FBXO21 and Kennedy disease: The expression of atrophy-related genes, including ubiquitin ligases FBXO21, FBXO30, FBXO32 and autophagy-related genes such as CTSL, BECN1, BNIP3, is not altered in muscle of SBMA individuals, resembling the molecular signature observed in denervated Smad4 knock-out and Noggin-overexpressing muscles [72], and supporting previous observations that skeletal muscle atrophy in SBMA has distinctive features compared to other forms of atrophy [56, 57, 67].