Description |
Duchenne muscular dystrophy (DMD) is caused by mutations in the dystrophin-encoding DMD gene.While the majority of DMD variants are deletions and duplications, large inversions are rarely reported due to the lack of effective detection methods. We report a case study of a DMD pedigree, in whichseveral patients exhibited a severe pathophysiology. The proband showed the disease phenotype at the age five including calf and forearm muscle hypertrophy, and pelvic-girdle muscle weakness. Since no dystrophin was detected in the muscle tissue by immuno-histochemistry, we initially used conventional approaches to identify pathogenic variants: multiplex ligation-dependent probe amplification (MLPA), and WES by next generation sequencing, but failed to detect the variant. Therefore, to identify the variant we built an advanced analysis pipeline which consists of RNA-seq, cDNA array capture sequencing, optical mapping, and long-read DNA sequencing. The RNA-seq and cDNA capture sequencing showed a complete absence of transcripts of exons 3-55. Optical mapping identified a 55Mb pericentric inversion between Xp21 and Xq21. Subsequently, the whole genome sequencing (WGS) using the nanopore-based long-read sequencing determined the exact inversion breakpoints at 32,915,769 and 87,989,324 of X chromosome. Using the information, we developed a PCR/Sanger sequencing diagnostic to detect the inversion in the family members. We applied the diagnostic to a female first cousin of the patient, who was already conceived at the time of our findings. Since the DNA sequencing result confirmed her as a non-carrier, she carried the fetus for the full-term delivery of a healthy child. |