TP53 and Li-Fraumeni syndrome: For instance, fibroblasts from Li-Fraumeni syndrome patients expressing missense p53 mutations including R175H undergo S-phase reentry after being exposed to spindle depolymerizing agents that disrupt mitotic spindles, leading to the generation of polyploid cells, whereas p53-null fibroblasts are blocked from reentry (Gualberto et al., 1998).