An extensive review of the literature on sex differences in human intelligence leads to the conclusion that there is strong evidence for sex differences in processing both verbal and spatial information. The few genetic studies that there are all point toward a sex-linked mode of inheritance of certain spatial abilities.

Signor Presidente della Repubblica Italiana, Signor Sindaco, Signor Ministro, Eccellenza Rev.ma, Signori Atnbasciatori, Signor Preside della Facoltà Medica dell'Università di Roma, Onorevoli Autorità, Congressisti di 30 Nazioni, Gemelli e Amid dei Gemelli,

Nel settembre del 1953 veniva inaugurate in Roma l'Istituto di Genetica Medica e di Gemellologia Gregorio Mendel. La fondazione faceva seguito ad un ambulatorio per gemelli presso il Protettorato di S. Giuseppe e poi presso la Clinica Medica dell'Università. Faceva seguito, specialmente, al volume « Studio dei Gemelli » edito nel 1951 e all'inizio della nostra Rivista Acta Geneticae Medicae et Gemellologiae, la quale è la prima voce di questo settore scientifico dal 1952.

Per i vent'anni dell'Istituto Mendel abbiamo aperto la celebrazione con il Congresso Internazionale di Neurogenetica ed ora la chiudiamo con il Primo Congresso Internazionale di Studi Gemellari. La Neurogenetica come specializzazione della Genetica Medica e gli Studi Gemellari come espressione scientifica della Gemellologia inquadrano bene il significato del lavoro che l'Istituto Mendel va sviluppando, e la vostra presenza, cosí autorevole, significativa e cordiale, dona il piú ambito coronamento civico, scientifico e umano al ricordo della nostra fondazione.

A sample of 47 MZ and 49 DZ pairs of Brazilian twins was investigated in relation to school achievement in six specific areas of study, as well as performance in the test of Dominoes, the Differential Aptitude Tests (DAT) and Griéger's Characterological Questionnaire. Significant F-ratios (variance within DZ/variance within MZ) were observed for the school grades obtained in five of the six areas considered, as well as for their general average; the same being true for the results on the indicated measure of general intelligence, six of the eight DAT tests, and two of the characterological elements. There is a clear positive relationship between the grades earned by the twins and their performance in the Dominoes test. Achievement in Portuguese and foreign language correlates positively with DAT's Sentences; and achievement in mathematics correlates positively with DAT's Numerical Ability, Abstract Reasoning, and Clerical Speed and Accuracy. The results show an agreement with previous estimates of the genetic determination of these variables, which is to a certain extent surprising if we consider the differences in sample sizes, age, and degree of schooling of the subjects, environmental differences, and the dissimilarities which exist between the homes and school systems of USA, Europe, and Brazil.

It is shown that the recent secular decline in DZ twinning rates in Italy was not solely due to secular changes in birth order or maternal age.

The extent of the decline differed in different maternal age-parity categories. It seemed to be greater in younger women than older ones for constant parity. The data gave no clear support to the suggestion that the decline is associated with social class.

It seems that this secular decline in Italy has not been greatly affected by the use of ovulation-inducing drugs.

Monozygotic twins are the best witnesses of the existence of a hereditary biological time, because they would not be identical if they had not also inherited the times of appearance and duration of their common hereditary information. The authors gave the name “chronogenetics” to this branch of genetics which concerns the temporal dimension of the gene and the mechanisms of transmission and manifestation of the temporal characteristics. The “Ergon/Chronon System” is suggested as a model to explain chronological heredity in terms of molecular genetics.

An example is offered of a chronogenetic analysis of puberty based on the study of puberty times in 157 female and 154 male twin pairs. This shows the hereditary conditioning of numerous chronogenetic parameters, the extrapolation of conclusions concerning the phenomenon of puberty, and the establishment, in this regard, of a borderline between hereditary and physical times.

A picture is finally drawn exemplifying Normal Hereditary Times (gametic, auxologic, homeostatic, and old-age recession times) and Pathological Hereditary Times (auxologic, cardiovascular, neoplastic, immunitary, metabolic, and antitoxic pathology times).

Provisional chronogenetic developments are indicated, and a possible advancement toward the recycling of the gene is hoped for.

A sample of 71 twin pairs (32 MZ, 39 DZ), of mean age 9.7 years, has been studied through various techniques in order to better understanding the interpersonal relation of twins, both within the pair and with respect to the members of the family group, and especially the mother. Zygosity, dominance, and birth order have been taken into account. The relation between MZ twins appears to be somehow less special than believed, whereas a special triadic relation appears to exist with the mother. A differentiated research of identity in MZs and autonomy in DZs is also noted (which contributes to a better understanding of problems of schizophrenia in twins). Finally, the relation between MZ cotwins shows mutual similarity and attachment to be lower than foreseen and, anyhow, of a far from misterious nature.

The significant differences in biochemical and chromosomal characteristics, and familial history observed between group of mothers who gave birth to children affected with G1-trisomy (Down's syndrome) and their age-matched controls, indicate that these three maternal variables, in addition to the well known variable of maternal age, are associated with etiology of the aneuploidy. Since attempts to find statistical correlation between these chromosomal and biochemical variables failed, it is believed that these three are unrelated, but very possible etiological factors.

A sample of 6052 newborn children (4968 whites, 1084 Blacks) issued from parents with a generally low socioeconomic level, was studied in relation to congenital anomalies and twinning rates.

The observed frequency of major malformations was 1.3% and of minor defects 2.0%. The twinning rate was 1.4%. Race differences were generally nonsignificant in these variables. These results are in agreement with those obtained in some other Brazilian series, but discrepancies were also observed.

A total of 13%0 of the malformations observed proved to be familial, Polydactyly being the most common anomaly encountered in this class. The frequency of malformations different from those present in the propositi is higher in their sibships than the general prevalence of defective children found among the sibs of normal babies (13% and 4% respectively).

Age, gestation length and exposure of the mothers to noxious agents during pregnancy were not significantly different when the parents of normal and malformed children were compared. On the other hand, as expected, the parents of twins are significantly older than those of single-born, and the gestation length was much reduced in pregnancies resulting in multiple births.

Cytogenetic, clinical, and other findings are presented on a pair of same-sex, monochorial MZ twins concordant for both trisomy 21 and congenital heart disease.

The literature on Down's syndrome in twins and on congenital heart disease in twins is reviewed and the exceptional occurrence of concordant congenital heart disease in MZ twins is stressed.

A selective loss (or a blocking) of rRNA genes in ageing oocytes, and its compensation through the retention of an acrocentric nucleolar organizer chromosome, is proposed as a possible mechanism responsible for the increased frequency of Down's syndrome with maternal age.

A pair of female mongoloid twins was studied when they were ten years old and, again, some thirty years later. A careful comparison was made of the similarities and differences between them in features or traits which have proved to be useful in determining the zygosity of like-sexed twins.

Though some of these characters can be, and frequently are, considerably modified in the presence of mongolism and so lose part of their value for that purpose, the differences noted in these twins, both as children and as middle-aged adults, are thought to outweigh their similarities and so warrant the conclusion that they are, indeed, dizygotic.

A number of facts that cannot be interpreted in terms of nuclear genes would seem to be interpretable in terms of cytoplasmic heredity. The hereditary role of the mitochondria has already been demonstrated in molds. The role of the cytoplasm (matrilineal heredity) has also been shown in some phanerogams, and analogous facts have been noted in insects and molluscs. In amphibians, the influence of an alteration of the egg cortical cytoplasm has been shown to reappear in the following generations. This cortical cytoplasm includes the morphological plan of the organism with its bilateral symmetry: mirror imaging in monozygotic twins would only be an extension of bilateral symmetry. In Tatusia novemcincta the twins may be morphologically or chemically different, which may only be explained by an unequal subdivision of a heterogenic cytoplasm. Similar facts are observed in human twinning. Monozygotic twins are usually discordant with respect to congenital malformations (especially symmelia and anencephaly), which may only be interpreted in terms of unequal distribution of cytoplasmic properties.

A human thoracopagus of slightly unequal twins having a common umbilical cord with exomphalos is described, with special reference to the cardiovascular system. The larger twin had single umbilical artery. The smaller twin had a large left umbilical artery which was in direct continuity with the aorta, a small right umbilical artery with sole connection to the right external and internal iliac arteries (right common iliac artery was absent), missing umbilical vein, a rudimentary nonfunctional heart with atresia of the truncus arteriosus, and a right-sided aortic arch. Exomphalos of both twins is accounted by the possible defective growth of umbilical mesoderm caused by abnormal umbilical vessels. Reversal of systemic circulation in the upper part of the body of smaller twin is discussed. The importance of a careful study of umbilical veins is emphasized.

A dermatoglyphic analysis has been carried out in 7 boys and 5 girls affected by Noonan's syndrome. No deviation from the general population values was found with respect to individual quantitative value, A line termination, absence of C line, a-b ridge count, hypothenar patterns, and presence of p proximal triradius on soles.

Whorls were however increased on fingertips and the axial triradius t, as in Turner's syndrome, was in 21% of the cases in position t′ or t″.

The effect of a given concentration of TrenimonR (6 × 20−8 mol/1) on the lymphocytes of 11 healthy subjects with morphologically abnormal karyotype was analysed in vitro. The research included 6 subjects with balanced translocations, one of them with a centric fusion. Of the remaining 5 subjects, 2 had a duplication in the paracentric region, 1 showed an inversion, and 2 had a marker chromosome.

In the group with morphologically abnormal chromosomes a higher sensibility to the influence of TrenimonR was found as compared with a control group with morphologically normal karyotype. The subjects with an atypical karyotype had 36 to 65% aberrations, the control group 28%. A localization of the breaks showed no increased aberration rates in the morphologically abnormal chromosomes.

A family is described with 21/22 translocation, where chromosome segregation appeared to follow theoretical expectations, rather than empirical risk figures, in male and female carriers alike.

The usefulness of prenatal genetic studies in genetic counseling is also demonstrated.

The dermatoglyphic analysis of a group of Italian patients with Cooley's anemia and Cooley's trait shows Cooley's anemia patients to undergo a significant increase of loops on fingers and a corresponding decrease of whorls. The total loops frequency correlates negatively with the ridge distribution per loop and the total ridge count is significantly decreased. The atd angles are larger. Minor changes in the distribution of patterns in the thenar and hypothenar areas are also observed. In the Cooley's trait patients, loops on fingers are more frequent than in controls, but no difference with Cooley's anemia series is observed. The above findings suggest that the gene(s) controlling loops formation in linkage disequilibrium with thalassemia mutant may have been favourably selected on the “thalassemia chromosome” in the malaria environment.

A girl is described, who, upon her first admission to our pediatric department in 1965, was supposed to have G-deletion syndrome II on the base of the chromosome findings in routine orcein-stained preparations and her clinical aspect. When, however, in 1972 a Q- and G-banding analysis was performed, the patient seemed to be a t(14q+; 22q—) translocation carrier.

These findings are discussed in relation to the known heterogeneity of the clinical picture of patients previously reported as having a G-deletion syndrome and in whom no banding studies were done.

Finally, the need for more extensive studies with the different techniques is stressed, particularly, in cases of Gq— chromosomes, of which the familial occurrence is suggestive of a hidden reciprocal translocation.

The risk of having a child affected by isolated congenital deafness (or deafmutism) is high, if the two parents are affected, if only one parent is affected, but belonging to an affected family, and if the couple has already an affected child.

The banding techniques currently employed in human cytogenetics for the identification of the individual chromosomes have been used to stain PHA lymphocytes and circulating leucocytes. The capacity of these techniques to localize singular chromosomes or chromosomal regions has been investigated.

It has been observed that among the four major categories of bands (Q, G, E and R) only the quinacrine staining is informative in interphase nuclei, because of its peculiarity to stain the long arm of the Y chromosome and few other heterochromatic regions. Interphase nuclei treated according to the C-bands show the presence of several heterochromatic masses, corresponding to the centromeric areas of individual chromosomes, but as such they cannot be recognized accurately. More specific and selective techniques, like G-11 and G-Y protocols, appear to be suitable to localize the centromeric regions of chromosome no. 9 and the long arm of Y chromosome. Variation of the incubation time in the alkali-saline solutions and of pH values have proven to be appropriate for the demonstration of other heterochromatic regions in interphase nuclei and in circulating leucocytes.

The “nuclear” approach to the study of specific heterochromatic regions of human chromosomes may be of practical interest into the investigation of several biological problems and into the detection of individuals carrying chromosome variants.