Human blood DNA fragments reveal chromosome-end packaging

In an observational study of human plasma, the liquid part of blood, researchers analysed cell-free DNA—DNA fragments circulating outside cells. They used these fragments to map chromatin, DNA packaged with proteins, at telomeres, regions that protect chromosome ends.

The most abundant six-letter DNA sequences were telomere repeats. The fragments indicated that nucleosomes, units of DNA wrapped around proteins, repeated every 145 base pairs at telomeres, compared with about 170 across the genome. Telomere fragments also carried patterns distinct from those elsewhere in the genome. Telomere fragment patterns became less abundant with age. This decline was greater in dyskeratosis congenita, a disorder affecting telomeres.