Genomic insights into Duchene muscular dystrophy: Analysis of 1250 patients reveals 30% novel genetic patterns and 6 novel variants

Duchenne muscular dystrophy (DMD/BMD) is the most common type of muscular dystrophy, together with Becker muscular dystrophy represent more than half of all cases. DMD is a single-gene, X-linked recessive disorder that predominantly affects boys, causing progressive muscle deterioration and eventually leading to fatal cardiopulmonary complications. This study aimed to implement a cost-effective molecular diagnostic method using the SALSA MLPA Kit (probe mixes 034 and 035) to screen a large group of Egyptian DMD patients. The study included 1250 clinically diagnosed DMD males, following complete family history, pedigree analyses and an accurate clinical examination and laboratory investigations mainly considering high levels of creatine phosphokinase (>2000 U/L). We also analysed the carrier status of 100 mothers of 100 probands to gauge the inherited mutation through their patients with familial disease. The negative results of MLPA were further analysed with NGS for ten patients and the results were validated for novel missense mutations, phenotype-genotype correlations were analysed using PolyPhen2 and mutation taster.

Results SALSA MLPA analysis confirmed the diagnoses in 733/1250 (58.6 %) DMD patients and the remaining of 517/1250 (41.4%) were negative. DMD patients having large deletions were 632/1250 (50.6%) while duplications occurred in 101/1250 (8%). The most common single exon deletion was 45 (50/632, 7.9%). In addition, 163 different deletion and duplication patterns were characterized among positive MLPA analyses. 30% of our studied cohort exhibited new patterns of rearragements in addition to seven cases of double deletion and duplication rearrangements identified, within nine patients. Using NGS, for small mutations detection, revealed six novel and three previously reported mutations among screened ten patients.

In conclusion, our findings expand the spectrum of known DMD mutations by offering an effective diagnostic method and identifying novel point mutations through NGS analysis. We recommend using NGS to uncover uncharacterized mutations in patients who test negative with MLPA, which could contribute to the treatment of DMD.