Using CRISPR/Cas9 System to Knock out Exon 48 in DMD Gene

Novel insight into FCSK-congenital disorder of glycosylation through a CRISPR-generated cell model

BACKGROUND

FCSK-congenital disorder of glycosylation (FCSK-CDG) is a recently discovered rare autosomal recessive genetic disorder with defective fucosylation due to mutations in the fucokinase encoding gene, FCSK. Despite the essential role of fucokinase in the fucose salvage pathway and severe multisystem manifestations of FCSK-CDG patients, it is not elucidated which cells or which types of fucosylation are affected by its deficiency.

METHODS

In this study, CRISPR/Cas9 was employed to construct an FCSK-CDG cell model and explore the molecular mechanisms of the disease by lectin flow cytometry and real-time PCR analyses.

RESULTS

Comparison of cellular fucosylation by lectin flow cytometry in the created CRISPR/Cas9 FCSK knockout and the same unedited cell lines showed no significant change in the amount of cell surface fucosylated glycans, which is consistent with the only documented previous study on different cell types. It suggests a probable effect of this disease on secretory glycoproteins. Investigating O-fucosylation by analysis of the NOTCH3 gene expression as a potential target revealed a significant decrease in the FCSK knockout cells compared with the same unedited ones, proving the effect of fucokinase deficiency on EGF-like repeats O-fucosylation.

CONCLUSION

This study expands insight into the FCSK-CDG molecular mechanism; to the best of our knowledge, it is the first research conducted to reveal a gene whose expression level alters due to this disease.

Identification of Two Novel Variants of the DMD Gene in Chinese Families with Duchenne Muscular Dystrophy

Background

Duchenne muscular dystrophy (DMD), an X-linked recessive neuromuscular disorder, is caused by pathogenic variants in the DMD gene encoding a large structural protein in muscle cells.

Methods

Two probands, a 6-year old boy and a 1-month old infant, respectively, were clinically diagnosed with DMD based on elevated levels of creatine kinase and creatine kinase isoenzyme. CNVplex and whole exome sequencing (WES) were performed for causal variants, and Sanger sequencing was used for verification.

Results

CNVplex found no large deletions or duplications in the DMD gene in both patients, but WES discovered a single-nucleotide deletion in exon 48 (NM_004006.2:c.6963del, p.Asp2322ThrfsTer16) in the proband of pedigree 1, and a nonsense mutation in exon 27 (NM_004006.2:c.3637A>T, p.K1213Ter) in the proband of pedigree 2.

Conclusion

The results of our study expand the mutation spectrum of DMD and enrich our understanding of the clinical characteristics of DMD. Genetic counseling was provided for the two families involved in this study.

CRISPR-Cas9 Gene Therapy for Duchenne Muscular Dystrophy

Discovery of the CRISPR-Cas (clustered regularly interspaced short palindromic repeat, CRISPR-associated) system a decade ago has opened new possibilities in the field of precision medicine. CRISPR-Cas was initially identified in bacteria and archaea to play a protective role against foreign genetic elements during viral infections. The application of this technique for the correction of different mutations found in the Duchenne muscular dystrophy (DMD) gene led to the development of several potential therapeutic approaches for DMD patients. The mutations responsible for Duchenne muscular dystrophy mainly include exon deletions (70% of patients) and point mutations (about 30% of patients). The CRISPR-Cas 9 technology is becoming increasingly precise and is acquiring diverse functions through novel innovations such as base editing and prime editing. However, questions remain about its translation to the clinic. Current research addressing off-target editing, efficient muscle-specific delivery, immune response to nucleases, and vector challenges may eventually lead to the clinical use of the CRISPR-Cas9 technology. In this review, we present recent CRISPR-Cas9 strategies to restore dystrophin expression in vitro and in animal models of DMD.

Dystrophin gene editing by CRISPR/Cas9 system in human skeletal muscle cell line (HSkMC)

OBJECTIVES

Duchene muscular dystrophy (DMD) is a progressive neuromuscular disease caused by mutations in the DMD gene, resulting in the absence of dystrophin expression leading to membrane fragility and myofibril necrosis in the muscle cells. Because of progressive weakness in the skeletal and cardiac muscles, premature death is inevitable. There is no curative treatment available for DMD. In recent years, advances in genetic engineering tools have made it possible to manipulate gene sequences and accurately modify disease-causing mutations. CRISPR/Cas9 technology is a promising tool for gene editing because of its ability to induce double-strand breaks in the DNA.

MATERIALS AND METHODS

In this study for the exon-skipping approach, we designed a new pair of guide RNAs (gRNA) to induce large deletion of exons 48 to 53 in the DMD gene in the human skeletal muscle cell line (HSkMC), in order to correct the frame of the gene.

RESULTS

Data showed successful editing of DMD gene by deletion of exons 48 to 53 and correction of the reading frame in edited cells. Despite a large deletion in the edited DMD gene, the data of real-time PCR, immune florescent staining demonstrated successful expression of truncated dystrophin in edited cells.

CONCLUSION

This study demonstrated that the removal of exons 48-53 by the CRISPR / Cas9 system did not alter the expression of the DMD gene due to the preservation of the reading frame of the gene.