Relative involvement of chromosome #21 in radiation induced exchange aberrations in lymphocytes of down syndrome patients

Abstract

It is not yet resolved as to what type of DNA double strand break repair operates in G 0 lymphocytes. We have employed Down syndrome (DS) lymphocytes with three copies of chromosome #21 to answer the question whether the presence of Three copies reduces the frequency of exchange aberrations involving this chromosome in comparison to normal cells with two copies of #21. Peripheral blood lymphocytes from three DS patients and two normal individuals were X-irradiated with 1 and 3 Gy. The frequencies of unstable aberrations were found to be higher in DS lymphocytes than normal lymphocytes after 3 Gy of X-rays. FISH studies employing chromosome specific DNA libraries for chromosomes #21 and #22 indicated that the frequencies of exchange aberrations per chromosome are similar in both disomic and trisomic condition. This indicates that the presence of an extra copy of chromosome #21 does not alter the yield, suggesting that homologous recombination does not play a major role in the repair of DNA strand breaks in human G 0 lymphocytes.