FRMPD1 (FERM and PDZ domain containing 1) is a membrane-localization adaptor protein that regulates G-protein signaling through protein-protein interactions. Structurally, FRMPD1 contains conserved FERM and PDZ domains and binds to multiple signaling partners via a highly conserved ~20 residue fragment 1. Its primary function is to stabilize membrane-bound AGS3 (activator of G-protein signaling 3) and promote its interaction with Gαi proteins 2. FRMPD1 accomplishes this by binding to the TPR domain of AGS3 and positioning it at the cell cortex and membrane extensions, where it can interact with Gαi in a regulated manner 2. FRMPD1 also interacts with LGN (Leu-Gly-Asn repeat-enriched protein) through a conserved binding motif and competes with other LGN partners including mInsc and NuMA for TPR domain binding 34. In retinal photoreceptors, FRMPD1 expression is controlled by a cell type-specific alternative promoter regulated by rod-specific transcription factors NRL and CRX 5. Clinically, FRMPD1 has been identified as an independent prognostic marker for biochemical recurrence in prostate cancer patients 6, and genetic variants near FRMPD1 are associated with facial morphology variation 7.