The identification of HOMER1 as an autism risk gene adds an important component to the network of PSD proteins causally implicated in autism, which now includes the products of the SHANK2[7], [42], SHANK3[23], NLGN3[43], NLGN4[43], SYNGAP1[7], and DLGAP2[7] genes (Fig. 1). The gene discussed is SYNGAP1; the disease is autism.