Ataxia-telangiectasia-like disorder in a family deficient for MRE11A, caused by a MRE11 variant

The Neglected Sibling: NLRP2 Inflammasome in the Nervous System

While classical NOD-like receptor pyrin domain containing protein 1 (NLRP1) and NLRP3 inflammasomal proteins have been extensively investigated, the contribution of NLRP2 is still ill-defined in the nervous system. Given the putative significance of NLRP2 in orchestrating neuroinflammation, further inquiry is needed to gain a better understanding of its connectome, hence its specific targeting may hold a promising therapeutic implication. Therefore, bioinformatical approach for extracting information, specifically in the context of neuropathologies, is also undoubtedly preferred. To the best of our knowledge, there is no review study selectively targeting only NLRP2. Increasing, but still fragmentary evidence should encourage researchers to thoroughly investigate this inflammasome in various animal- and human models. Taken together, herein we aimed to review the current literature focusing on the role of NLRP2 inflammasome in the nervous system and more importantly, we provide an algorithm-based protein network of human NLRP2 for elucidating potentially valuable molecular partnerships that can be the beginning of a new discourse and future therapeutic considerations.

Gene-Level Associations in Patients With and Without Pathogenic Germline Variants in CDKN2A and Pancreatic Cancer

PURPOSE

Pancreatic ductal adenocarcinoma (PDAC) is a component of familial melanoma due to germline pathogenic variants (GPVs) in CDKN2A. However, it is unclear what role this gene or other genes play in its etiology.

MATERIALS AND METHODS

We analyzed 189 cancer predisposition genes using parametric rare-variant association (RVA) tests and nonparametric permutation tests to identify gene-level associations in PDAC for patients with (CDKN2A+) and without (CDKN2A-) GPV. Exome sequencing was performed on 84 patients with PDAC, 47 CDKN2A+ and 37 CDKN2A-. After variant filtering, various RVA tests and permutation tests were run separately by CDKN2A status. Genes with the strongest nominal associations were evaluated in patients with PDAC from The Cancer Genome Atlas and the UK Biobank (UKB). A secondary analysis including only GPV from UKB was also performed.

RESULTS

In RVA tests, ERCC4 and RET showed the most compelling evidence as plausible PDAC candidate genes for CDKN2A+ patients. In contrast, the findings in CDKN2A- patients provided evidence for HMBS, EPCAM, and MRE11 as potential new candidate genes and confirmed ATM, BRCA2, and PALB2 as PDAC genes, consistent with findings in The Cancer Genome Atlas and the UKB. As expected, CDKN2A- patients were more likely to harbor GPVs from the 189 genes investigated. When including only GPVs from UKB, significant associations with PDAC were seen for ATM, BRCA2, and CDKN2A.

CONCLUSION

These results suggest that variants in other genes likely play a role in PDAC in all patients and that PDAC in CDKN2A+ patients has a distinct etiology from PDAC in CDKN2A- patients.

RFC1-Related Disease

In 2019, a biallelic pentanucleotide repeat expansion in the gene encoding replication factor C subunit 1 (RFC1) was reported as a cause of cerebellar ataxia with neuropathy and vestibular areflexia syndrome (CANVAS). In addition, biallelic expansions were shown to account for up to 22% of cases with late-onset ataxia. Since this discovery, the phenotypic spectrum reported to be associated with RFC1 expansions has extended beyond the initial conditions to include pure cerebellar ataxia, isolated somatosensory impairment, combinations of the 2, and parkinsonism, leading to a potentially broad differential diagnosis. Genetic studies suggest RFC1 expansions may be the most common genetic cause of ataxia and are likely underdiagnosed. This review summarizes the current molecular and clinical knowledge of RFC1-related disease, with a focus on the evaluation of recent phenotype associations and highlighting the current challenges in clinical pathways to diagnosis and molecular testing.

An in-silico analysis to identify structural, functional and regulatory role of SNPs in hMRE11

Meiotic recombination 11 (MRE11) is a component of the tri-molecular MRE11-RAD50-NBS1 (MRN) complex, which functions as an exonuclease and endonuclease which is involved in identifying, signalling, protecting and repairing double-strand breaks in DNA (DSBs). Ataxia-telangiectasia-like disorder (ATLD) 1 and Nijmegen breakage syndrome (NBS)-like disorder are MRE11 associated diseases. In the present study, we used an integrated computational approach to identify the most deleterious SNPs and their structural and functional impact on human MRE11. Five of the 68 observed non-synonymous SNP (nsSNPs; I162T, S273C, W210C, D311Y and R364L) should be worked on due to their strong possible pathogenicity and the risk of changing protein properties. All the nsSNPs were highly conserved and decrease the protein stability located in the MRE11 nuclease and MRE11 DNA binding presumed domain. R364L and I162T were predicted to be involved in post-translational modification (PTM) sites. Furthermore, we also analysed the regulatory effect of noncoding SNPs on MRE11 gene regulation in which 6 SNPs were found to affect gene regulation. All six noncoding SNPs predicted chromatin interactive site whereas only one SNP was noted its association with miRNA binding site which disrupts 5 miRNA conserved site. These findings help future studies to get more insights into the role of these variants in the alteration of the MRE11 function. Communicated by Ramaswamy H. Sarma.

A novel, ataxic mouse model of ataxia telangiectasia caused by a clinically relevant nonsense mutation

Ataxia Telangiectasia (A-T) and Ataxia with Ocular Apraxia Type 1 (AOA1) are devastating neurological disorders caused by null mutations in the genome stability genes, A-T mutated (ATM) and Aprataxin (APTX), respectively. Our mechanistic understanding and therapeutic repertoire for treating these disorders are severely lacking, in large part due to the failure of prior animal models with similar null mutations to recapitulate the characteristic loss of motor coordination (i.e., ataxia) and associated cerebellar defects. By increasing genotoxic stress through the insertion of null mutations in both the Atm (nonsense) and Aptx (knockout) genes in the same animal, we have generated a novel mouse model that for the first time develops a progressively severe ataxic phenotype associated with atrophy of the cerebellar molecular layer. We find biophysical properties of cerebellar Purkinje neurons (PNs) are significantly perturbed (e.g., reduced membrane capacitance, lower action potential [AP] thresholds, etc.), while properties of synaptic inputs remain largely unchanged. These perturbations significantly alter PN neural activity, including a progressive reduction in spontaneous AP firing frequency that correlates with both cerebellar atrophy and ataxia over the animal’s first year of life. Double mutant mice also exhibit a high predisposition to developing cancer (thymomas) and immune abnormalities (impaired early thymocyte development and T-cell maturation), symptoms characteristic of A-T. Finally, by inserting a clinically relevant nonsense-type null mutation in Atm, we demonstrate that Small Molecule Read-Through (SMRT) compounds can restore ATM production, indicating their potential as a future A-T therapeutic.

MRN Complex and Cancer Risk: Old Bottles, New Wine

The MRN complex, composed of MRE11A, RAD50, and NBN, mediates vital molecular functions to maintain genomic stability and hence protect against related disorders. Germline mutations in the MRN genes predispose to three different syndromes: ataxia-telangiectasia-like disorder (MRE11A deficiency), Nijmegen breakage syndrome (NBS; NBN deficiency), and NBS-like disorder (RAD50 deficiency). The potential cancer component of these syndromes in addition to the close physical and functional proximity of the MRN complex to BRCA1 has promoted the MRN genes as candidate risk genes for developing breast cancer. This notion has been challenged by independent large-scale population-based studies. Despite having their two-decade old candidacy as breast cancer genes close to being refuted, it has recently been reported that the MRN genes rise to have potential new roles in clonal hematopoiesis. In this article, we discuss the history and current status of MRN genes' clinical utility in breast cancer and then focus on their recently uncovered and less understood roles in clonal hematopoiesis that likely predispose to health-related disorders such as hematologic malignancies and/or cardiovascular morbid events.

Post-Translational Modification of MRE11: Its Implication in DDR and Diseases

Maintaining genomic stability is vital for cells as well as individual organisms. The meiotic recombination-related gene MRE11 (meiotic recombination 11) is essential for preserving genomic stability through its important roles in the resection of broken DNA ends, DNA damage response (DDR), DNA double-strand breaks (DSBs) repair, and telomere maintenance. The post-translational modifications (PTMs), such as phosphorylation, ubiquitination, and methylation, regulate directly the function of MRE11 and endow MRE11 with capabilities to respond to cellular processes in promptly, precisely, and with more diversified manners. Here in this paper, we focus primarily on the PTMs of MRE11 and their roles in DNA response and repair, maintenance of genomic stability, as well as their association with diseases such as cancer.

MRN complex is an essential effector of DNA damage repair

Genome stability can be threatened by both endogenous and exogenous agents. Organisms have evolved numerous mechanisms to repair DNA damage, including homologous recombination (HR) and non-homologous end joining (NHEJ). Among the factors associated with DNA repair, the MRE11-RAD50-NBS1 (MRN) complex (MRE11-RAD50-XRS2 in Saccharomyces cerevisiae) plays important roles not only in DNA damage recognition and signaling but also in subsequent HR or NHEJ repair. Upon detecting DNA damage, the MRN complex activates signaling molecules, such as the protein kinase ataxia-telangiectasia mutated (ATM), to trigger a broad DNA damage response, including cell cycle arrest. The nuclease activity of the MRN complex is responsible for DNA end resection, which guides DNA repair to HR in the presence of sister chromatids. The MRN complex is also involved in NHEJ, and has a species-specific role in hairpin repair. This review focuses on the structure of the MRN complex and its function in DNA damage repair.

Beyond Typical Ataxia Telangiectasia: How to Identify the Ataxia Telangiectasia-Like Disorders

BACKGROUND

Ataxia telangiectasia is one of the most common causes of autosomal recessive cerebellar ataxias. However, absence of telangiectasia, normal levels of alpha-fetoprotein and negative genetic test may direct to alternative diagnosis with similar phenotypes such as ataxia telangiectasia-like disorders (ATLD).

CASES

We report two instructive cases of ATLD: the first case with ataxia telangiectasia-like disorder type 1 related to MRE11A gene, and the second case with ataxia telangiectasia-like disorder type 2 related to PCNA gene.

LITERATURE REVIEW

ATLD is an unusual group of autosomal recessive diseases that share some clinical features and pathophysiological mechanisms with ataxia telangiectasia (AT). ATLD may be associated with mutations in the MRE11A (ATLD type 1) and PCNA (ATLD type 2) genes. ATLD belongs to the group of chromosomal instability syndromes. The reason for the term ATLD is related to the similar pathophysiological mechanisms observed in AT, which is characterized by chromosomal instability and radiosensitivity.

CONCLUSIONS

In this review, the main clinical features, biomarkers, brain imaging and genetics of ATLD are discussed. Mutations in the MRE11A and PCNA genes should be included in the differential diagnosis for early onset cerebellar ataxia with absence of telangiectasia and normal levels of alpha-fetoprotein.

A Survey of Reported Disease-Related Mutations in the MRE11-RAD50-NBS1 Complex

The MRE11-RAD50-NBS1 (MRN) protein complex is one of the primary vehicles for repairing DNA double strand breaks and maintaining the genomic stability within the cell. The role of the MRN complex to recognize and process DNA double-strand breaks as well as signal other damage response factors is critical for maintaining proper cellular function. Mutations in any one of the components of the MRN complex that effect function or expression of the repair machinery could be detrimental to the cell and may initiate and/or propagate disease. Here, we discuss, in a structural and biochemical context, mutations in each of the three MRN components that have been associated with diseases such as ataxia telangiectasia-like disorder (ATLD), Nijmegen breakage syndrome (NBS), NBS-like disorder (NBSLD) and certain types of cancers. Overall, deepening our understanding of disease-causing mutations of the MRN complex at the structural and biochemical level is foundational to the future aim of treating diseases associated with these aberrations.

Hematopoietic Stem Cell Transplantation for DNA Double Strand Breakage Repair Disorders

The ubiquitous presence of enzymes required for repair of DNA double strand breaks renders patients with defects in these pathways susceptible to immunodeficiency, an increased risk of infection, autoimmunity, bone marrow failure and malignancies, which are commonly associated with Epstein Barr virus (EBV) infection. Treatment of malignancies is particularly difficult, as the nature of the systemic defect means that patients are sensitive to chemotherapy and radiotherapy. Increasing numbers of patients with Nijmegen Breakage syndrome, Ligase 4 deficiency and Cernunnos-XLF deficiency have been successfully transplanted. Best results are obtained with the use of reduced intensity conditioning. Patients with ataxia-telangiectasia have particularly poor outcomes and the best treatment approach for these patients is still to be determined.