Fanconi anemia with sun-sensitivity caused by a Xeroderma pigmentosum-associated missense mutation in XPF

Two siblings with Fanconi anemia (FANCQ, ERCC4/XPF) presenting with tumor-mimicking lesions in the brain and acute neurological deterioration

The complementation Q group (FANCQ) subtype of Fanconi anemia (FA) caused by the ERCC4/XPF mutation is very rare. Two siblings, aged 13 and 10 with Fanconi phenotypic features, presented with right hemiparesis and focal-onset seizures. In both cases, cranial magnetic resonance imaging (MRI) showed mass-like lesions accompanied by peripheral edema and calcification. In one case, oral steroid treatment and surgical excision were performed, while in the other case, the cranial lesion regressed just with steroid treatment and without surgery. Both siblings remained wheelchair-bound due to neurological dysfunction. One case died due to hepatocellular carcinoma. ERCC4/XPF gene mutation was detected in both siblings.

DNA Damage Response and Mismatch Repair Gene Defects in Advanced and Metastatic Prostate Cancer

Alterations in DNA damage response (DDR) and related genes are present in up to 25% of advanced prostate cancers (PCa). Most frequently altered genes are involved in the homologous recombination repair, the Fanconi anemia, and the mismatch repair pathways, and their deficiencies lead to a highly heterogeneous spectrum of DDR-deficient phenotypes. More than half of these alterations concern non- BRCA DDR genes. From a therapeutic perspective, poly-ADP-ribose polymerase inhibitors have demonstrated robust clinical efficacy in tumors with BRCA2 and BRCA1 alterations. Mismatch repair-deficient PCa, and a subset of CDK12-deficient PCa, are vulnerable to immune checkpoint inhibitors. Emerging data point to the efficacy of ATR inhibitors in PCa with ATM deficiencies. Still, therapeutic implications are insufficiently clarified for most of the non- BRCA DDR alterations, and no successful targeted treatment options have been established.

Therapeutic implications of germline vulnerabilities in DNA repair for precision oncology

DNA repair vulnerabilities are present in a significant proportion of cancers. Specifically, germline alterations in DNA repair not only increase cancer risk but are associated with treatment response and clinical outcomes. The therapeutic landscape of cancer has rapidly evolved with the FDA approval of therapies that specifically target DNA repair vulnerabilities. The clinical success of synthetic lethality between BRCA deficiency and poly(ADP-ribose) polymerase (PARP) inhibition has been truly revolutionary. Defective mismatch repair has been validated as a predictor of response to immune checkpoint blockade associated with durable responses and long-term benefit in many cancer patients. Advances in next generation sequencing technologies and their decreasing cost have supported increased genetic profiling of tumors coupled with germline testing of cancer risk genes in patients. The clinical adoption of panel testing for germline assessment in high-risk individuals has generated a plethora of genetic data, particularly on DNA repair genes. Here, we highlight the therapeutic relevance of germline aberrations in DNA repair to identify patients eligible for precision treatments such as PARP inhibitors (PARPis), immune checkpoint blockade, chemotherapy, radiation therapy and combined treatment. We also discuss emerging mechanisms that regulate DNA repair.

Revisiting the structural features of the xeroderma pigmentosum proteins: Focus on mutations and knowledge gaps

The nucleotide excision repair pathway is a broadly studied DNA repair mechanism because impairments of its key players, the xeroderma pigmentosum proteins (XPA to XPG), are associated with multiple hereditary diseases. Due to the massive number of novel mutations reported for these proteins and new structural data published every year, proper categorization and discussion of relevant observations is needed to organize this extensive inflow of knowledge. This review aims to revisit the structural data of all XP proteins while updating it with the information developed in of the past six years. Discussions and interpretations of mutation outcomes, mechanisms of action, and knowledge gaps regarding their structures are provided, as well as new perspectives based on recent research.

The Fanconi anemia pathway and Breast Cancer: A comprehensive review of clinical data

The development of breast cancer depends on several risk factors, including environmental, lifestyle and genetic factors. Despite the evolution of DNA sequencing techniques and biomarker detection, the epidemiology and mechanisms of various breast cancer susceptibility genes have not been elucidated yet. Dysregulation of the DNA damage response causes genomic instability and increases the rate of mutagenesis and the risk of carcinogenesis. The Fanconi Anemia (FA) pathway is an important component of the DNA damage response and plays a critical role in the repair of DNA interstrand crosslinks and genomic stability. The FA pathway involves 22 recognized genes and specific mutations have been identified as the underlying defect in the majority of FA patients. A thorough understanding of the function and epidemiology of these genes in breast cancer is critical for the development and implementation of individualized therapies that target unique tumor profiles. Targeted therapies (PARP inhibitors) exploiting the FA pathway gene defects have been developed and have shown promising results. This narrative review summarizes the current literature on the involvement of FA genes in sporadic and familial breast cancer with a focus on clinical data derived from large cohorts.

DNA cross-link repair safeguards genomic stability during premeiotic germ cell development

Germline de novo mutations are the basis of evolutionary diversity but also of genetic disease. However, the molecular origin, mechanisms and timing of germline mutagenesis are not fully understood. Here, we define a fundamental role for DNA interstrand cross-link repair in the germline. This repair process is essential for primordial germ cell (PGC) maturation during embryonic development. Inactivation of cross-link repair leads to genetic instability that is restricted to PGCs within the genital ridge during a narrow temporal window. Having successfully activated the PGC transcriptional program, a potent quality control mechanism detects and drives damaged PGCs into apoptosis. Therefore, these findings define a source of DNA damage and the nature of the subsequent DNA repair response in germ cells, which ensures faithful transmission of the genome between generations.

Impact of XPF rs2276466 polymorphism on cancer susceptibility: a meta-analysis

Association between the xeroderma pigmentosum complementation group F (XPF)rs2276466 located in the excision repair cross complementation group 4 (ERCC4) gene and cancer susceptibility has been widely investigated. However, results thus far have remained controversial. A meta-analysis was performed to identify the impact of this polymorphism on cancer susceptibility. PubMed, Embase and Science-Web databases were searched systematically up to May 20, 2018, to obtain all the records evaluating the association between the rs2276466 polymorphism and the risk of all types of cancers. We used the odds ratio (OR) as a measure of effect, and pooled the data in a Mantel-Haenszel weighed random-effects meta-analysis to provide a summary estimate of the impact of this polymorphism on gastrointestinal cancer, neurogenic cancer and other cancers (breast cancer and SCCHN). All the analyses were carried out in STATA 14.1.11 case–control studies that consisted of 5730 cases and 6756 controls, were eventually included in our meta-analysis. The significant association was observed between the XPFrs2276466 polymorphism and neurogenic cancer susceptibility (recessive model: OR = 1.648, 95% CI = 1.294–2.098, P<0.001). Furthermore, no significant impact of this polymorphism was detected on decreased gastrointestinal cancer risk (dominant model: OR = 1.064, 95%CI = 0.961–1.177, P = 0.233). The rs2276466 polymorphism might play different roles in carcinogenesis of various cancer types. Current evidence did not suggest that this polymorphism was directly associated with gastrointestinal susceptibility. However, this polymorphism might contribute to increased neurogenic cancer risk. More preclinical and epidemiological studies are still imperative for further evaluation

Heterogeneity and overlaps in nucleotide excision repair disorders

Nucleotide excision repair (NER) is an essential DNA repair pathway devoted to the removal of bulky lesions such as photoproducts induced by the ultraviolet (UV) component of solar radiation. Deficiencies in NER typically result in a group of heterogeneous distinct disorders ranging from the mild UV sensitive syndrome to the cancer-prone xeroderma pigmentosum and the neurodevelopmental/progeroid conditions trichothiodystrophy, Cockayne syndrome and cerebro-oculo-facio-skeletal-syndrome. A complicated genetic scenario underlines these disorders with the same gene linked to different clinical entities as well as different genes associated with the same disease. Overlap syndromes with combined hallmark features of different NER disorders can occur and sporadic presentations showing extra features of the hematological disorder Fanconi Anemia or neurological manifestations mimicking Hungtinton disease-like syndromes have been described. Here, we discuss the multiple functions of the five major pleiotropic NER genes (ERCC3/XPB, ERCC2/XPD, ERCC5/XPG, ERCC1 and ERCC4/XPF) and their relevance in phenotypic complexity. We provide an update of mutational spectra and examine genotype-phenotype relationships. Finally, the molecular defects that could explain the puzzling overlap syndromes are discussed.

Functional Comparison of XPF Missense Mutations Associated to Multiple DNA Repair Disorders

XPF endonuclease is one of the most important DNA repair proteins. Encoded by XPF/ERCC4, XPF provides the enzymatic activity of XPF-ERCC1 heterodimer, an endonuclease that incises at the 5’ side of various DNA lesions. XPF is essential for nucleotide excision repair (NER) and interstrand crosslink repair (ICLR). XPF/ERCC4 mutations are associated with several human diseases: Xeroderma Pigmentosum (XP), Segmental Progeria (XFE), Fanconi Anemia (FA), Cockayne Syndrome (CS), and XP/CS combined disease (XPCSCD). Most affected individuals are compound heterozygotes for XPF/ERCC4 mutations complicating the identification of genotype/phenotype correlations. We report a detailed overview of NER and ICLR functional studies in human XPF-KO (knock-out) isogenic cells expressing six disease-specific pathogenic XPF amino acid substitution mutations. Ultraviolet (UV) sensitivity and unscheduled DNA synthesis (UDS) assays provide the most reliable information to discern mutations associated with ICLR impairment from mutations related to NER deficiency, whereas recovery of RNA synthesis (RRS) assays results hint to a possible role of XPF in resolving R-loops. Our functional studies demonstrate that a defined cellular phenotype cannot be easily correlated to each XPF mutation. Substituted positions along XPF sequences are not predictive of cellular phenotype nor reflect a particular disease. Therefore, in addition to mutation type, allelic interactions, protein stability and intracellular distribution of mutant proteins may also contribute to alter DNA repair pathways balance leading to clinically distinct disorders.

A Homozygous Missense Mutation in FANCA Gene in a 46,XY Female with Gonadal Dysgenesis

Fanconi anemia (FA) is a pleiotropic condition with 2 characteristic phenotypic markers of hematological and cytogenetic changes. The phenotype of patients with FA is very heterogeneous, associated with an array of congenital malformations affecting the skeletal, renal, genital, and/or central nervous systems. Here, we report on a 46,XY female who presented with gonadal dysgenesis and microcephaly. Exome sequencing showed that she was homozygous for a rare variant in the FANCA gene (c.4232C>T, p.P1411L, rs201494304). Both parents were heterozygous for the mutation. The FA mutation was associated with an atypical clinical presentation, and thus exome sequencing provided essential data that otherwise would have been overlooked in the diagnosis of this patient.