computer; however, calculations of the individual dose estimates for each survivor are now in progress, but are not available at this time. For this reason, no attempt has been made to analyze the present data in terms of parental radiation doses.

2 Materials and Methods

The sample subjects of the present survey were selected primarily from the RERF F1 mortality study cohort (Kato et al. 1966). This cohort includes children born between 1 May 1946 and 31 December 1958 to parents, one or both of whom were the residents of Hiroshima and Nagasaki ATB. The samples were later expanded to include children who were born after 1959 through the end of 1972. The contribution of the extended samples was about 10% of the total.

In this analysis, the exposed group consists of children born to parents, one or both of whom were located within 2000 m from the hypocenter and who had T65DR dose estimates of more than 1 rad. The control group consisted of children born to parents (1) one or both of whom were exposed distally (2500 m or more from the hypocenter) with estimated doses of less than 1 rad, or (2) were not present in the city ATB.

About 40% of the total individuals in the original samples were not included in this study, because they had died (5%), or migrated outside the contactable areas of both cities (35%). Of the remaining individuals, approximately 74% agreed to participate in this study. Thus, the participation rate of this survey was 45% of the total original sample.

After obtaining consent from the F1 participants and, if necessary, their parents, they were invited to visit the RERF clinic. At that time they were interviewed by nurses to obtain medically-related information and a blood sample was drawn. If requested, a physical examination was performed.

Heparinized blood specimens, 1 to 2 ml per person, collected from each participant, were cultured for 2 days, and then harvested for chromosome preparations using the conventional Giemsa staining methods, the details of which have been described elsewhere (Awa et al. 1978).

In each case, ten well-spread metaphases were examined directly under the microscope, and three of them were photographed for detailed karyotype analysis. Cases with less than ten scorable metaphases were regarded as culture failure. The rate of failure was about 0.1% of the total blood samples in the two cities. When an abnormality was suspected, 100 or more cells were examined.

In addition to the conventional stain, both Q- and C-band preparations (Caspersson et al. 1971; Sumner 1972) were used as a routine procedure. The G-banding method of Seabright (1971) was also applied to cases suspected of having abnormality. When family studies were performed on probands with structural rearrangements, high resolution banding techniques (Yunis et al. 1978; Pai and Thomas 1980) were employed for the precise identification of breakpoints of the chromosomes involved in the aberrations. A description of the type of chromosome abnormalities was made following the standardized nomenclature of ISCN (1978, 1981, 1985).

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