Editor—Telomeres are specific chromatin structures that cap chromosome ends and protect against chromosome degradation and end to end fusion.1 As conventional DNA polymerases cannot fully replicate the ends of linear DNA, a progressive loss of telomeric sequences occurs in each round of DNA replication. Telomerase adds telomere repeats onto chromosome ends to overcome this end replication problem.1 Telomerase activity is detectable in human germ cells, most immortalised cell lines, and in 80-90% of human tumour samples, in which the telomere length is preserved.2 However, telomerase activity is not detected in most normal human somatic cells, with the result that telomere loss occurs with each cell division. After extended doublings, these cells enter a period of slow growth called senescence or crisis and stop dividing. This process may depend on critical telomere loss in one or a few chromosomes. The shortest telomere in a cell may also play an important role in oncogenesis.2 Recently, low level telomerase activity has been detected in several human somatic cells, for example, lymphocytes, endothelial cells, hair follicle cells, colonic crypt cells, and basal layer cells of the epidermis.3 In spite of this activity, telomeres shorten after each successive round of DNA replication. We report here the analysis of telomere length and telomerase activity in two cultures of human amniotic fluid cells (AL1 and AL2), showing a progressive decrease in both with ageing.

Samples were obtained by amniocentesis at 14 weeks’gestation and subcultured over a period of 108 days. DNA extraction, chromosome spreads at metaphase, and cellular extracts were simultaneously performed in three stages. The first stage was 22 days after the initiation of culture (mean population doubling (MPD) 14.7), the second stage was established 64 days after the initiation of culture (MPD 42.7), and the final stage was …