Analyzing the type and frequency of patient-specific mutations that give rise to Duchenne muscular dystrophy (DMD) is an invaluable tool for diagnostics, basic scientific research, trial planning, and improved clinical care. Locus-specific databases allow for the collection, organization, storage, and analysis of genetic variants of disease. Here, we describe the development and analysis of the TREAT-NMD DMD Global database (http://umd.be/TREAT_DMD/). We analyzed genetic data for 7,149 DMD mutations held within the database. A total of 5,682 large mutations were observed (80% of total mutations), of which 4,894 (86%) were deletions (1 exon or larger) and 784 (14%) were duplications (1 exon or larger). There were 1,445 small mutations (smaller than 1 exon, 20% of all mutations), of which 358 (25%) were small deletions and 132 (9%) small insertions and 199 (14%) affected the splice sites. Point mutations totalled 756 (52% of small mutations) with 726 (50%) nonsense mutations and 30 (2%) missense mutations. Finally, 22 (0.3%) mid-intronic mutations were observed. In addition, mutations were identified within the database that would potentially benefit from novel genetic therapies for DMD including stop codon read-through therapies (10% of total mutations) and exon skipping therapy (80% of deletions and 55% of total mutations).
Cellular responses to DNA damage reflect the dynamic integration of cell cycle control, cell–cell interactions and tissue-specific patterns of gene regulation that occurs in vivo but is not recapitulated in cell culture models. Here we describe use of the zebrafish embryo as a model system to identify determinants of the in vivo response to ionizing radiation-induced DNA damage. To demonstrate the utility of the model we cloned and characterized the embryonic function of the XRCC5 gene, which encodes Ku80, an essential component of the nonhomologous end joining pathway of DNA repair. After the onset of zygotic transcription, Ku80 mRNA accumulates in a tissue-specific pattern, which includes proliferative zones of the retina and central nervous system. In the absence of genotoxic stress, zebrafish embryos with reduced Ku80 function develop normally. However, low dose irradiation of these embryos during gastrulation leads to marked apoptosis throughout the developing central nervous system. Apoptosis is p53 dependent, indicating that it is a downstream consequence of unrepaired DNA damage. Results suggest that nonhomologous end joining components mediate DNA repair to promote survival of irradiated cells during embryogenesis.
Background: Recent short-term clinical trials in patients with Duchenne Muscular Dystrophy (DMD) have indicated greater disease variability in terms of progression than expected. In addition, as average life-expectancy increases, reliable data is req
Survival in Duchenne muscular dystrophy (DMD) has increased in recent years due to iterative improvements in care. We describe the results of the CARE-NMD survey of care practices for adults with DMD in the UK in light of international consensus care guidelines. We also compare the UK experience of adult care with the care available to pediatric patients and adults in other European countries (Germany, Denmark, Bulgaria, Czech Republic, Hungary, and Poland). UK adults experience less comprehensive care compared to children in their access to specialized clinics, frequency of cardiac and respiratory assessments, and access to professional physiotherapy. Access to the latter is especially poor when compared to other European adult cohorts. Although the total number of nights in hospital (planned and unplanned admissions) is lower among UK adults than elsewhere in Western Europe, social inclusion lags behind other Western European countries. We observe that attendance at specialized clinic is associated with more frequent cardiac and respiratory assessments among adults, in line with international best practice. Attendance at such clinics in the UK, though comparable to other countries, is still far from universal. With an increasing adult population living with DMD, and cardiac and respiratory failure the leading causes of death in this population, we suggest the need for an urgent improvement in adult access to specialized clinics and to consistent, comprehensive best practice care.
Nonhomologous end joining is the most common mechanism of DNA double-strand break repair in human cells. Here we show that nonhomologous end joining can occur by two biochemically distinct pathways. One requires a fraction containing the Mre11-Rad50-NBS1 complex. The other requires a fraction containing a novel, approximately 200-kDa factor that does not correspond to any of the previously described double-strand break repair proteins. The two pathways converge, sharing a common requirement for the DNA ligase IV-XRCC4 complex to catalyze the final step of phosphodiester bond formation. Whereas the Mre11-Rad50-NBS1-dependent pathway does not require, and may be inhibited by, DNA-dependent protein kinase-mediated phosphorylation, the new pathway depends on this phosphorylation for release from a DNA-dependent protein kinase-mediated reaction checkpoint. The existence of two distinct pathways, which are differentially regulated by the DNA-dependent protein kinase, provides a possible explanation for the selective repair defects seen in DNA-dependent protein kinase-deficient mutants.
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