The prevention of hereditary diseases after birth is essentially based on the detection of these diseases at their preclinical level. This may be made possible through a careful pedigree examination and possible identification of a “genealogical alarm”, as well as a detailed clinical examination of the subject and possible identification of preclinical signs of the pathogenesis, i.e., of a “clinical alarm”. The respective roles of chronogenetics and of gemellology in this approach are reviewed.

The occurrence of different types of hemoglobin variants in India has been well-documented in urban populations and in certain tribal areas. Beta-thalassaemia and hemoglobins D, E, H, S, and rare variants like Hb Lepore, have been found in varying percentages. There is a higher incidence of Hb E in the Eastern region and of Hb D in certain Northern populations. The association of Hb E with beta thalassaemia G6PD deficiency has been established. The relationship with other environmental factors, like malaria, is not yet clear.

The agglutinin levels of 250 parturient women and their newborn babies were studied and the modifying influence of 16 variables evaluated. The most important factor in this variability is the AB0 phenotype. The agglutinin titers are generally higher in milk than in plasma or saliva. Blacks always show salivary agglutinins in higher frequencies than Whites. Within each fluid the amount of anti-A and anti-B are always highly correlated (r 0.59-0.79). Associations were also observed between the titers in plasma and milk (r 0.25-0.30). The plasma and milk anti-A levels of the 0 mothers are correlated with those of their 0 children (r 0.28-0.37), but the anti-B are not. Socioeconomic conditions may affect the salivary anti-A and anti-B titers.

Over the past 50 years a large number of methods have been proposed for estimating heritability from twin studies. The present paper describes the most commonly cited of these estimates as a first step in evaluating their usefulness. A critical review will then follow.

A survey of twin births in Denmark in relation to the total number of births from 1911 to 1974 shows a significant decrease in the dizygotic twin birth rate for all maternal age groups. The possible environmental causes of such a decrease are discussed.

The negative influence of some insecticides on male fertility has been noted. We report our cytogenetic observations on a group of infertile insecticide workers. Increased chromosomal breakage was a constant finding and the Y chromosome was especially damaged. This may account for impaired spermatogenesis. Furthermore, the involvement of heterochromatic chromosomal variants both in the individual susceptibility to the chemically induced damage and in the reproductive fitness is emphasized.

Two unrelated patients carrying imbalances involving the long arm of chromosome 6 are described. In the first trisomy 6q21→qter had segregated from a maternal translocation t(6 ; 16)(q15 ; q24). The clinical data of the proposita are compared with those of three other published cases. A partial 6q trisomy syndrome is postulated characterized by: growth deficiency of prenatal onset, psychomotor retardation, craniofacial abnormalities (microcephalia, hypertelorism, downward slanting palpebral fissures, flattened nasal bridge, long philtrum, hypoplastic perioral features, large jaw resulting in a round appearance of the face, receding chin, malformed ears) and dysmorphic extremities (contractures of limbs due to short flexor tendons, hypoplastic fingers, toes and nails). In the second case, monosomy 6q221→qter resulted from a de novo rearrangement and was responsible for mental retardation and facial dysmorphism (reduced biparietal diameter, hypotelorism, absent eyebrows, prominent nose, ptosis, receding chin, dysmorphic ears). Studies of HLA and PGM3 segregation showed normal inheritance patterns and ruled out the location of these genes in bands 6q221→qter.

The case of a boy is reported showing the typical symptoms of Down's syndrome, in whom the chromosome analysis revealed a mosaic karyotype: 50% 48,XYY,+21/50% 47,XY,+2l. Findings of 92 cases from the literature are summarized to show the frequencies of double gonosome-autosome aneuploidies compared with single trisomies. Referring to the different chromosomes involved, the aneuploid cell formation, the frequencies of combinations, as well as the tendency to mosaic formation are analyzed. The age of parents at the time of birth and the life expectancy are described as well as the clinical symptoms. Theories concerning the origin of double aneuploidies are discussed.

A patient with multiple congenital malformations due to partial 8q trisomy is reported. Karyotype-phenotype correlations suggest the possibility that partial trisomy 8q is a nosologically distinct syndrome.

Various reagents were tested for the purpose of developing an improved Giemsa staining technique for the differential staining of sister chromatids in human chromosomes. Reagents like acids, bases, buffers, protein denaturants and proteolytic enzymes were all potent inducers of differential staining. The best results were obtained by brief trypsinization followed by extraction of nucleic acids by incubation in hot HCl. There was poor contrast between unifilarly and bifilarly BrdU substituted chromatids in slides from which trypsin treatment was omitted. The method of slide preparation as they affect the spreads of BrdU substituted metaphases were also evaluated. The results support the role of these reagents in the conformational changes and structural lesions of chromosomal protein leading to differential staining.

A survey was carried out among fisher-women in Pallepalam, in Nellore District of Andhra Pradesh, to determine the prevalence and pattern of consanguinity and its effects on fertility, mortality, and morbidity. Of the 106 marriages investigated, 54.72% were consanguineous with predominant proportions of first cousin (36.79%) and uncle-niece (13.21%) marriages. The average inbreeding coefficients for autosomal and sex-linked genes were found to be 0.0405 and 0.0448 respectively. The differences between consanguineous and nonconsanguineous marriages were studied with respect to fertility, mortality and morbidity.

The author agrees with earlier writers that most of the differences observed in monozygotic pairs are due to unusual or extreme environmental factors acting before or during the twins' birth. Although they are typical of development in twins, these environmental factors can hardly be considered typical of development in other individuals. This point, as a review of the literature shows, is often overlooked by those who study twins in the childhood or adult age ranges. As a result the inferences drawn from twin differences are frequently mistaken, or at least quite exaggerated so far as the significance of postnatal influences in non-twins is concerned. At the same tihe, if allowance is made for the environmental biases peculiar to twin studies, the findings may be said to establish more about the importance of heredity in the medical and behavior sciences than most investigators have thought. In the author's opinion the largest single source of bias is the mutual circulation that exists during prenatal development of the majority of monozygotic pairs. Data on that circulation's difference-producing effects are reviewed and related to studies of mature twins. Effects of lateral inversions (asymmetry reversals) and of “natal” factors (chiefly conditions of delivery) are also reviewed, and methods of judging the importance of all three of the biasing conditions are outlined. Need for obtaining systematic and complete information about the natal factors is stressed.