ACE and isolated hemihyperplasia: The role of the RAS in the biology of IH has been recently demonstrated by the expression of angiotensin-converting enzyme (ACE) (Figure 5A) and the angiotensin II receptor 2 (ATIIR2) (Figure 5B) isoform; the effect of angiotensin II (ATII) in inducing IH-derived blast cell proliferation (25); and the promotion of cellular proliferation in IH by ATII via the activation of ATIIR2, in vitro (63).