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.

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 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 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 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″.

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.

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 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.

A baby with alpha-chain thalassemia hydrops fetalis was born to an Iraqian Jewish couple of Iraqi-Kurdish extraction. Hemoglobin Bart's constituted only 40% of the total hemoglobin, much less than usually found in alpha-thalassemia hydrops fetalis.

That this is a particular expression of hemoglobin H disease is considered. The likelihood of two alpha-chain loci, rather than one alpha-chain locus, in this family, is also discussed.

Plasma dopamine beta hydroxylase (DBH) activity was determined in MZ twins and in siblings of both sexes. The enzyme activities were found to be virtually identical in MZ twins. DBH activity was less similar in same-sex sibs, but still significantly correlated. These results indicate that plasma DBH activity is genetically determined.

Different mathematical approaches to study the extent of genetic variation of natural populations are reviewed. The modern understanding of the gene structure permits new interpretations of existing concepts like fixation or inbreeding. A more recent measure of genie divergence, which at molecular level is designed to measure net codon differences is also seen to be related with gene diversity in a substructed population. It is argued that such variations are produced and preserved possibly by simultaneous action of migration, mutation, selection, and random genetic drift. At the present moment it is very difficult to isolate out the effect of each factor because of varying degrees of variation at the different gene sites and between different sets of populations.

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.

The world distribution of the Australia antigen, the agent responsible for hepatitis in man, is reviewed on the basis of the available literature, with the addition of a personal research on a sample of German donors.

The distribution of ABO blood groups was studied in 459 Chinese and 65 Malay newborns with deficiency of G6PD, and in 1181 Chinese and 535 Malay newborns with normal levels of the enzyme. Similarly, the distribution of Rhesus blood groups was studied in 248 G6PD deficient Chinese newborns and in 255 normal subjects. No association between the ABO blood groups and G6PD deficiency was observed in either Chinese or Malays. For the Rhesus system there was found to be a statistically significant decrease in the frequency of genotypes containing the complex R 1 in G6PD deficient subjects compared with that in normal subjects.

An analysis is attempted to throw more light on the inheritance of rhesus factor in humans and the Fisher-Race and Wiener's concepts are respectively evaluated.

It is claimed that the Rh-Hr locus is not comprised of the recombination of C, D, E, c and e genes, much less the help of the auxiliary (d) which merely appears to be a conventional approach derived from an even principle of recombination for a polyhybrid cross.

As for Wiener's rare or common mutants of Rh-Hr in humans and the emergence of different agglutinogens like a sort of genetic proliferation, no such parallel of inheritance has yet been found in experimental plants or animals.

Probably the scarcity of certain genotypes is due to the rare chance of fertilization or embryonic development due to incompatibility between certain mutants of Rh-Hr genes, similar to ABO-Rh incompatibility.

Present concepts on the etiology of childhood tumours are reviewed. The differences in clinical manifestations of the hereditary and nonhereditary types are illustrated with data on retinoblastoma and on nephroblastoma. Notwithstanding these differences it is most likely that the fundamental etiologic process is the same in both and that it consists in successive mutational events. The possible consequences of the association of retinoblastoma with a deletion of chromosome 13 in some cases are discussed. Several explanations for the association of Wilms' tumour and aniridia are also discussed.

This paper presents a general view on congenital malformations and a summary of some anatomic, clinical, epidemiological and genetic aspects of congenital heart diseases. Some “recommendations” for research are also briefly mentioned.

The traits, earlobe attachment, hand clasping and arm folding, are found to show a high degree of homogeneity in the Tamil Brahmans.

The latter appear to be closest to the Bengali Brahmans, with respect to all three traits, and differ significantly from other Brahman populations, with respect to earlobe.