TCTN3 (tectonic family member 3) is a ciliary transition zone protein essential for primary cilia assembly and function. 1 It localizes to the ciliary transition zone and is a critical component of the tectonic protein complex required for ciliogenesis and regulation of ciliary membrane composition. 1 TCTN3 plays a vital role in sonic hedgehog (Shh) signaling pathway regulation, with tectonic-deficient models showing Shh-related developmental defects. 1 Pathogenic TCTN3 variants cause primary ciliopathies characterized by mid-hindbrain malformation. Mutations underlie Joubert syndrome 18, presenting with cerebellar vermis agenesis, the diagnostic molar tooth sign on brain MRI, ataxia, cognitive impairment, and abnormal eye movements. 2 3 TCTN3 variants also cause orofaciodigital syndrome type 4 (OFD4), featuring oral cavity and facial abnormalities, digit defects, and growth retardation, with some cases displaying atypical features including scaphocephaly and seizures. 4 Additional manifestations in TCTN3-related disorders include polydactyly, encephalocele, and congenital heart disease with reduced cardiomyocyte contractility. 5 6 Recently, TCTN3 has been implicated in papillary thyroid carcinoma progression through STAT1-mediated upregulation, promoting cell-cycle progression, migration, and invasion. 7 These findings expand TCTN3's roles beyond developmental ciliopathies to cancer biology.