We recently developed a method to detect subtle changes in the prenylation of Rab GTPase proteins (11, 12) and showed in three patients for the first time that prenylation of Rab proteins, as well as Rap1A, is indeed defective in peripheral blood mononuclear cells (PBMCs) from MKD and could be a biomarker that distinguishes this disease from other autoinflammatory disorders with similar clinical features (13). Here, RAB6A is linked to mevalonic aciduria.