Importance of muscle biopsy to establish pathogenicity of DMD missense and splice variants

Hannah F Jones; Samantha J Bryen; Leigh B Waddell; Adam Bournazos; Mark Davis; Michelle A Farrar; Catriona A McLean; David R Mowat; Hugo Sampaio; Ian R Woodcock; Monique M Ryan; Kristi J Jones; Sandra T Cooper

doi:10.1016/j.nmd.2019.09.013

Importance of muscle biopsy to establish pathogenicity of DMD missense and splice variants

Neuromuscul Disord. 2019 Dec;29(12):913-919. doi: 10.1016/j.nmd.2019.09.013. Epub 2019 Sep 25.

Authors

Affiliations

¹ Kids Neuroscience Centre, The Children's Hospital at Westmead, Sydney, New South Wales 2145, Australia; Discipline of Child and Adolescent Health, University of Sydney, Sydney, New South Wales, Australia; Department of Clinical Genetics, Children's Hospital at Westmead, Sydney, New South Wales, Australia.
² Kids Neuroscience Centre, The Children's Hospital at Westmead, Sydney, New South Wales 2145, Australia; Discipline of Child and Adolescent Health, University of Sydney, Sydney, New South Wales, Australia.
³ Department of Diagnostic Genomics, PathWest Laboratory Medicine, QEII Medical Centre, Perth, Western Australia, Australia.
⁴ Department of Neurology, Sydney Children's Hospital, Sydney, New South Wales, Australia; Discipline of Paediatrics, School of Women's and Children's Health, UNSW Medicine, UNSW Sydney, New South Wales, Australia.
⁵ Anatomical Pathology and Victorian Neuromuscular Laboratory Service, Alfred Health and Monash University, Australia.
⁶ Centre for Clinical Genetics, Sydney Children's Hospital, Sydney, New South Wales, Australia.
⁷ Department of Neurology, Sydney Children's Hospital, Sydney, New South Wales, Australia.
⁸ Department of Neurology Royal Children's Hospital, Murdoch Childrens Research Institute and University of Melbourne, Parkville, Victoria, Australia; Murdoch Childrens Research Institute, Melbourne, Victoria, Australia.
⁹ Kids Neuroscience Centre, The Children's Hospital at Westmead, Sydney, New South Wales 2145, Australia; Discipline of Child and Adolescent Health, University of Sydney, Sydney, New South Wales, Australia. Electronic address: [email protected].

PMID: 31706698
DOI: 10.1016/j.nmd.2019.09.013

Abstract

A precise genetic diagnosis of a dystrophinopathy has far-reaching implications for affected boys and their families. We present three boys with DMD single nucleotide variants associated with Becker muscular dystrophy presenting with myalgia, reduced exercise capacity, neurodevelopmental symptoms and elevated creatine kinase. The DMD variants were difficult to classify: AIII:1 a synonymous variant in exon 13 c.1602G>A, p.Lys534Lys; BIII:1 an essential splice-site variant in intron 33 c.4674+1G>A, and CII:1 a missense mutation within the cysteine-rich domain, exon 66 c.9619T>C, p.Cys3207Arg. Complementary DNA (cDNA) analysis using muscle-derived mRNA established splice-altering effects of variants for AIII:1 and BIII:1, and normal splicing in CII:1. Western blot analysis demonstrated mildly to moderately reduced dystrophin levels (17.6 - 36.1% the levels of controls), supporting dystrophinopathy as a probable diagnosis. These three cases highlight the diagnostic utility of muscle biopsy for mRNA studies and western blot to investigate DMD variants of uncertain pathogenicity, by exploring effects on splicing and dystrophin protein levels.

Keywords: Becker muscular dystrophy; Duchenne muscular dystrophy; Missense variants; Muscle biopsy; Splice variants; mRNA studies.

Publication types

Case Reports

MeSH terms

Adolescent
Adult
Biopsy
Blood Proteins / genetics*
Creatine Kinase / blood
Diagnosis, Differential
Family
Humans
Male
Muscle, Skeletal / pathology*
Muscular Dystrophy, Duchenne / diagnosis
Muscular Dystrophy, Duchenne / genetics*
Muscular Dystrophy, Duchenne / pathology*
Mutation, Missense*
RNA Splicing*

Substances

Blood Proteins
DMD circulating plasma factor
Creatine Kinase