Our group and others have previously shown that 5FU induces white blood cell loss and neutropenia by depleting immune cells in bone marrow and inducing cell cycle arrest.9 Additionally, this toxicity has been linked to DPD enzyme activity and catabolism of 5FU.14,31 We have extended this to show that livers from Obese mice have reduced dypd mRNA expression and DPD protein expression concomitant with reduced white blood cells throughout three cycles of 5FU. The gene discussed is DPYD; the disease is neutropenia.