MKS1 encodes a component of the transition zone complex, a structural barrier at the base of primary cilia that regulates protein diffusion between the cilium and plasma membrane 1. MKS1 is essential for ciliogenesis, functioning in centrosome migration to the apical surface and regulating ciliary length and number through modulation of centrosome duplication [UniProt]. The protein is also required for proper cell branching morphology and ciliary-dependent signaling. Mutations in MKS1 cause ciliopathies characterized by primary ciliary dysfunction. MKS1 variants are a major cause of Meckel-Gruber syndrome (MKS), a syndromic neural tube defect often resulting in perinatal lethality 2. MKS1 mutations also cause Joubert syndrome, presenting with characteristic cerebellar malformations (molar tooth sign), neurological dysfunction including ataxia and cognitive impairment, and in some cases agenesis of the corpus callosum 2. Additionally, MKS1 is implicated in Bardet-Biedl syndrome, which manifests as renal ciliopathy with cyst formation, kidney dysfunction, and systemic complications 3. Clinically, MKS1-related diseases demonstrate variable expressivity despite fully penetrant inheritance 4. The identification of MKS1 variants in diverse ciliopathy presentations underscores the critical role of transition zone integrity in multiple organ systems and developmental processes dependent on ciliary function.