However, while PDE5 protein expression was unchanged in CH mice relative to controls (Fig 5E), PDE5 activity was significantly elevated by 4.1 fold (2175±424 pmol cGMP hydrolyzed/min/mg protein vs. 531±165 pmol cGMP hydrolyzed/min/mg protein) in CH mice compared to controls at 21d (Fig 6C). The gene discussed is PDE5A; the disease is cyclic hematopoiesis.