Non-deletion mutations in Egyptian patients with Duchenne muscular dystrophy

Abstract

Duchenne muscular dystrophy (DMD) is the most common form of muscular dystrophies affecting approximately 1:3500 male live births. Deletion of the dystrophin gene accounts for approximately 65% of mutations, duplications occur in 6–10% while the remaining 20–30% are point mutations, small deletion/insertions, or splicing mutations.
Aim: To study non-deletion mutations in a sample of Egyptian patients with DMD as most previous studies focused on deletion mutations.
Patients and methods: The study included 25 patients with DMD from 18 different families from the genetics clinic, Children’s Hospital, Ain Shams University. Diagnosis was made based on typical clinical findings, high CPK and EMG result. Molecular analysis included Polymerase Chain Reaction (PCR) followed by multiplex ligation-dependent probe amplification (MLPA) to those patients with no deletion by PCR. Direct sequencing of the whole dystrophin gene was done to those patients who had no deletion or duplication by the previous 2 methods.
Results: Non-deletion mutation included duplications (5 families (27.8%)) which are higher than previously reported and point mutation (c.583C>T) in only one family. Deletion mutations were found in 9 families (50%) and no mutation found in 3 families (16.7%). Interestingly, 60% of the duplications were located in the distal region of the dystrophin gene. A frame shift mutation was identified in most patients (93%) except one with duplication of exons 50–51 who had an unexpected severe disease with an early age of onset. Also, an intragenic deletion involving the 50 end of the dystrophin gene (deletion of muscle protomor and exon 1) was found in another patient with severe disease without cardiac involvement.
Conclusion: The relative higher frequency of duplication mutations in Egyptian patients with DMD may indicate that MLPA and not PCR should be preferred for molecular testing of Egyptian patients with DMD.

Keywords: Duchenne muscular dystrophy; Deletion; Duplication; Egypt; MLPA; Sequencing