Summary
The consanguinity rate in Japan has rapidly decreased during the last 20 years. Possible causes of such decrease were analyzed by comparing chronological changes in the mean number of opposite-sex first cousins and in the rate of first-cousin marriage among 12,448 grandchildren of 891 proband women, using family registers,koseki, at a public office in Nagano Prefecture. The number of married opposite-sex first cousins for each individual had been as many as 10–12 for grandchildren of proband women born during the years 1840–1889, and began to decrease only recently, whereas the rate of first-cousin marriage has steadily decreased from 5–6% to 0% in accord with the trend in the whole country. Thus, the reduction of family size has not played a major role in the recent decrease in consanguinity rate, but may promote it in the new future.
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This study was supported by Scientific Research Grants from the Ministry of Education, Science and Culture, of Japan No. 0413 in 1964 and No. 0412 in 1965, a Grant from the Toyo Rayon Foundation for the Promotion of Science and Technology 1965–1967, and a Grant from the Ministry of Health and Welfare for Research on Handicapped Children in 1974–1976.
A part of the present study was reported at the 39th Annual Meeting (1967) of the Genetic Society of Japan and at the 13th (1968) and 21st (1976) Annual Meetings of the Japan Society of Human Genetics by Tanaka and Yokoo (1967 and 1968) and Tanaka (1976).
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Tanaka, K., Hayase, R. Less important role of family size reduction in the recent drastic decrease of consanguineous marriage in Japan. Jap J Human Genet 22, 245–250 (1977). https://doi.org/10.1007/BF01874068
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DOI: https://doi.org/10.1007/BF01874068