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DDB2
damage specific DNA binding protein 2
DDB2 is located on the short (p) arm of chromosome 11, at band 11p11.2. Arm ratio per GRCh38 - banding schematic.
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Overview
DDB2 (damage specific DNA binding protein 2) resides on chromosome 11 and encodes a 427-amino-acid protein integral to nucleotide excision repair, the primary pathway for removing bulky DNA adducts caused by ultraviolet radiation. The encoded protein operates as part of a multi-subunit complex that surveys genomic DNA for distortions characteristic of UV-induced pyrimidine dimers and other photolesions. Biallelic pathogenic variants in DDB2 cause xeroderma pigmentosum complementation group E, a recessive disorder characterised by extreme photosensitivity, freckling in sun-exposed areas, and markedly elevated risk of skin malignancies from childhood. Recognition of DDB2-related conditions is clinically important because early diagnosis enables rigorous photoprotection strategies and dermatological surveillance.
What the gene does
The DDB2 protein functions as the substrate-recognition subunit of the UV-damaged DNA-binding (UV-DDB) complex, partnering with DDB1 to scan chromatin for helix-distorting lesions introduced by ultraviolet exposure. Upon encountering cyclobutane pyrimidine dimers or 6-4 photoproducts, DDB2 binds directly to the damaged site and recruits downstream repair factors, including the XPC complex, which commits the lesion to nucleotide excision repair. This handoff ensures that damaged nucleotides are excised and replaced with accurate sequence. DDB2 also participates in chromatin remodelling at damage sites, facilitating access for repair enzymes. Beyond lesion recognition, the protein influences cell-cycle checkpoint activation in response to genotoxic stress, helping cells pause division until DNA integrity is restored. The WD repeat domains within DDB2 mediate protein-protein interactions essential for complex assembly, whilst specific residues around amino acids 334-336 confer photolesion-binding specificity.
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Chromosome location
DDB2 is located at chromosomal band 11p11.2 on the short arm of chromosome 11. The gene spans a modest genomic interval and comprises ten exons that are transcribed and spliced to yield the mature messenger RNA template for the 427-residue protein. This pericentromeric region of chromosome 11 harbours multiple genes involved in DNA metabolism and stress response pathways.
Protein structure
The DDB2 protein comprises 427 amino acids organised into several functional regions. The N-terminal segment (amino acids 1-30) is disordered and may provide regulatory flexibility. Two short regions (amino acids 68-79 and 87-98) are both required for interaction with DDB1, the obligate partner protein. The central and C-terminal portions contain seven WD repeats: WD 1 spans amino acids 116-151, WD 2 covers 159-194, WD 3 extends from 203-238, WD 4 occupies 244-287, WD 5 runs from 290-329, WD 6 spans 343-386, and WD 7 comprises amino acids 396-420. These WD repeats fold into a characteristic beta-propeller structure that mediates molecular recognition. Embedded within WD 4 is the DWD box motif (amino acids 256-274), which is implicated in ubiquitin ligase recruitment. A critical photolesion recognition region at amino acids 334-336 lies between WD 5 and WD 6, directly contacting damaged DNA bases.
Key variants
Pathogenic variants in DDB2 are predominantly loss-of-function alleles, including nonsense mutations, frameshifts, and splice-site alterations that abolish protein expression or disrupt the WD-repeat architecture. Missense changes affecting the photolesion recognition region or DDB1-binding interfaces can similarly impair damage detection. Because xeroderma pigmentosum group E follows autosomal recessive inheritance, affected individuals typically carry biallelic pathogenic variants, whilst heterozygous carriers remain asymptomatic.
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.1063C>T | p.Arg355Ter | Pathogenic | ★★☆☆ | not provided |
c.702+1G>T | - | Pathogenic/Likely pathogenic | ★★☆☆ | Xeroderma pigmentosum, group E |
c.730_733del | p.Lys243_Lys244insTer | Pathogenic/Likely pathogenic | ★★☆☆ | Xeroderma pigmentosum, group E |
c.818G>A | p.Arg273His | Pathogenic/Likely pathogenic | ★★☆☆ | not provided |
g.(47238024_47238408)_(47254511_47256123)del | - | Pathogenic | ★☆☆☆ | Xeroderma pigmentosum |
c.1187C>A | p.Ser396Ter | Pathogenic | ★☆☆☆ | Xeroderma pigmentosum, group E |
c.574C>T | p.Arg192Ter | Pathogenic | ★☆☆☆ | not provided |
c.640C>T | p.Arg214Ter | Pathogenic | ★☆☆☆ | not provided |
c.937C>T | p.Arg313Ter | Pathogenic | ★☆☆☆ | Xeroderma pigmentosum, group E |
c.919G>T | p.Asp307Tyr | Pathogenic | - | Xeroderma pigmentosum, group E |
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 DDB2 variants cause xeroderma pigmentosum complementation group E (XP-E), a DNA repair disorder marked by extreme sensitivity to sunlight, progressive freckling and pigmentary changes in sun-exposed skin, and profoundly increased risk of cutaneous malignancies including basal cell carcinoma, squamous cell carcinoma, and melanoma, often arising in childhood or adolescence. Some individuals also develop ocular surface abnormalities and, less commonly, neurological features, though XP-E is generally considered the mildest xeroderma pigmentosum subtype with fewer systemic manifestations than other complementation groups.
No disease links recorded for this gene in our reference set.
Inheritance pattern
Conditions caused by pathogenic DDB2 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
DDB2 appears on multiple NHS Genomic Medicine Service gene panels, reflecting its role in hereditary cancer predisposition and neurodevelopmental conditions. The gene holds green (diagnostic-grade) classification on the Adult solid tumours cancer susceptibility panel, the Childhood solid tumours panel (condition ID R359), the Childhood solid tumours cancer susceptibility panel, the Developmental Disorders Genotype-to-Phenotype (DDG2P) database, the White matter disorders and cerebral calcification narrow panel, and the Xeroderma pigmentosum, Trichothiodystrophy or Cockayne syndrome panel (R227). This multi-panel presence underscores the clinical importance of identifying DDB2 variants in both paediatric and adult patients with photosensitivity, early-onset skin cancer, or unexplained white-matter abnormalities.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Frequently asked questions
What is the role of DDB2 in preventing skin cancer?
DDB2 detects UV-induced DNA damage and recruits repair machinery to excise and replace damaged nucleotides, preventing mutations that can initiate skin cancer. When both gene copies carry pathogenic variants, this surveillance system fails, allowing UV-induced mutations to accumulate and dramatically raising the risk of basal cell carcinoma, squamous cell carcinoma, and melanoma from an early age.
How is xeroderma pigmentosum group E inherited?
Xeroderma pigmentosum group E follows autosomal recessive inheritance, meaning an affected individual has inherited a pathogenic DDB2 variant from each parent. Parents who each carry one pathogenic variant are typically unaffected but have a 25 per cent chance with each pregnancy of having a child with two pathogenic copies and therefore the condition.
Why does DDB2 appear on white-matter disorder panels?
Although DDB2 is classically associated with skin photosensitivity and cancer, some patients with DNA repair defects exhibit neurological involvement, including white-matter changes on brain imaging. The gene's inclusion on the NHS White matter disorders and cerebral calcification panel reflects recognition that impaired DNA repair can occasionally affect the central nervous system, though neurological features are less common in XP-E than in other xeroderma pigmentosum subtypes.