The reason for the increased speed of shortening, particularly visible in het R349P desminopathy muscle fibers, cannot unambiguously be explained at current, especially considering our recent finding that slow-type MHC I isoforms were upregulated in R349P desmin knock-in muscles, while fast-twitch MHC II isoforms were downregulated [19]. The gene discussed is DES; the disease is Desminopathy.