Point mutation in the human dystrophin gene: identification through western blot analysis

Using antibodies directed against the amino-terminus of dystrophin, we identified a truncated protein in a Duchenne muscular dystrophy patient. Antibodies directed against the carboxy-terminus failed to identify any cross-reactive material, a result consistent with premature termination of dystrophin translation. The estimated molecular mass of 126 kDa predicted the approximate location of the mutation in the mRNA and in the gene. Sequencing of cloned PCR products from patient muscle cDNA revealed a nonsense mutation, which was confirmed by direct sequencing of amplified patient genomic DNA. The mutation, a G to T transversion, at position 3714 changes a glutamic acid codon to an Amber stop codon. Translation of mRNA containing this mutation would be expected to result in a truncated protein with a molecular mass of 133 kDa, in close agreement with the 126 kDa estimated by Western blot analysis. This is the first reported case of a point mutation in this very large human gene.