The cause of hyperpigmentation, such as solar lentigo and seborrheic keratosis, is the excessive accumulation of melanin pigments in the epidermal basal layer. Melanin pigments are synthesized in the melanosomes, which are specific organelles produced by melanocytes in the basal layer. Melanosomes
LEOPARD syndrome is a phenotypic expression of mutations in several genes: PTPN11, RAF1, and BRAF. All these genes are responsible for Ras/MARK signaling pathway, which are important for cell cycle regulation, differentiation, growth, and aging. Mutations result in anomalies of skin, skeletal, and