Measurements of the chymotrypsin-like activity in OPMD muscles in the presence of heterozygous mutants of proteasome subunits showed that it was reduced to wild-type levels by the Rpn10 mutation, although this reduction was not observed with mutants of the other proteasome subunits, Rpn11 and Prosβ4 (Fig 4A). This evidence concerns the gene CTRL and oculopharyngeal muscular dystrophy.