TBC1D23 is a putative Rab GTPase-activating protein that serves as a critical regulator of endosome-to-Golgi trafficking 1. The protein functions as a bridging factor, simultaneously binding to trans-Golgi golgins (including GOLGA1 and GOLGA4) and the WASH complex on endosome-derived vesicles, facilitating vesicle capture and trafficking 2. Structurally, TBC1D23's C-terminal domain adopts a pleckstrin homology fold that selectively binds phosphatidylinositol 4-phosphate (PtdIns(4)P) while interacting with FAM21 on the opposite surface 2. The protein forms a direct complex with FAM91A1, cooperating to regulate endosomal trafficking of KIAA0319L, which is important for axonal growth 3. TBC1D23 also plays a role in STING-mediated innate immunity by regulating TBK1 trafficking from endosomes to the trans-Golgi network, affecting interferon production and antitumor immune responses 4. Homozygous mutations in TBC1D23 cause pontocerebellar hypoplasia type 11 (PCH11), a non-degenerative neurological disorder characterized by microcephaly, cerebellar and pontine hypoplasia, developmental delay, and ataxia 1. The protein's essential role in vesicular trafficking makes it critical for proper brain development and neuronal function.