Ciinicai Phenotypes And Gene Mutation Analysis Of Duchenne/Bccker Muscular Dystrophy

ObjectiveDuchenne muscular dystrophy (DMD; OMIM#310200) and Becker musculardystrophy (BMD; OMIM#3003376) are X-Linked recessive disorders occurring in1:3000to1:6000male births. Both DMD and BMD are caused by defects in thedystrophin gene Located at Xp21.2, which encodes a14-kb transcript and composed of79exons, spanning more than2200kb of genomic DNA.The mutational spectrum of the dystrophin gene is complex, including exonic copynumber variations and small mutations confined mostly to coding exons and deepintronic mutations. Deletion of one or more exons account for approximately60-70%ofmutations. A Larger duplication may Lead to in-frame or out-of-frame transcripts andaccount for5-10%of mutations. Small mutations (small deletions or insertions,single-base changes, and splicing mutations) account for approximately25%-35%ofmutations in males with DMD and about10%-20%of males with BMDIn order to analyses the dystrophy gene mutation types and size variation, anddiscuss the DMD/BMD molecular genetic diagnosis strategy, more two methods wereperformed to detect the DMD gene in Duchenne/Becker muscular dystrophy patients,Methods（1） Children with creatine kinase level abnormal, progressive muscle weakness andmovement function back to the chief who saw a doctor in our hospital werechosen form June2011to May2012, patients were diagnosed DMD/BMD,whoconformed to the rules according to the onset age, Gower ’s character positive, false of the gastronomies muscle hypertrophy, elevated levels of serum creatinekinase.（2） Multiplex Ligation-dependent probe amplification (MLPA) and Next-generationsequencing (NGS) were applied for detecting genetic disorders of patients withclinical suspected DMD/BMD.（3） Sanger sequencing technologies were performed to confirm.Results（1） There24cases were DMD, and4ones BMD.（2） Pathogenic mutations detection was performed in28cases with DMD.22positive results in28cases were detected by MLPA, and16of the22cases withdeLetione,4cases with duplication, combine delete and duplicate mutationswere find out in other2cases.（3） NGS technology were performed to detect5cases with MLPA(+) and6caseswith MLPA(-),which were chosen optionally.3cases were detected the mutationLocation and the size of deletion(exon51deL，chrX:31779857-31795289；exon53deL， chrX:31685440-31747548； exon51-55deL，chrX:31632504-31827732) and2ones duplication(exon45dup，chrX:31970766-32023816；exon55dup，chrX:31540860-31649750), which were consistent withMLPA.（4） Sanger sequencing was confirmed to the deletion mutations and point mutations.（5） In28cases, except1case of disease-causing gene mutation was detected, therewere25cases children with DMD/BMD clinical phenotype and genotyperelation conform to the open reading frame, and coincidence rate was92.6%.Conclusion（1） DMD gene mutations types were various, including exon deletion and/orduplication and point mutation.（2） MLPAis an efficient method for detecting deletion and duplication of DMD. （3） NGS not only can detect both deletion duplication and point mutations, but alsocan determine the Location of break point and the size of gene segmentsaccurately. It may be a powerful tool at in molecular diagnosis and prognosticjudgment of DMD.（4） In this study, clinical phenotypes conformed to genotypes in92.6%childrenwith, with in-depth discussion about the type of DMD gene mutation and thedevelopment of gene capture–nest generation of sequencing technology, therelations of DMD/BMD clinical phenotype and genotype will be furtherelucidated.（5） In this study, it is recommended that the DMD/BMD genetic diagnosis strategiesas follows:1. According to X linkage, gastrocnemius muscle hypertrophy,proximal muscle weakness, increased serum CK, or electromyogram and musclepathological myopathy in performance, establish a clinical diagnosis;2. Theapplication of MLPA analysis set up preliminary molecular diagnosis;3. If youneed prenatal diagnosis, and the MLPA found no mutation, DMD whole genomeanalysis was established the final diagnosis;4. The prognostic judgment andgenetic counseling were performed final genetic diagnosis.