ANPEP and Duchenne muscular dystrophy: We and others have shown that mdx mice display low circulating levels of ApN.9, 34 Replenishment of ApN by transgenesis mitigated the dystrophic phenotype by attenuating inflammation while improving regeneration, muscle function, and physical performance.9 Likewise, increasing serum ApN by moderate exercise was associated with improved muscle function in mdx mice.35 On the contrary, complete depletion of ApN levels greatly aggravated the phenotype.10 As yet, it is still unclear whether circulating ApN levels are also decreased in DMD patients.