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PALB2
partner and localizer of BRCA2
PALB2 (partner and localizer of BRCA2) encodes a protein essential for DNA repair, working closely with BRCA1 and BRCA2 to maintain genome stability. PALB2 provides instructions for a protein that acts as a molecular bridge between BRCA1 and BRCA2, two critical tumour suppressors.
PALB2 is located on the short (p) arm of chromosome 16, at band 16p12.2. Arm ratio per GRCh38 - banding schematic.
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Overview
PALB2, which stands for partner and localizer of BRCA2, encodes a 1186-amino-acid protein that serves as a central coordinator in the cellular response to DNA damage. The protein functions as a scaffold, recruiting BRCA2 to sites of DNA breaks and enabling high-fidelity repair through homologous recombination. This process is essential for preserving the integrity of genetic information each time cells divide.
Pathogenic variants in PALB2 disrupt these repair mechanisms, leading to accumulation of DNA damage over time. Heterozygous carriers face substantially elevated lifetime risks for several cancer types, most notably breast cancer in both women and men, as well as ovarian and pancreatic cancers. The inheritance pattern is autosomal dominant with incomplete penetrance, meaning that although a single altered copy increases cancer susceptibility, not all carriers will develop disease.
PALB2 is recognised as one of the 78 genes included in the American College of Medical Genetics and Genomics (ACMG) Secondary Findings list version 3.2, reflecting its clinical actionability. Carriers may benefit from enhanced surveillance protocols and risk-reducing interventions. In the UK, PALB2 is included in multiple NHS Genomic Medicine Service test directories, including familial breast cancer, inherited ovarian cancer, and inherited pancreatic cancer pathways, ensuring that relevant findings trigger appropriate clinical follow-up.
What the gene does
The PALB2 protein orchestrates homologous recombination, the most accurate pathway for repairing double-strand DNA breaks. When such breaks occur-whether through normal cellular processes, replication errors, or environmental exposures-PALB2 rapidly localises to the damage site and brings together the key repair machinery. Its N-terminal region physically binds BRCA1, whilst a distinct C-terminal domain recruits BRCA2 and RAD51, the recombinase enzyme that catalyses strand exchange during repair.
This bridging function is critical: BRCA1 arrives early at the break and modifies chromatin to make the site accessible, whilst BRCA2 delivers RAD51 filaments to the exposed DNA. PALB2 physically links these two steps, ensuring that repair proceeds efficiently and without delay. The protein's chromatin-association motif (ChAM) enables it to engage directly with nucleosomes, facilitating access to DNA within densely packed chromatin structures. PALB2 also interacts with DNA polymerase eta (POLH), stimulating DNA synthesis during the later stages of repair.
Beyond its structural role, PALB2 exhibits DNA-binding activity with preferences for specific conformations: it binds most avidly to displacement loops (D-loops), followed by double-stranded and then single-stranded DNA. This selectivity helps guide repair machinery to the appropriate DNA intermediate at each stage of recombination. The protein's oligomerisation-its ability to form multi-protein complexes-concentrates repair factors at damage foci, creating localised hubs of activity visible as nuclear dots under microscopy.
Disruption of PALB2 function forces cells to rely on error-prone repair pathways such as non-homologous end joining, which simply ligates broken ends together without reference to a template. Over time, this leads to chromosomal rearrangements, deletions, and other genomic instability hallmarks observed in PALB2-associated tumours. The protein's role extends beyond canonical DNA repair: it participates in replication fork protection, ensuring that stalled forks can restart without collapsing into breaks, and contributes to cell-cycle checkpoint signalling that halts division when damage exceeds repair capacity.
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Chromosome location
PALB2 is located on chromosome 16 at position 16p12.2, within the short (p) arm. This chromosomal region is gene-dense and has been associated with other developmental and cancer-related genes. The PALB2 gene spans approximately 38 kilobases of genomic DNA and comprises 13 exons that are transcribed and spliced to generate the mature messenger RNA encoding the 1186-amino-acid protein. The coding sequence is distributed across these exons, with functional domains encoded by specific exonic regions that are subject to alternative splicing in some tissues, though the predominant isoform is constitutively expressed across cell types.
Protein structure
The PALB2 protein is organised into distinct functional regions that mediate its interactions with partner proteins and DNA substrates. The N-terminal DNA-binding region (amino acids 1-579) exhibits preferential binding to D-loop structures over double-stranded and single-stranded DNA, reflecting the protein's engagement with recombination intermediates. Within this broader N-terminal segment, the first 319 residues are required for interaction with BRCA1, enabling PALB2 to localise to DNA-damage sites marked by BRCA1. The initial 200 amino acids mediate binding to RAD51, whilst the first 160 residues are essential for oligomerisation and concentration at damage foci.
A short coiled-coil motif spans amino acids 9-41, likely contributing to protein-protein interactions, whilst several disordered regions (amino acids 52-72, 95-157, 252-273, 346-365, 440-525, 679-698, and 774-798) provide structural flexibility. Intrinsically disordered segments often serve as dynamic linkers or sites for post-translational modification. The chromatin-association motif (ChAM), located at amino acids 395-446, is required for chromatin binding and nucleosome engagement, enabling PALB2 to access DNA within its physiological chromatin context.
The C-terminal half (amino acids 853-1186) encompasses binding sites for RAD51, BRCA2, and DNA polymerase eta (POLH), consolidating PALB2's role as a multi-protein scaffold. A region spanning amino acids 775-1186 is specifically required for POLH interaction and stimulation of POLH-mediated DNA synthesis. The distribution of binding interfaces across the length of the protein suggests that PALB2 adopts an extended conformation when fully engaged with its partners, positioning catalytic activities at optimal proximity to the DNA substrate.
Key variants
Pathogenic variants in PALB2 include nonsense mutations, frameshift insertions or deletions, and splice-site alterations that result in loss of protein function. Missense variants cluster in the functional domains-particularly those mediating BRCA2 and BRCA1 binding-where single amino-acid substitutions can disrupt critical protein interfaces. Founder mutations have been identified in specific populations: for example, certain variants are recurrent in individuals of Finnish, French-Canadian, and Polish ancestry.
Variant interpretation follows ACMG/AMP guidelines, incorporating functional assays that assess homologous recombination capacity, BRCA2 binding, and localisation to DNA-damage foci. Loss-of-function variants are generally classified as pathogenic, whilst missense changes require additional evidence from segregation studies, case-control data, and experimental characterisation. Carriers of pathogenic PALB2 variants exhibit variable penetrance, with cancer risk modified by family history, hormonal exposures, and potentially other genetic factors (lifetime breast cancer risk estimates range from approximately 35% to over 60% depending on these factors).
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 |
|---|---|---|---|---|
g.(?_23603162)_(23603669_?)del | - | Pathogenic | ★★★☆ | PALB2-related cancer predisposition |
c.1592del | p.Leu531fs | Pathogenic | ★★★☆ | Familial cancer of breast |
c.2524_2535delinsTCAGA | p.Ala842fs | Pathogenic | ★★★☆ | Hereditary cancer-predisposing syndrome |
c.2787_2788dup | p.Asn930fs | Pathogenic | ★★★☆ | Familial cancer of breast |
c.3113G>A | p.Trp1038Ter | Pathogenic | ★★★☆ | Familial cancer of breast |
c.3350G>A | p.Arg1117Lys | Pathogenic | ★★★☆ | Hereditary cancer-predisposing syndrome |
c.3549C>A | p.Tyr1183Ter | Pathogenic | ★★★☆ | Hereditary cancer-predisposing syndrome |
c.514_517del | p.Ser172fs | Pathogenic | ★★★☆ | Familial cancer of breast |
c.532del | p.Glu178fs | Pathogenic | ★★★☆ | Familial cancer of breast |
c.682C>T | p.Gln228Ter | Pathogenic | ★★★☆ | Hereditary cancer-predisposing syndrome |
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
Heterozygous pathogenic variants in PALB2 confer increased breast cancer risk following an autosomal dominant inheritance pattern with incomplete penetrance. Women carrying a pathogenic PALB2 variant face substantially increased lifetime breast cancer risk, with estimates varying by family history and specific variant. Male breast cancer is also observed at elevated rates among PALB2 carriers, reflecting the gene's role in both sexes. Ovarian cancer risk is moderately increased, though less pronounced than in BRCA1 or BRCA2 carriers. Pancreatic cancer represents another important association, with PALB2 variants accounting for a measurable proportion of familial pancreatic cancer cases. Beyond cancer predisposition, biallelic (homozygous or compound heterozygous) PALB2 variants cause Fanconi anaemia subtype FA-N, a rare recessive disorder characterised by bone marrow failure, developmental anomalies, and extreme cancer susceptibility in childhood. This phenotypic spectrum-from adult-onset cancer predisposition in heterozygotes to severe childhood disease in biallelic carriers-underscores the gene's dosage sensitivity.
Inheritance pattern
Conditions caused by pathogenic PALB2 variants typically follow autosomal dominant inheritance.
Each child has a 50% chance of inheriting the pathogenic variant, regardless of sex.
UK clinical status
PALB2 is classified as a Tier 1 gene within the ACMG Secondary Findings list version 3.2, indicating high clinical actionability. PALB2 features on NHS Genomic Medicine Service cancer predisposition panels reflecting both the cancer risks in heterozygous carriers and the developmental phenotypes seen with biallelic variants. In the UK, PALB2 holds green (high-evidence) status on cancer predisposition panels including the Familial Breast Cancer panel, the Inherited Breast Cancer and Ovarian Cancer panel (R208), the Inherited Ovarian Cancer (without breast cancer) panel (R207), the Inherited Pancreatic Cancer panel (R367), and the Inherited Prostate Cancer panel (R430), reflecting its established role in female and male breast cancer predisposition as well as emerging evidence for risk in pancreatic and prostate cancers.
Beyond cancer susceptibility, PALB2 features on the Confirmed Fanconi Anaemia or Bloom Syndrome panel (R229), recognising its recessive role in Fanconi anaemia. It is additionally listed on paediatric panels including Childhood Solid Tumours (R359) and Childhood Solid Tumours Cancer Susceptibility, as well as general panels such as Adult Solid Tumours Cancer Susceptibility and Haematological Malignancies Cancer Susceptibility. The gene's presence on the DDG2P (Developmental Disorders Genotype-to-Phenotype) panel, Fetal Anomalies panel (R21), and Radial Dysplasia panel reflects the developmental phenotypes associated with biallelic variants. This extensive panel representation ensures that PALB2 variants identified in diverse clinical contexts trigger appropriate genetic counselling and management.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Diet & lifestyle considerations
Research into lifestyle factors and cancer risk in PALB2 variant carriers is evolving, though evidence remains less extensive than for BRCA1 or BRCA2. General population studies suggest that limiting alcohol intake may reduce breast cancer risk, and some data indicate this association may also apply to carriers of moderate-penetrance genes such as PALB2. Alcohol metabolism generates acetaldehyde, a DNA-damaging agent, which could theoretically impose additional stress on cells already compromised in homologous recombination.
Maintaining a healthy body weight has been associated with lower breast cancer incidence in the general population, particularly for postmenopausal disease. Whether body mass index modifies risk specifically in PALB2 carriers is not yet definitively established, but minimising excess adiposity aligns with broader cancer-prevention strategies. Physical activity demonstrates protective associations in large epidemiological studies, potentially through effects on hormone levels, insulin sensitivity, and immune function. Whilst no intervention trial has targeted PALB2 carriers specifically, these lifestyle measures are generally recommended as part of comprehensive risk management.
Avoiding smoking reduces additional mutagenic exposure and is particularly relevant given the pancreatic cancer risk in PALB2 carriers; tobacco use is a well-established pancreatic carcinogen. Reproductive and hormonal factors-such as age at first birth, breastfeeding duration, and use of combined hormonal contraception or hormone replacement therapy-may modulate breast cancer risk, though their specific impact in PALB2 carriers requires further study. Any lifestyle modification should be discussed with a healthcare provider within the context of an individualised risk-management plan.
Supplement considerations
There is no conclusive evidence that any dietary supplement can prevent cancer in individuals carrying pathogenic PALB2 variants. Some research has explored whether antioxidants such as vitamins C and E, or other micronutrients, might support DNA repair or reduce oxidative stress, but results from randomised trials in the general population have been inconsistent and sometimes suggest harm at high doses. Folic acid and other B vitamins participate in nucleotide synthesis and methylation pathways relevant to DNA maintenance, yet supplementation trials have not demonstrated clear cancer-preventive effects in high-risk groups.
Curcumin, resveratrol, and various polyphenols have been investigated for potential anti-cancer properties in laboratory models, but translation to human benefit-particularly in genetically predisposed individuals-remains unproven. Omega-3 fatty acids have attracted interest for anti-inflammatory effects, though evidence for breast or pancreatic cancer risk reduction is limited. Vitamin D status has been correlated with cancer outcomes in observational studies, but intervention trials have not confirmed a causal protective effect.
Anyone considering supplements should first consult a healthcare provider, as some compounds can interact with medications or investigational agents, and high-dose supplementation may carry unforeseen risks. A balanced diet rich in fruits, vegetables, whole grains, and lean proteins is generally advisable, but this should not be seen as a substitute for evidence-based surveillance or risk-reducing interventions appropriate for PALB2 carriers.
Frequently asked questions
What does PALB2 stand for?
PALB2 stands for 'partner and localizer of BRCA2', reflecting the protein's role in recruiting BRCA2 to sites of DNA damage and coordinating the repair of double-strand breaks.
How does PALB2 relate to BRCA1 and BRCA2?
PALB2 acts as a molecular bridge between BRCA1 and BRCA2, physically linking BRCA1 (which marks DNA-damage sites) to BRCA2 (which delivers the RAD51 recombinase for repair). This partnership is essential for accurate homologous recombination.
What cancers are associated with PALB2 variants?
Pathogenic PALB2 variants increase the risk of breast cancer in both women and men, ovarian cancer, and pancreatic cancer. The magnitude of risk varies by cancer type, family history, and specific variant.
Is PALB2 testing included in NHS cancer predisposition panels?
Yes, PALB2 is included on multiple NHS Genomic Medicine Service panels with green (high-evidence) status, including familial breast cancer, inherited ovarian cancer, and inherited pancreatic cancer panels. It is also part of the ACMG Secondary Findings list.
Can PALB2 variants cause conditions other than cancer?
Yes, individuals who inherit pathogenic PALB2 variants from both parents (biallelic carriers) can develop Fanconi anaemia subtype FA-N, a rare recessive disorder characterised by bone marrow failure, developmental anomalies, and very high childhood cancer risk. Heterozygous carriers do not develop Fanconi anaemia.
Are there specific populations with founder mutations in PALB2?
Yes, certain PALB2 pathogenic variants are found at higher frequencies in specific populations, including individuals of Finnish, French-Canadian, and Polish ancestry. Founder mutations arise when a variant becomes common in a population descended from a small ancestral group.