Despite being first described several years ago, the roles of the Schlafen (SLFN) family of proteins remain largely unknown. The SLFN genes are preferentially expressed in lymphoid tissues and differentially regulated during thymocyte maturation. It is thought that many play roles in cell growth, hemopoietic cell differentiation, and T cell development and maturation. Most members contain at least one divergent AAA domain (AAA_4) that may play a role in ATP binding. Although also known as SLFN3, a Schlafen family member that may be a marker of T cell activation, human SLFN12 has relatively low homology to SLFN3 in other species. Loss of the SLFN12 gene due to deletion is associated with Kabuki syndrome, a multiple congenital anomaly syndrome, suggesting SLFN may play a role in this genetic condition.