Furthermore, ectopically expressed AFF-1 and EFF-1 were capable of driving fusion of heterologous cells and, in some cases, could substitute for viral fusogens in pseudotyped virus infection assays, but only when the proteins were expressed in adjacent cells (in the case of cell-cell fusion) or target cells (in the case of virus fusion assays) (Podbilewicz et al., 2006; Sapir et al., 2007; Avinoam et al., 2011; Perez-Vargas et al., 2014). The gene discussed is AFF1; the disease is viral infectious disease.