May be involved in ciliary biogenesis or function. Interacts with TMEM67. Localizes at the transition zone, a region between the basal body and the ciliary axoneme. TMEM218 mutations result in ciliary dysfunction leading to a broad spectrum of disorders, collectively termed ciliopathies. Overlapping clinical features include retinal degeneration, renal cystic disease, skeletal abnormalities, fibrosis of various organ, and a complex range of anatomical and functional defects of the central and peripheral nervous system. The ciliopathy range of diseases includes Meckel-Gruber syndrome, Bardet-Biedl syndrome, Joubert syndrome, and nephronophtisis among others. Single-locus allelism is insufficient to explain the variable penetrance and expressivity of such disorders, leading to the suggestion that variations across multiple sites of the ciliary proteome influence the clinical outcome. The disease is caused by variants affecting the gene represented in this entry. Belongs to the TMEM218 family.