors in psychiatric disorder. Among the conditions to be considered are schizophrenia, manic-depressive psychosis, Huntington's chorea, karyotype abnormalities, presenile and senile disease, and the psychobiological ageing process itself.