Megakaryocyte generation. (A) Megakaryocyte (MK) colonies on day 12 from bone marrow–derived CD34⁺ cells from a control donor or a patient with trisomy 18p with 3 copies of the PACAP gene. (B) Number of CFU-MKs from 5 × 10³ bone marrow–derived CD34⁺ cells from 4 unrelated control donors or a patient with trisomy 18p. Bars represent the means plus or minus SD of the CFU-MK counts of 1 plate from the patient and 4 plates from 4 controls (*P < .001). (C) MK colonies on day 12 in wild-type and PACAPTg9 mice. Sca1⁺ bone marrow cells from wild-type mice develop into more and larger colonies compared with those of PACAPTg9 mice. MK are also larger (arrow) in wild-type mice. (D) Number of CFU-MKs from 5 × 10⁴ bone marrow–derived Sca1⁺ cells from 8 PACAPTg9 mice or 5 wild-type littermate controls. Bars represent the means plus or minus SD of the CFU-MK counts of 1 plate for each PACAPTg9 and wild-type mouse (*P < .001).