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TCTN2
tectonic family member 2
TCTN2 is located on the long (q) arm of chromosome 12, at band 12q24.31. Arm ratio per GRCh38 - banding schematic.
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Overview
TCTN2 belongs to the tectonic protein family, a group of molecules that regulate the structure and function of primary cilia. Primary cilia serve as cellular sensory organelles, detecting signals from the surrounding environment and translating them into cellular responses that guide tissue development and homeostasis. The protein encoded by TCTN2 localises to the transition zone, a specialised region at the base of the cilium that acts as a selective barrier controlling which molecules can enter or exit the ciliary compartment.
Pathogenic changes in TCTN2 impair transition zone integrity, leading to ciliopathies-a family of multisystem disorders arising from defective cilium assembly or signalling. Because primary cilia are present on cells throughout the body and coordinate critical pathways during embryonic development, TCTN2-related conditions typically affect multiple organ systems simultaneously. The gene follows an autosomal recessive inheritance pattern, meaning two altered copies are required for disease to manifest.
What the gene does
The TCTN2 protein functions as a structural component of the ciliary transition zone, a region approximately 200 nanometres in diameter situated between the ciliary base and the axoneme shaft. This zone establishes a diffusion barrier that prevents inappropriate mixing of membrane components between the cilium and the rest of the cell surface, ensuring that signalling receptors and ion channels are properly compartmentalised.
Tectonic family member 2 works in concert with other transition zone proteins to form membrane-associated complexes that anchor ciliary structures and regulate protein trafficking. The transition zone serves as a quality control checkpoint, admitting cargo destined for the ciliary compartment whilst excluding non-ciliary components. This selective gating function is essential for maintaining the unique biochemical composition of the cilium, which in turn enables proper reception and transmission of extracellular signals.
During embryonic development, primary cilia coordinate several signalling cascades crucial for tissue patterning, including pathways that specify left-right body axis, limb development, kidney tubule formation, and neural tube closure. TCTN2 supports these processes by maintaining structural integrity of the transition zone throughout periods of rapid cellular differentiation.
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Chromosome location
TCTN2 is located on chromosome 12 at position 12q24.31, within the long arm of the chromosome. The genomic region encoding TCTN2 spans multiple exons that are transcribed and spliced together to produce the mature messenger RNA template for protein synthesis. This chromosomal region contains several other genes involved in developmental processes, though TCTN2 functions independently within its specific ciliary pathway.
Protein structure
Domain architecture has not been experimentally characterised in detail for this protein. The TCTN2 polypeptide chain comprises 697 amino acids that fold into a three-dimensional structure capable of interacting with other transition zone components and membrane lipids. Structural predictions suggest the protein contains multiple transmembrane segments that anchor it within ciliary membranes, though precise domain boundaries and functional motifs remain subjects of ongoing investigation.
Key variants
Pathogenic variants in TCTN2 are rare and predominantly consist of loss-of-function changes that prevent production of a functional protein. These include nonsense variants that introduce premature stop codons, frameshift variants arising from small insertions or deletions, and splice-site changes that disrupt normal RNA processing. Missense variants affecting critical amino acids required for protein folding or interaction with binding partners have also been reported. The spectrum of variants reflects the gene's autosomal recessive inheritance pattern, with affected individuals typically carrying two altered copies.
Sample of pathogenic variants
10 pathogenic / likely-pathogenic variants from ClinVar, ranked by review status (expert-panel-reviewed first). This is a sample; recurrent founder variants in a specific population may not appear here - see the full ClinVar listing via the link above.
| Variant (HGVS) | Protein change | Classification | Evidence | Associated condition |
|---|---|---|---|---|
c.1317C>G | p.Tyr439Ter | Pathogenic/Likely pathogenic | ★★☆☆ | Joubert syndrome |
c.1498del | p.Gln500fs | Pathogenic/Likely pathogenic | ★★☆☆ | Joubert syndrome |
c.1550dup | p.His517fs | Pathogenic/Likely pathogenic | ★★☆☆ | Meckel syndrome, type 8 |
c.1788G>A | p.Trp596Ter | Pathogenic/Likely pathogenic | ★★☆☆ | Joubert syndrome 24 |
c.1806dup | p.Thr603fs | Pathogenic/Likely pathogenic | ★★☆☆ | TCTN2-related disorder |
c.191-2A>T | - | Pathogenic/Likely pathogenic | ★★☆☆ | Meckel-Gruber syndrome |
c.267+1G>A | - | Pathogenic/Likely pathogenic | ★★☆☆ | TCTN2-related disorder |
c.487C>T | p.Gln163Ter | Pathogenic/Likely pathogenic | ★★☆☆ | Joubert syndrome |
c.800_801del | p.Val267fs | Pathogenic/Likely pathogenic | ★★☆☆ | Joubert syndrome and related disorders |
c.916C>T | p.Gln306Ter | Pathogenic/Likely pathogenic | ★★☆☆ | Meckel syndrome, type 8 |
Evidence stars indicate ClinVar review status. Individual variant interpretation should always be performed by a qualified clinical laboratory - many variants remain classified as Variants of Uncertain Significance (VUS) pending more research.
Associated conditions
Biallelic pathogenic variants in TCTN2 cause rare ciliopathy syndromes characterised by overlapping developmental abnormalities affecting the central nervous system, kidneys, eyes, and limbs. Clinical manifestations may include brain malformations such as agenesis or hypoplasia of midline structures, cystic kidney disease, retinal dystrophy, polydactyly, and skeletal anomalies. The severity and combination of features vary between affected individuals, reflecting the pleiotropic effects of disrupted ciliary signalling across multiple developmental pathways. These conditions are collectively rare, with prevalence estimates not well established for individual TCTN2-associated phenotypes.
No disease links recorded for this gene in our reference set.
Inheritance pattern
Conditions caused by pathogenic TCTN2 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
TCTN2 is recognised on multiple NHS Genomic Medicine Service gene panels reflecting its role in ciliopathy disorders. The gene holds green classification status on the Developmental Disorders Genotype-to-Phenotype (DDG2P) panel and appears on specialist panels including Fetal Anomalies, Intellectual Disability, Neurological Ciliopathies, Ophthalmological Ciliopathies, Rare Multisystem Ciliopathy Disorders, Renal Ciliopathies, and Skeletal Dysplasia. Green status indicates strong evidence linking TCTN2 variants to the associated conditions, supporting its inclusion in clinical diagnostic testing pathways for patients presenting with relevant phenotypes.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Frequently asked questions
What inheritance pattern does TCTN2 follow?
TCTN2-related conditions follow an autosomal recessive inheritance pattern, meaning an affected individual inherits one altered copy of the gene from each parent. Carriers, who have one working copy and one altered copy, typically do not show symptoms.
How common are TCTN2-related conditions?
TCTN2-related ciliopathies are rare, though precise prevalence figures are not well established. These disorders represent a small subset of the broader ciliopathy spectrum, which collectively affects an estimated 1 in several thousand live births.
Can TCTN2 variants affect more than one organ system?
Yes, because primary cilia are present throughout the body and coordinate multiple developmental pathways, TCTN2 variants typically affect several organ systems simultaneously. Common combinations include brain, kidney, eye, and skeletal involvement, though the specific pattern varies between individuals.