The percentage of CD41+CD42b+ cells representing the mature megakaryocytes was significantly higher in T21-1 (83.7 ± 1.5%) compared to D21-1 (74.9 ± 1.3%) (Figure 3A, p = 0.019), in agreement with the previously reported effects of trisomy 21 on the promotion of erythro-megakaryocytic lineage expansion [27]. This evidence concerns the gene GP1BA and trisomy 21.