making muscle wasting history

Dystrophin is not only present in the muscle fibers but also in other organs like the brain and the retina of the eyes.

The dystrophin in the muscle with a molecular weight of 420kd, kilodaltons (420,000 times heavier than one atom of hydrogen) is the largest of five isoforms (proteins of different size) In the brain, this normal dystrophin, but also the four smaller ones, are found predominantly at the synapes, where the nerve cells connect to each other, and the walls of the blood vessels in the brain, in the so called blood-brain barrier. That means these dystrophins are important for communication between the nerves and also for the correct activity of the blood-brain barrier which lets only those substances pass that are necessary for the normal function of the brain.

The dystrophin gene has seven promoters, base sequences on which on which the protein biosynthesis is initiated. The first three promoters at the beginning of the gene control the sythesis of the normal protein, the other four are farther inside the gene. The closer a promoter is to the end of the gene the shorter the dystrophin produced. This means, that mutations which have occured before that particular promoter do not affect the production and the structure of the protein intiated by that promter. For instance, Duchenne boys with mutations in the first half of their gene can still produce their short dystrophin isoforms for the brain in contrast to those with mutations in the later regions of the gene, whose brain dystrophins will then also be absent. This explains why some duchenne boys have learning and behavior difficulties and other boyys only a few or none at all.

As the different dystrophin isoforms have also been found in the retina of the eye, the location of the mutation seems to be respondsible for the colour vision difficulties of some duchenne boys

Information from Professor Francesco Muntoni quoted in Research Aproaches for a Therapy of Duchenne Muscular Dystrophy 2008