Defects in DNA repair can cause various genetic diseases with severe pathological phenotypes. Fanconi anemia (FA) is a rare disease characterized by bone marrow failure, developmental abnormalities, ...and increased cancer risk that is caused by defective repair of DNA interstrand crosslinks (ICLs). Here, we identify the deubiquitylating enzyme USP48 as synthetic viable for FA-gene deficiencies by performing genome-wide loss-of-function screens across a panel of human haploid isogenic FA-defective cells (FANCA, FANCC, FANCG, FANCI, FANCD2). Thus, as compared to FA-defective cells alone, FA-deficient cells additionally lacking USP48 are less sensitive to genotoxic stress induced by ICL agents and display enhanced, BRCA1-dependent, clearance of DNA damage. Consequently, USP48 inactivation reduces chromosomal instability of FA-defective cells. Our results highlight a role for USP48 in controlling DNA repair and suggest it as a potential target that could be therapeutically exploited for FA.
In the 1980s, a research team led by Parisian scientists identified several unique DNA sequences, or haplotypes, linked to sickle cell anemia in African populations. After casual observations of how ...patients managed this painful blood disorder, the researchers in question postulated that the Senegalese type was less severe. The Enculturated Gene traces how this genetic discourse has blotted from view the roles that Senegalese patients and doctors have played in making sickle cell "mild" in a social setting where public health priorities and economic austerity programs have forced people to improvise informal strategies of care.
There is much interest in the tissue of origin of circulating DNA in plasma. Data generated using DNA methylation markers have suggested that hematopoietic cells of white cell lineages are important ...contributors to the circulating DNA pool. However, it is not known whether cells of the erythroid lineage would also release DNA into the plasma.
Using high-resolution methylation profiles of erythroblasts and other tissue types, 3 genomic loci were found to be hypomethylated in erythroblasts but hypermethylated in other cell types. We developed digital PCR assays for measuring erythroid DNA using the differentially methylated region for each locus.
Based on the methylation marker in the ferrochelatase gene, erythroid DNA represented a median of 30.1% of the plasma DNA of healthy subjects. In subjects with anemia of different etiologies, quantitative analysis of circulating erythroid DNA could reflect the erythropoietic activity in the bone marrow. For patients with reduced erythropoietic activity, as exemplified by aplastic anemia, the percentage of circulating erythroid DNA was decreased. For patients with increased but ineffective erythropoiesis, as exemplified by β-thalassemia major, the percentage was increased. In addition, the plasma concentration of erythroid DNA was found to correlate with treatment response in aplastic anemia and iron deficiency anemia. Plasma DNA analysis using digital PCR assays targeting the other 2 differentially methylated regions showed similar findings.
Erythroid DNA is a hitherto unrecognized major component of the circulating DNA pool and is a noninvasive biomarker for differential diagnosis and monitoring of anemia.
Monoubiquitination and deubiquitination of FANCD2:FANCI heterodimer is central to DNA repair in a pathway that is defective in the cancer predisposition syndrome Fanconi anemia (FA). The “FA core ...complex” contains the RING-E3 ligase FANCL and seven other essential proteins that are mutated in various FA subtypes. Here, we purified recombinant FA core complex to reveal the function of these other proteins. The complex contains two spatially separate FANCL molecules that are dimerized by FANCB and FAAP100. FANCC and FANCE act as substrate receptors and restrict monoubiquitination to the FANCD2:FANCI heterodimer in only a DNA-bound form. FANCA and FANCG are dispensable for maximal in vitro ubiquitination. Finally, we show that the reversal of this reaction by the USP1:UAF1 deubiquitinase only occurs when DNA is disengaged. Our work reveals the mechanistic basis for temporal and spatial control of FANCD2:FANCI monoubiquitination that is critical for chemotherapy responses and prevention of Fanconi anemia.
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•Reconstitution of the Fanconi anemia (FA) pathway using recombinant proteins•FANCB dimer coordinates FANCD2:FANCI monoubiquitination by two FANCL RING-ligases•FANCC and FANCE provide FANCL specificity toward DNA-bound FANCD2:FANCI dimers•Deubiquitination of FANCD2:FANCI by USP1:UAF1 occurs only when DNA is removed
van Twest et al. report the biochemical reconstitution of FANCI:FANCD2 monoubiquitination by the Fanconi anemia core complex using only recombinant proteins. The authors uncover the mechanistic basis for temporal and spatial control of FANCD2:FANCI monoubiquitination that is critical for chemotherapy responses and prevention of Fanconi anemia.
Background
Most patients with anemia are diagnosed through clinical phenotype and basic laboratory testing. Nonetheless, in cases of rare congenital anemias, some patients remain undiagnosed despite ...undergoing an exhaustive workup. Genetic testing is complicated by the large number of genes involved in rare anemias and the similarities in the clinical presentation of the different syndromes.
Objective
We aimed to enhance the diagnosis of patients with congenital anemias by using targeted next‐generation sequencing.
Methods
Genetic diagnosis was performed by gene capture followed by next‐generation sequencing of 76 genes known to cause anemia syndromes.
Results
Genetic diagnosis was achieved in 13 out of 21 patients (62%). Six patients were diagnosed with pyruvate kinase deficiency, 4 with dehydrated hereditary stomatocytosis, 2 with sideroblastic anemia, and 1 with CDA type IV. Eight novel mutations were found. In 7 patients, the genetic diagnosis differed from the pretest presumed diagnosis. The mean lag time from presentation to diagnosis was over 13 years.
Conclusions
Targeted next‐generation sequencing led to an accurate diagnosis in over 60% of patients with rare anemias. These patients do not need further diagnostic workup. Earlier incorporation of this method into the workup of patients with congenital anemia may improve patients’ care and enable genetic counseling.
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