PROBLEMS OF CHROMOSOME 21 MOSAICISM. A REVIEW
N. V. Kovaleva
Institute of Obstetrics and Gynaecology after D. O. Ott, RAMS, St. Petersburg;
e-mail: kovaleva@robotek.ru
Despite the great efforts contributed to studies on the trisomy 21 etiology, basic mechanisms of nondisjunction
are still poorly understood. Even less is known about mosaic variant of trisonomy 21. In this paper, some
problems of masaicism are considered: (1) estimation of the prevalence of mosaicism in patients affected with
Down syndrome, (2) determination of population rate of parental mosaicism, (3) evaluation of the role of ovarian
mosaicism in etiology of Down syndrome, (4) origin of the extra chromosome, (5) mechanisms of production of mosaic
lines, (6) phenomenon of skewed sex ratio (female predominance, in fetuses particularly), (7) effect of maternal
age.
Key words: trisonomy 21, mosaicism, age, sex ratio
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