31.1 Introduction

One out of 3500 boys is born with the Duchenne muscular dystrophy (DMD). Females are carrier for this disease. This hereditary disease occurs due to the absence or very less expression of dystrophin protein, which acts as an important structural component present within the muscle tissue and provides stability to the dystroglycan complex structure (DGC) of the cell membrane. As a result of mutation or impaired function of dystrophin gene, dystrophin protein synthesis gets impaired hence non-functional dystrophin protein is formed causing the DMD. The credit of identification of this gene goes to Louis M. Kunkel. He identified the gene in the year 1987 after the reported discovery of the mutated gene causing Duchenne muscular dystrophy (DMD) in 1986 . The DMD is a recessive X-linked disease which occurs due to frameshift mutation in the dystrophin gene. An allelic counterpart of the DMD is the Becker's muscular dystrophy (BMD). The severity of BMD is less as compared to DMD and the appearance of symptoms is later than in DMD. The person affected with BMD generally loses their ability to walk at the age of around 30 years. In DMD dystrophin protein is absent whereas in BMD partially functional dystrophin protein is synthesized that is why BMD is less severe than DMD.

31.2 Dystrophin gene

The dystrophin gene is located on the short arm (p arm) of the X chromosome at the band 2, sub-band 1 and sub-sub-band 2 (Xp21.2). It is the longest known human gene and has a size of 2,400 Kbp approximately 0.1% of the human genome. The transcription of the dystrophin gene takes around 16 hours. The transcribed mature mRNA after splicing is about 14 Kbp. There are about 79 exons (18 isoforms) which code for the dystrophin protein. The dystrophin protein consists of about 3500 amino acid and has a molecular weight of 427KDa.