AbstractBACKGROUNDIn utero rubella virus (RV) infection of a fetus can result in birth defects that are often collectively referred to as congenital rubella syndrome (CRS). In extreme cases, fetal death can occur. In spite of the availability of a safe and effective vaccine against rubella, recent worldwide estimates are that more than 100,000 infants are born with CRS annually.RECENT PROGRESSRecently, several significant findings in the field of cell biology, as well as in the RV replication and virus‐cell interactions, have originated from the authors' laboratory, and other researchers have provided insights into RV teratogenesis. It has been shown that 1) an RV protein induces cell‐cycle arrest by generating a subpopulation of tetraploid nuclei (i.e., 4N DNA) cells, perhaps representative of the tetraploid state following S phase in the cell cycle, due to its interaction with citron‐K kinase (CK); 2) RV infection induces apoptosis in cell culture, and 3) CK functional perturbations lead to tetraploidy, followed by apoptosis, in specific cell types.CONCLUSIONSBased on several similarities between known RV‐associated fetal and cellular manifestations and CK deficiency–associated phenotypes, it is reasonable to postulate that P90‐CK interaction in RV‐infected cells interferes with CK function and induces cell‐cycle arrest following S phase in a subpopulation, perhaps representative of tetraploid stage, which could lead to subsequent apoptosis in RV infection. Taking all these observations to the fetal organogenesis level, it is plausible that P90‐CK interaction could perhaps be one of the initial steps in RV infection–induced apoptosis‐associated fetal birth defects in utero. Birth Defects Research (Part A), 2004. © 2004 Wiley‐Liss, Inc.