The similarity between the virulence phenotype of the NTPD1 null mutant and previously generated L. major LPG mutants in which assembly of the entire phosphoglycan chain has been disrupted is striking [4], [53], and strongly suggests that LPG chain elongation during stationary phase is both critical for promastigote virulence, and likely to underlie the major function of this glycoconjugate during the early stages of infection in the mammalian host. The gene discussed is APOE; the disease is infection.