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Published on: May 24, 2016
WGS and RNA Studies Diagnose Noncoding DMD Variants in Males With High Creatine Kinase
Leigh B Waddell1, Samantha J Bryen1, Beryl B Cummings1
1Kids Neuroscience Centre (L.B.W., S.J.B., A.B., F.J.E., H.J., S.A.S., G.L.O., E.C.O., N.F.C., K.J.J., S.T.C.), Kids Research Institute, The Children's Hospital at Westmead, New South Wales, Australia; Discipline of Child and Adolescent Health (L.B.W., S.J.B., A.B., F.J.E., S.A.S., G.L.O., E.C.O., N.F.C., K.J.J., S.T.C.), Faculty of Medicine and Health, The University of Sydney, Westmead, New South Wales, Australia; Analytic and Translational Genetics Unit (B.B.C., J.L.M., T.T., E.V., D.G.M., M.L.), Massachusetts General Hospital, Boston; Medical and Population Genetics (B.B.C., J.L.M., T.T., E.V., B.W., S.S., D.G.M., M.L.), and Center for Mendelian Genomics (B.B.C., J.L.M., E.V., B.W., S.S., D.G.M., M.L.), Broad Institute of MIT & Harvard, Cambridge, MA; Functional Neuromics (F.J.E., S.T.C.), Children's Medical Research Institute, Westmead, New South Wales, Australia; Murdoch Children's Research Institute (S.S.), Parkville, Victoria, Australia; Department of Diagnostic Genomics (M.R.D., F.F., R.G.), PathWest Laboratory Medicine WA, Nedlands, Australia; Department of Clinical Genetics (S.A.S., A.M., K.J.J.), Children's Hospital at Westmead, New South Wales, Australia; Department of Genetic Medicine (M.C.T.), Westmead Hospital, New South Wales, Australia; Discipline of Genomic Medicine (M.C.T., A.M.), Sydney Medical School, The University of Sydney, New South Wales, Australia; Centre for Clinical Genetics (D.R.M.), Sydney Children's Hospital, Randwick, New South Wales, Australia; School of Women's and Children's Health (D.R.M., M.A.F.), UNSW Medicine, UNSW Sydney, Australia; Department of Neurology (M.A.F., H.S.), Sydney Children's Hospital, Randwick, New South Wales, Australia; Department of Clinical Genetics (A.M.), Nepean Hospital, Sydney, Australia; Genetic Health Service NZ (K.N.), Wellington, New Zealand; Neurology Laboratory (M.-X.W.), Royal Prince Alfred Hospital, Camperdown, New South Wales, Australia; Central Clinical School (M.-X.W.), Faculty of Medicine and Health, The University of Sydney, Camperdown, New South Wales, Australia; Anatomic Pathology (A.C., C.C., N.G., S.A.), The Children's Hospital at Westmead, New South Wales, Australia; Anatomic Pathologist (D.N.K.), Department of Pathology and Molecular Medicine, University of Otago, Wellington, New Zealand; and Harvard Medical School (D.G.M.), Boston, MA.
Whole-genome sequencing and RNA studies identified genetic variants in the DMD gene for boys with suspected dystrophinopathy. Dystrophin levels correlate with disease severity, from Duchenne to myalgia.
Area of Science:
- Genetics
- Molecular Biology
- Neuromuscular Disorders
Background:
- Dystrophinopathies, including Duchenne and Becker muscular dystrophies, are genetic disorders affecting muscle function.
- Diagnostic challenges exist for identifying causative genetic variants, especially when standard methods fail.
- Understanding the relationship between dystrophin levels and clinical presentation is crucial for diagnosis and potential therapies.
Purpose of the Study:
- To evaluate the diagnostic utility of whole-genome sequencing and RNA studies in boys with suspected dystrophinopathy.
- To identify critical levels of wild-type dystrophin that correlate with different clinical phenotypes, ranging from Duchenne to myalgia.
- To assess the effectiveness of PCR of muscle cDNA for diagnosing DMD variants.
Main Methods:
- Whole-genome sequencing and muscle RNA sequencing were performed on 7 males with elevated creatine kinase.
- PCR of muscle complementary DNA (cDNA) was used to analyze dystrophin (DMD) pre-messenger RNA (pre-mRNA) splicing.
- Quantitative Western blot was employed to determine dystrophin protein levels relative to controls.
Main Results:
- Splice-altering variants in the DMD gene were identified in all 7 families.
- Four individuals showed remnant normally spliced DMD mRNA due to abnormal splicing and nonsense-mediated decay.
- Quantitative Western blot revealed correlations: 0-5% dystrophin for Duchenne, 10%±2% for Becker, and 15%±2% for myalgia without weakness.
Conclusions:
- Whole-genome sequencing combined with RNA studies effectively identified DMD splice-altering variants, though RNA sequencing faced challenges with the large DMD gene.
- PCR of muscle cDNA proved to be a simple and informative diagnostic method.
- A fractional increase in normal dystrophin levels between 5% and 20% is clinically significant, aligning with previous findings and informing genetic therapy strategies.

