Molecular human genetics and the Duchenne/Becker muscular dystrophy gene.

Abstract

To isolate the gene involved in a human inherited disorder without prior knowledge of the defective protein product is a direct application of molecular human genetics and has been termed ‘reverse genetics’ (Orkin, 1986) or ‘positional cloning’. The phenotype associated with the disease, its segregation in families and linkage to genetic markers, and any associated cytogenetic abnormalities provide the information necessary to localize the disease gene to a precise chromosome map position. This map position then focuses experimental approaches to isolate the gene by collecting genomic DNA from the region and analysing it for candidate genes for the disease. Once the correct gene has been identified and the nucleotide sequence obtained, information can be gained on the structure and possible function of its protein product. The gene can be used to construct fusion proteins for antibody production thus allowing the cell biology of the protein to be studied and related to the pathophysiology of the disease. In this chapter the various aspects of molecular human genetics will be discussed in relation to the cloning and analysis of the Duchenne/Becker muscular dystrophy gene and study of its protein product dystrophin. The relationship between phenotype and genotype will be discussed in the light of the unusual organization and size of the dystrophin gene.