TTC12 is a cytoplasmic protein essential for assembling dynein arm complexes in motile cilia and sperm flagella. Loss-of-function mutations in TTC12 cause primary ciliary dyskinesia (PCD), characterized by selective defects in inner dynein arms (IDAs) in respiratory cilia and both outer and inner dynein arm defects in sperm flagella, revealing distinct assembly mechanisms between these organelles 1. Ultrastructural analyses confirm that TTC12 deficiency results in inner dynein arm ultrastructural abnormalities 2. Beyond ciliary function, TTC12 is part of the NTAD gene cluster (NCAM1-TTC12-ANKK1-DRD2) on chromosome 11, which influences dopaminergic neurotransmission 3. Genetic variants in TTC12 associate with nicotine dependence in African-American and European-American populations 4, and with smoking behavior in adolescents through effects on striatal dopamine signaling 5. TTC12 variants also show shared genetic architecture with problematic alcohol use and psychiatric disorders including major depression and schizophrenia 6. These findings indicate TTC12 has dual roles: a primary ciliary function in dynein assembly and a secondary role in addiction vulnerability through dopaminergic pathways, though the mechanistic connection between these functions remains unclear.