Novel mutation in exon 56 of the dystrophin gene in a child with Duchenne muscular dystrophy

Abstract

Duchenne type muscular dystrophy (DMD) is an allelic X-linked recessive disorder caused by mutations in the gene encoding dystrophin. Genotype analysis has shown that deletion mutations account for approximately 65% of all cases, and 5-10% are duplications, while the remaining 30% of affected individuals may have smaller mutations, including point mutations, small deletions or small insertions. In this study, we present the case of a 4-year-old boy with typical clinical features of DMD, who developed normally until the age of 2. However, at age 3 he presented his first symptom, a tendency to fall, had difficulty in rising from the floor and in walking on his toes. At age 4 he had a waddling gait and could no longer climb stairs. A physical examination revealed proximal muscle weakness, calf hypertrophy, deep tendon hyporflexia and a positive Gower's sign. To identify the disease-causing gene in the proband, all coding regions (exons 1-79) of the dystrophin gene were PCR-amplified and sequenced. A novel duplication (c.8284dupA) in exon 56 of the dystrophin gene was identified, which was predicted to generate a frameshift mutation and create a premature termination codon (p.Ile2762Asnfs*10). This mutation was further confirmed by single-strand conformation polymorphism (SSCP) analysis, which revealed an extra band found in exon 56 of the dystrophin in the proband; however, this was not present in his family members or in the 100 matched normal controls. The data presented in this study may aid in expanding the spectrum of mutations causing DMD. To our knowledge, we demonstrate for the first time that a small duplication mutation can cause severe DMD.