Measurement of the Y chromosome has been made in 508 males examined for military service. There was a normal Gaussian distribution of the length of the Y chromosome.

The frequency of mentally retarded males was significantly higher than expected among those with a comparatively large Y (Y/F ≧ 1.00). It is concluded that there may be an association between the length of the Y chromosome and certain types of mental retardation.

The Authors report on the steps involved in the computerization (coding of data, card punching and tape recording) of a Twin Register initiated in 1942 and currently approaching 11,000 cases of multiple births.

The Register is permanent in that it involves continued updating of information and addition of new cases. It includes twins of any age, sex, zygosity and health condition.

The experience gained in the reported project can be usefully shared in wiew of international cooperation and standardization.

The polymorphisms of constitutive heterochromatin regions, present on chromosomes 1, 9, 16 and Y, are inherited in a Mendelian fashion. The C-band heteromorphism has been reported to be associated with various types of cancer. Heterochromatin is considered to play a role in protecting genome against the mutagens. Changes in the quantity and proportion of the different types of satellite DNA might increase the genetic susceptibility in people with heterochromatic variations, which in turn cause chromosome instability and predispose the individual to cancer. We report a case of bilateral retinoblastoma with complete absence of pericentromeric heterochromatin on one of the chromosomes number 9. A similar deficiency of pericentromeric heterochromatin on chromosome number 9 and 16 has been reported in a phenotypically normal individual and a Down syndrome case, respectively. This deficiency was found to be inherited from the father in all the three cases. Complete absence of pericentromeric heterochromatin of chromosome 9 is not being reported in association with cancer syndromes. Further studies are necessary to understand the role of this factor in normals and in those with cancer susceptibility, specially with retinoblastoma and the paternal origin of this deficiency.

Perinatal mortality in twins is found to vary widely in six developed countries for which national data are available. The influence of factors such as birth weight, maternal age, and parity is examined, but no consistent trend is found.

In order to examine the genetic variance and heritability of serum total cholesterol, high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C) and triglycerides, a total of 349 pairs of same-sexed twin neonates born in four major general teaching hospitals in Taipei City were studied. Based on the placental pattern and 12 red blood cell antigens, 271 monozygotic (MZ) and 78 dizygotic (DZ) twin pairs were identified. There was a significant genetic variance for total cholesterol, HDL-C, LDL-C, and triglycerides both unadjusted and adjusted for sex, gestational age and placentation. The unadjusted heritability of total cholesterol, HDL-C, LDL-C, and triglycerides was 0.59, 0.30, 0.25 and 0.75, respectively; while the corresponding adjusted heritability was 0.74, 0.38, 0.31, and 0.49, respectively. Intrapair variance of serum lipids was not significantly different between monochorionic and dichorionic MZ twins.

Twin and pedigree data are presented which indicate that relative length of hallux and adjacent second toe is based on simple Mendelian genetic factors. The normal anatomical trait involves two alleles and a single autosomal locus. The factor for relatively long hallux is recessive to the one for relatively long second toe. There is no evidence of sex influence. Penetrance is 100%. Expressivity is variable, and bilateral discordance is observed in a minority of heterozygous subjects. In every such case, the dominant genotype is expressed in the right foot. The recessive and dominant phenotypes occur, respectively, in 76% and 24% of the greater Cleveland area Caucasian population. Gene frequencies in this population are 87% and 13%, respectively, for the recessive and dominant allele.

A case of 8 trisomy syndrome, identified on the basis of the heat denaturation technique, has been detected in a patient with mental retardation, congenital malformations, and peculiar ocular anomalies. This observation confirms that, even without evidence of mosaicism, this chromosome does not seriously upset the viability of cells and could be less deleterious to the individual than trisomy 13, 18, or 21.

The mental development is not too much impaired and the skeletal abnormalities are mild, as compared to those found in previously reported cases. On the other hand, the cardiovascular system is involved and the ocular lesions are complex. They include prominent eyes, epicanthus, hypertelorism, antimongoloid slant of palpebral fissures, ectopia of lacrimal point, megalocornea, enlarged iridocorneal angle, subatrophic papilla, tortuosities of retinal vessels, absence of deep perception.

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.

In a retrospective survey of 336 mothers of recently born multiples, 71% reported suspicions of twin pregnancy prior to medical confirmation. Primiparous and multiparous reports of symptoms may be utilized to significantly increase the early diagnosis of the presence of multiples.

The Author reports on the simultaneous appearance of a skin manifestation of the B.B.S. disease in female Twins. Partly diffuse and partly nodose infiltrations, with tendency to peripheral extension and central resolution constituted the clinical picture of the disease: (diffuse, small nodose variety of Boeck's sarcoids). In both cases the localisation was on the right cheek, the time-course was very similar. The histological picture was almost identical and was represented by infiltrations of epiteloid-cells with concentrical distribution.

The Authors describe from the electro-phoretic, biochemical, spectrophotometric and chromatographic points of view the slow Hb as observed in 5 family groups from Ferrara and Bologna, in 4 of which they found an Hb L, while the 5th presented an Hb D. A new Hb is therefore added to the numerous abonrmal hemoglobines already found in Italy (Hb S, Hb G, Hb D, Hb K, Hb H, Hb J, abundant Hb A2): the Hb L, which is rather frequent in the region of Ferrara.

As for the Hb D, its presence in different regions of Italy is stressed, in as far as the first family, previously described, came from Calabria, and the present one from Bologna.

Parents of a sample of 76 same sexed pairs of twins aged 3 to 9 months completed a mailed similarity questionnaire. It included the Bonnelykke et al.'s questionnaire and a four anthropological variable scale. To improve each of these two methods, three other combined methods were carried out and results were compared with the biological zygosity diagnosis. The Bonnelykke et al.'s classification combined with anthropological scale (method 4) gave only 1.2% misclassified in the whole sample. It is concluded that zygosity diagnosis using this type of procedure to distinguish MZ and DZ pairs would be important not only for epidemiological study but also for pediatricians and parents.

The maternal risk factors that correlate with small-for-dateness among twins have been analyzed using a sample of 659 twin pairs and a matched sample of singletons. Non-marital status, job involvement, and the previous delivery of a low-birth weight (<2,500g) infant present a negative interaction with twinning, as low gestational age-adjusted birth weight does not correlate significantly with these risk factors among twin gestations, while it does among singleton gestations. On the other hand, the effects of parity, habitual maternal weight, smoking during pregnancy, and twinning are additive on gestational age-adjusted birth weight. Indeed, the decrease in adjusted birth weight associated with these risk factors is of the same magnitude among twins and singletons and is statistically significant in both cases. These findings suggest that exposure of twin pregnancies to these latter risk factors, and particularly to smoking during pregnancy, can lead to the delivery of newborns with extremely low birth weights.

Inbreeding effect revealed as mortality and morbidity in general may be ascribed to deleterious mutations generally present at different loci of the ancestors common to each consanguineous mating. A new coefficient (E) is suggested to measure this effect. On the basis of this theory, a new method to estimate the load of mutations disclosed by inbreeding has been presented elsewhere, and is now extended. In this method, the load is estimated without introducing gene frequency notions. Genetic loads estimated through our method are in rather close agreement to those estimated through the classical theory of Morton, Crow and Muller (MCM).

In this preliminary report, which is part of a wider and more detailed study still in progress, I am reporting mainly the twins' mental state and associated physical abnormalities. For this purpose, I am surveying all the 2442 long-stay patients admitted during 30 years (1 September 1938-31 August 1968) to the Stoke Park Hospital Group, Bristol, which provides 1800 beds for mentally retarded patients of both sexes and of all ages. The survey's sample is shown in Tab. I.

The hereditary component of the chronological development of bones and teeth has been studied, in 40 twin pairs aged 5-7 years, through dental age (defined on account of the mineralization of the permanent dentition's dental buds) and bone age (denned on account of the presence and form of the hand ossification nuclei).

The statistical analysis shows a correlation coefficient of 0.95 in MZ and 0.84 in DZ twins for dental age; and of 0.94 in MZ and 0.81 in DZ twins for bone age.

The following are therefore the estimates of the hereditary component (based on Holzinger's formula) for the two parameters studied:

An old problem of gemellary research lies in the determining cause of gemellogenesis. Two new observations of the family order, in agreement with other similar results, are further evidence in favour of the opinion that in the origin of twins a certain part can be played by some hereditary property of the paternal side.

Gemellary research is the best method to establish the respective importance of heredity and environement in the developement of man. A new problem of gemellary research has arisen owing to the fact that MZ twins can differ in some illness, without the common causal analysis heredity-environement being able to give a satisfactory explanation. For example in the case of cancer it is demonstrated that the “autonomous” genesis of an illness must be taken into account i. e. without an appropriate hereditary cause or without an esogenous cause visible for all. Such an “autonomous” genesis of an illness has become undestandable only on the basis of microphysical knowledge.

We evaluated the relative influence of genetic and environmental factors on leukocytes, lymphocytes, neutrophils, monocytes, erythrocytes, reticulocytes, hemoglobin, platelets, T lymphocyte subsets, and NK marker cells in monozygotic (MZ) and dizygotic (DZ) twins. Peripheral blood components were measured in 154 healthy twin pairs (118 MZ pairs and 36 DZ pairs) and lymphocyte subsets in 48 healthy twin pairs (38 MZ pairs and 10 DZ pairs).

Platelets and erythrocytes showed higher intraclass correlations in the MZ pairs than in the DZ pairs in the males. However, in the females, the intraclass correlations for these components were similar between the MZ and DZ pairs. Neutrophils and monocytes showed low intraclass correlations in the MZ pairs. The absolute number of CD4+ cells and the CD4+/CD8+ cell ratio showed high intraclass correlations regardless of age in the MZ pairs in both males and females. The intraclass correlation for the absolute number of CD3+ cells was low in pairs aged ≥ 60 years in the MZ pairs. The absolute numbers of CD16+ cells and CD56+ cells showed high intraclass correlations regardless of age in the MZ pairs.

The syndrome of ataxia-telangiectasia was studied from a genetic standpoint on a material consisting of 7 original cases from four families, and of 31 cases from the literature. A cytogenetic analysis in one patient showed the normal diploid chromosome number, while the application of Brugger's test showed a random distribution of affected members in the investigated sibships. The observed frequency of affected individuals corresponds to the one to be expected, assuming a recessive monofactorial inheritance of the syndrome. Considering the small number of consanguineous marriages observed between parents of affected individuals, the conclusion can be drawn that ataxia-telangiectasia is not so rare a condition as it is generally assumed. The responsible gene shows a pleiotropic and lethal effect.

Although the heritability of general intelligence has been the subject of much study and can be considered to be well established, the heritability of specific factors in intellectual functioning has not as yet been the object of such intense scientific inquiry.

The recent work of Nichols (1965), utilizing a large sample of twins from the National Merit Scholarship testing program and employing a battery of tests measuring achievement in five different academic areas, is an excellent pioneering study. Nichols used a composite score derived from the five subtests, presuming this to be a measure of general ability, and he found that MZ twins were much more alike than DZ twins with respect to the composite score; about 70% of the variance in the composite could be attributed to heredity. The novel result of his investigation is his discovery that the specific subject areas also have significant heritability components. When the influence of the composite general ability upon subtests was removed statistically, the residual subtest scores also showed considerable heritability.

A limitation of Nichols' findings is that the subtests do not offer any potential theoretical link to basic factors in mental functioning. Such measures, however, may be provided by the fundamental factor analytic explorations of Guilford and his associates during the past twenty years. Since our own interest has been in the area of creative thinking and esthetic judgment, we have restricted ourselves in the present investigation to the use of tests in those areas whose factorial classification has been studied previously.