A case study of Duchenne muscular dystrophy caused by Alu element insertion in DMD gene and analysis of its gray-hair symptoms.

Abstract

Duchenne muscular dystrophy (DMD) is a severe X-linked recessive genetic disorder caused by mutations in the DMD gene, which leads to a deficiency of the dystrophin protein. The main mutation types of this gene include exon deletions and duplications, point mutations, and insertions. These mutations disrupt the normal expression of dystrophin, ultimately leading to the disease. In this study, we reported a case of DMD caused by an insertion mutation in exon 59 (E59) of the DMD gene. The affected child exhibited significant abnormalities in related biochemical markers, early symptoms of DMD, and multiple gray hair. His mother and sister were carriers with slightly abnormal biochemical markers. The mother had mild clinical symptoms, while the sister had no clinical symptoms. Other family members were genetically and physically normal. Sequencing and sequence alignment revealed that the inserted fragment was an Alu element from the AluYa5 subfamily. This insertion produced two stop codons and a polyadenylate (polyA) tail. To understand the impact of this insertion on the DMD gene and its association with clinical symptoms, exonic splicing enhancer (ESE) prediction indicated that the insertion did not affect the splicing of E59. Therefore, we speculated that the insertion sequence would be present in the mRNA sequence of the DMD gene. The two stop codons and polyA tail likely terminate translation, preventing the production of functional dystrophin protein, which may be the mechanism leading to DMD. In addition to typical DMD symptoms, the child also exhibited premature graying of hair. This study reports, for the first time, a case of DMD caused by the insertion of an Alu element into the coding region of the DMD gene. This finding provides clues for studying gene mutations induced by Alu sequence insertion and expands the understanding of DMD gene mutations.