The present study was conducted to evaluate some cytogenetic and immunological parameters in Down syndrome (DS) children and their parents. Ten families with children of DS were selected; in addition five families with normal children were included as a control group. The cytogenetic parameters; blastogenic index (BI), mitotic index (MI), chromosomal aberrations (CA), micronucleus (MN), sister chromatid exchange (SCE) and replicative index (RI) were assessed in lymphocytes of cultured peripheral blood. Blast index, MI and RI were decreased in DS children while their parents were in normal range when compared with control group. A significant increase was observed in SCE, CAs and MN for DS children and their parentsThe cell division used to determine the sensitivity of DS children and their parents to the anticancer drug Methotrexat and 6-Thioguanine.However, the patients were categorized according to their response to the drugs, as a sensitive (S) and resistant (R) groups.All DS children and their mothers were resistant to 6-TG at a concentration 20µg/ml, while their fathers were sensitive. At the concentration 4µg/ml of MTX all mothers was resistant, while the 30% of DS children and 40% of their fathers were resistant. In the case of control groups all of them are sensitive. The DS children and their parents’ blood were also tested for the lymphocyte transformation test and phagocytosis against Staphylococcus aureaus. The lymphocyte transformation and phagocytosis percentage were lower in DS children compared with normal children and their parents with normal range.
