TP53 and Down syndrome: Importantly, induction of p53 and up-regulation of the p53 pathway has been shown to occur in the human 5q- syndrome.23 Immunohistochemical analysis showed moderate to strong p53 expression in erythroid cells in bone marrow trephine sections from patients with the 5q- syndrome, and gene expression profiling demonstrated that the p53 pathway is significantly deregulated in the CD34+ cell population of these patients.23 The accumulation of p53 protein in bone marrow erythroid precursors of patients with the 5q- syndrome has been confirmed in other studies.24,25