Required for ciliogenesis. Localizes to vesicles en route to the base of cilium. The disease is caused by variants affecting the gene represented in this entry. TMEM138 and TMEM216 genes are adjacent and are aligned in a head-to-tail configuration. They share some cis regulatory region and display coordinated expression. Genes were joined by chromosomal rearrangement at the amphiboan to reptile evolutionary transition around 340 million years ago (PubMed:22282472). Belongs to the TMEM138 family.