Tubulin, a major component of the cytoskeleton, has multiple isotypes in metazoans encoded by conserved genes. The study identifies TUBB4B variants in patients with primary ciliary dyskinesia (PCD) that specifically affect centriole and cilia biogenesis. These variants disrupt microtubule dynamics and cilia formation in a dominant-negative manner, leading to distinct ciliopathies. Structural studies show that different TUBB4B variants disrupt distinct tubulin interfaces, classifying patients into three ciliopathies. TUBB4B is essential for motile cilia assembly in specific tissues, and its mutations cause diverse clinical presentations, including PCD-only, sensory ciliopathy (SND-only), and syndromic ciliopathy (PCD+SND). TUBB4B mutations disrupt cilia and centrosomes in patient respiratory cells, affecting cilia length and number. TUBB4B is a cilia-specific tubulin, and its variants have different effects on microtubule dynamics and tubulin heterodimer formation. TUBB4B mutations act in a dominant-negative manner, causing distinct clinical phenotypes. TUBB4B is localized to centrioles and cilia, and its mutations affect different tubulin surfaces depending on the clinical phenotype. The study highlights the importance of TUBB4B in ciliary function and establishes a link between tubulinopathies and ciliopathies. The findings suggest that specific tubulin isotypes have unique and non-redundant subcellular functions, and that tubulin diversity underlies the diversity of cilia seen in vivo.Tubulin, a major component of the cytoskeleton, has multiple isotypes in metazoans encoded by conserved genes. The study identifies TUBB4B variants in patients with primary ciliary dyskinesia (PCD) that specifically affect centriole and cilia biogenesis. These variants disrupt microtubule dynamics and cilia formation in a dominant-negative manner, leading to distinct ciliopathies. Structural studies show that different TUBB4B variants disrupt distinct tubulin interfaces, classifying patients into three ciliopathies. TUBB4B is essential for motile cilia assembly in specific tissues, and its mutations cause diverse clinical presentations, including PCD-only, sensory ciliopathy (SND-only), and syndromic ciliopathy (PCD+SND). TUBB4B mutations disrupt cilia and centrosomes in patient respiratory cells, affecting cilia length and number. TUBB4B is a cilia-specific tubulin, and its variants have different effects on microtubule dynamics and tubulin heterodimer formation. TUBB4B mutations act in a dominant-negative manner, causing distinct clinical phenotypes. TUBB4B is localized to centrioles and cilia, and its mutations affect different tubulin surfaces depending on the clinical phenotype. The study highlights the importance of TUBB4B in ciliary function and establishes a link between tubulinopathies and ciliopathies. The findings suggest that specific tubulin isotypes have unique and non-redundant subcellular functions, and that tubulin diversity underlies the diversity of cilia seen in vivo.