Abstract

A study of the interphase chromatin structure of lymphocytes in healthy subjects, patients with Down's syndrome, and their parents and sibs was carried out by AO labelled fluorometry using our modification of DNP cell thermal denaturation. Analysis by the Sperry Univac 90/30-B computer showed that in 40% of healthy subjects the lymphocyte chromatin melting profiles had a regularly repeated curve with six (seven) maxima at definite temperatures. In the remaining 60% some regularly repeated deviations were present and were correlated with the sex of the subject examined. There were five subgroups in the female group and seven subgroups in the male group. In 97% of patients with Down's syndrome the lymphocyte chromatin melting profiles gave curves with three maxima at temperatures of 65, 85, and 92 degrees C (+/- 2 degrees). Maxima at 78 and 45 degrees C were absent. In 80% of the mothers of probands with Down's syndrome and in 30% of female sibships, lymphocyte melting profiles also produced curves with three maxima: 65, 85, and 92 degrees C (+/- 2 degrees). In view of the fact that similar changes were observed in mothers and female sibs only, we propose that some women may have genotypical peculiarities which may possibly contribute to the origin of this chromosome pathology.