SADS is characteristic of HGPS cells that undergo premature arrest. (A) Frequency of distended satellites in early passage cells from two HGPS patients (1-yr-old HGADFN155 and 8-yr-old HGADFN167) and the older healthy mother of HGADFN167, HGMDFM090 (n = 100 in one of three representative experiments). (B) A 20-min BrdU pulse demonstrates that very few early passage HGADFN167 cells with decondensed satellites label, confirming that cells with SADS are rarely in S phase (n = 202). (C) Almost all cells that did not incorporate BrdU during a 48-h label had distended satellites (n = 100). (D–F) DNA FISH to α-sat (green) and sat II (red) shows that some HGPS cells have normal appearing compact satellites (E), whereas senescent cells in both the HGADFN167 (D) and HGADFN155 (F) cell lines contain SADS. Also notice the blebbed nuclear membrane (DAPI; F) characteristic of laminopathies. Arrows and arrowheads indicate a particularly distended α-sat signal that is enlarged in the corresponding insets.