A survey of chromosomal abnormalities has been carried out in Italy since 1966. Among the 1,551 subjects examined, the following abnormalities were found: 2 cases of C/C translocation, 1 of D/C, 5 of D/D, and 9 of D/G; 2 cases of Patau's syndrome with D trisomy; 4 cases of Edwards' syndrome; 176 cases of Down's syndrome, of which 163 with regular trisomy, 4 with mosaicism, 7 with D/G translocation, 1 with G/G translocation, and 1 with C/G translocation; 10 cases with 47,XXY complement; 1 case with 46,XY/47,XXY/48,XXXY mosaicism; 4 cases with 45,XO karyotype; 3 with 45,XO/46,XX, 1 with 45,XO/46,XY, 2 with 45,XO/46,XXr and 1 with 45,XO/46,XXi mosaicism; 2 cases with 47,XYY complement; 2 phenotypic females with 46, XY karyotype; and 5 leukaemic patients with Ph chromosome.

Furthermore, several kinds of normal variants were observed, such as no. 9 prominent secondary constriction, chromosome-D or -G enlarged short arm, 16-pair heteromorphism, Y-chromosome polymorphism, and satellited E chromosome.

The frequency of structural chromosomal aberrations has been examined in peripheral blood lymphocyte cultures from 18 normal individuals. A mean rate of aberrations was observed of 7.38%, and a mean breakage/metaphase index of 0.036. Individual values ranged, for the aberration index, from 4% to 15%; and, for the breakage/metaphase index, from 0.00 to 0.08. Only gaps and breakage were observed. The translocation cross and chromatid-ring observed derive from a series of experiments on homologous plasma cultures. As for the influence of different cultural environments, it has been observed that the rate of spontaneous aberrations behaved independently from the age of the blood sample, from the addition of penicillin in the culture, and from the concentration of phytohemoagglutinin. Using veal's fetal serum, the rate of aberrations failed to show any variation, even with a time of culture prolonged up to 96 hours; while, using homologous plasma, the time of culture having been prolonged, structural aberrations have shown a considerable increase. The study of the mitotic index in the different cultural conditions has indicated the possibility of favoring the growth of leucocyte cultures.

The first-degree relations of 433 rheumatic propositi were examined for evidence of rheumatic fever (RF) or rheumatic heart disease (RHD). The families of 470 control propositi were examined in identical fashion. Of the total propositi, 378 propositi were matched with 378 control propositi for sex, age group, and ethnic community (European or Afro-Asian origin). Of 738 sibs of rheumatic propositi, 19.6% had RF or RHD and of 586 sibs of controls, 3.1% had RF or RHD (P<0.001).

In the matched families 2,985 first-degree relations of the propositi were examined: 142 had RF and 141 had RHD, a total of 9.5%. In the members of the families of the rheumatic propositi 232 rheumatics were found in 1,486 first-degree relations (15.6%), while in the control families 51 rheumatics were found among 1,499 (3.4%).

Comparisons and analyses were made of expected and observed numbers according to sibship size using the method of truncated analyses (Lenz-Hogben method). This analysis supported the hypothesis of a simple mendelian recessive inheritance. Unbiased estimates of P, the population frequency of affected individuals, were consistent with the value P = 0.25, expected for a mendelian recessive character. The rheumatic fever clustering in families in this study was compatible with a simple recessive mendelian inheritance.

Respiratory distress syndrome occurred in 77 of 1,130 liveborn twins (1: 15) and appears to be more frequent than in singletons. This increase cannot be entirely accounted for by the higher prematurity rate of twins over singletons. In 46 twin pairs with at least one affected, there was a significantly higher concordance rate among MZ than DZ pairs, suggesting that genetic factors are of some etiologic importance in this disease.

For a diallelic autosomal character, the correlation between parental total score and offspring total score (known as the parent-offspring correlation) given by + √{s(1 + 3F)/[(s + 1) + F(3s − 1)]}, is used here to estimate F, the constant which is commonly interpreted as coefficient of inbreeding. When the family records include varying number of children, a reasonably good estimate of F is exhibited which agrees fairly with other available estimates.

The Y/E index (Y/16-18 chromosomes) has been studied in a Swedish population of 74 men. The following results have been obtained: M = 0.734 ± 0.0238 with a range from 0.57 to 0.90. The values agree well with those of a Finnish population previously described. The use of the Y/E index in 15 paternity cases is exemplified.