Additionally, Fat3 is expressed by multiple BC types, including GRIK1-positive OFF-CBCs, and GRIK1 levels were reduced in the OPL of Fat3 mutant mice (Figs. S2, 3, and 7), as were levels of PTPσ, a synaptic protein that binds to FAT3 (Fig. 6). The gene discussed is GRIK1; the disease is breast cancer.