The most common disease-causing mutation of factor XIII deficiency is corrected by CRISPR/CAS9 gene editing system

Abstract

Factor XIII (FXIII) deficiency is one of the most severe congenital bleeding disorders, with an estimated incidence of one person per one million. Patients with severe FXIII deficiency present a wide range of clinical manifestations, including umbilical cord bleeding, intracranial haemorrhage and recurrent miscarriages. Due to the high rate of life-threatening bleeding, primary prophylaxis is mandatory from the time of diagnosis. Although replacement therapy is the most common therapeutic choice, gene therapy remains the only curative option. In the present study, we assessed the efficacy of the clustered regularly interspaced short palindromic repeats - CRISPR-associated protein 9 (CRISPR/Cas9) system in the correction of the most common FXIII disease-causing mutation (c.562 T > C). A dermal fibroblast was harvested from the human skin biopsy of a young patient with FXIII deficiency. Sanger sequencing was used to confirm the presence of c.562 T>C mutation in the patient and in the harvested fibroblasts. PX459 vector was digested with BbsI restriction enzyme, and after annealing and ligation of two 20-bp guide-RNAs (g-RNAs) close to the PAM (NGG) sequence, the constructed vectors were amplified in Escherichia coli Top 10. Transfection was performed by a nucleofector device, and DNA extraction was performed after puromycin selection and serial dilution from potentially transfected colonies. A 50-bp template oligonucleotide was used to aid homologous repair for correction of the underlying mutation and synonymous mutation as an internal control. The synonymous mutation (AAT to ACT) near the mutation site was used as internal control. Sanger sequencing was done in order to check the gene correction. The c.562 T > C mutation was detected in homozygote state in the primary fibroblasts of the patient and wild-type alleles were confirmed in the normal individual. Colony PCR and sequencing revealed successful cloning of the designed gRNAs. The detected mutation was corrected from a homozygote mutant state (c.562 T > C) to a homozygote wild type in transfected dermal fibroblasts of the patient. The control mutation, as an internal control, was also corrected in the same fibroblasts in the heterozygote manner. The result of the study shows that the CRISPR/CAS9 gene editing system is an effective tool for correction of point mutations in transfected fibroblasts of patients with congenital FXIII deficiency and represents a new, potentially curative, option.