Cell models are often the first step for therapy development. This step is called in vitro (‘in glass’ referring to the glass culture dishes that were used in the past). For DMD, usually muscle cell cultures are used. Compounds are tested in cells to show their mechanism of action, i.e. can they induces the expected changes on cell signalling, protein production, growth or differentiation. Furthermore, it gives an indication of the toxicity of the compound, i.e. do the cells survive?