FLG and Alzheimer disease: Regarding AD, multiple studies have demonstrated that miRNAs are involved in many pathogenetic mechanisms, including immune cell maturation; regulation of the innate and adaptive immune systems [54,55,56]; suppression of Th1 cytokine expression through NFκB pathway regulation [59,60,61]; promotion of AD-related cytokines, such as IL-4, IL-17 and IL-1β [65]; and epidermal barrier function impairment targeting hyaluronan synthase 3 [71], but also the improvement of epidermal barrier function, opposing the negative regulation of filaggrin, loricrin and involucrin induced by IL-13 [75].