A resolved discrepancy between multiplex PCR and multiplex ligation-dependent probe amplification by targeted next-generation sequencing discloses a novel partial exonic deletion in the Duchenne muscular dystrophy gene

Advances in Dystrophinopathy Diagnosis and Therapy

Dystrophinopathies are x-linked muscular disorders which emerge from mutations in the Dystrophin gene, including Duchenne and Becker muscular dystrophy, and dilated cardiomyopathy. However, Duchenne muscular dystrophy interconnects with bone loss and osteoporosis, which are exacerbated by glucocorticoids therapy. Procedures for diagnosing dystrophinopathies include creatine kinase assay, haplotype analysis, Southern blot analysis, immunological analysis, multiplex PCR, multiplex ligation-dependent probe amplification, Sanger DNA sequencing, and next generation DNA sequencing. Pharmacological therapy for dystrophinopathies comprises glucocorticoids (prednisone, prednisolone, and deflazacort), vamorolone, and ataluren. However, angiotensin-converting enzyme (ACE) inhibitors, angiotensin receptor blockers (ARBs), and β-blockers are the first-line to prevent dilated cardiomyopathy in dystrophinopathy patients. Duchenne muscular dystrophy gene therapy strategies involve gene transfer, exon skipping, exon reframing, and CRISPR gene editing. Eteplirsen, an antisense-oligonucleotide drug for skipping exon 51 from the Dystrophin gene, is available on the market, which may help up to 14% of Duchenne muscular dystrophy patients. There are various FDA-approved exon skipping drugs including ExonDys-51 for exon 51, VyonDys-53 and Viltolarsen for exon 53 and AmonDys-45 for exon 45 skipping. Other antisense oligonucleotide drugs in the pipeline include casimersen for exon 45, suvodirsen for exon 51, and golodirsen for exon 53 skipping. Advances in the diagnosis and therapy of dystrophinopathies offer new perspectives for their early discovery and care.

Novel Partial Exon 51 Deletion in the Duchenne Muscular Dystrophy Gene Identified via Whole Exome Sequencing and Long-Read Whole-Genome Sequencing

Duchenne muscular dystrophy (DMD), one of the most common progressive and severely disabling neuromuscular diseases in children, can be largely attributed to the loss of function of the DMD gene on chromosome Xp21.2-p21.1. This paper describes the case of a 10-year-old boy diagnosed with DMD. Whole exome sequencing confirmed the hypothesized large partial exonic deletion of c.7310-11543_7359del (chrX:g.31792260_31803852del) spanning exon 51 and intron 50 in DMD. This large deletion was verified to be de novo by PCR, and the two breakpoints were further confirmed by Sanger sequencing and long-read whole-genome sequencing. Notably, this partial exonic deletion was the only complex variation in the deep intron regions or intron–exon junction regions in DMD. In addition, the case study demonstrates the clinical importance of using multiple molecular genetic testing methods for the diagnosis of rare diseases.

A Novel FLCN Intragenic Deletion Identified by NGS in a BHDS Family and Literature Review

Birt-Hogg-Dubé syndrome (BHDS, MIM #135150), caused by germline mutations of FLCN gene, is a rare autosomal dominant inherited disorder characterized by skin fibrofolliculomas, renal cancer, pulmonary cysts and spontaneous pneumothorax. The syndrome is considered to be under-diagnosed due to variable and atypical manifestations. Herein we present a BHDS family. Targeted next generation sequencing (NGS) and multiplex ligation-dependent probe amplification (MLPA) revealed a novel FLCN intragenic deletion spanning exons 10-14 in four members including the proband with pulmonary cysts and spontaneous pneumothorax, one member with suspicious skin lesions and a few pulmonary cysts, as well as two asymptomatic family members. In addition, a linkage analysis further demonstrated one member with pulmonary bullae to be a BHDS-ruled-out case, whose bullae presented more likely as an aspect of paraseptal emphysema. Furthermore, the targeted NGS and MLPA data including our previous and present findings were reviewed and analyzed to compare the advantages and disadvantages of the two methods, and a brief review of the relevant literature is included. Considering the capability of the targeted NGS method to detect large intragenic deletions as well as determining deletion junctions, and the occasional false positives of MLPA, we highly recommend targeted NGS to be used for clinical molecular diagnosis in suspected BHDS patients.

Molecular diagnosis of dystrophinopathies in Morocco and report of six novel mutations

Dystrophinopathies are the most common genetic neuromuscular disorders during childhood, with an X-linked recessive inheritance pattern. Because of clinical and genetic heterogeneity of dystrophinopathies, genetic testing of dystrophin gene at Xp21.2 is constantly evolving. Multiplex Polymerase Chain Reaction (MPCR) is used in the first line to detect common exon deletions of dystrophin gene (accounting for 65% of mutations), followed by the Multiplex Ligation-dependent Probe Amplification (MLPA) technique to reveal deletions of exons outside the usual hotspot and duplications in male and female carriers. (MLPA adds another 10-15% positive cases to MPCR). Recently, Next Generation Sequencing allows to screen for rare large and point mutations. We report here, molecular analysis results of dystrophin gene during 27 years in a large Moroccan cohort of 356 patients, using the multiplex polymerase chain reaction (MPCR) to screen for hot-spot exon deletions. First applications of whole dystrophin gene sequencing in our lab lead to the identification of six novel mutations.

A resolved discrepancy between multiplex PCR and multiplex ligation-dependent probe amplification by targeted next-generation sequencing discloses a novel partial exonic deletion in the Duchenne muscular dystrophy gene

BACKGROUND

The genetic diagnosis of Duchenne muscular dystrophy (DMD) has been complicated by the large size of the gene and its heterogeneous mutational spectrum. Multiplex PCR and multiplex ligation-dependent probe amplification (MLPA) are two well-established mutation screening methods. Here, we applied targeted next-generation sequencing (NGS) to clarify discrepant results between multiplex PCR and MLPA in a Chinese patient with DMD.

METHODS

MLPA was performed to confirm multiplex PCR results obtained previously. Targeted NGS was then used to analyze the full-length DMD gene including introns.

RESULTS

Multiplex PCR had previously identified an apparent deletion of exon 43 in the patient with DMD, but current MLPA indicated that exon 43 was present. Targeted NGS to clarify the genetic diagnosis identified a novel mutation, c.6241_c.6290 + 1109del1159insAC, which caused partial deletion of exon 43. This mutation removed the annealing sequence of the exon 43 reverse primer in multiplex PCR but had no influence on the hybridization site of the MLPA probe. Therefore, the discrepancy between the two methods was caused by partial exonic deletion that escaped MLPA detection.

CONCLUSION

Targeted NGS disclosed a novel partial exonic deletion in the DMD gene as the cause of discrepancy between multiplex PCR and MLPA. Targeted NGS could be used to provide a more accurate genetic diagnosis of DMD, particularly in cases of partial exonic deletions, which will be of benefit in patient management and the identification of disease carriers.