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CD3D
CD3 delta subunit of T-cell receptor complex
CD3D is located on the long (q) arm of chromosome 11, at band 11q23.3. Arm ratio per GRCh38 - banding schematic.
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Overview
CD3D is located on chromosome 11 and encodes a 171-amino-acid protein that forms part of the CD3 complex alongside CD3γ, CD3ε, and CD3ζ chains. Together, these proteins cluster around the antigen-recognising TCR, converting extracellular antigen recognition into intracellular biochemical signals that activate T cells.
T cells are central to adaptive immunity, coordinating responses to pathogens and maintaining immunological memory. When the CD3 complex is disrupted by pathogenic variants in CD3D, T-cell development and function can be severely impaired, leading to profound immunodeficiency. The gene is inherited in an autosomal recessive manner, meaning two altered copies are typically required to cause disease.
What the gene does
The CD3δ protein works as a signal transduction module within the T-cell receptor complex. When the TCR recognises a peptide-MHC molecule on the surface of an antigen-presenting cell, the CD3 chains translate this binding event into intracellular signals that drive T-cell activation, proliferation, and differentiation.
CD3δ pairs with CD3ε to form a heterodimer, which assembles with other CD3 components and the TCR α and β chains to create the complete receptor complex. This architecture is essential for surface expression of the TCR and for the stability of the entire assembly on the cell membrane.
The signalling capacity of the complex depends on specialised motifs in the cytoplasmic tails of the CD3 chains. When the TCR engages its ligand, kinases phosphorylate these motifs, initiating cascades that ultimately activate transcription factors, cytokine production, and effector functions necessary for immune responses.
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Chromosome location
CD3D is located on the long arm of chromosome 11 at position 23.3 (11q23.3). This chromosomal region contains several genes involved in immune function and haematopoiesis. The relatively compact gene structure contributes to efficient transcription in developing and mature T lymphocytes.
Protein structure
The CD3δ protein comprises 171 amino acids organised into an extracellular immunoglobulin-like domain, a transmembrane region, and a cytoplasmic tail. The cytoplasmic tail contains an immunoreceptor tyrosine-based activation motif (ITAM) spanning amino acids 138-166, which serves as the primary docking site for intracellular kinases during signal transduction. The ITAM's conserved tyrosine residues become phosphorylated upon TCR engagement, recruiting signalling proteins that propagate the activation signal downstream.
Key variants
Pathogenic variants in CD3D are rare but can profoundly disrupt T-cell development and function. Most reported variants are loss-of-function changes that prevent normal expression of the CD3δ protein or impair its ability to assemble into functional receptor complexes. Because the gene follows autosomal recessive inheritance, individuals typically require variants in both gene copies to manifest clinical features.
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.18dup | p.Leu7fs | Pathogenic/Likely pathogenic | ★★☆☆ | Immunodeficiency 19 |
c.202C>T | p.Arg68Ter | Pathogenic | ★★☆☆ | Immunodeficiency 19 |
c.274+5G>A | - | Pathogenic/Likely pathogenic | ★★☆☆ | CD3D-related disorder |
c.279C>A | p.Cys93Ter | Pathogenic | ★★☆☆ | Immunodeficiency 19 |
g.(?_118209789)_(118213421_?)del | - | Pathogenic | ★☆☆☆ | Immunodeficiency 19 |
c.107del | p.Asn36fs | Pathogenic | ★☆☆☆ | Severe combined immunodeficiency disease |
c.15del | p.Leu7fs | Pathogenic | ★☆☆☆ | Immunodeficiency 19 |
c.237C>G | p.Tyr79Ter | Pathogenic | ★☆☆☆ | Immunodeficiency 19 |
c.271C>T | p.Arg91Ter | Pathogenic | ★☆☆☆ | Immunodeficiency 19 |
c.40_41dup | p.Leu15fs | Pathogenic | ★☆☆☆ | Immunodeficiency 19 |
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 CD3D cause severe combined immunodeficiency (SCID), a life-threatening condition characterised by absent or severely reduced T-cell numbers and impaired cellular immunity. Affected individuals present in early infancy with recurrent, severe infections, failure to thrive, and susceptibility to opportunistic pathogens. Without intervention such as haematopoietic stem cell transplantation, outcomes are generally poor. The condition is clinically and genetically heterogeneous, with defects in multiple genes capable of producing similar phenotypes.
No disease links recorded for this gene in our reference set.
Inheritance pattern
Conditions caused by pathogenic CD3D 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
CD3D is included on the NHS Genomic Medicine Service panel for primary immunodeficiency or monogenic inflammatory bowel disease (green classification, R15), reflecting its role in severe immune disorders. It also appears on the COVID-19 research panel (green classification), highlighting interest in genetic determinants of immune responses to viral infections. Green classification indicates strong evidence linking the gene to the specified conditions, supporting its use in diagnostic testing pathways.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Frequently asked questions
How is CD3D inherited?
CD3D follows an autosomal recessive inheritance pattern. This means a child must inherit a pathogenic variant from both parents to develop the associated condition. Carriers with one altered copy typically remain healthy.
What is the role of CD3D in the immune system?
CD3D encodes a structural and signalling component of the T-cell receptor complex. The CD3δ protein helps assemble the receptor on the cell surface and transmits activation signals when the receptor recognises foreign antigens, enabling T cells to coordinate immune responses.
Can CD3D variants be detected through carrier screening?
Yes, CD3D is included in autosomal recessive carrier screening panels. Testing can identify individuals who carry one pathogenic variant, which is useful for reproductive planning and assessing recurrence risk in families with a history of severe immunodeficiency.