Hypothyroidism in the soleus muscle causes a 2A→β-slow MyHC change (Nwoye et al. 1982; Diffee et al. 1991b; Caiozzo et al. 1992; Haddad et al. 1997), but in a fast muscle, hypothyroidism causes a 2B→2X→2A shift in MyHC expression that does not proceed to β-slow MyHC expression (Caiozzo et al. 2000; Zhong et al. 2010). Here, MYH6 is linked to hypothyroidism.