Duchenne explained Glossary of research terms Other protein targets Utrophin represents a novel target for treatment of Duchenne. It is naturally found in very low levels in the body. Utrophin production is switched off in mature muscle fibres and dystrophin takes over. The similarity between the two proteins suggests that in Duchenne, the upregulation of utrophin could compensate for the absence of dystrophin and could protect healthy muscle function, regardless of mutation type. Research is currently taking place to identify small molecules that could increase the amount of utrophin in the body. These small molecules are often called utrophin up-regulators. An example is Summit’s Ezutromid (SMT- C1100) which is currently in a phase 2 clinical trial called PhaseOut (interim 24-week data review). Utrophin is slightly smaller than dystrophin, yet Becker’s patients prove encouraging in the fact that not necessarily all the parts of dystrophin are required for adequate muscle function. This could represent a universal treatment for all DMD patients and could potentially be complementary to other Duchenne therapies. Another utrophin modulator in development, SMT022357, is an oral second-generation utrophin modulator which was demonstrated to reduce muscle damage in mdx mice. Myostatin is a protein produced naturally in the body and inhibits muscle growth. In mdx mice, myostatin inhibitors have been shown to reduce fibrosis in muscles. At present there are 2 new myostatin inhibitors in Phase 2 of clinical development: PF-06252616, sponsored by Pfizer, and Adnectin (BMS 986089) which is sponsored by Bristol Myers Squibb (BMS).