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TMEM216
transmembrane protein 216
TMEM216 is located on the long (q) arm of chromosome 11, at band 11q13.1. Arm ratio per GRCh38 - banding schematic.
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Overview
TMEM216 provides instructions for producing transmembrane protein 216, a component of the cellular machinery that builds and maintains primary cilia. Primary cilia are hair-like projections extending from nearly all human cells, functioning as sensory antennae that detect chemical signals and coordinate developmental programmes during embryonic growth and tissue maintenance. The TMEM216 protein localises to specialised structures at the ciliary base, where it participates in quality control mechanisms that regulate which proteins enter or exit the cilium. Disruption of TMEM216 function interferes with ciliary assembly and signalling, resulting in developmental disorders collectively termed ciliopathies. These conditions typically follow autosomal recessive inheritance, meaning pathogenic variants in both gene copies are required for disease manifestation.
What the gene does
The TMEM216 protein functions within the transition zone, a specialised compartment at the base of primary cilia that acts as a selective barrier controlling molecular traffic between the cilium and the cell body. This gating function ensures that ciliary membrane composition remains distinct from the surrounding plasma membrane, enabling cilia to perform their sensory and signalling roles effectively. TMEM216 interacts with other transition zone proteins to form multi-protein complexes that anchor ciliary membranes and regulate the passage of signalling molecules. During embryonic development, primary cilia coordinate morphogen gradients-chemical signals such as Sonic hedgehog and Wnt-that pattern tissues and organs. The TMEM216 protein helps maintain the structural integrity of transition zone complexes, thereby supporting the cilium's capacity to transduce extracellular signals into appropriate cellular responses. Loss of TMEM216 function compromises transition zone organisation, leading to abnormal ciliary structure, impaired signal transduction, and developmental anomalies affecting the brain, skeleton, kidneys, and other organs.
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Chromosome location
The TMEM216 gene resides on the long arm of chromosome 11 at position 11q13.1, a region containing clusters of genes involved in developmental regulation and cellular signalling. The gene comprises multiple exons that together encode a relatively compact 145-amino-acid protein. This chromosomal region is subject to recombination events, and founder mutations in specific populations have been documented for TMEM216-related ciliopathies.
Protein structure
Domain architecture has not been experimentally characterised in detail for this protein. The TMEM216 protein is classified as a transmembrane protein based on sequence prediction algorithms that identify hydrophobic segments capable of spanning lipid bilayers. Structural studies suggest the protein adopts a multi-pass transmembrane topology, embedding within ciliary membranes at the transition zone. The compact size of TMEM216 and its specific membrane localisation pattern distinguish it from larger ciliary structural components, indicating a specialised regulatory or scaffolding function rather than a primary architectural role.
Key variants
Pathogenic variants in TMEM216 are typically loss-of-function alterations, including nonsense mutations that introduce premature stop codons, frameshift variants arising from small insertions or deletions, and splice-site changes that disrupt normal transcript processing. Missense variants affecting conserved residues critical for protein stability or interaction with partner proteins have also been identified. The variant spectrum reflects the gene's relatively small coding sequence, with founder effects observed in certain populations leading to recurrent pathogenic alleles.
No pathogenic or likely-pathogenic ClinVar variants recorded yet for this gene.
Associated conditions
TMEM216-related disorders fall within the ciliopathy spectrum, a group of conditions arising from defective ciliary structure or function. The most frequently diagnosed condition associated with pathogenic TMEM216 variants is Oral-facial-digital syndrome type VI (Varadi-Papp), characterised by craniofacial malformations including cleft lip or palate, tongue anomalies, and polydactyly. Affected individuals may also exhibit cerebellar hypoplasia, intellectual disability, and renal cysts. The severity and specific features vary among individuals, reflecting genetic background and the nature of the underlying variants.
Inheritance pattern
Conditions caused by pathogenic TMEM216 variants typically follow autosomal recessive inheritance.
When both parents are carriers, each child has a 25% chance of being affected, 50% of being a carrier, and 25% of being unaffected.
UK clinical status
TMEM216 appears on multiple NHS Genomic Medicine Service gene panels reflecting its role in multi-system developmental disorders. The gene holds green (high-evidence) classification on panels including DDG2P, Fetal anomalies, Intellectual disability, and several ciliopathy-specific panels such as Neurological ciliopathies, Ophthalmological ciliopathies, Renal ciliopathies, and Rare multisystem ciliopathy disorders. It is also listed on the Retinal disorders, Skeletal dysplasia, and Structural eye disease panels, indicating the broad phenotypic spectrum observed with TMEM216 variants. These panel memberships support the gene's clinical utility for diagnostic testing in individuals presenting with multi-organ features consistent with ciliopathy.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Frequently asked questions
What inheritance pattern do TMEM216-related conditions follow?
TMEM216-related ciliopathies are inherited in an autosomal recessive manner, meaning an affected individual typically carries pathogenic variants in both copies of the gene, one inherited from each parent. Carrier parents generally do not show symptoms but have a 25% recurrence risk with each pregnancy.
Can TMEM216 variants affect only one organ system?
Whilst Oral-facial-digital syndrome type VI is the most common presentation, the phenotypic spectrum can vary. Some individuals exhibit prominent craniofacial or skeletal features, whilst others may have more significant neurological or renal involvement, reflecting the broad role of cilia in coordinating development across multiple tissues.
Is TMEM216 included in UK NHS clinical testing panels?
Yes, TMEM216 is listed with high-evidence (green) status on numerous NHS Genomic Medicine Service panels, including those for foetal anomalies, intellectual disability, and various ciliopathy categories, reflecting its established clinical relevance for diagnostic evaluation.