“…Subsequent studies of singleton and multiplex families [Spiker et al, 1994], and twin studies, revealed higher than expected concordance rates in families, and high concordance rates for autism among MZ twins [Ritvo et al, 1985a; Steffenburg et al, 1989; Bailey et al, 1995; Greenberg et al, 2001; Ronald et al, 2006], but not among dizygotic (DZ) twins [Bailey et al, 1995]. This commentary will expand my first piece on the autism spectrum disorders (ASDs) [Fisch, 2005] and will review the recent literature on linkage and attempts at gene identification in autism.…”