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

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Importance of muscle biopsy to establish pathogenicity of DMD missense and splice variants
Neuromuscular Disorders ( IF 2.7 ) Pub Date : 2019-12-01 , DOI: 10.1016/j.nmd.2019.09.013
Hannah F Jones ₁ , Samantha J Bryen ₂ , Leigh B Waddell ₂ , Adam Bournazos ₂ , Mark Davis ₃ , Michelle A Farrar ₄ , Catriona A McLean ₅ , David R Mowat ₆ , Hugo Sampaio ₇ , Ian R Woodcock ₈ , Monique M Ryan ₈ , Kristi J Jones ₁ , Sandra T Cooper ₂

Affiliation

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.
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 Diagnostic Genomics, PathWest Laboratory Medicine, QEII Medical Centre, Perth, Western Australia, Australia.
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.
Anatomical Pathology and Victorian Neuromuscular Laboratory Service, Alfred Health and Monash University, Australia.
Centre for Clinical Genetics, Sydney Children's Hospital, Sydney, New South Wales, Australia.
Department of Neurology, Sydney Children's Hospital, Sydney, New South Wales, Australia.
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.

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.

中文翻译：

肌肉活检对确定 DMD 错义和剪接变异的致病性的重要性

对肌营养不良症的精确基因诊断对受影响的男孩及其家庭具有深远的影响。我们介绍了三个患有与贝克尔肌营养不良症相关的 DMD 单核苷酸变异的男孩，这些男孩表现为肌痛、运动能力降低、神经发育症状和肌酸激酶升高。DMD 变体难以分类： AIII：1 外显子 13 c.1602G>A，p.Lys534Lys 中的同义变体；BIII:1 是内含子 33 c.4674+1G>A 中的必需剪接位点变体，而 CII:1 是富含半胱氨酸结构域内的错义突变，外显子 66 c.9619T>C，p.Cys3207Arg。使用肌肉来源的 mRNA 进行的互补 DNA (cDNA) 分析确定了 AIII:1 和 BIII:1 变体的剪接改变效应，以及 CII:1 中的正常剪接。蛋白质印迹分析表明肌养蛋白水平轻度至中度降低 (17. 6 - 36.1% 的控制水平），支持肌营养不良症作为可能的诊断。这三个案例突出了肌肉活检在 mRNA 研究和蛋白质印迹中的诊断效用，通过探索对剪接和肌营养不良蛋白水平的影响来研究不确定致病性的 DMD 变异。

更新日期：2019-12-01

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