| Chromosome disorders, one of the most important genetic diseases, are the most frenquent cause of mental retardation. These disorders are thus important public health problems for no entirely satisfactory prevention measures now exist. A better knowledge of their etiologic factors and their pathogenesis could have important practical implications for prevention. It is well known that maternal age is one of etiologic factors. But maternal age is just the effects of accumulated environmental factors on human body. As life level advancing, the environment around us has being changed. There are more and more radiative materials in our lives. In order to search for environmental factors related with chromosome disorders, a hospital-based case-control study about Down syndrome was carried out. Laboratory experiments were carried out to analyse the relationship between ionizing radiation and chromosome non-disjunction, and its pathogenesis.In the epidemiological part, patients were collected from October 1999 to December 2002 (They consulted doctors in Shanghai Xinhua hospital pediatric hospital of Fudan university, Henan province genetic institute) , controls were healthy children who were similar to patients at age, gender, born place and so on. Patients were diagnosed according to their karyotype[47, XY, +21 or 47, XX, +21 or 47, XY(XX), +21/46, XY(XX)]. We surveyed the object ' s parents conditions including their general state, exposed environmental factors, healthy conditions, drugs taking etc.The risk factors were evaluated by uni- and multi-unconditional logistic model used SPSS10. 0. We collected 66 patients and 55 healthy children in last 3 years. The results of statistics showed that maternal age of DS had a tendency to decrease. The results of maternal exposed factors multi-unconditional logistic model showed that long time and low dose radiation and smoked were significantly related with DS. Other Factors, such as abortion , drinking ., intake of MSG (monosodium glutamate) contraceptive tablet, anti-infection drug leaded to a higher incidence of DS. The results of paternal exposed factorsmulti-unconditional logistic model showed that smoke, intake of MSG and hepatitis were significantly related with DS. Other factors, such as drinking leaded to a higher incidence of DS.In the laboratory experiment part, human peripheral blood, cultured cells and ICR mice were study objects. The changes of mitotic chromosome numbers were measured by human metaphase chromosome counts and statistic analyzed used x2-test . The changes of meiotic chromosome numbers were measured by mice one-cell zygote chromosome counts and statistic analyzed usedx2-test .The effects of low dose ionizing radiation on the expression of topoisomerase II were measured by immunocytochemistry , Western blot and RT-PCR. The effects of low dose ionizing radiation on mitotic chromosome non-disjunction of the cultures were more outstanding than that of the whole blood. The rate of chromosome non-disjunction was higher than that of control group from 0. 1Gy group(P < 0. 05), and had the tendency of increase as dose increased. The rate of chromosome non-disjunction was higher when radiation time was 3 times than that of 1 time at the same dose (P< 0. 05), and had the tendency of increase as radiation frequency increased. The effect of low dose ionizing radiation on meiosis chromosome non-disjunction was remarkable from 2 Gy( P< 0. 05), and had the tendency of increase as dose increased. When radiation time was added up to 3 times, the rate of meiosis chromosome non-disjunction was significant higher than 1 time at the same dose(P< 0. 05), and had the trend of increase as radiation time increased. The expression of topoisomerase II of cultured cells treated low dose ionizing radiation decreased and then returned as time went. And become outstanding as radiation dose and frequency were added. Inhibitor of topoisomerase II could cause chromosome non-dis juction in mitosis and meiosis.And the co-effect of Inhibitor of topoisomerase II and ion...
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